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Old Jan 18, 2009, 06:45 PM
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I tried to feed the Voltage for 8 Cells to the balnacer port and the 33.6V as well. I got some 4.20 Values but also others 5xx.
The input resistance seems to be too low for my voltage devider.
There is NO chance to save anything within my service menu (iMax B8).

May be, the second page of the menu is for adjusting then Balancer, because my B8 has 8 trimmers!

The current measurement is not very exact. I get 0.12A while charging with 0.1A; 0.85A instead of 0.8A. The LM2904 OPAmp with the R020 current shunt seems not to be very precise

I found a curious Error in the input voltage divider:
The voltage was OK with low current flowing, but was too high with current flowing. So it overloaded the Lipos!
I guess there was a wrong resistor assembled (1002 instead of 1003).

May be someone can confirm...
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Old Feb 17, 2009, 09:57 AM
Episyrphus balteatus
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Sweden
Joined Dec 2008
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Quote:
Originally Posted by hktan73
Hi dusk,
that is exactly what I had made, but only for 3 cells.
I use 68 ohms 1% 1/4W resistors simply because I happen to have some laying around. Although 1 % resistors, I get very close reading on them when
plug to the battery and measure with multimeter. I got same 3 digits on all.

I use it to test the balancer voltage readout on my IMAX B6.

I am surprise to see that even in LIPO CHARGE mode the readings jumps up and down as if it is doing balacing. It will stable down after a few seconds for about 1 second and start fluctuating again.
During the stable display my readings are 4.19,4.17,4.13 with a slightly discharge battery pack. Can't plug a full pack for charging right?

This values tallies with what I normally gets after charging. My battery will charge to 4.18 4.20 4.24

I am thinking a similar one for 6 cells will be what we need to calibrate the charger.

Unfortunately my menu 1 is not accessible from the beginning.
Hi!

Can someone please give me some advice on setting up this resistor thingie? I have found a guy that has a variable power supply and a really precise multimeter that will help me with this calibration.

I talked to my local electronics store today (they are the best in my country) about setting up the resistor grid and the guy said that he couldnīt tell me what value the resistors should be since we didnīt know the internal resistance of the charger. Did we miss something or is he right?
How should the grid be connected? Is it just a matter of expanding the grid "hktan73" posted (see his diagram)?

What should the values of the resistors be if I want to be really accurate?

Cheers!
/Fred (From Sweden)
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Old Feb 17, 2009, 05:27 PM
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Quote:
Originally Posted by Paxman
How should the grid be connected? Is it just a matter of expanding the grid "hktan73" posted (see his diagram)?

What should the values of the resistors be if I want to be really accurate?
Since the internal resistance of a lipo is quite low, I would assume that the internal resistance would be quite high to limit the current.

I would try it with reasonably high resistor values. Five resistors in series, forming a five way voltage divider. Then make sure you get the exact voltage value at each of the six connection points.

My guess would be, that if you get the resistor values badly wrong, then the charger would just fail to calibrate and you could try it again with different resistor values.

Let us know how you go.
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Old Feb 18, 2009, 12:54 PM
Episyrphus balteatus
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Quote:
Originally Posted by dusk
Since the internal resistance of a lipo is quite low, I would assume that the internal resistance would be quite high to limit the current.

I would try it with reasonably high resistor values. Five resistors in series, forming a five way voltage divider. Then make sure you get the exact voltage value at each of the six connection points.

My guess would be, that if you get the resistor values badly wrong, then the charger would just fail to calibrate and you could try it again with different resistor values.

Let us know how you go.
This is what I donīt get...is the resistor value arbitrary? As I understand it in a "normal" circuit you need an exact value on the resistor to decrease the voltage. Say that you have 24 V system in your truck and want to use a 12 V application in it you need a resistor with an exact value to reduce the voltage by half. Or am I wrong?

Of course I will post all my results...if I get any!

Cheers!
/Fred
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Old Feb 18, 2009, 04:45 PM
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Canberra, Australia
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Quote:
Originally Posted by Paxman
This is what I donīt get...is the resistor value arbitrary? As I understand it in a "normal" circuit you need an exact value on the resistor to decrease the voltage. Say that you have 24 V system in your truck and want to use a 12 V application in it you need a resistor with an exact value to reduce the voltage by half. Or am I wrong?
The resistor values are arbitrary (up to a point). They do have to be as close to each other as possible.

I guess that in the truck example you are referring to, the load is in series with the resistor. In our case, the resistors go all the way from +ve to -ve, and the load is in parallel with each of the resistors.

The value of the resistors is only relevant with reference to the measuring circuit inside the charger. If the circuit has a high resistance, then any reasonable value for our resistors will do.

