|Oct 25, 2009, 07:47 PM|
Improved simple auto disconnector for battery charging/testing
I've found this high current battery cut-off switch/load tester that anyone can make quite useful.
This is an update of a very simple circuit I described at:
It's better, simpler and quicker to build. In fact it only really needs two components in addition to a LiPo monitor (plus the connecting wires of course) to work! Best of all, it requires no modifications to the LiPo monitor which works just as before.
You need one of these (Picture1) plus a cheap auto relay and one diode.
See also an update in post 11 for a couple of variations.
Junsi has introduced their PowerLog 6S since I wrote this post and, although more expensive, is attractive. It makes a complete test system by adding only the one auto relay (and diode) since it has the capacity in software to stay disconnected after triggering. It's the "Hold NC" option in the "Alarm Output" menu. No need for the latching second relay. Gives you a complete Wattmeter, 6S LiPo cell meter, tacho, temperature measurement, mAh meter, kV meter and servo tester in one. Very neat piece of work and very accurate. Couldn't be simpler.
What does it do?
Essentially we are adding a mechanical switch to a sophisticated LiPo (also Pd or NiMh) battery monitor to disconnect the battery when either the total, or any individual cell, voltage reaches a pre-set level. The switch (relay) can easily handle up to 150Amps depending on the model and fully isolates the battery from the monitor.
You can use it to:
All you need is the CellLog 8S LiPo monitor and a few other components (Picture2). The CellLog is made by Junsi and is my pick for the best LiPo monitor so far. It is very well designed and made, weighs only 18g, has a built in logger that will keep track of each cell voltage every 2 secs for up to 36 hours, and can connect to a PC to use the open source LogView software. It will monitor up to an 8S LiPo or any battery to 43V with a resolution of 1mV and has a comprehensive screen display that is quite readable. Critically, it has an external alarm output that can switch when the total or any cell voltage goes above or below a set value. It can also be precisely calibrated cell-by-cell using an external voltmeter if required. The alarm output switching circuit is rated at 49V and 500mA max. which is plenty to operate a heavy duty auto type relay directly. The output circuit is an open collector transistor, which is used as a switch and doesn't supply any power.
Currently HobbyCity are selling the CellLog8S for US$27.98. It comes with the lead required to connect to the relay as well as a general-purpose battery sensor cable, USB cable and software CD.
UPDATE: The CellLog 8M is exactly the same but without any PC connection for logging. It's about $14:00
Picture 3 shows a completed one in action discharging a LiPo into a car indicator globe load.
The circuit is trivial.
If you know absolutely nothing about electronics , this thing is extremely simple to make and if you can solder a connector to a battery wire you can make one. I've put the step-by-step details in the next post.
If you are familiar with electronics, it's obvious. Just connect an automotive horn/accessory relay to a 10-15V supply from your charger supply or a spare 3S flight pack using the CellLog output in line with the coil as the switch and with a snubbing diode across the relay coil. These relays typically come as SPST or SPDT with 30 -150 Amp 28V DC contacts and coil currents between 100 and 200mA at 12V. They are pretty cheap at the local discount auto parts shop. Typically $2-$10 depending on rating and quality. Use the CellLog menu to set the output to be NC. If using a resistive discharge load, the relay will cycle when the voltage drops below the cut-off then rises again as the load is disconnected. I like it because I use lamps as a load and they flash at me when the cycle ends but if you want a clean disconnect, add a second small DPDT 12V relay with a push button operated self-latching circuit to drive the big one. (See Post 11 for details.) Not sophisticated but simple, reliable and effective!
Last edited by jj604; Nov 15, 2011 at 03:07 PM. Reason: Reference to update in later post
|Oct 25, 2009, 07:57 PM|
Making the simple disconnector - part 1
How to make the high current battery cut-off switch/load tester.
This should enable you to make one even if you know nothing about electronics at all. You do need to be able to do simple soldering.
You need a CellLog 8S LiPo monitor plus a cheap auto relay and one diode.
You can get the auto relay at any auto parts or electrical shop. They are used throughout your car to switch heavy currents such as the horn or lights and are commonly called a "horn relay". Picture 4 shows a typical standard cheap 30Amp version. The connections are printed on the top of this one but they all are pretty much the same. If it has 4 connections, two are for the 12V coil (which closes the contacts when the voltage is applied) and the other two are the heavy duty switch contacts. If it has 5 connections (most common) then it has additional contact which is connected when no voltage is applied. We don't need it and I removed mine to make it easier to assemble everything by soldering all the parts and wires to the 4 relay contacts. See picture 5.
