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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In defense of fusing your discharge line, and bypassing your bms for discharge. Humans make mistakes, a discharge bms should be be able to stop a human error short circuit and the resulting fire. A fuse may also be able to prevent that fire if setup correctly. You have to ask yourself do you trust complex software (bms), a simple thin wire (a fuse), or yourself (very human, I assume). As a software dev I can tell you unequivocally the human is the weakest link.
It’s also worth noting bigger board manufactures like lacroix frequently use fuses.
To prevent the fuse from vibrating to death you should pad you fuse box thoroughly.
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Worth noting is also that if you’re looking to draw 40A you dont pick the BMS that supports 40A.
You pick something that gives you 25% headroom. Beeing superman is cool untill you eat the asphalt
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I might be misunderstanding but it looks like the human errors can only really happen in the build process? I guess you could assemble something that just barely works and then accidentally shorts later due to vibrations, but in that case I’d still rather have a chance of the board working long enough to stop and then going up in flames
There are stories I’ve read where human error during maintenance caused a short. I seen builds with leads that could easily be pinched together by flex. Humans just tend to make mistakes, predicting all of them is not practical, so we should assume they may mess up in almost any way. placing the fuse as close as possible the terminal of your pack reduces the chance of a fire by limiting the distance in which a human can mess up the leads. The human can still cause a short with the balance leads, but they may fuse themself out, or you might be able to use pico fuses there, but I have never done that.
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The main reason for this is that DALY bms are over rated 25% on continuous discharge and cut out fast after compared to others that have lower continuous ratings but can accept amp pulses that are much higher.
They are perfectly fine if you bypass but i would personally look elsewhere if you want to use it for all it’s features.
Install a fuse, bypass bms and call it a day
Not on discharge. Never fuse your discharge unless you have non-electrionic braking.