If it was me, I would choose a value for the resistors, such that it is as low as possible, but still limits the current sufficiently to prevent the source voltage from dropping and the resistors from getting hot.
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Old Feb 18, 2009, 05:23 PM
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@Paxman: I'm not sure about the sense of the resistors, as I own a imax B8 which is different. It has 8 adjustable trimmers inside to calibrate the balancer measurement.
But, if it makes sense to build such a voltage divider, You should normally use resistors as low as possible. But keep in mind the current flowing from the power supply.
Assuming, that the input resistance of the BC6 measurement circuit keeps to be constant, one can use a outside divider with variable resistors (may be 1KOhm fix + 100 Ohm variable in series for each resistor) and calibrate them by measuring the voltage at each input pin. Apply 25.2V and adjust 4.2V,8.4V,12.6V ... It is necessary to repeat each adjustment after any single change of one resistor. You should use a precise Voltmeter with a high input resistance.
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Old Feb 18, 2009, 05:23 PM
Episyrphus balteatus
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Quote:
Originally Posted by dusk
The resistor values are arbitrary (up to a point). They do have to be as close to each other as possible.

I guess that in the truck example you are referring to, the load is in series with the resistor. In our case, the resistors go all the way from +ve to -ve, and the load is in parallel with each of the resistors.

The value of the resistors is only relevant with reference to the measuring circuit inside the charger. If the circuit has a high resistance, then any reasonable value for our resistors will do.

If it was me, I would choose a value for the resistors, such that it is as low as possible, but still limits the current sufficiently to prevent the source voltage from dropping and the resistors from getting hot.
Ah, so this is what I was missing! In my grid the resistors are in parallel with the different circuits and I was thinking resistors in series for the truck circuit example. In the grid the resistors are only there to avoid short circuit, not to lower the voltage?

I got a tip from a guy on a swedish forum to use 100 ohms resistors, do you think that would be a good value as long as they are really precise? What would be the difference with a low value v.s. a higher?
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Old Feb 18, 2009, 07:21 PM
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Quote:
Originally Posted by Paxman
Ah, so this is what I was missing! In my grid the resistors are in parallel with the different circuits and I was thinking resistors in series for the truck circuit example. In the grid the resistors are only there to avoid short circuit, not to lower the voltage?

I got a tip from a guy on a swedish forum to use 100 ohms resistors, do you think that would be a good value as long as they are really precise? What would be the difference with a low value v.s. a higher?
Have a closer look at diagram in post #28. That's what you need, but with 6 resistors.

The resistors neeed to be exactly the same. I like the idea of using variable resistors to tune the circuit. Best bet would be to get some 1% accurate resistors and then variable resistors 2% the size of the main resistors.

Using low value resistors would result in higher currents, more heat and a possible voltage drop accross your power source.
Using high value resistors exposes you to the possibility of the accuracy of your voltage divider being compromised by the measuring circuit inside the balancer.
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Old Apr 17, 2009, 11:43 PM
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calibration worked for me without resistor upgrade

I had the same problem with my IMAX B6 - the charge voltages were all different after balance charging. ( e.g. 4.18/4.16/4.19/4.16/4.23 /3.99)
The cell #6 was always in danger by getting deep discharged to 2.89
when the other cells went down to 3.7V during use.

Because I use six-cell LiPos, I decided that it would be easiest for me to charge all 6 cells of a LiPo individually to exactly 4.2V each with the IMAX by putting two wires into the balancer ports of one cell after the other - checking with my multimeter that I reached exactly 4.2V. When done I calibrated with hidden-menu-1 (holding stop & inc at power-on with the corretly loaded LiPo connected to the IMAX B6).

And that all worked very well !!! - when now loading my 6 cell Lipo after use/discharging, I get e.g. 4.19/4.19/4.18/4.19/4.20/4.19 - I am very happy with that.

So the baseline is - dont mess with the resistors - you do not need to change them - just go for the calibration - but you need a perfect 6 x 4.2V source - and you'll be very happy with your IMAX B6 !

Hint/Question to the producers of IMAX B6 - why dont you do the calibration in your factory ???

Many Many thanks especially to "Dusk" and to everybody on this thread for the valuable information !!
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Old Apr 28, 2009, 11:46 PM
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Would there be a reason that the menu #1 will not start to check & calibrate each individual cell? I plug it in, hold the two buttons, unit starts scanning through the numbers & settles in on 3038 if I have the two deans connector in series & hooked to the charge port, if I don't have the charge port hooked up the number goes higher every time I re-arm the chrger, highest I saw was over 6400. Do I need to plug in the balancing taps AFTER it has scanned through the 4 digit value?

