Exabits Posted April 22, 2020 Report Share Posted April 22, 2020 So I'm looking at getting THIS bms for lithium pack I want to make. The problem is I'm not quite sure how to make it turn off and on with car ignition. I'm a bit confused with the wiring and I'm not even sure its possible with this programmable bms. Here's what I have so far but not sure if this is right or it will even work the way I think. Link to comment Share on other sites More sharing options...
slowfkncar Posted April 22, 2020 Report Share Posted April 22, 2020 Every bms I've worked with never had a 12v remote trigger nor did they need to be disconnected from the pack as they are actually powered by the cells, its fine if it just idles there. *wiring is correct, make sure your pack can handle whatever charge current you plan to throw at it and since you bypassed the bms output, DO NOT short the terminals. Link to comment Share on other sites More sharing options...
Exabits Posted April 22, 2020 Author Report Share Posted April 22, 2020 I must of been tired last night. There's no way that wiring I posted was correct as it would create a dead short at both the isolator and relay. I have revised it after getting some sleep. I do believe this is correct now. Somebody can feel free to correct me if I'm wrong or maybe it can be simplified. Also, maybe you're right about the bms just staying on, I just didn't want the parasitic loss on the battery when not being used. Link to comment Share on other sites More sharing options...
slowfkncar Posted April 22, 2020 Report Share Posted April 22, 2020 Grounding that battery before the BMS pretty much makes the BMS useless, you'll want to at least keep balancing and charge current protected which means you can't ground the cells directly to the chassis or it completely skips the BMS. I don't mind putting the amps on the B- pad, you could always fuse them instead of using the C- terminal but at least keep the alternator (chassis ground) on C- so that it will charge the pack with a functioning balancing feature. Link to comment Share on other sites More sharing options...
Exabits Posted April 23, 2020 Author Report Share Posted April 23, 2020 Hmm, I see what you're saying. After some research I think the solution will be to get a different bms, one with a p- and b-. Thanks for the help and guidance! I got it figured out now. Link to comment Share on other sites More sharing options...
slowfkncar Posted April 23, 2020 Report Share Posted April 23, 2020 You're welcome, also, P- & C- are commonly a shared terminal for most off grid bms, no reason to separate them with a car audio setup unless you want to cut off charging (alt) while drawing from the battery. I've installed 3 of these cheap ebay bms, all of them regulate charging through the shared P-/C- or can be bought with a separate charge port as an option if needed. http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=174122758263&category=48619&pm=1&ds=0&t=1584153469000&ver=0&cspheader=1 Whatever you go with, the three main things you need are balancing,over/under volt protection & if your alternator puts out more current than your pack can safely take, you'll need a current regulated charging feature. Link to comment Share on other sites More sharing options...
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