simple high current balancer

[Dan Baldwin]

The circuit depicted here is for experimental purposes only. Any person using the circuit, or any part of the circuit depicted here does so at their own risk.

This balancer would be the circuit for 1 cell. One would have to be built for each cell in the pack to be balanced. Although normally balancing current would be very small to keep a battery pack in balance, this balancer is capable of sinking 2 amps (or higher) with an appropriate heat sink. It is intended as an external balancer to be used while charging the battery pack. The LED turns on as low as 5 milliamps balance current. It will not work well with pulsing type chargers such as the Astro Flight 109 charger. Don't be misled by the simplicity of the circuit. It will clamp the voltage to within 2 millivolts from 20 milliamps to 2 amps. The LED will turn on with as little as 5 milliamps balancing current. If the pass transistor should fail, it is protected from putting a short on the cell by using a resettable fuse. A regular glass fuse could also be used. The cost is about $4.56/cell without the circuit board.


Mouser Parts List
qtys shown per balancer

1 652-MFR185 RESETABLE FUSE .58
1 511-TIP137 PNP POWER DARLINGTONS .68
1 531-PT10MH-1K 1K OHM POT .40
1 604-L934SGC T-1 GRN 300 MCD 50 DEG SUP BRITE LED .18
1 511-TL431ACZ ADJUSTABLE SHUNT REGULATOR .28
1 511-2N3906 PNP GENERAL PURPOSE SIGNAL XISTOR .06
1 567-290-1AB T0-220 HEAT SINK .38
1 532-4880M TO-220 mounting kit for TIP137 .77
1 75-516D107M035 100 mfd cap .28
1 581-BF014D0103K .01 mfd cap .09
1 581-BF014D0104K .1 mfd cap .11
1 72-RWM410-1-5 1 ohm 3 watt .32
1 271-10K 10 K 1% RESISTOR .09
1 271-15K 15 K 1% RESISTOR .09
1 660-CF1/4L102J 1K 5% RESISTORS .05
2 660-CF1/4L121J 120 OHM 5% RESISTOR .05
2 660-CF1/4L331J 330 OHM 5% RESISTORS .05

Dan

Disclosure;
although I have built and tested this circuit, I have not used it to balance any battery packs. I (at least at present) do not balance my packs.

[gPearce]

Dan Baldwin---OK it looks good now how about a description about how it works and how to set it up-----please.
TIA--G Pearce

[Dan Baldwin]

The diagram below shows how to hook up the balancers while charging a 3 cell battery pack, but any number of cells could be charged in series as long as each cell had a balancer hooked up as shown. The charger shouldn't be set any higher than 2 amps with the circuit shown although higher current could be used if a larger fuse was used. This circuit has not been tested higher than 2 amps. To do the initial adjustment, a load ( a resistor as shown, or a 12 volt light bulb) is put in series with balancer, and 12 volts is applied. The LED will be on. An accurate voltmeter (a DVM) is put across the balancer, and the pot is adjusted for a 4.2 volt reading.

Let me know if anything isn't clear enough.

Dan

[Dan Baldwin]

principle of operation;
The TL431 is a precision adjustable shunt regulator. The TIP137 darlington transistor pair is a booster for the TL431, making it capable of handling much higher currents. The TIP137 is rated at 8 amps continuous current. When the TL431 begins to conduct because the voltage has risen to the set voltage, the transistor that controls the LED will turn on before the TIP137, so the LED will turn on with even the slightest current flow.

Dan

[Larry3215]

Cool!

Larry

[gPearce]

Dan Baldwin--Thanks for the additional info.
I guess there is no hope for cells being charged in parallel??
G Pearce

[DNA]

Lipo cell balancers such as this circuit eliminate the need for charging cells in parallel, so they can be left in their series connections in the pack without having to disconnect the cells and rewire them in parallel. You will need cell taps on the pack.

However, if you want to charge cells in parallel, you could do that too and just use one of the 4.2v cell balancers for the cells you have connected in parallel as long as you don't go over the 2 amp charge rating.

[Dan Baldwin]

Another method of balancing cells is to use a separate charger and power supply for each cell. That method was being discussed in another thread (http://www.rcgroups.com/forums/showthread.php?t=248268&page=4), and it's what prompted me to post this information. I will be posting another circuit that would work for charging 1 lipoly cell from a 5 volt power supply within a few days if I get the time to breadboard it to make sure it works as advertised.

Dan

[dkselw]

Just a thought.
If the packs are always charged with the balancer connected then it is unlikely that the balancer will need to conduct much current.
You could limit the current through the pass transistor with a resistor instead of the polyfuse.
For the cases where the pack is severely out of balance something like the PQ PCM Guard wired up with the balancers would disconnect charging power if any cell exceeded 4.35V. You may then need to manualy restart charging in this case.

[Dan Baldwin]

Your absoutely right. If I were building this for myself, I would probably do as you suggest and put a current limiting resistor in series with the pass transistor, but I have noticed that some of the guys on the board are concerned that the "wimpy" balancers won't balance their big packs. If the balancer were limited to 1 amp, and your pack was severely out of balance, you might have to charge the pack once at 1 amp to get it balanced, but you could charge it normally after that.

Dan

[dkselw]

I think the method I was suggesting in conjunction with an overvoltage guard like the PQ PCM Guard will balance a large pack.
With my Supernova 3000 you may have to manualy restart charging.
If you used a charger which did not require a manual start such as one of the simple DIY CC/CV chargers you will end up with a charged and balanced pack eventually without manual intervention. The PQ PCM Guard will cycle the charge on and off to allow the balancers to do there job.

[DNA]

If you're using a CC/CV charger to charge the pack, as the voltage nears 4.2v per cell, the current near the end of the charge will be decreasing and will be much less than the 2 amps that was set initially.

[Larry3215]

The only real down side, from my point of view, in useing balancers on packs is that you need to know which tap goes to which cell and in which order. This is not hard to determine, but you will have to be carefull to plug the correct balancer lead into the correct tap every time.

Thats where isolated, 1 cell chargers would be more plugNplay and safer for newbies and the electricaly chalanged. It would not matter which tap you pluged which charger into.

Larry

[Dan Baldwin]

Larry
You're right that you have to be careful to get the balancers hooked to the right lead every time, but if you use a small connector like the Deans Micro 4r, you only have to worry about it once, when you wire the connector. Even if you use separate chargers for each cell, you still have to get the leads right. I think that newbies and the electrically challenged would have trouble tearing their packs apart to attach connectors regardless of the balancing technique used.

DNA
The only time a balancer would see the full charger current is in the unlikely event that one cell reaches 4.2 volts while others in the pack are still far enough below that voltage that the charger is still putting out full current. I thing you're right. The capacity of this balancer is overkill.

dkselw
The point I was trying to make is that if you have balancers that can handle near full charge current, you don't need the PQ PCM Guard at all. It would certainly be a good idea to use the PQ PCM Guard as an additional safety.

