newb123 said:
As I can monitor total voltage on the Wattmeter, perhaps just use the BMS to balance charge?
Potentially dangerous, as if a cell goes below the safe level, it can be damaged. If it's unbalanced badly enough compared to others, you can actually run it to zero or even reverse it.
Any of those can cause damage enough to make it a fire risk. But you won't know if it's even happened, unless you measure each cell when the bike's performance changes, or after you stop.
Its only purpose during riding is to cutout if a cell goes to for ex. 2 volts or overcurrent?
Yes, it's purpose is to keep you from damaging cells, and potentially having a fire during charge or discharge, etc.
So I don't recommend running without the BMS.
If it's current limit is what is stopping you, then it is protecting the cells from being damaged by drawing more current from them than they can handle, and overheating and/or dropping too low in voltage.
(assuming that the BMS's current limit is set / designed to what the cells themselves are actually capable of. If it is already higher than what they can handle, then it's already possible to damage them even with the BMS, and much more likely without it).
Since the BMS is already allowing at least 35A, which means over 17A per cell, then if it's cutting off because of the current limit, it means your controller is drawing more than that already.
So if you run without the BMS, you'll draw even more than 17A per cell, and I doubt that the cells are even designed to handle that much current when they are in brand new condition, which, if yours are used, are not.
If you draw too much current thru the cells, they heat up, and can be damaged, creating a fire risk if they get hot enough. (the core of the cells will heat up faster than the outside, so they can get pretty hot pretty quickly before you know there's a problem if the current is high enough vs what they can handle)
With used cells, they're often different enough in capability from each other to be different internal resistances, whcih means they heat up at different rates, so you'd ahve to monitor each cell's temperature to know if something is going wrong. Alternately, if you can test each cell's internal resistance (requires a tester for this; some RC chargers can do it, but I don't know how accurate they are), and then use a sensor(s) on just the cell(s) with the highest resistance, as those will heat up the most.
Ok I tested all cells after a short ride, all balanced at 4.13 volts
That just tells you they're at the same voltage when at rest. It doesn't tell you anything useful about why the problem is happening.
You must test while current is flowing at the rates you normally use it at, while charging, and while discharging, to find out if there is a problem with the cells under those conditions, causing your problem.
the BMS Im using is rated at 42 volts (not 48, as mistakenly previously posted) but, Im using the 36 volt sense wire harness. Wondering if, that is the problem.
42v is the full voltage of a 36v (10s) pack.
If you are using 10 cells in series, then that is correct.
If you are not using 10 cells in series, then you need either a different BMS or to wire it up per it's instructions for however many cells you do have.
Once I charge to 42 volts, the BMS, using the 36volt sense wire option harness, is reading an over discharge of 42 and cutting out? I has a over discharge protection feature
42v is not over discharged. It is the full voltage of a 36v pack.
42v would be over discharged for a 60v or 72v pack, for instance, because those have enough cells in series that 42v divided by that number of cells would be less than the damage-level voltage of those cells.
If it was an over *charge* problem, then it would not continue to charge the pack, cutting off the charge port.
If the charge port is the same as the discharge port, it would cut off both, and you could not use it on the bike at all--the bike would get no power and would not run at all, and your wattmeter would not work either.