The only other thing you need (apart from the connecting wires and plugs) is a diode. Pretty much any power type diode will do as it doesn't do anything in the circuit. It's only (vital) job is to protect your CellLog from any voltage spike when the relay is switched off. Otherwise the momentary high voltage could wreck the CellLog output transistor. If you haven't got an electronics shop handy, you will find diodes in almost any electronic junk that runs off the mains and has a transformer power supply in it. The older style transformer plug-packs ("wallwarts" in the US) usually have two or four inside. A diode is generally a black cylinder with a white or colored band at one end.
Picture 6 shows how the whole thing goes together. Start by soldering the diode across the coil terminals (Pictures 7 and 8). Then add the various wires. The ONLY critical thing is to make sure the RED wire from the 10-15V supply goes to the banded end of the diode. If you get it the wrong way round, the CellLog will have a brief but merry life as it carries the short circuit current.
I assembled mine by using Deans plugs and added a simple switch so I could turn it on and off regardless of what the CellLog was doing (recommended). I soldered the parts directly to the relay connectors (Pictures 9 and 10).
|Oct 25, 2009, 08:06 PM|
How to make the high current battery cut-off switch/load tester - part2
By building some damwalls with masking tape and pouring in 5 min epoxy it ends up as a rugged potted unit. Pictures 11 and 12.
Plug your flight battery and load into the main connectors, add a 10-15 V supply (I used a spare retired 3S LiPo). Go into the CellLog menu and set the cut-off voltages you want (p10 in the manual) and set the Alarm Output Signal Type Setting to be NC (page 13 number 3 in the manual). When you plug in the balance lead the relay will close and stay closed until the alarm output triggers. The load will be disconnected, then will connect again as the battery voltage recovers. If using light globes as a load the effect is to flash at a slower and slower rate at the end of the discharge to attract your attention. The battery voltage will never go under the set cut-off however.
Note: You shouldn't leave the CellLog permanently connected after discharge however as it draws a small but significant (8mA) current to operate. Eventually it would discharge your LiPo.
As mentioned in the previous post you can use it to:
Connecting the two filaments together gives a 25 watt load at 12V. This is fine for 1,2 and 3S. Connecting two globes in series for 24V nominal works for 4, 5 and 6S (and so on). You connect them in parallel to increase the current at the same voltage. Commonly people use 4 globes in parallel as a "standard" field load for 3S or less. I made up a set of 6 globes with 3 in parallel as a 12V load and another parallel 3 in series with the first as a 24V load. It makes it easy to wire with just two plugs to connect either load. See pictures 13,14,15.
<EDIT>I have added a diagram in Post 118 showing the principle for two globes which may help folks understand how it is wired <EDIT>
See Table1 for the currents I got with the 6 globe setup. You can increase the current by increasing the number of globes.
Last edited by jj604; Jun 26, 2010 at 01:19 AM. Reason: Minor correction
|Oct 26, 2009, 01:07 AM|
Thanks, John. Bit embarrasingly simple really but often useful gadgets are.
Did you get the CellLog to do useful work at a higher sampling rate as asked in one of your early posts? It wasn't clear to me if the firmware upgrades were incresing the internal sample rate or it was just a LogView config adjustment.
|Oct 26, 2009, 02:37 AM|
New York City, USA
Joined Oct 2003
Don't know, waiting for approval from the client to purchase some CellLogs. But since it's listed in the firmware readme as an upgrade, it better be part of the firmware!
|Oct 26, 2009, 06:27 AM|
John, I just upgraded the firmware to 2.0.5. Under the System menu there is now an option "Rec. interval" which can be set between 0.5 and 60 seconds in 0.5 sec intervals.Very nice!
|Oct 26, 2009, 07:06 PM|
I had thoughts of making something like this, though my electronics knowledge/experience suffers. I came up with almost the same thing but didn't pursue it any further. Nice little "how to" that is very practical, cheers for putting it up
|Oct 26, 2009, 07:34 PM|
Way to simple ,way to versatile there fore there must be something wrong somewhere. I really do not need another gadget but am tempted to build one anyway.
This would be a great cottage industry product for someone to produce in small batches and market.
David at Progressive RC carries the iChargers and CellLog8S for those state side in the market for one.