Dan

[dkselw]

Using the tap connector on the polyquest batteries you can't get the order wrong either.
I just brought up the idea of using the PQ PCM Guard partly for extra safety and also because if you limit the current through the balancers you can make the circuitry smaller and you don't have to worry about getting rid of as much heat.
I guess its all a trade off.

[Larry3215]

Those are all good points. With Polyquest you would make up a single conector and be done with it.

I was thinking of all my Tanic and homemade packs with JST taps.

I like that there are so many new good options coming onto the scene!

Larry

[dowd]

Although it was designed as a balancer, it seems that if you set the cutoff on this circuit for 8.4 volts instead of 4.2, you could use it in parallel with your 2-cell pack and you could charge off of a regular nicad variable current charger. Might be a nice use of one of those old unneeded nicad chargers to get a lipoly variable current charger. Prob'ly be better if you turn down the current once the LED comes on though.

Dowd

[Dan Baldwin]

The first one of these I built was for my brother, and it is set at 8.4 volts so he can use it with his hitec cg340 charger to charge his lipolys at any rate he wants. Yes, you can turn down the current so that the LED just stays on to keep the heat to a minimum. He also has a 12 volt light bulb he can use as a current limiter instead of the CG340.

Dan

[Larry3215]

Dan

I am haveing trouble finding all the parts at Digikey.

The TIP137 and MFR185 do not come up on a search.

Do you have a part number for the LED as well?

Also is the TO-92 type ok?

Thanks!

Larry

[Larry3215]

Also, I am assuming 1/4 watt resistors?
Anything special needed for the cap?

I want to build 3 of these and get them tested :)

Thanks!

Larry

[Dan Baldwin]

I bought most of the parts from Mouser, so I have included the part numbers from my purchasing. I've noticed that the Mouser search doesn't seem to work right recently. I have had trouble finding some parts too. 1/4 watt resistors will be fine. I suggest putting a 1 ohm current limiting resistor in between the collector of the TIP137 and the MFR185. That resistor will need to be a larger, perhaps 2 watts. The transistor that is used to turn on the LED isn't critical. I actually used the PNP tansistor shown below. If you don't anticipate large balancing currents, you can use small screw on TO-220 heat sinks as shown below. You can use any LEDs you want. I use super bright LEDs because they're nifty. If you want REALLY nifty, you could use blue or white LEDs, but they're a lot more money. Make sure that you check proper operation of the balancers, and calibrate them to 4.2 volts BEFORE you hook them to the batteries. There is nothing critical about the capacitor. I chose these particular pots because they are 1) inexpensive, and 2)tamper resistant. It takes a small allen wrench to adjust them. Mouser shows that all the parts listed below are in stock.

Dan

511-TIP137 PNP POWER DARLINGTONS .68
531-PT10MH-1K 1K OHM POT .40
604-L934SGC T-1 GRN 300 MCD 50 DEG SUP BRITE LED .18
511-TL431ACZ ADJUSTABLE SHUNT REGULATOR .28
511-2N3906 PNP GENERAL PURPOSE SIGNAL XISTOR .06
567-290-1AB T0-220 HEAT SINK .38

[Larry3215]

I just ordered enough parts to build 9 balancers. Thats the most I would ever use at one time. They should be here this weekend. Ill put a few together and test em out.

Thanks Dan!

Larry

[Dan Baldwin]

Then you won't be happy that I found a couple of little problems. I had made a few changes that I didn't think would have any bad effects on the circuit that I published, but I was wrong. A couple of changes need to be made. You will need to change the value of a resistor (120 ohms instead of 330 ohms) and add a couple of capacitors. 1 .1 mfd and 1 2.2 mfd. Those changes seem to work fine, but I'll really wring it out later today.

Sorry.

Dan

EDIT
Schematic changed

[Larry3215]

No biggie. They are additions, so I didnt order anything I dont need.
Should I wait till you do some more testing?

larry

[Dan Baldwin]

Good idea. I'll work it over later this afternoon.

Dan

[Dan Baldwin]

I was having problems with oscillation, but the scematic shown above (I changed it again) is stable.


Dan

[Larry3215]

This is the one to go with then?

Not bad, you added 2 caps and one resistor and changed one it looks like.

Should add less than a buck to the cost.

I should have parts by the weekend and will get some built and tested and report back.

Larry

[Dan Baldwin]

yup, that otta do it.

BTW $5.00/cell? I come up with more like $3.00/cell. Of course that's not including printed circuit board.

Dan

[Larry3215]

OK then, show me your list an I'll show ya mine ;)

My wife says I the best over spender she has ever married :)

I would not mind saveing $200 per.

Larry

Larry

[Dan Baldwin]

Okay, we have a beer on this, right? You've seen the list above;

511-TIP137 PNP POWER DARLINGTONS .68
531-PT10MH-1K 1K OHM POT .40
604-L934SGC T-1 GRN 300 MCD 50 DEG SUP BRITE LED .18
511-TL431ACZ ADJUSTABLE SHUNT REGULATOR .28
511-2N3906 PNP GENERAL PURPOSE SIGNAL XISTOR .06
567-290-1AB T0-220 HEAT SINK .38

Those parts add up to $2.01. Additionally you need;
6 misc resistors @ .05ea .30
1 100 mfd cap 75-516D107M035 .28
1 .01 mfd cap 581-BF014D0103K .09
1 .1 mfd cap 581-BF014D0104K .11
1 1 ohm 3 watt 72-RWM410-1-5 .32
Mouser shows that all parts are in stock

For a grand total of $3.11/cell. Did I miss anything?

I can probably save that additional $.11 if you make me.

Dan

[Larry3215]

OK, you win.... What's your favorite beer :)

Larry

[Larry3215]

OOps - you forgot the fuse:
652-MFR185 for $.58 each

A couple of questions:
1) do we only need to heat sink the TIP137 or do we also need one for the KSP2907?

2) Are the heats sinks conected to the circuit electricaly in any way (its been many years since I did this sort of thing)?

I am planing bread board construction on these and then heat shrink them to prevent shorts between the boards. I was going to leave the sinks exposed, but dont want to chance a short between units while they are bounceing around on the bench or in the charging fire box.

Thanks again!

Larry

[Dan Baldwin]

My favorite beer is free beer. Dang. I thought I had the MFR185 in the first list. That brings the total to $3.69.

Only the TIP137 needs a heat sink. If you don't insulate the heat sink, it will end up connected to the collector of the TIP137, so it would have to be treated as a live connection. You would be better off to insulate them. The case of the transistor, however will still be live, so you need to be careful that they don't get together. You could use TO-220 mounting kits (mouser #532-4880M) at $.68 ea in qty of 10, but that would mean that the total would be over $4.00, and you would win, so I suggest using a mica insulator (mouser #532-77-11) at $.10 in qty of 10 and shoulder washers (mouser #532-7721-7PPS) for .15 in qty of 10, then use your own #4-40 screws and nuts. That way the total is $3.94/cell, and I still win.

