If I’m doing capacity tests, what voltage cut off should I use on the discharge for AA and AAA and also 14500’s?
1.1v for NiMH and 2.8v for Li-Ion?
2 Thanks
What are you using for the test?
Most capacity charges define the lower limit and you don’t have control of that. A few allow some choices.
You “may” have some control of the charge/discharge rate, which WILL affect lower voltage determination. The higher the amp draw, the quicker it will hit low voltage termination and “bounce back”. Very low amp draw will give you higher capacity reading than higher amp draw. Old cells with higher internal resistance will terminate more quickly than newer cells even when using low amp draw.
FWIW I tend to use 1.0v for NiMh, and 3.0v for Li. For discharge current I generally use 1/5 capacity spec to see what the manufacturers ‘claims’ to be using. (I RARELY see claimed capacity for any cell, even when brand new).
If I want to see “what the cell will do” I push the amp draw up, which WILL change/lower the capacity seen.
I have a dedicated discharge unit for capacity test that I can push to 2.6A, way higher than capacity chargers will do.
I’m using some fairly advanced chargers I have from when I flew RC things as my MiBoxer doesn’t have the option.
I started messing with the discharge rate on NiMH’s’s as it was quite high and as I understand it’s more accurate to do it like that, whilst I was in there thought as you could I may as well select the optimum cutoff voltage.
I’m not looking to take the batteries too low, just a level that gives an accurate indication of how much charge they currently hold and how good they are and also possibly using it to cycle as some of them have just sat unused and I’m sure it’ll help.
I went to do it with Lipo’s and it’ll let me change the rate but just quotes it as 3.7v i.e. a single cell which I can’t alter so don’t know what level it’ll take it down to although I belive one of the other’s I can set a cutoff as well.
Thanks to you both of you though 
Which RC charger? I have an Accucell-6 and a Turnigy MAX80W. Both “work” fine, but I’ve learned the charge/discharge accuracy is poor on the Turnigy. AC-6 seems OK.
Since those chargers use resistors to discharge, they get hot and are limited in discharge current. I can tune the rate within limits, but I can’t set low cut-off. That’s based automatically on cell chemistry (voltage basically).
I’m assuming yours has the option of using balance ports? Mine do and I can do multiple cell Li-packs with that as long as they have a balance tap. I’ve converted a number of NiXX power packs to lithium and always build them with balance taps.
I’ve adapted a holder for single ‘can’ cells. Got to admit, since getting out of RC and into BLF I don’t use the RC chargers much. They are still good for some odd jobs.
Got a [Wattmeter]? With a bit of ingenuity and some light bulbs you can create a simple/manual discharge device that works pretty well…but you have to watch it like a hawk so it doesn’t over discharge. Been there, done that on some new lithium packs I was testing.
Aggghhh … ha ha … this mad me laugh … yes have the light bulb setup which I made myself, I think from memory I bought a slightly more advanced interface (2nd time around) that had a voltage cut off.
It’s in a stationary cupboard and hasn’t been out for a while, it’d be a big learning curve to set it up again.
Chargers … iCharger 306b and a later I think licensed dual version of the same from hobby king.
Because I don’t like discharging batteries on there because any heat created is bad for a decent charger I’ve been using an old Sigma … if that blows I’m not bothered.
Regarding capacity testing of lithium ion cells, the IEC61960 standard says:
“The cell or battery shall be discharged, in an ambient temperature of 20C +/- 5C, at a constant current of 0.2A, until its voltage is equal to the specified end-of-discharge voltage.”
The manufacturer specified end-of-discharge voltage for many cells is 2.5V.
You must have been into RC later than I did. I was literally on the cusp of moving from NiXX > Lithium. The chargers I have don’t have nearly the capability of your iCharger. Same general characteristics, but not the power.
BLF, a lot like the RC Forums, is a learning environment. I thought I had a handle on ‘batteries’ when I started here. The reality is I had a basic education. But, that was a foundation to learn from. I suspect you may have a similar experience.
The Japanese prefer 2.50v for their discharge floor, but the South Koreans utilize the 2.75v number.
Chris