Did i break my battery?

Custom.Jerry

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Hello my name is Jerry and I am new to the forum and building ebikes. Not a native speaker so please do not mind the bad grammar.

Here is my problem I just finished building my e bike last part was the battery. It is a derby senda with a qs 138 90h with a votol em 200. I decided to cut cost on the battery because I did not do my research right and could not get it road legal. So I bought a battery that could do 120a and 200a peak 40ah 72V. But when programing the controller I forgot to send it to the controller so it was still running 200a and 550a peak. I know stupid mistake. After riding 2-3 km I knew somting was wrong because it was just to insanity fast. So I headed back but it died on me a couple 100m before my house.... so is my battery broken is shows 48v and does not charge can someone tel me what could be wrong with it. I have not opened it up jet.

I hope someone can help me thanks in advance.

Gr. Jerry
 

HumanPerson

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Hi Jerry and Welcome! :)

Do you have an extra controller to hook up? It sounds like you may have fried the controller.
 

Nelson37

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No reason whatsoever to believe it is the controller. It was not driven beyond its specs.

Now, when a 72V battery reads 48V, and will not charge, AND was driven beyond its specs, THAT is a VERY GOOD reason to believe there is likely a problem with the battery.

Test AGAIN, fresh battery in DVM, then time to open up the battery and look for the melted connector.
 

HumanPerson

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No reason whatsoever to believe it is the controller. It was not driven beyond its specs.

Now, when a 72V battery reads 48V, and will not charge, AND was driven beyond its specs, THAT is a VERY GOOD reason to believe there is likely a problem with the battery.

Test AGAIN, fresh battery in DVM, then time to open up the battery and look for the melted connector.
Good point there Nelly ;)
 

Nelson37

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Giving this some thought, very high odds the BMS blew. Hopefully, it took the bullet so that the cells might live. Likely a bit pricey, but a lot cheaper than that controller, not too much wiring to replace. Solder on main power leads, balance wire plug SHOULD be re-usable.

Would need to do some serious testing on all the parallel groups, some possible cell damage, also inspect contacts. Neither of these tend to be of maximum quality on less-expensive packs.

DVM at main power leads into the BMS, then output, then the individual balance connections.

The pack should not have gotten to that low a voltage, both the controller and the BMS should have prevented this. Many BMS have a "default" output when broken in various ways which could explain the 48V reading.
 

Custom.Jerry

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Thanks for te responses the BMS is 150 450peak no Bluetooth so it could be the bms. I am 100% sure it is the battery sadly i do not have a spare i got it fom china and had to wait 2.5 months for it to arrive. So I hope is is not the cells. What do you mean by DVM . How can I chek if the bms is broken? I wil open it up tomorow. Is it possible that ther is just a bad connection?

And ones again thanks for the quick responses it is much appreciated
 

Nelson37

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Digital Volt Meter. Analog is not good enough. Need 2 digits past the decimal, one will do but 2 is really better.

You're gonna test input and output plugs on the battery, then test these directly at the main wire connections from the battery at the BMS.

IOW, test input and output both THRU the BMS and BEFORE the BMS.

If battery voltage out and BMS voltage out is significantly different, then look for fuses, hopefully, next is charge for extended time, WITH MONITORING, then attempt charge thru output ports. Testing voltage both ways repeatedly. If response to charge thru output, do this for limited time and then go back to charge thru input, again with repeated testing. Most BMS have limited or no overcharge protection thru the output port.

You can take the balance plug off, then test parallel groups directly. Numbering could be tricky, hopefully BMS connector is labeled, black and red1, then red2, etc. Voltages will add, 4.2, 8.4, 12.6, etc. Take notes and do the math, you are looking for each cell group voltage, and any that are way low, ie above would be 4.2, 4.2, 4.2, perfect but if next group is 15.0, subtract the previous group at 12.6, current group is only 2.4, MAJOR problem.

The testing of the cells should be done first as this could indicate a possible dangerous condition, where charging must be done to individual groups before attempting to charge battery as a whole.

Also look thoroughly for burnt connections or melted tabs or strips, the above test may help pinpoint these.

It's a matter of what overheated first, never overlook the possibility there could be more than one problem.
 

Custom.Jerry

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Thank you for the advice I did not open it up. now when I measure is shows 75v and when I plug in the charger 84v but the charging indicator is not running and the fan in the charger is also not running I am leaving it under charge for about 2 hours and wil chek back if is has more v in it and I wil hook it up to the bike and see if I may be very lucky.
 

Nelson37

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Well, that's better, if that 48V reading was accurate, still a problem, if that reading was possibly in error, that would be much better.

If it still fails to charge, and will not get to 84V, will have to open the pack.

This may be something for a professional, as you are dealing with potentially lethal voltages and there is significant risk involved.
 

Custom.Jerry

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It there is no significant change after 2 hours of charging still around 75v but when I plug it in to my bike it shows 52v on the laptop and when I turn the key off and on it jumps to 69 and than drops in time to 52v I think I wil leave it charging for atleast 12 hours before I attempt to open it up. Jes it would be best to bring it to a Profesional except there are non around where I live.
 

Nelson37

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You have a laptop connected to the bike??? Or did you mean the bike display?

That controller may have some USB connectivity and maybe some software which could show a LOT more information.

Dropping so far in voltage indicates some serious issues.

Monitor CONSTANTLY during charging. Could be in a dangerous state.
 

Custom.Jerry

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Jes I mean I have a laptop connected to the controller. It is strange that is shows 52 on the controller software and 75 on the volt meter and it shows 84v on the volt meter when the charger is connected
 

HumanPerson

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sounds pretty wild there Jerry.
Be careful mate, these things can cause crazy burns on skin and blow off fingernails.
 

Nelson37

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do you unplug the controller to use the voltmeter?

If so, can you rig a load, like a light bulb, and use the voltmeter at the same time?

Generally, a damaged battery will show extreme voltage sag under load, but rebound quickly when load is removed.

The 84 with charger connected is not unusual.
 
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