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Discussion Starter · #1 ·
So out of nowhere my 48v 20ah lithium ion battery pack started tripping the bms board at anything over half throttle. I swapped the motor for a different motor, still does it. I swapped speed controllers for another speed controller... still does it. Tried both new parts together, still does it! Did my battery pack **** the bed on me or something? Really confused and frustrated. Halp!
 

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Every time a electronic BMS trips it gets a little bit weaker...

I always recommend putting a fuse or breaker that is rated for less than what the BMS trips at.

For instance if you had a 50 amp BMS I would put in a 45 amp breaker.

With that said let's get your pack up and running...

Try to locate where the BMS is so you don't have to cut off all of the heat shrink.

Use a plastic razor blade ( you can find them at the hardware stores in the paint section they are yellow plastic)

Carefully cut around the BMS to gain access.

Take pictures and notes exactly how the cables are plugging into the BMS if you plug it in backwards it will instantly fry the new one that you're going to get off of eBay or Amazon don't worry they are fairly inexpensive around $15 to $25 make sure you replace it with the exact one that was in the battery pack...

Use gorilla tape or flex seal tape to seal the pack back up
 

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Yep, if your bms trips, throw it away. Replace it with a Daly with tge proper amps for your setup. I have a btr 20ah that was nothing but problems, threw a daly 60a bms on it and its a beast now. My buddies wife gets 28 miles on her 1500w brushless setup!
 

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Yep, if your bms trips, throw it away. Replace it with a Daly with tge proper amps for your setup. I have a btr 20ah that was nothing but problems, threw a daly 60a bms on it and its a beast now. My buddies wife gets 28 miles on her 1500w brushless setup!
You have to match the BMS to your batteries cells discharge rate you absolutely cannot just throw a bigger higher amperage BMS on it!!!!

If you try to put a 60 amp BMS on a 30 amp pack and something happens to the speed control or motor it 100% definitely will catch on fire and you will be responsible for paying the fire department to come put it out with that special foam they use for lithium ion batteries...
 

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Discussion Starter · #6 ·
I figured I'd try and describe what's going on a little better to see what you guys think wether it's the board or if my pack is crapping out. It's almost acting like it's not charging despite the battery meter reading full. You know that squelch noise an overvolted system makes on a full charge? Mine doesn't do that anymore and I found that I can do brief 1 second full throttle launches if I'm already moving and attempt even a slight hill without increasing throttle it will trip the bms... kinda like if the battery was dead and entering safety mode although the meter reads half life left.
 

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So after the bms trips, how do you get it to start again? I dont believe that battery has a bms reset button. Do you have a mounted volt meter? When the bms trips what does the voltmeter show?
 

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Discussion Starter · #8 ·
So after the bms trips, how do you get it to start again? I dont believe that battery has a bms reset button. Do you have a mounted volt meter? When the bms trips what does the voltmeter show?
Unfortunately I have to plug the pack back into the charger to get it to reset as I have no external reset button, and my battery gauge is push button style that lights up a series of LED lights to indicate charge level so sadly I don't know what my voltage read out is at the moment. I'm gonna see if my neighbor will help me out with his ohm meter thing and see if we can run some tests today.
 

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That battery you got from amazon is a pretty decent battery. A plain overvolted setup should NOT be tripping that bms. Thats strange.
 

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You need a amp meter to find out how many amps your pulling before the BMS trips
 

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Or he could wire a fuse between battery and controller......start with a 20, then a 30, etc. You'll find out (ballpark) how many amps before the bms blows. If your 20a fuse survives and the bms trips, return the battery!
 

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Discussion Starter · #12 ·
Ok so it appears my battery has acquired the phantom voltage. I plugged it in for 4 hours, charger said it was full but my battery indicator says it's only 75% charged. Ran a voltage test and without load it reads 51v, under load it dipped down to 44v. Is this actually a battery problem or is there a chance my charger is being dumb?
 

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In chinese batteries i do see a lot of voltage sag. It should come back up though even if you keep the load on. So for ex, battery is sitting at 50v, apply hard throttle, it drops to 45v, keep hard throttle on and battery should climb back up to 47 or 48v. Doesnt explain why you have to plug your charger in after it shuts off to get it working again though.
 

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Discussion Starter · #14 ·
In chinese batteries i do see a lot of voltage sag. It should come back up though even if you keep the load on. So for ex, battery is sitting at 50v, apply hard throttle, it drops to 45v, keep hard throttle on and battery should climb back up to 47 or 48v. Doesnt explain why you have to plug your charger in after it shuts off to get it working again though.
My guess is under load it's dipping below voltage cut off for some reason, which kinda makes sense if it's not properly charging from either a bad charger or some battery related issue
 

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That could be the case, I dont even know what the voltage cutoff is for the stock controller. But you shouldnt have to plug in the charger to fix that issue. Just cutting power to the controller for a sec would fix that.
 

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Discussion Starter · #16 ·
That could be the case, I dont even know what the voltage cutoff is for the stock controller. But you shouldnt have to plug in the charger to fix that issue. Just cutting power to the controller for a sec would fix that.
Idunno... my bms shuts the battery right down, even my indicator won't work until I plug it in for a second (literally) and the board resets
 

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Interesting conversation. The battery will drop or sag underload roughly 5 volts, but will climb back up a few, then be back close to starting voltage after the load is gone. Obviously a little bit lower because you used some of the voltage.
 

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Discussion Starter · #18 ·
Interesting conversation. The battery will drop or sag underload roughly 5 volts, but will climb back up a few, then be back close to starting voltage after the load is gone. Obviously a little bit lower because you used some of the voltage.
Yeah so it appears my battery has acquired the phantom voltage and is telling the charger it's fully charged when it's not
 

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That sucks. If you decide to buy another battery, I would then find out what happened to that pack. And then repair. Try the BMS first, if that isnt it, gently pull apart the pack if possible, test each individual cell and then you can probably replace the few dead ones and get one of those Builder packs and rebuild your pack.
 

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Discussion Starter · #20 ·
That sucks. If you decide to buy another battery, I would then find out what happened to that pack. And then repair. Try the BMS first, if that isnt it, gently pull apart the pack if possible, test each individual cell and then you can probably replace the few dead ones and get one of those Builder packs and rebuild your pack.
I'm far from an electrician but I suppose I could give it a shot, what's the worst that could happen right? 🔥💀😂
 
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