Nope as long as you set it to 10 amps it is safe. You just shouldn’t overload the batteries more than they can handle.
I simplify a lot, to be honest I don’t know or have the energy to refresh all the details but to get some amount of power you have to follow P = I * U. Current times voltage equals power(watt). Then it all gets more complicated with conversion, efficiencies, the specific workings of a brushless dc motor and so on…
My example with 3.78 volts would mean that the voltage from the batteries would need to be converted somehow. For example when plugging in your wall charger for your phone into a 230 V outlet it converts to e.g 5 V. Your phone is then charged with 5 V at something like 3 A. But from the wall on the 230 V you only have about 0.065 A.
The realistic scenario with the 3A batteries connected 3 in parallell would be 40 V * 9 A = ~360 Watts of power. It could be enough to get someone forward, e.g electric scooters or bikes commonly have 250 Watts of power. So it would probably work fine to some extent.
Lithium ion cells typically can’t be run at their max rating for very long. A cell like the LG LGDAS31865 would have a very thin current collector. Though, I couldn’t find any data sheets that monitored temperatures for this specific cell.
good implementation would be a 2nd battery input (super small, low current) that you hook up to your BMS output.
Then if there is an issue the BMS cuts power like its supposed to, the vesc notices the lack of voltage in the 2nd battery input and takes some action like slowly powering down or whatever the user chooses.
This aint a bad idea, and it doesn’t even actually require the second battery. Just need the VESC to be able to read the voltage on the BMS output and take action when that voltage drops to zero.
I wonder if a hardware module could be made which takes the BMS output and sends the VESC data over UART, then write a LISP script on the VESC to read that data and take action.
You went a bit overboard on your neg terminals m8 lol. Also, you want to stay away from spot welding in the middle of the neg terminals. There’s an internal weld in the cell that can be damaged if you weld on top of it.
I’m assuming you’ve dialed in your current for the welder and the nickel has passed the pull test on a spare cell?
Crap, I just did the second lot and I had one electrode near the centre, the other near the edge and went radially 6-8 welds per cell. Voltages are all clear though, I guess time will tell if I’ve caused any internal damage.
So ive done some more testing with a single battery, but im not happy with the consistency of the welds. I tried a bunch on the knife again and after on a spare cell. Sometimes a weld rips when I pry it off (which is good) but sometimes it doesnt rip and its a lot easier to get off. Im already at 40 or 50ms on the weld pulse and reading most posts it should be around 30ms. So I think I will order another battery to get some more amps.
Welds are supposed to get off with prying. Or at least they are solid enough, if you need to pry on them. That’s why you only do a pull test when testing. These welds should not transfer any loads, that’s the holder or glue for.
Thanks @Linesflag you prompted me to do some more research on spotwelding and found out I dont need much pressure on the probes. So now im just putting a small pressure on the probes and im getting better welds that also tear off when ripping the nickel off. Gues this should be sufficient but I will do some more testing to be sure.
Ideally you get little spikes of nickel left on the cell, try holding the probes a little closer together (I go for a 1mm to 2mm air gap between the electrodes with them 30deg from vertical) when welding, and stay clear of the center ~6mm diameter circle of the negative terminal
These look a little cold for my taste, but this also depends on how thick your nickel is. On thicker stuff you won’t get any tearouts without reaallly cranking up the heat. That being said, if you glue your cells together, they are fine. Professional welds look no different.
whats the proper way to check for good/bad cells? I have 3 p-groups, A total of 20 cells that I’ve pulled from packs that weren’t draining/balancing properly, I’d like to find the bad cells and reuse the rest of these brand new cells