I can almost taste it now

Dan

[Larry3215]

Don, I will get that beer on the way :)

Two other questions just occured to me.

1) What is the max input over voltage these can handle/shunt away from the cell?

In other worrds - will they protect from selecting the wrong cell count on the charger?

I was just looking at my DVM and noticed it has a listed accuracy of 1%.

I assume that is % of full scale range. My options for range are 2 volts and 20 volts. 1% of 20 volts is .2 volts. That does NOT sound accurate enough to set the balancers.

2) Short of buying a very expensive Fluke meter (you would loose for sure then), how can I accurately set the balancer voltage?

You are doing us all a BIG service with this circuit and I am makeing you earn your free beer :)

Larry

[Dan Baldwin]

Boy, the questions keep getting trickier. Next you'll ask if I stopped beating my wife.

1) What is the max input over voltage these can handle/shunt away from the cell?
In other worrds - will they protect from selecting the wrong cell count on the charger?

Although this circuit is intended to balance packs, it is not intended to protect against setting the wrong cell count,yes, they will protect from selecting the wrong cell count but;
you would have to hold the charge current to under 2 amps
you would need larger heat sinks than those I suggested

2) Short of buying a very expensive Fluke meter (you would loose for sure then), how can I accurately set the balancer voltage?

I have no intentions of loosing by that much, so I'll see if I can help you with calibration. There are several ways that you can calibrate the balancers. You could do something as simple as setting them 1% low, so you know your safe even if the meter is wrong. One problem with that is that your CCCV charger (you are using a CCCV charger aren't you?) would never stop charging because it would never see full voltage.

You could start by setting the balancers on the low side, and gradually turn them up until the charger will show that a pack is fully charged. Keep in mind that if the balancers are set low, they will be sinking the whole charge current once the batteries get to full charge, so they will get hot. If you do this, keep the charge current low. Depending on what kind of charger you have, you might even be able to hook up the balancers without the batteries in circuit to set them.

You could go into the local electronics store with a 9 volt battery in your pocket and ask for a demo of their best high resolution meter, measure your battery voltage (on the volts scale, not on the battery test setting), write down that number, and check the same battery on your DVM at home. That will give you a correction factor for your meter.

I think that there are some voltage references available that are much tighter than 1%. I'll look and post the results if I find them. I want to be able to check calibration on my meters as well.

I never thought I'd have to work so hard for a beer

Dan

[Dan Baldwin]

Digi-Key has a precision 5 volt reference (LM4040AIZ-5.0-ND) that is rated for .1% initial accuracy. That should be close enough. You could use that to check calibration on your DVM.

Dan

[Larry3215]

This is from the Data sheet for the voltage reference. I want to be sure I understand this correctly.

"In a conventional shunt regulator application (Figure 1) , an
external series resistor (RS) is connected between the supply
voltage and the LM4040. RS determines the current that
flows through the load (IL) and the LM4040 (IQ). Since load
current and supply voltage may vary, RS should be small
enough to supply at least the minimum acceptable IQ to the
LM4040 even when the supply voltage is at its minimum and
the load current is at its maximum value. When the supply
voltage is at its maximum and IL is at its minimum, RS should
be large enough so that the current flowing through the
LM4040 is less than 15 mA.
RS is determined by the supply voltage, (VS), the load and
operating current, (IL and IQ), and the LM4040’s reverse
breakdown voltage, VR."

The formula they give and a circuit is shown in the attached pics.

I assume Vs is a 12 volt source ( I have one handy).
I dont know how much my DVM draws when measureing voltages, but lets assume 1 ma?
Also allow 1 ma for Iq

So Rs should be 3.5 ohms?

Does that sound rite?

Larry

[Larry3215]

Dan, I owe you some of that really expensive free beer :)

Larry

[Dan Baldwin]

No, I'm afraid you have the decimal point off by a few places. A 3.5 ohm resister would yield a current draw of 2 amps! That won't work. The IL and IQ in the formula are in amps, you used MA. A 3.5K would work just fine. I would probably use a 1K resister because that would yield a current draw of 7MA which is about in the middle of the allowable range. The current drawn by your DVM will probably be less than 10 microamps, or less than 1/100th of 1 MA, so you really don't have to take that into account. If you order an LM4040 make sure it is the "A" type because it is the .1% reference.

Dan

[Larry3215]

Oops.

Well, whats a decimal place or two among drinking buddies :)

Thanks Dan!

Larry

[Larry3215]

Well darn.

I built the first balancer and it does not work :(

I suspect I got the pinout of one (or all) of the transistors wrong.

I'm too tire to go back and chck now tho.

Here is how I thought it went?
(its been a long time)

Larry

[Dan Baldwin]

Larry

It doesn't work because I didn't get my beer yet.

Your pinouts of the TIP137 and the 2N3906 look right if I assume that the picture you drew of the 2N3906 is a top view, but the TL431 doesn't have an emitter, base and collector, so the pinout you show can't be right. The schematic I posted shows a pictorial view of the TL431 from the top, so you need to hook it up as shown on the schematic. with the flat side of the TL431 facing you with the leads on the bottom, the left lead goes to the wiper of the voltage pot, the middle lead goes to - or ground, and the right lead goes to the resistors that go to the transistors. What does the balancer do when you hook it up to a 12 volt power supply through a resister. Open circuit, with about 12 volts across the balancer, or low voltage across the balancer. Does the LED come on? If you post a couple of pictures I can take a look and see if I can spot the problem, but I think it's the beer.

Dan

[Larry3215]

It goes low voltage - .8 or so - and the lite stays off no matter what the pot setting.

I will go thru and double check all the conections. I did it on a breadboard and it is really ugly :) I could easily have gotten something in the wrong place.

Larry

[Larry3215]

OOps - one discrepance I just noticed - I have 2N2907 instead of 2N3906. Could that be the problem?

P.S. I have written a strong letter of protest to the beer shipper I used. I suspect he may have side tracked the shipment before it got to you ;)

Larry

[dowd]

Since Dan hasn't had a chance to answer yet, I'll emerge from my normal lurking mode, and take a stab here. But if Dan tells you something else, believe him since I've never built this circuit.

Since the 2n2907 is also a pnp with a reasonable voltage and current rating it should be fine to drive the led. So I don't think that is your problem.

It sounds like the TIP might be full on. Since it is on a breadboard, try lifting the wire connected to the Base of the TIP and see if the voltage across the circuit rises from 0.8 volts. If it does then the TIP is full on when it shouldn't be. Take a look at the voltage on the base of the TIP. Something is pulling it low, which turns it on.

Take a really close look at the way you wired the 431; it controls the TIP. Take another look at Dan's schematic and keep in mind that he shows the top view of the 431. Also confirm the values of the resisters.

