Never got an answer to this. I know that the BMS will rate the capacity of the pack at the lowest block. But if you have a known good module, and one where the capacity isn't as good, can you pair them to "fool" the BMS? When matching modules together for blocks, should you match highest and lowest capacity together, or match similar capacity modules together?
BMS sees 14 blocks via voltage sensing harness which uses those voltage 14 signals to calculate resistance, capacity, etc..
Yes... Or the opposite is more common when people have one bad module and decide to replace both modules in the block with more powerful replacement modules and then that block no longer matches the other blocks. I always say that you'll have better results if you only replace one module in a block. And yes, you can re-arrange all the modules for optimal performance if you get good data on all of them. But getting good data without super expensive equipment is really hard.
Also wanted to ask as I am getting close to the step, I've seen some people slowly discharge all modules to the same voltage, and I've also seen people reverse the modules around so all the negative and positive posts face the same direction and wire them all together to balance the modules. Isn't it also somewhat crucial when putting it back together, that the voltages of all the modules are within 10% of each other?
I would do that on lead batteries, not NIMH. If you have zero equipment other than a volt meter, get 6 brake lights from the auto place, solder them all up so they light at the same time and put alligator clips on them. Attach them and the meter up and drain each module down to some voltage below 7.2 volts like 7.1 or even better 7.0 Reinstall in car, they will leak enough volts and energy back up to fire the car up one time and then it can charge itself up. If any of them drop right down or under your target, they were discharged and need charging, most regular car chargers can throw some power in them, hit it at 2 to 6 amp charge for 5 minutes and visit it again an hour later with your brake light bulbs
This is referred to as balancing because all blocks are supposed to have same voltage and discharge and recharge at the same rate. Lithium are balanced from below which requires discharge and then all negative terminals and all positive terminals connected so they balance to same voltage. But NiMH are balanced from above which requires a super low charge of under 1/2 an amp into a fully assembled pack. Modules that reach max charge will dissipate any more charge as heat (using cooling fans is essential) while it waits for other modules to get full charged.
If I can get all the modules to roughly the same voltage before installing, will the BMS sort things out?
Yes... Just use your headlight bulb (if it's standard 12v 50w halogen) to discharge everything down to lowest voltage module.
Sorry to bring an old post but I'm trying to understand what way is the best for matching modules by the capacity. I use RC chargers in order to regain some capacity of a module and then based on the numbers I try to pack a battery. For example the latest battery that I did is gen2 prius, after running some charging/discharging cycles, I let it to sit for a few days and then I did a load test on each modules for 2 min under 9.6amps(115w) of a load. I took 6 modules from another battery and put them into this battery pack to have enough modules with the same capacity. Based on what I know you have to put modules in order to make blocks in close range of the capacity, but at the same time you have to put the strongest blocks in the middle where is more heat happens to be. If you would have a chance can you take a look at this Google sheet? This sheet has both, cycles for the battery, load test of the battery, and what modules to pair with what. Thank you!