Thanks for sharing John
Last edited by everydayflyer; Oct 26, 2009 at 07:56 PM.
|Oct 28, 2009, 04:37 PM|
Using as a low tech but accurate battery tester
This simple thing can be quite surprisingly useful as a battery tester for folks who don't want to get all serious about it but who could use an accurate record of their battery's performance. It is also very rugged and portable for field use. The secret is the smarts built into the CellLog. It will accurately measure the time of discharge into a "standard" load and also give you the end of discharge voltages for each cell. Given it has a resolution of 1mV and can be accurately calibrated for each cell if you want to, it's quite impressive. Write these on the pack with the date and temperature, test them every now and then, and that's all most people need to keep track of how their packs are doing. Attach it to your PC using the supplied cable and free LogView software, add your wattmeter/Eagletree/EmeterII and you have a poor man's CBA (albeit without the variable constant current or power test capacity). Not bad for less than $40 and 30 minutes work.
The original circuit (which does not permanently disconnect the load when the cut off voltage is reached) is less than ideal since you want the CellLog to store the time from start to first cut off not the additional time as it cycles.
The two modifications below fix that. The first is the simplest and uses two identical auto relays and diodes. Has the advantage of not having to source anything from an electronics shop and is easy to make. Just glue the two relays together with epoxy and solder everything to the robust relay terminals to make a compact little unit. Easy and quick BUT it does put the load of two heavy duty relay coils on the CellLog. Should be well within specs (<500mA) for most relays, which are normally 100-200mA coil current, but it is a bit inelegant. The second uses a 12V Double Throw, Double Pole relay to drive the big one. You need to get one of these from an electronics shop. They are a very common relay and used in hobby kits etc. With this configuration, the only load on the CellLog is the small relay coil (a few mA) and even the smallest of these 12V DTDP relays will switch 1 A so you can drive a really robust 12V power relay to do the load switching. If you change the push button "START" switch to a normal toggle switch you can use it in either "cycle" or "cut off" mode but you need to remember to switch it off again after you have started to get the latter. The ON/OFF switch is there to disconnect the load at any time if you want to. It is normally left on in these two circuits and can be omitted if you want since the load can always be safely disconnected by unplugging either the balance lead from the CellLog or the 10-15V supply.
Configuring the CellLog
The Cellog has a fairly comprehensive menu structure and is navigated with only 3 buttons so can be a bit confusing. Here's step by step instructions for setting it up for this project.
Connect the balance connector of the battery to the CellLog.
NOTE: Pin 1 MUST be connected to the -Ve of the battery. Normally this is a BLACK wire on a balance connector. Pin 1 is clearly marked on the CellLog case but it is hard to see because it is a black molding.
The CellLog comes up after 2 initialization screens with the last monitoring screen you were using so will depend on what you did last. The steps below should work regardless of what screen you start from.
The CellLog has only 3 buttons and all normal functions are achieved by Pressing or Holding one button at a time only. Press means to push the button and let it go immediately. Hold means to press the button and hold it for more than 3 secs until the screen changes. The 3 buttons are TYPE, HOLD and MENU which are also the functions for UP, DOWN and ENTER. Which function depends on what you are doing but it is fairly obvious.
Note that the label on the button HOLD refers to a function in the CellLog not the action of Holding.
Worth remembering is that in most cases Holding the MENU (Enter) button takes you back one screen or step or to the MAIN MENU.
Setting the correct output for the alarm circuit From the normal monitoring screen:
1. Hold the MENU (Enter) button till the MAIN MENU screen appears
2. Press the HOLD (Down) button once to reach System
3. Press the MENU (Enter) button
4. Press the HOLD (Down) button 2 times to reach ALM Output
5. Press the MENU (Enter) button
6. Press the HOLD (Down) button once to reach NC
7. Press the MENU (Enter) button to select NC
8. Hold the MENU (Enter) button 3 times till the normal monitoring screen appears
Setting the alarm voltage and trigger functionFrom the normal monitoring screen:
1. Hold the TYPE (Up) button till the SELECT TYPE screen appears
2. Press the HOLD (Down) button as many times as necessary to reach the type of battery you are testing. Default (no press) is LiPo, and there is LiLo and LiFe plus 5 “User n” labels. You can set separate alarm voltage conditions for all 8. They can all be renamed to anything you want for convenience. It’s a bit tedious but works –see the manual page 10. For example you could set up a set of alarm conditions named “Standard” for bench testing.