And did you add in the additional components in Dan's updated schematic?

Another thought, what value resister did you put in series with the 12 volt supply to drive this circuit in place of the battery while you test it?

Good luck,

Dowd

[Dan Baldwin]

Yeah, What he said. Dowd's instructions were perfect, so do what he said. Sorry I took so long getting back to you. I was out flying.

Dan

[Larry3215]

Will check now - I went flying too :)

Larry

[Larry3215]

Problem found!

I did not check the resistors as I put them in - I trusted Mouser !!!

My 330 ohm resistors are actually 330K!!!

Like I said before - whats a decimal place or two or three ?

Sheesh!

I'll change that out and try again.

I dont know if I have any of those on hand - how close does it have to be? Would 360 ohms work?

Thanks for the help!

Larry

[Larry3215]

OK, I found some 330's and now we are a lot closer.

Put the meter on and the 12 volt source and yes! It lites up and I can adjust voltage from about 4.05 to 4.35 volts.

But... the lite stays on the whole time?

I tried plugging it into one of my packs where the cell voltage is at 4.11.

The lite still stays on no matter how I adjust the pot.

Any ideas?

We are getting close!

Larry

[Larry3215]

Discharged the pack down to 3.3 volts per cell and the lite still stays on.

Any chance I blew something?

Larry

[dowd]

You mentioned using your battery to test this circuit. Be VERY CAREFUL attaching a battery until this circuit is checked out and adjusted. This circuit is designed to provide basically a short circuit to the input if the input is above the set voltage. If your battery happens to be above the set voltage then the circuit will put a short on the battery causing a high discharge current. Fortunately there is a resettable fuse in the circuit to address this. But don't tempt fate.

If you are going to hook up a battery to the circuit before it is all set up, then put a small resister in series with the battery to protect the battery. Do you have a resister in the range of 0.1 to 100 ohms? Hmm, I guess you could even use a larger resister and it would work OK. The main thing is to protect your battery from a short while adjusting this circuit.

But the fact that you can set the voltage between 4.05 and 4.35 volts is excellent. This is the exact range of voltage you would expect based on the resister values Dan specified for the 431. So it seems that your circuit is basically working properly. By that I mean that the 431 is turning on the darlington transistor at the right voltage so everything except the LED circuit is doing what it should. Since you used a different transistor to drive the LED than Dan did, it is likely you just need a slightly different bias circuit than Dan had on the transistor driving the LED. So this is probably not a big problem.

First understand what the circuit is doing. The 431 acts like an adjustable zener diode. The voltage divider formed by the two fixed resisters and the pot control the "zener" voltage. If the input of the 431 coming from the pot goes above 2.5 volts, the 431 will turn on and turn on both the LED transistor and the darlington transistor. The darlington just provides the ability to handle more current and makes sure you keep a nice sharp knee. The other transistor is just there to turn on the LED at the right voltage.

The fact that the LED is on while you have the power supply and resister hooked up is fine. The circuit is conducting all of the time so that the LED should be on. But the fact that you connected the 3.3 volt battery to it and the LED was still on seems to indicate that the LED driving the transister is never turning off. If you hooked up the LED circuit per the diagram, you may need to add a pullup resister from the base of that 2N2907 up to the battery input to get the LED to come on and off when you want it to.

Here is what you might do to get your LED working right:
-First set the voltage on the circuit. Maybe start with a setting of 4.25 volts. (but deciding on the exact right voltage could be a whole thread all by itself)
-Then you need to provide an input voltage just below this set point to test your LED driver. Maybe provide a voltage of about 4.15 or 4.2V. Maybe you could use a voltage divider off of your power supply to get the proper voltage, or better yet maybe your power supply is adjustable. If you want to use your battery as the test voltage then remember what I said about protecting it.
-Now you need to play with the biasing of the transistor for the LED, Maybe adding the pullup resister or changing the value of the base resister. Start with maybe adding a 10kohm pullup and go up or down in resister value as necessary to get the LED just barely lit up. As you put a smaller value pullup resister (like maybe a 5K instead of the 10K I suggested) it will pull the base of the 2N2907 up towards the emitter and turn it off, which would tend to turn off the LED.

Two important things to remember:
1.Protect the battery with a resister(Yeah, I'm a broken record- sorry about that)
2.I said "maybe" a lot because I'm just sitting at my computer with no components around me and haven't breadboarded anything. So take everything I say with a grain of salt and see what dan has to say about this. :)

Dowd

[Larry3215]

Thanks for the tips Dowd!

I had my what meter in-line with the battery to be sure it wasnt drawing tooo much current it didnt even register.

I put my DVM in-line and the circuit only draws 10 to 20 MA max over the entire pot adjustment range and the lite stayed on all the time. That is with a cell voltage of 3.8.

Then I re-did the conections and the current went up to 2.01 amps and the lite was out! Hmmmmmm.

Its late and I may be doing something stupid. I will re-try all this tomorrow.

One qusetion - could you draw a quick sketch of where the pull up resistor goes? Keep in mind you are dealing with someone who has not done this sort of tinkering in a loooooong time :) I am way beyond rusty.

Thanks for the help!

Larry

[dowd]

The 10 to 20 milliamp is probably the current of the LED. This is good. It means the circuit was off with a 3.8 volt input.

When the current went up to 2 amps, the circuit probably turned on and the series resistance of your meter limited the current. It's good the meter limited the current. That is taking the place of the current limit resister I was suggesting. One question is why the circuit turned on.

Hmmm is right. If this is still on the breadboard it could be you had a loss of ground on the voltage divider. Check the connections on the, I think it was 15K, resister. That would have turned on the circuit and caused your current to jump up.

I really can't explain the light going out when the current went up though. That just seems wrong. Maybe you lost the ground on the LED too?

I'll try to sketch up something showing the pullup resister, but its just a thought. I'm not sure it will work right.

Dowd

[dowd]

Here is what I meant. I've never attached a picture before. Hopefully it works.

Dowd

[Dan Baldwin]

Dowd
The circuit Larry is working with does have a 1 ohm resistor in series with the collector of the TIP137 (see page two of this thread), so he should be relatively safe to hook it up to a battery for short periods. The TL431 draws a minimum of about .5 MA even when it's not turned on, so there does have to be a pullup path, but the resistors on the base of the TIP137 serve that purpose so the additional pullup resistor isn't necessary. Please keep helping out. You may think of something that I don't.

Larry, you might want to recheck the values of the 2 resistors on the base of the TIP137. Maybe one of them is still a 330k, or maybe they gave you 120k instead of 120 ohms. When you had the circuit hooked up with a 330 ohm resistor in series with a 12 volt power supply, the LED should stay on all the time because the circuit is regulating the voltage all the time. Once it's set to about 4.2 volts and hooked across a battery that is significantly lower voltage than 4.2 volts, the LED should go out. Make sure that the LED transistor pinout is correct, and if it is, you might want to try changing the transistor. Any general purpose PNP transistor will work for turning on the LED. It doesn't have to be the one I specified.