I also tried menu # 2. A charged to 12.56 volts, it was showing 12.31 volts, the closest I could get was 12.47 volts by going all the way to +20.


Has anyone here used the Turnigy Accucel-6 charger? I'm wondering if it has the same problems as the Imax, don't want to buy one to find out its the same lemon that this one has turned out to be.
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Old Apr 29, 2009, 12:21 AM
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Quote:
Originally Posted by ktaylor
Would there be a reason that the menu #1 will not start to check & calibrate each individual cell?
I had a similar result when the cell voltage was not close enough to what the charger was expecting. If I remember correctly, both the charge plug and the balance connector need to be plugged in the entire time.

Another possibility is that your voltage source or battery is correct, but the resistors in the charger are so far out of spec, that the charger is not able to compensate for the error.
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Old Apr 30, 2009, 05:20 PM
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calibration options

Hello I'd like to know if it would be possible to calibrate the unit with 2 3cell lipos.

I bought a Bantam BC6-10 after reading this thread because I didn't want to take any chances with my lipos, but I'd still like to get this clone working... it's a mystery B6, and the menus are identical and my voltages are off. I didn't think it was a big deal but thankfully I read the results and the consequences before doing too much(hopefully!) damage.

Im going to go back and re-read the posts on the calibration procedure but essentially I'd like to know if I can calibrate with 2 3 cells somehow... or can I calibrate with just a 3 cell? Would I be able to go back and do the other 3 later?

Sorry if I dont fully understand the options... I'd just like to do it right and not mess anything up.

Bolts
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Old Apr 30, 2009, 05:38 PM
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Quote:
Originally Posted by bolts
Hello I'd like to know if it would be possible to calibrate the unit with 2 3cell lipos.
Yes, just set them in series. You will need a 2x3S to 6S balance adapter.

Quote:
Originally Posted by bolts
or can I calibrate with just a 3 cell? Would I be able to go back and do the other 3 later?
No, if you try with just 3 cells, the balancer will terminate the calibration process.
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Old Apr 30, 2009, 07:07 PM
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My Story:-
-
I have a Turnigy Accucel 6, since approx last October.
(believe same...pcb almost identical to Imax b6, from viewing other threads)
-
Noticed that the total voltage was over-reading....found how to correct this a while back (from memory...tweaked to limit...think now only 20mV out for 6s pack)
-
Could see that the individual charger cell readings, although closely balanced to 10mV throughout CV part of charge, did not quite add up to total V.
-
Ignored this, presuming all balancing fine, and at least I knew final voltage was accurate.
-
Casually checking actual individual cell voltages today.....all not well.
-
1st 3 x cells:-
-
Charger.............4.17-4.18-4.17
Actual...............4.17-4.22-4.19
-
These reading discrepancies are virtually consistent regardless of the pack being charged on same ports.
-
-
Desperately surfed in attempt to find further hidden menus, to come across this goldmine of a thread. (found the long one relating to swapping out a bunch of tiny surface-mounted resistors for higher tolerance equivalents.....despite much practical practical "hobby" electronics experience, not sure brave enough to tackle this !!)
-
Anyhow....I will charge my 2 x 3s packs on another charger/balancer, and do my best to balance all, then nervously attempt the "Stop/Inc" on power up.
-
-
For those who have tried this, please advise following:-
-
a) Presuming it is available, do I just leave it totally alone to sort itself out, or do I have to depress any button to exit it?
b) If I screw up in any way, totally ruining its ablilty to balance, do you suspect that JUST the balance funtionality would be the only thing affected, needing me just resort to external balancer?
-
Not sure of other risks in doing this....agree it would be a real luxury to be able to repeatedly perform this calibration....looks like impossibility with all being locked down.
-
-
All info in this thread very much appreciated....thanks.
-
Steve
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Old Apr 30, 2009, 07:55 PM
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Quote:
Originally Posted by SteveM
I will charge my 2 x 3s packs on another charger/balancer, and do my best to balance all, then nervously attempt the "Stop/Inc" on power up.
Some people have reported that when using battery packs to calibrate, the final calibrated voltage is a fraction less than the original battery pack voltage. So do not undercharge the battery. Make sure it is at least 4.20 per cell, maybe even 4.21 or 4.22

Quote:
Originally Posted by SteveM
a) Presuming it is available, do I just leave it totally alone to sort itself out, or do I have to depress any button to exit it?
It's been a while, but I think that it did it all itself. Either way, it's not too hard.

Quote:
Originally Posted by SteveM
b) If I screw up in any way, totally ruining its ablilty to balance, do you suspect that JUST the balance funtionality would be the only thing affected, needing me just resort to external balancer?
Yes, only the calibration of the balancer circuit is affected and the charger can still be used as a non-balancing charger with an external balancer.
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