3. Press the MENU (Enter) button to select the label
4. Press the HOLD (Down) button 2 times to reach Alarm
5. Press the MENU (Enter) button
6. Press the TYPE (Up) and HOLD (Down) button as required to reach Cell Voltage, Pack Voltage or Time Over. Press MENU (Enter) to select the one you want to set.
a. You can set an upper voltage limit HV a lower voltage limit LV or a maximum cell voltage difference ΔV for the cells. Pressing MENU (Enter) moves from one to another. TYPE (Up) and HOLD (Down) increases or decreases the value. Holding the MENU (Enter) button returns to the previous screen.
b. You can set an upper voltage limit HV a lower voltage limit LV or a maximum pack voltage difference ΔV for the whole battery.
c. You can set a Time over alarm to limit the total time of the test.
7. Hold the MENU (Enter) button as many times as required till the SELECT TYPE screen appears. Choose the battery type you are configuring and press the MENU (Enter) button.
8. Press the HOLD (Down) button twice, then the MENU (Enter) button to get to the ALARM SETTING screen.
9. Press the HOLD (Down) button three times, then the MENU (Enter) button to get to the ALARM TRIGGER screen.
10. Press the TYPE (Up) and HOLD (Down) button as required then press the MENU (Enter) button to toggle on or off which alarm conditions you want to disconnect the battery. You can choose none (doesn’t make much sense though!) or all four if you like.
Hold the MENU (Enter) button as many times as needed until you get back to the normal monitoring screen, or just unplug the CellLog – it’s quicker.
Last edited by jj604; Jan 12, 2011 at 10:24 PM.
|Nov 01, 2009, 06:45 PM|
Using as a low tech but accurate battery tester UPDATE
Just to clarify the statement below, "It will accurately measure the time of discharge into a "standard" load."
The CellLog of course measures the elapsed logging time. If you want the accurate time of discharge you have to start the log when the discharge starts (easy) and end it when the discharger switches off (bit harder since you have to sit around and wait for it to switch). It's MUCH easier to just up load the file to Logview and read it from the graph.
I've attached some pictures of the two relay version using the DPDT relay. Still very compact and rugged if assembled using the 5min epoxy method.
|Nov 08, 2009, 08:44 PM|
I cobbled one of these together using a rather heavy duty (1/4'" dia. contacts) relay that I happened to have laying around(us Hams have such stuff),set Low Voltage Alarm for cells and 3.85V Connected a 3 bulb (#1157) array for the load and a fully charged 3S 3300 and in 8 minutes it was flashing merely away. Disconnected load and cells settled to 3.89 which suits me just fine for storage.
Another data point: Using 1157s 4 of total 2S2P discharging a 3S LiPoly 3.5 amps. 500 mAh discharged in 8:40 ( approx. 58 mAh. per minutes)Not exacly super fast but bulbs are not blinding bright,stay much cooler and should last a whole lot longer and besides same load can be used for a 4-6S and discharge rate will increase with volts.
3S 2200 discharged in 12:15 , 711 mAh discharged
3S 2200 discharged in 12:40 , 732 mAh discharged.
3S 2250 discharged in 11:35 , 683 mAh discharged.
I can allready see that this will become my standard discharge to storage device as it is simplier that using most chargers and a whole lot simplier
than firing up one of my CBA IIs.
Last edited by everydayflyer; Nov 09, 2009 at 05:25 PM.
|Nov 09, 2009, 02:15 AM|
So Charles, what happened to, "Way to simple ,way to versatile therefore there must be something wrong"?
I think it was Albert Einstein who said, "Things should be as simple as possible - but no simpler." After all, credit goes to Junsi who did all the electronic applied-magic bits.
It is somehow satisfyingly crude and effective though.
|Nov 09, 2009, 06:43 AM|
One of my favorites has always been that "anything can be improved to the point that it no longer works."
Want an example? If you are over say 40 years old remember how clean your mother's wash was? They have improved laundry detergent to the point it barely cleans anymore.
I have one real complaint with the Cell Log. It is to darn small. If the display was say 3 " wide X 2" high there about it would be near perfect. I understand the mini size / weight so it can be used airborne and I understand larger displays are more expensive and use more current but a bench / ground based unit would be killer.
I may wire an obnoxious alarm (beeper) to mine that sounds each time relay opens and place the relay in an enclosure but then I have other such project that I have been using for years that I never seemed to get around to finishing / dressing up.
Thanks for the inspiration.
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