Dan

[dowd]

Dan,

Now I see the resister in series with the TIP. I missed that earlier and became immediately worried when he mentioned putting the lipo into the circuit while on the breadboard, and with the voltage possibly set below the lipo voltage. I got all weak in the knees and dashed out a reply.

Actually, I wasn't concerned about the pullup of the 431 or your darlington circuit. It seemed that before he rebuilt the circuit on the breadboard, the 431 and TIP appeared to be working great. He reported being able to set the voltage exactly to the expected range which really clinched that for me as working.

In fact it seemed clear that at one point while he had the 3.8 volt battery attached, that the shunt was off as expected, but the LED was still on, because he was only pulling 20-40 ma.

So I thought that might be due to the fact that he used a different transister in the LED drive circuit than you had designed. That is why I suggested altering the bias on the LED transister by putting in a large value pullup to help turn it off.

But now that he rebuilt the circuit I think it got worse; I was suggesting he may have lost a couple of ground connections.

Such is life with breadboards, amazing little things for trying things out, but finicky and messy.

I like your circuits; any more to post?

Dowd.

[Dan Baldwin]

Dowd
The only other circuits I have posted at present are a 2 cell lipoly CCCV charger. I'm using variations of this to charge as high as 3 amps, and to charge 3 cells, although it won't charge 3 cells from 12 volts.
http://www.rcgroups.com/forums/showthread.php?t=270573

and Andy W was looking for a simple analog servo exerciser, so I drew one up and posted it.
http://www.rcgroups.com/forums/showthread.php?t=269145&page=1&pp=15
If there's anything in particular you'd like to see, ask, and I might be able to help.

One of the problems with breadboarding is that it's very easy to short things out or, as you say, to pull something loose, and I suspect that that is what Larry will find. Since he was so close yesterday, I'm sure he'll find the problem and fix it.

Larry
I'll be around most of the day today, and I'll be checking in frequently to see how you're doing. Last night I was working on building my MM Tantrum until late, so I didn't check in and I left you hanging. Sorry. You can downgrade my beer to plain ole ordinary imported if you want.

Dan

[dowd]

Dan,

I guess that Larry will be checking the circuit in two stages. First with his 12V supply and resister to set the voltage and make sure the LED is on. Then put in a lower voltage to look for LED off and make sure the shunt is off(by monitoring current with his meter).

What voltage do you suppose he should set the circuit for?
What battery voltage do you think he should use to check for the LED off and shunt off?

Dowd

[Dan Baldwin]

The circuit as drawn has a VERY sharp knee, and the LED will only turn on when the circuit is trying to shunt. I couldn't see any voltage change from 10 MA to 2 amps on my meter with a resolution of .01 volts. A cell at any voltage below 4.2 volts should turn the LED off. If the LED stays on, there is a problem in the LED circuit, or in the value of the resistors in the base of the TIP137.

Larry
Take a quick look at the colors on all the resistors. There shouldn't be any yellow bands at all. If you still have some, you might still have some over 100k resistors in circuit. I think that eventually, the balancers will have to be set at whatever voltage allows his charger to recognize that the pack is fully charged. Probably the best bet is to measure the voltage on a pack just before it gets to the end of charge, divide that voltage by 3 (assuming it is a 3 cell pack) and use that voltage plus .01 or .02 volts to set the balancers.

You still out there Larry?

Dan

[dowd]

Dan,

That all makes sense. So if he still has the battery at 3.8 volts, for example, that should be fine to plug in and make sure the balancer is off when it should be.

And then when he first uses the three balancers in-circuit during a charge I would think he should just make sure that he never has all three LEDs on?

Also, you said something in an earlier post that got me wondering about Larry's reported problem of the LED being on when it shouldn't be.

I believe you mentioned that the 431 will pull 0.5 ma or more through the bias circuit for the TIP, even when it is not turned on.

It struck me that, if this current is high enough to provide sufficient voltage drop away from the high side, and if the gain is high enough on his 2N2907 transister, it might be possible that this could turn on the 2N2907 and light up the LED. How likely does this seem?

I haven't looked that close when using the 431 before, so I'm really not sure how much current to expect before you hit the knee.

(I guess that idly musing over other peoples' circuits is much easier than designing my own. So let me know if you get tired of my silly questions) :)

Dowd

[Larry3215]

Sorry guys. I have been under the weather the last few days.

I'll try to do some more complete testing tonight. I need to verify all the Mouser parts.

The circuit probably has a better chance of working if it uses the correct parts :)

Larry

[Dan Baldwin]

The current flow for that .5 MA idle current drawn by the 431 comes from the 330 ohm resister, 120 ohm resistor in the TIP137 base circuit. The idle current will produce a voltage of about .2 volts on the 2N2907 holding it off solidly. The 2N2907, like all silicon bipolar single transistors, has to have a voltage of about .6 volts to start turning on. The TIP137, on the other hand, has about a 1.2 volt turn on, because it's a darlington pair, and you have to actually forward bias 2 junctions.

Silly questions don't bother me, although I might start charging for answers.

Dan


Edut fur speling curektion

[Dan Baldwin]

Larry
At least if you use the right parts you can blame me when it doesn't work.

Dan

[dowd]

The current flow for that .5 MA idle current drawn by the 431 comes from the 330 ohm resister, 120 ohm resistor in the TIP137 base circuit. The idle current will produce a voltage of about .2 volts on the 2N2907 holding it off solidly. The 2N2907, like all silicon bipolar single transistors, has to have a voltage of about .6 volts to start turning on.

Ok, I get all of that. I was reflecting back to your earlier statement that the 431 could pull a minimum of 0.5 amp. I inferred from "minimum" part of your statement that it could pull more than the 0.5 amp under some situations, and was wondering how much more it might pull.

If it could pull, for example, 2 ma instead of 0.5 for some reason (and I have no clue how likely this is), you would have about 0.9 volt drop on the 450 ohms, giving about 0.2 volts across the 1Kohm resister, for a base current of up to 0.2 volt/1Kohm = 0.2 ma. If the transistor had a gain of say 100, then you could get 20 ma through the LED which should be sufficient to light it up.

But this tenuous chain of logic leads back to the thing I was wondering about but don't really know.

I'm wondering how much above the 0.5 ma you might expect, and under what circumstances. I didn't see anything in the datasheet to tell me. Might have missed it. Does it only vary within a few tenths of a ma? Is it a component-variation thing or based on the circuit or both?

Like I said, I have never really looked that close at this aspect of the 431 circuit design before.

(hoping I haven't hit the point of getting charged yet) :D

[Dan Baldwin]

A valid concern, Dowd, but I see in the datasheet http://www.st.com/stonline/books/pdf/docs/4467.pdf
that the minimum cathode current for regulation is .6 MA max, and the off state cathode current is 1000 NA, so we should have a safety factor of over 2:1 to prevent the LED from turning on prematurely.

