Recently i changed my bms from 30a discharge to 40a discharge and it has started completely cutting off on me mid ride with no good explanation. all the settings for the esc are correct just the bms decided “no thx” and doesnt wanna work after a few seconds of full throttle. should i bypass to charge only or should i go back to my original 30a?
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If it still charges fine, bypass it and just use it for charge. Discharging through the BMS is usually a bad idea for our purposes.
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The only reason I have discharged through a bms was to use the e-switch built into the bms. Are you using a bms integrated e-switch?
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would i need a fuse as well just in case?
no i am using a loop key that has anti spark connectors
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You should have your charge port fused, but not your discharge line
I agree with Tech.shit bypassing would be the better option
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ive got a 10s4p battery so would i be safe with having the battery current max as 20a after bypassing? cause im pretty sure ill never pull that from a 10s4p
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Depends on the cells you’re using.
currently. i have absolutely no idea lmao i do know they are lg cells tho. but very soon im gunna be spot welding a 10s4p with panasonic ncr18650bd batteries so ill probably just do the bypass on the new pack
You should know the model and check the @Battery_Mooch current rating for that cell, then multiply by 4 to get your maximum current number for VESCTool.
It’s probably a good idea to bypass on this battery anyways, and your next one. If your BMS cuts the flow you’ll no longer have brakes. Brakes are important.
i knew them for a bit but i lost the order info on where i harvested them from. they were originally from a lime scooter battery but i do not remember which year it came out. but the panasonic ones i have done a bit of research for and i trust panasonic with my life
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Found his article on the cells. so should the max current be 20a or should it be 40a?
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You can do 40A, or you could do 32A to have some overhead room for current spikes.
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fair point
what brand BMS is it?.
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Daly
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no experience with using daly as discharge sadly. Had a few supower and bestech that worked just fine at 40A tho
As implied by @b264 ‘s link, this is a topic that has been discussed a lot, so this isn’t meant as a snarky dismissal but IMO you’d have a better time searching old threads first and then coming back with specific questions. For example if you’re not sure you understood something right (like you don’t know how you would apply a certain wiring diagram for your setup and want to check, or what a specific term like continuous discharge means), you get much more out of peoples’ responses than just asking a beginning question
@tech.shit seems to have you mostly covered, your logic of using 40A makes sense but I think his suggestion to go to 32 and keep headroom is a better idea as he outlined. IMO 32 is a better plan because Mooch mentions his tests are done in open air on one cell, not a bunch of cells stuck together sharing heat. Plus also cell longevity will be better.
One thing that you’ll probably encounter elsewhere but that is really important: don’t put a fuse on your discharge line. IMO using a discharge BMS isn’t a good idea because all it does is protect the batteries by cutting power in an emergency, and it is much more important to be able to keep control of the board and brake safely than to save the batteries. But a fuse adds this risk of cutting power on top of being a mechanical point of failure (fuses can vibrate themselves to death), and not at all smart (fuses only blow if a current threshold is passed or they wear out, whereas a BMS is actively monitoring a few different indicators of a pack’s health and could theoretically come back on). Fuses on your discharge line are a huge liability.
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