Putting a load on a battery tester

I want to make a battery tester for lipo batteries with balancing leads. I want to test each lead separately. Do I need to put a load on each pin to get an accurate reading? There are numerous circuits for this, but none I found mention a load on the battery. Thanks

Lipo tester devices are cheap and convenient, I know that making your own might be the whole point.

I have a hand-made one on a retracting key-chain thing, I clip,it to my pants pocket and have it ready to unfurl in an instant. I used a stack of LED self-powered voltmeter modules. Instant! Quiet! Nerdly!

New lipos should almost not need balancing, but inevitably they do.

So to check a battery, you must check cell by cell. To charge a battery, you should use a balance charger.

To check a cell under load, it must be, um, loaded.

So a full up 4s battery checker, for example, could be made with four load resistors and 4 of those little self-powering LED voltmeters.

But typically lipo state of charge is determined by unloaded voltage, at least for batteries that are not old or damaged.

Testing under load is good for disqualifying a pack or seeing how it might perform in real circumstances. In the field I wouldn't bother.

If you just put a load across the entire battery and measure the balance leads, you probably 98 percent home. It would def point up an underperforming cell.

Automotive light bulbs are good for that, you can get them in various voltages and wattages.

a7

Thanks for the response.
I have purchased several myself, but where is the fun in buying one when I can build one. This really is a winter exercise to play around with Arduino.
I would like to build one that I can plug the balancing pins into and get the readings of each cell all at once using a lcd display.
I get the point of >>>To check a cell under load, it must be, um, loaded.<<< What I was wondering though is what specs I should be using to load them with. I was planning to use a resistor (maybe 100 to 300 ohms) to use for the load.
The batteries will be 3 to 6 cells.
Thanks again!

100R or 300R is hardly going to "load" a 6 cell.
Think about using a couple of 12v auto brake lamps in series for the 6 cell and just one for the 3 cell on the main leads.
They are around 21w (brake or indicator) if memory serves correct, cheap, plentiful.
If you feel that is too much, use a couple of the 5w lamps.
No need to work out resistor resistance values or wattages.

Actually I will be loading each cell. With your advice, I’ll put a 6 volt light on each lead. Thanks again

A 6 volt bulb with 3.7. volts nominal on it isn't going to get you much of a load.

A 1 ohm resistor is more like a real load, and 2 or 3 or 4 in parallel might be more like what you draw in use, depend of course on your use case.

I drain 1000 mAH batteries in 5 minutes… do the maths, that's huge current.

But testing under load for state of charge is not necessary for lipo chemistry - good lipo cells can be evaluated easily as their voltage correlates usefully to SOC.

You should know about and check in with the ppl at

a7

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