We have nearly reached the point where I'll start charging you for correct answers, but I still won't charge for incorrect answers or wild guesses (WAGs) like this one.

Dan

[Larry3215]

Well, at least I am consistant :(

I checked everything I could on the first one and it looked good.

So I decided to build a new one, double checking all values and pinouts.

It behaves exactly the same way.

It lets me adjust the voltage to whatever I want between 4.02 and 4.3 aprox.

But when I plug in a cell at lower voltage (3.77) the LED stays on.

When I plug in a cell at a higher voltage (4.11) it stays on as well.

Adjusting the pot has no efect.

Any ideas?

Larry

[Larry3215]

New info - I pluged in a cell at 4.11 volts and measured voltage at the balancer input while I adjusted the pot.

Voltage stayed at 4.11 untill I lowered the pot - then voltage droped as it should, but the led did not go out.

My conclusion is the the circuit seems to be working, but I did something wrong in the LED part.

Larry

[Larry3215]

Both balancers behave in exactly the same way - so I get points for that dont I?

:rolleyes:

Larry

[Larry3215]

On the off chance you can tell anything from a picture (other than my sloppy breadboard technique) here are front and back views. Despite what it looks like, there are no shorts.

Larry

[Larry3215]

More pics - here is how I am doing the pinouts.

The 431 is viewed from the top as well.

The LED has one short leg and thats how I orient it.

Larry

[dowd]

You definitely get points for consistency. I looked over the boards and I'm not seeing the problem.

And to clarify, when you plug in the 3.77v battery the LED should be off. But whenever you are plugged into the 12V power supply and resister, the LED should be on regardless of the pot setting.

Maybe Dan will see something.

Dowd

[dowd]

Based on your observations I think you are right. The circuit seems to be working except for the LED part.

Curious and curiouser.

Dowd

[dowd]

If you plug in the 3.77 volt battery, does the LED still stay lit?

With this battery plugged in what voltage do you measure from the + battery input point on your board to the cathode of the 431? (it's where the 1Kohm resister attaches to the 431)

This voltage should be less than 0.7 volts.

If the voltage is less than 0.7 volts and the LED is on, I will wonder if you got some bad transisters from Mouser. Seems kind of unlikely though.

I think Dan had suggested trying a different PNP transister. Do you have any around that didn't come in this order? Possibly some that are a different part number? If so it might be worth changing a transistor.

Oh well, enough kibitzing for the night.

Dowd

[Dan Baldwin]

Don't you guys ever sleep?

I'm looking at your pictures now, Larry, and I don't see anything obvious yet. I have seen TO-92 transistors that had a different pin out, so that is one remote possibility. Can you give me the exact part number of that transistor that you ordered from mouser? Did you use the part number I suggested for the TL431? Have you actually checked the values of the resistors with a meter? For the purposes of troubleshooting, set the balancer to 4.2 volts with the set up rig, and leave it set there. Hook the balancer up to a cell that you know is below 4.2 volts. It's probably best to hook it up through your watt meter so you can see if something turns on that isn't supposed to. Try the voltage measurement that Dowd suggested. What voltage do you see? Try shorting out the 330 ohm resistor that goes from the base of the TIP137 to the positive rail (nothing bad should happen). Does the LED go out?

Dan

[dowd]

Sleep? A bold proposal. Based on your recommendation I'll consider it.

I looked back through the thread and in post 44 Larry said "I have 2N2907 instead of 2N3906" I didn't see any additional reference to a specific mouser part number. He mentioned the 2N2907 again in his photograph above of the actual parts. And that does look like a TO-92 case to me.

Here is a data sheet on a TO-92 case 2N2907 from ST:
http://www.st.com/stonline/books/pdf/docs/8870.pdf

[Larry3215]

Here is the parts list from the order. I will look and eyeball them when I get home.

9 652-MFR185 9 0.580 5.22
1.85A 30V
Bourns Radial Lead Resettable Fuses

9 567-290-1AB 9 0.380 3.42
TO-220 VERT/HORZ BLK
Wakefield Heatsink

9 512-KSP2907ACTA 9 0.090 0.81
.
Fairchild Small Signal Transistors

9 511-TL431ACZ 9 0.280 2.52
2.5-36V Prog Adjust
ST Voltage References

9 604-L934SGC 9 0.180 1.62
GREEN WATER CLEAR
Kingbright LED Super Bright

9 531-PT10MH-1K 9 0.400 3.60
10MM RND 1K OHM
Piher Trimmer Potentiometers

9 511-TIP137 9 0.680 6.12
PNP Power Darlington
ST Power Bipolar Transistors

18 71-RN60D-F-330K 18 0.210 3.78
1% 330K OHM
Vishay/Dale 1/4W 1% Metal Film Resistors

9 71-RN60D-F-45.3 9 0.210 1.89
1/4W 1% 45.3 OHM
Vishay/Dale 1/4W 1% Metal Film Resistors

9 71-RN60D-F-75 9 0.210 1.89
1/4W 1% 75 OHM
Vishay/Dale 1/4W 1% Metal Film Resistors

9 71-RN60D-F-1.0K 9 0.210 1.89
1/4W 1% 1K OHM
Vishay/Dale 1/4W 1% Metal Film Resistors

9 71-RN60D-F-15K 9 0.210 1.89
1/4W 1% 15K OHM
Vishay/Dale 1/4W 1% Metal Film Resistors

9 71-RN60D-F-10K 9 0.210 1.89
1/4W 1% 10K OHM
Vishay/Dale 1/4W 1% Metal Film Resistors

9 280-CR5-1.0 9 0.390 3.51
PWR 5W 1.0
Xicon 5W 5% Cement Power Resistors

9 539-CK06104K 9 0.600 5.40
100V 0.1uF 10%
Mallory Monolithic Ceramic Capacitors

Larry

[Dan Baldwin]

Sleep? A bold proposal. Based on your recommendation I'll consider it.


It was a question, not a recomendation. Lord knows I get plenty of beauty sleep, but I just keep getting uglier, (now you know why I don't post a picture of myself) and I lose many hours a night to this useless ritual. I was thinking about trying your method.

Yes, I checked out the data sheet on the 2907, and it looks like a plain old TO-92 with the base in the middle, but I have seen transistors (long ago) that looked like a TO-92, but had the base on the left and collector in the middle. I just want to make sure that Larry hasn't stumbled into one of those.

Sleep less, fly more
Dan

[Dan Baldwin]

Larry
I see a couple of resistors that don't look familiar to me, 45.3 ohm and 75 ohm. Did you buy those to add up to 120 ohm? None of the values in this circuit are critical, so 5% resistors are fine, you don't need to use the 1%. That applies to the 120 ohm as well. Anything in that range is fine. Have you done any voltage checks yet? I checked the datasheet on the transistors, and they should be fine.

