72v e-moped battery no bms? Dead?

jspec1

100 µW
Joined
Jun 30, 2021
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8
So I just picked up this Tomos Moped conversion and was told the battery is dead. I test it and it has 66v on it. The issue is there is no BMS unless it is built into the controller somehow. Any advice how to proceed? I am under the impression that I can just add a bms and seal up the battery better? Let me know.
 

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id check the voltage of each p-group to see if their ok
then id rip off the nickel with the leads soldered to them
relocate the wires so you pull the amps evenly through the pack
have you looked at active cell balancers instead of bms?
 
The BMS is pretty much never in the controller, but yours looks like a homemade battery that never had a BMS to start with.
You'll prob need to keep splitting it open to get at the other side of the cell groups to meter them. If one group is really dead in there somewhere, and has been for awhile, the whole thing could be toast unless you start cutting it apart and rebuilding it. It's not safe to charge up a group that's been dead for awhile to try to get an old battery working. It will work right then but can make a fire hazard long term.
Even then, the new cells can end up not matching discharge curves with the old ones, so can require constant rebalancing.

You need to be able to get at both ends of the top cell of each of the 20 groups. You don't want to jam the voltmeter probes into the crack too hard to try to get at them, it can tear thru the shrinkwrap on the positive ends and short the center button to the rim of the can, which is negative all the way to the top edge.
20210913_092556~2.jpg
Cool ride btw, needing a new battery wouldn't be the worst thing as projects go.
 
I split the battery as you can see below. I put the negative lead on the negative charge cable and measured the cells as you can see.

3.33v
10.33v
17.33v
21.10v
28.09v
35.1v
42.1v
49.1v
56.1v
63.1v
66.8v at the Andersen connector
 

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You're getting pairs of groups mostly.
Now that it's split, just touch your probes to each end of one of the cans of the 20 rows.
Most meters are polarity protected, so you will see alternating pos/neg as you go, or you can switch the probes each row also.
Standing it up on end will make it easier, or one end hanging off the bench, since you need to get to the side that's touching the bench.

If they're all at about 3.3v like the first one, that's great, and maybe means the battery is fine, and the problem is in the controller or something.
3.3v is pretty close to low voltage as you want to go, but not damaging the battery low, like say 3.0v or lower might.
 
Maybe it's even just low enough to trigger the low voltage cutout on the controller, and charging it up might fix the whole problem.

🤞
 
1-3.33v
2-3.49v
3-3.50v
4-3.49v
5-3.49v
6-3.50v
7-0.155v
8-3.48v
9-3.49v
10-3.46v
11-3.50v
12-3.49v
13-3.49v
14-3.49v
15-3.50v
16-3.49v
17-3.49v
18-3.47v
19- 3.49v
20-3.50v

Looks like 7 is dead.
 
Whats weird is when I plug the pack into the charger 84v and test voltages again they are all around 3.5 except that rom 7 measures around 21v.
 
That's how things catch on fire eventually. The voltage of the one bad group goes from zero to high voltage as it's jacked up internally, so basically none of the electricity is soaking into that group, but just getting turned into heat.

The charger is stopping at 84v like it should, and cutting off the amps flowing into the battery, so all that is pretty normal actually for having a jacked up group.

And about 3.5 x 19=66.5, plus about 21=87.5 so again, sounds about right for being jacked up.

If you try to fool the charger by say discharging the one high group to make the charger come on again to catch the rest of them up, that's where it starts getting dangerous.
 
If you can't find a new battery, at least that one isn't as hard to cut apart to put in a new group as some are.

Depending on your safety situation, like if you're not storing it near where lots of people could catch on fire, you could maybe go lipo batteries.
 
So I tried to put a hobby charger on bank 7 and it says connection break. So what I just pull the nickel strips up and separate bank 7 and replace it with fresh cells? The cells are LGDBM361865 P181F291A1 /2 any idea where to find them? I also think they are glued together.
 
He was talking about removing the bad group completely and don't replace it. This is an option, it is up to you. will lose some distance and a few mph. You can just replace the bad pack. I would test the others and decide if there are any other packs on the way out. The best would be spread out he new cells in the other packs, trying to balance the number of weaker and stronger cells. Now that is a lot of work.

by jspec1 » Sep 15 2021 9:12am

So I tried to put a hobby charger on bank 7 and it says connection break. So what I just pull the nickel strips up and separate bank 7 and replace it with fresh cells? The cells are LGDBM361865 P181F291A1 /2 any idea where to find them? I also think they are glued together.
 
I think this pack is a lost cause. I can save 1/2 the pack but the rest are glued together. Looks like I would need about 35 of these LG cells to make the pack again. Joy.
 
Cut the nickel strips so the bad row is isolated. Then no worries about shorting the casings, Still have to be careful. Then I wonder if this would work to cut thru the hot melt glue?

https://www.amazon.com/Perfect-Mini-Electric-Foam-Cutter/dp/B071RRL63S/ref=asc_df_B071RRL63S/?tag=hyprod-20&linkCode=df0&hvadid=219682717104&hvpos=&hvnetw=g&hvrand=14322942637020338980&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9021703&hvtargid=pla-396482353892&psc=1
 
docw009 said:
Cut the nickel strips so the bad row is isolated. Then no worries about shorting the casings, Still have to be careful. Then I wonder if this would work to cut thru the hot melt glue?

https://www.amazon.com/Perfect-Mini-Electric-Foam-Cutter/dp/B071RRL63S/ref=asc_df_B071RRL63S/?tag=hyprod-20&linkCode=df0&hvadid=219682717104&hvpos=&hvnetw=g&hvrand=14322942637020338980&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9021703&hvtargid=pla-396482353892&psc=1

I wish it was hot glue. It looks like he used crazy glue. I have already pulled the pack apart to the bad row. I am going to pull the whole pack apart and see what cells are salvageable. Then put it back together correctly with a BMS. Those cells are like $7 each.
 
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