Watchamacallit said:
Measuring using the balance lead (so negative on b0, red to b1/b2/b3 etc) and the increase is around 3.49-3.47 between each one.
So for example, readings were:
3.47,
6.96
10.45
.. etc
Not sure if i'm doing it right or if that increment even matters, but thought i'd bring it up just in case.
Not sure what you mean by "that increment". :?
You may already be testing and recording the right information, but I'll go into more detail just so you can be sure:
The thing you are testing is the cell voltages. Those do matter. So does the difference between them. You're not looking for an average difference, you're looking for the actual exact difference, because the bigger the difference in voltage, the bigger the difference in the groups' charge state (whcih may mean a difference in capability, or capacity, etc).
So what you want to measure and record is each cell group voltage. Doing this at the BMS pads for the balance connector, starting from the BMS B- wire if the most negative wire of the balance connector isn't equal to B-. (if it is equal, then reading from B- to most negative balance pad will read 0v; anything else should indicate there is a cell group there, and that the most negative balance pad is the positive of that group, and you need to record that voltage as well).
You can measure by keeping the black meter lead on the B- wire, and moving the red lead to each solder pad of the balance connector in turn, starting at the most negative one and ending at the most positive one. But you have to set the meter to 200vdc for this (because otherwise you can only get a few cells in before you're at a higher voltage than the meter can read at 20vdc and it then gives you it's "out of range" reading), which is less precise*** than the 20vdc mode you can use if you measure by moving the leads together as pairs instead, so that when you move the red lead to the next pad, you then move the black wire to the one you moved the red lead from.
That will instead give you an actual list of voltages, starting at "cell group 1" which is the most negative, that doesnt' require any calculations to determine.
As noted before, tenths of a volt difference between any cells is bad. A couple of hundredths, not so much.
***it may not matter about precision (number of decimal places) because the meter may not actually be that accurate...but if the display is a 4-digit then you only get one decimal place for a 200vdc range, which is not enough to really tell cell state (need at least two decimal places, which you would still get in a 20vdc range for a 4-digit meter). If it's a 5-digit meter, then you do still get 2 places even at 200vdc range.
If you use autoranging it will just switch to the higher mode when necessary, but the readings in that mode will have less decimal places, and can't necessarily be directly compared with those made at the lower range. (the more accurate (better at measuring) the meter, and the more precise (more decimal places) the meter is, the less difference this makes).
Ah ok great, thanks for the clarification - i was a bit worried at first as i thought it ONLY output 40a continually, meaning the moment i plugged it in and up to a motor it would wizz off at full speed and/or blow up lol (Which is hugely impractical for the intended use of course, but sometimes i do like to assume the worse lol)
Ah; i see the misconception: a battery doesnt' force current into a controller/motor. The motor places an electrical load on the controller based on the physical load on the motor, which then pulls more current from the battery to help the motor overcome it's load.
The battery is only going to be powering a few higher wattage buck converters (12v, x2 5v etc), fairly powerful LED lights and a magic pie edge motor (pulls around 30a absolute maximum for brief periods) so compared to most people I dont think i really stress these batteries.
Unfortunately it isn't a comparison between others' use of similar batteries that matters for how a battery behaves; it's the actual load on it vs it's actual condition.
So, for example, even though I have packs on my trike that are made of EIG cells the same as one of the Zero motorcycles used, and some other EVs I can't recall the names of, the performance of mine won't be nearly the same, even though I put a lot less load on them than those EVs, mostly because the ones I have are old, and well-used.
However, it is likely that you aren't loading yours heavily, probably not even pushing them a little, as far as the cells' capabilities.
The problem you ran into is the BMS, heat, and having nowhere for the heat to go.