Dan

[Larry3215]

I cant do any more untill I get home tonight, but I will then.

Yea - I couldnt find any 120's, but then I discovered I had some left over from an old charger project.

Thanks!

Larry

[dowd]

Yes, I checked out the data sheet on the 2907, and it looks like a plain old TO-92 with the base in the middle, but I have seen transistors (long ago) that looked like a TO-92, but had the base on the left and collector in the middle. I just want to make sure that Larry hasn't stumbled into one of those.


After I saw the specific part number that Larry bought, I was looking at the Fairchild data sheet for these transistors rather than the ST data sheet
http://www.fairchildsemi.com/ds/KS/KSP2907A.pdf

And I saw an interesting note:
"Suffix “-C” means Center Collector (1.Emitter 2.Collector 3.Base)"

Now there is a "C" in the manufacturers part number. KSP2907ACTA

Do you suppose these facts are related?
:D

[Dan Baldwin]

By George, I think you've got it

It didn't seem possible that these transistors were collector center because Larry used the part number I pulled out of my purchasing, and I haven't found any transistors that were "twisted", but reviewing my purchasing, I ended up not ordering those transistors for some reason. I'm not using that part number. Larry, try reversing the collector and the base on the 2907 of one of the balancers and see if you LED starts working.

Good homework Dowd
Sorry Larry

Darn!! Now I think I owe you both a beer

Dan

[dowd]

I'm still waiting for Larry's check to be sure this is the BFTCSOTBOTCLHB.

If so then I'll just take it as credit against my next set of silly questions. :)

Dowd

[Dan Baldwin]

I'm about 85-90% certain that that is the problem, so I think I'll go to bed. I'll check in in the morning.

Dan

[Larry3215]

"dowd]If you plug in the 3.77 volt battery, does the LED still stay lit? "

Yes

"With this battery plugged in what voltage do you measure from the + battery input point on your board to the cathode of the 431? (it's where the 1Kohm resister attaches to the 431)

This voltage should be less than 0.7 volts. "

volts = .076

"If the voltage is less than 0.7 volts and the LED is on, I will wonder if you got some bad transisters from Mouser. Seems kind of unlikely though.

I think Dan had suggested trying a different PNP transister. Do you have any around that didn't come in this order?

No

Larry

[Larry3215]

Sorry guys - I got home late and then I had wife/child/brother/dog issues :)

Darn family doesnt have thier priorities in the correct places ;)

I'll reverse a transistor and see.

Larry

[Larry3215]

Yureka!

We have lift off!

That was it - one little "C" - at least it wasnt a whole decimal place this time :)

OK, now Im gonna build at least one more and try it out on a 3S pack or two.

For starters, I think I'll calibrate them by plugging into an almost fully charged cell and setting it so the lite just goes off.

I havent ordered the voltage reference yet.

Thanks to both of you!

Larry

[Larry3215]

Quick question - I havent put the heat sinks on - how many amps can they handle without the sink? I'll limit my charge to that level.

Larry

[Larry3215]

OK. I got number 3 built and calibrated to the same cell.

I'm delibrately un-balancing a 3S1P 2200 pack now - discharging one cell by 60 mahr and another by 100. Then I'll put it on my Schulze at a low setting (0.2 amps for a start) and see if it blows up or balances :)

This is really great!

These are easy to build (once you know which pin is which) and cheep enough to do a bunch!

I need to come up with a cheep, easy, insulated enclosure/mounting system next.

THANKS!

Larry

[dowd]

No heat sink huh? Would be better to go ahead and screw one on each of the TIPs.

I think 0.2 amps would be ok. If you have a balancer that is dumping 0.2 amps you probably have 20 ma of that on the LED leaving 0.18 amps dumped at 4.2 volts through the shunt. So you have about 0.18 volts on the resister so that leaves about 4 volts on the TIP. 4 volts at .18 amps is about 3/4 watts. Gut feel is that should be OK. Surface area on a 1 watt resister is probably about the same as the TIP case.

If you find that you have the LED lighted on all three balancers during the charge, stop the charge because your charger may not ever think it is done; and the batteries aren't going to get any more charged anyway.

So it is official Dan - we found the big fat tom cat sitting on the back of the couch licking his ba... :D :D :D

Dowd

[Larry3215]

First results are exactly as advertised
Cell voltages were 4.05, 4.15 and 4.17 at the start of the charge.

!
Pluged in all 3 balancers and all had the led's off.

Started charging at .5 amps.

About 1 minute into charge the hi cell led slowly starts to glow - voltage = 4.18

About 2 minutes later cell 2 starts to glow - voltage = 4.18

Checked temps on the TIP137 and its 117 deg F - that seemed a little hi for no heat sink so I turned down charge amps to .2.

My Schulze decided to die on me - so Im useing an Astro 109 now.

It is in C3 mode at .2 amps - its going to take several minutes to get that last .02 volts into the last cell.....

Cell 3 led comes on at 4.18 volts!!

The Astro reads 12.58 volts and refuses to end charge.

I then turned up each balancer a bit at a time untill all led's are out again.

The Astro goes up to 12.6 and starts doing its pulse charge C3 thing and all led's are pulsing in time. Each cell bounces between 4.19 - 4.20.

The Astro will never end with these settings so I stop the charge.

Cell 1 = 4.18
Cell 2 = 4.19
Cell 3 = 4.20

I need to put the 12 volt source back on each balancer and do an actual calibration - but that can wait for some sleep :)

I am very pleased with the results. The balancers kept the hi cell from over charging and brought the two low cells very close - even with only a guess and by golly calibration!

Excelent job Dan and dowd!!

Larry

[dowd]

Uh oh. :eek:
The Astro 109 is not a Constant Current/Constant Voltage charger. It does some really funny things at the beginning and end of charge. It might not be appropriate to use this type of balancer with it. In fact I think Dan may have brought that up at the beginning of the thread.

And putting an almost fully charged pack on an Astro 109 can be a problem too which can lead to fireballs. Hmmm. It seems like this balancer could protect from the problem of blowing up packs on an astro charger. It certainly won't let the charger overcharge the cell. But you would always have to stop the charger at the end since it will always end up pulsing all three LEDs. It is basically designed to overcharge cells. So don't increase the voltage setting on the balancer based on what the Astro does.

What do you think Dan? Have you ended up designing an Astro-109-Battery-protector here in addition to a balancer?

