How did I break my battery?

[jmiller75]

I had a rickety old bike with a BBS02 750W motor and a 48V battery from Luna cycle. They have worked great together for years. A friend gave me an old Specialized mountain bike so I decided to switch the system over to this newer rig. Everything seemed to have gone well but when I plugged the system in I seemed to have killed my battery. I am nearly certain the battery was topped off before the switch (which only took a few hours). I had the controller hooked up then I plugged the Anderson connectors together (I may have heard a small arc, maybe not). The display was on for a second then off. Then it would not turn on again. This battery has a button you can press to see what the charge level is. I've never really used it though. But pressing this button seems to indicate the battery is essentially discharged. But putting it on the charger doesn't do anything (as if it were already full)

I seem to remember using a multi-meter on this battery's leads and getting 51-53V. Now it reads 0V. I cracked open the case to see if anything was obviously wrong. Everything LOOKS okay but still no voltage across the internal leads. I found this one tiny wire that MAYBE has come undone. I tried to get a shot of the little guy. In the attached photo you can just see it dangling above the left end of that label.



I'll try Lunacyle as well but thought someone here might be able to help also.

Thanks!!

 

[AussieRider]

Hi J. Welcome to the forum.
Does the little wire have aging black blog on the end? If so, it's the over temp sensor. Is there a fuse anywhere? Could be internal in line or panel mount next to the on/off switch. You could try a volt meter. Connect red to red. Black lead first on the black direct from the battery to the BMS. Volts on the meter? If not, the battery is toast. If you have volts, go to black lead from BMS to output. No volts? You've got a dead BMS. If you have volts on the black. Lead between the battery & BMS but volts are low you may have a dead cell or two. Unplug the sensor wire plug from the BMS & connect the red lead of your meter to the red wire of the plug. Black lead to the first white wire next to red. Should have about 3.7 volts & as you move to each white wire moving away from red, volts should go up in steps of about 3.7 volts. If any step is less or zero, you have a weak or dead cell & the BMS LVC is shutting down.
Hope this helps.
AussieRider

 

[LeftieBiker]

My guess is that when you connected the leads "hot" there was a power surge and an internal fuse in the battery blew. If no fuse then maybe a connection melted.

 

[dogman dan]

I don't see the disconnected wire. But if you can find where it used to connect, connect it back up.

you can test the voltage of each cell group using the contacts in the plug with all the white wires, as said above.

And have a damn good hard look at those andersons. You might just need to replace one, or just shove it back in the housing all the way.

Once in a while in troubleshooting, you do something, whatever, and then get odd results. But what you did has nothing to do with the results. If your battery is that old, its is possible that while it sat awhile, a short internally grew another crystal, and now you have a dead cell group. This is why I say check the voltage at cell group level. If that looks good, your bms may have just died at the random moment you moved the kit to another bike.

In any case, at two years, its time to start saving for the next battery. They don't all die in two years, but it will by now have some diminished capacity for sure.

 

[jmiller75]

Connect red to red. Black lead first on the black direct from the battery to the BMS. Volts on the meter? If not, the battery is toast. If you have volts, go to black lead from BMS to output. No volts? You've got a dead BMS.

Thanks all! Yeah so across the battery pack I am getting full voltage. But from red lead to the black lead leaving the BMS I get nothing. As AussieRider said it looks like a bad BMS. Do those just go kaput sometimes like that? I'm just trying to figure out if I did something wrong. I feel like I have plugged and unplugged this battery before but not had this problem.

If it is in fact the case that I have a bad BMS, is it worth it (or possible) to only replace just that part instead of buying a whole new battery pack? Would seem a waste of a bunch of good cells.

Thanks again for the the help!! P.S. It does looks like the wire I thought was disconnected is in fact a heat sensor as suggested.

 

[amberwolf]

Thanks all! Yeah so across the battery pack I am getting full voltage. But from red lead to the black lead leaving the BMS I get nothing.

This means most likely the BMS has shutdown to prevent damage to the pack. Sometimes taht's because of an actual problem, sometimes it's because the BMS thinks there is a problem when there isn't.

It could be a fuse on the BMS board itself, typicaly these are surfacemount types that look like a little "white" ceramic block wtih little metal caps, and are no bigger than a grain of rice, but may actually look like a regular glass or ceramic tubular fuse. Most of them dont' have a fuse, but some do.

If the surge during connection was higher than the BMS current limit, it may have shutdown to protect it from what it thinks is a short circuit.

If unpluggng it from the bike and leaving it for a few minutes doesn't reset that, then sometimes plugging the charger into the battery's charging port will reset it.

If that doesnt' work, disconnect the charger and try discharging the battery a little bit by connecting a load (toaster oven, 100w+ incandescent lamp, etc) to the actual battery main + and -, rather than to the BMS output wires. Let it run utnil the pack has dropped in voltage by a volt or two, then disconnect the load. Then hook the charger back up, and see if it resets the BMS output after it's recharged it. (one BMS I have here, that looks like yours, on an old LUna pack, does wierd stuff like this all the time, which is why the original owner sent it to me).

Some BMSs have a reset button (or pair of pins that can be shorted together), that will reset it to normal operation. (mine doesn't).

If it is in fact the case that I have a bad BMS, is it worth it (or possible) to only replace just that part instead of buying a whole new battery pack? Would seem a waste of a bunch of good cells.

IF the cells are fine, then a new BMS would fix the problem for much cheaper. There are quite a few different kinds availabe, some with more features than others, including some able to monitor stuff via your phone (bluetooth BT).

Thanks again for the the help!! P.S. It does looks like the wire I thought was disconnected is in fact a heat sensor as suggested.

Yes it is.
Somethign to note is that some BMSs with those sensors may shutdown their output if the sensor is disconnected (PTC), but usually not--they would instead shutdown if the sensor resistance is too low. (NTC).

 

[jmiller75]

By the way just to get back to close the loop. Y'all were basically right on. The folks from Lunacycle also seemed to think that the security settings on the BMS were inadvertently tripped. To clear those settings and get back to normal functioning I had to 'jump' the battery https://lunacycle.com/jumping-your-luna-shark-battery-pack/. I did not own the adapter mentioned in that link but found it pretty easy to create the work around mentioned at the bottom of the link.

Thanks for all the help!!

 

[amberwolf]

It's good that worked for yours---Unfortunately it doesn't restart them all. Neither does the drain-and-recharge method I used on mine. :/