Board stopped braking this morning

Hi! I have read about ti but I would like to know a final answer to what happened. Basically I just left my home, 10s board charge to 41.2V (I do not charge it to 100%). After 200 meters I had to brake hard due to a truck leaving a parking spot and basically the board braked at first, then it suddently stopped for 1 second before brake again. I lost the balance and fell. Now I know that when the battery is fully charge this is a mechanism to protect the VESC and battery, but I thought that charge it to 41.2V nad set the overvoltage detection to 57V would prevent it. There is something else I could do it to avoid it for next time? Settings: 10s3p 30Q battery pack BMS 60A charge/discharge Diyeboard 90mm hub motors Motor max 50 / min -55 (now lowered to -50) Battery max 30 / min -6 Dual vescs.

Thanks!

probably your bms did not balance the cells because you dont charge ti fully, and when the charging current came in the bms cut of the power

Are you using the BMS to discharge? Or is discharge. Bypassed from the BMS?

If you are discharging through the bms… It is the bms fault trying to prevent over charge.

@Acido @Deckoz Thank guys for the reply. Yes my bms is also discharge. I used for the past 2 months without problem but I have to say that this morning was just after have left my apartment and I braked quite hard. I also thought is the bms that prevent the overcharge. I was hoping that by charging the battery to 41.2V instead of 42 would avoid this problem. Apparently it helps normally but if I brake too hard from the beginning than I run it the problem. At least this morning :confounded:

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you need to accumulate 8wh to make your battery go from 4.12 to 4.2v per cell and that’s a lot because you brake for like 3-4 seconds

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exactly, that’s why I use to charge to 41.2V. The brake stopped working after half second, so could be the first strong peak the cause. The thing is that it’s scary.

While yes he needs 8wh to charge the battery to rest at 4.2/cell. Voltage spikes from braking can easily over volt even at 41.2 with heavy braking.

I would switch to bypass discharging for safety (your own not the boards).

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Thats funny. I almost dove in front of a car the other day when my dog (6 month old german shepherd) slipped her collar. I swear I’d take a bullet for that dog, but when she tried to bite my bludgeon last night I almost put a straight up a WWE smack down on her :slight_smile:.

Not that I value my board over my dog, but you know…

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I’m not well versed in BMSs and stuff, but I charge my battery to 100% at least once a week until the BMS cuts off power. The display remains at 100% for a while, presumably while balancing cells.

So tell me if I am flawed in my thinking here: if @rey8801 never charges to 100%, could the P groups potentially be out of balance, one near to 100%, and when a strong charge current comes back to the BMS, it doesn’t accept the strong current because it detects an out of balance P group?

Just a thought… I guess all BMSs are different, not sure what bara ships his batteries with but even at 100% 41.9/42.0 volts I’ve never had a problem braking when starting out my ride.

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The only thing a discharge BMS does is add another failure point to the equation imo. The only time I would use a bms for discharge is if the BMS had a built in antispark :slight_smile:

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Well… My P groups should also be balanced during the discharge phase.

Ok good to know that even an increase in voltage for a half second can do that. So the BMS I used is has charge and discharge at the same port.

To use it only for charging I would need to remove the B- and the the load negative I guess. Which is the safe way to do it? Can I just go backwards in the step. So first the load negative and then the B- (thicker wire)? Thx a lot

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So basically you would take the -c for the load line, and connect directly to the battery negative terminal

Yellow is remove, blue is the new line

Leave the line for the charger(I know the edge of the yellow is slightly touching it because fat finger drawing)

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OK so I leave the big B- I only remove the load Negative from the BMS and connect the load - to battery negative. Right? It’s so stupid that I put such huge BMS for nothing…I guess is a learning curve

Yes that is correct. Remove the load- from the -c connection and connect directly to battery negative.

Do you already have an Antispark in your circuit?

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yes I have both a antspark switch and a loop key. Thanks for the help

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Ok cool, wasn’t sure if you were using a switch on the bms. But since you already have them in place, just changing the load negative to be connected to battery negative will make your setup bypass discharge

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Thanks. Yes my anti sparks are place befoer the VESCs so no problem for that. Thanks man! Appreciate…

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I always fully charge my board and at the end of my street theres a long hill and I usually brake on it, no problems ever

You just need to set your bms settings correctly

Non configurable BMS? How do you set BMS settings with no interface???