Dowd

[Dan Baldwin]

Larry
I think the TIP137s are rated at 100 deg C (212 F), but I wouldn't dream of running them that hot. Warm transistors are just fine, even good and warm, but if you can't hold your finger on them, probably too hot. The Astro 109 doesn't work well with this balancer, or any other as far as I know. It will turn the normally snappy 109 into a real slug. It will take longer than a normal CCCV charger with the balancers attached. If you haven't ordered the voltage references yet, you really don't need to. I think the best bet would be to do as I described earlier; hook up a battery pack to the Schulze charger (hopefully you'll get it fixed), with your voltmeter across the leads. Write down the highest voltage that it gets to just before it trips out. The voltage really shouldn't change much at all during the last 10 minutes or so of charging. Divide that number by 3 for a 3 cell pack, and set the balancers for that voltage plus a little (perhaps .02 volts). The balancer LEDs should only turn on if the pack is out of balance. I have some part numbers for some small, cheap plastic enclosures from Mouser. You could screw down the balancers inside (or use servo tape), put the LEDs on the front, and drill holes in the side of the case to bring the leads out.

Dowd
Job well done. We couldn't have done it without you. You now have enough credit for 10 silly questions. I think we need to shoot that damn tomcat.

Dan

[Larry3215]

Uh oh. :eek:
The Astro 109 is not a Constant Current/Constant Voltage charger. It does some really funny things at the beginning and end of charge. It might not be appropriate to use this type of balancer with it. In fact I think Dan may have brought that up at the beginning of the thread.

And putting an almost fully charged pack on an Astro 109 can be a problem too which can lead to fireballs. Hmmm. It seems like this balancer could protect from the problem of blowing up packs on an astro charger. It certainly won't let the charger overcharge the cell. But you would always have to stop the charger at the end since it will always end up pulsing all three LEDs. It is basically designed to overcharge cells. So don't increase the voltage setting on the balancer based on what the Astro does.

What do you think Dan? Have you ended up designing an Astro-109-Battery-protector here in addition to a balancer?

Dowd

Yea - the Astro is far less than optimun to use as a balancing charger - but it works to some degree, as long as you keep the limitations in mind.

That darn C3 pulsed phase is a real nuisance tho. If you keep the amps down low it will give the low cells a chance to come up in charge, but the charger will never turn off unless the balancers are set to bypass at just over 4.2 volts. In any case - the balancers extend the charge time with an Astro waay longer at best.

It is possible to over volt a fully charged pack with an Astro 109, but you do have to work at it a bit.
You need to charge at over 1C to get the cells to go over 4.3 volts per cell - thats the Astro's threshold for cell count change. Also version 1.4 of the software on the Astro will only change/increase the cell count durring the C1 phase, which charges at 1/2 the indicated value. It (C1) only last 3 minutes. So you have to really pump in the amps to get the cell voltage to jump that far in 3 minutes.

Version 1.3 will change cell count durring C1 and C2 (and possibly c3 , but I'm not sure), so the older software is much easier to over charge a pack.

In any case - under normal circumstances you should NOT charge a fully charged pack - my example above should NOT be done unless you know what you are doing and are monitoring cell voltages at all times!!! It is very risky to top-off a lipo pack with an Astro 109 unless you are watching what is going on carefuly and continuosly!

A cccv charger is by far the best way to use any balancer. I would only use the Astro in a real pinch - like I was in - and then ONLY if you are absolutely SURE of what you are doing - and then I still would NOT recomend it - you will die and burn your house down and kill your cat for sure!! Ok - enough disclamers :)

Larry

[Larry3215]

Larry
I think the TIP137s are rated at 100 deg C (212 F), but I wouldn't dream of running them that hot. Warm transistors are just fine, even good and warm, but if you can't hold your finger on them, probably too hot. The Astro 109 doesn't work well with this balancer, or any other as far as I know. It will turn the normally snappy 109 into a real slug. It will take longer than a normal CCCV charger with the balancers attached. If you haven't ordered the voltage references yet, you really don't need to. I think the best bet would be to do as I described earlier; hook up a battery pack to the Schulze charger (hopefully you'll get it fixed), with your voltmeter across the leads. Write down the highest voltage that it gets to just before it trips out. The voltage really shouldn't change much at all during the last 10 minutes or so of charging. Divide that number by 3 for a 3 cell pack, and set the balancers for that voltage plus a little (perhaps .02 volts). The balancer LEDs should only turn on if the pack is out of balance. I have some part numbers for some small, cheap plastic enclosures from Mouser. You could screw down the balancers inside (or use servo tape), put the LEDs on the front, and drill holes in the side of the case to bring the leads out.

Dowd
Job well done. We couldn't have done it without you. You now have enough credit for 10 silly questions. I think we need to shoot that damn tomcat.

Dan

All good points Dan, and yes I know the limits of the Astro.

Great job and very well done to both of you!

I agree on the calibration idea and I will do that as soon as I get the Schulze fixed.

These balancers would work just as well with any cheep cccv charger - I dont think you really need a Schulze.

My plan for the balancers is to use them on an occational basis. Probably every 5 to 10 charge cycles.

At the field on a typical days flying, I ususlly charge a pack from one to three times. I dont feel its necessary to balance on every charge.

I have been monitoring my packs long enough to know they dont go out of balance hardly at all after 3 charges. If fact the most imbalance I have ever seen is mabey .03 volts after a dozen or more cycles. For some reason, new packs/cells seem to go out more and then they settle down after they are "broken in" - mabey 3 to 5 cycles.

In any case - these are for my piece of mind much more than as a necessity. So I will keep them at my charging station at home and plug them into my packs and set the charger to a fairly low amp level (under 2 amps for sure) and balance the packs once a week or so or as needed. I check individual cell voltages about that often anyway.

Once again - THANKS!

Larry

[Larry3215]

As soon as I get a cccv charger working I plan to do some more deliberate un-balanceing and testing and I'll start a thread in the battery section to report on how it goes. Im already certain it will be just fine tho :)

Larry

[Dan Baldwin]

Larry, I'm very sorry about the mixup over the pinout of the transistors. It wouldn't be quite so bad if you hadn't ordered the transistors that I suggested. I'll have to find a way to make it up to you.

Keep me up to date as far as how they work out

Dan

[Larry3215]

Larry, I'm very sorry about the mixup over the pinout of the transistors. It wouldn't be quite so bad if you hadn't ordered the transistors that I suggested. I'll have to find a way to make it up to you.

Keep me up to date as far as how they work out

Dan

Dont sweat it. That was a very simple thing to over look.

Becides - if other people build these (and I hope they do!) at least they will know what to look out for.

So, overall, I think it was a good thing :)

Larry

[Dan Baldwin]

Special thanks to Dowd for gently rubbing my nose in my screwup. Maybe I should give you credit for more than 10 silly questions. :rolleyes: NAW. :D

Dan

[dowd]

Larry,

You seem to have a very good understanding of the pitfalls of the 109 so I'll try to suppress the lecture. :)
I look forward to reading your reports on actually using the balancers. I have been wondering if I should bring out the taps and balance my cells. But I don't really know how much they get unbalanced. I use only two cell packs.

What kind of connector are you using to bring out all of the points between the cells?

Dowd

[dowd]

Dan,

Given how frequently I goof up I didn't dare get too obnoxious about it.

I would gratefully accept a higher allotment of silly questions. Silly questions are my specialty.

Dowd