New em3ev battery not working.

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diffcamp   1 µW

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New em3ev battery not working.

Post by diffcamp » Nov 08 2018 8:19pm

I finally got my battery in the mail today, but I've hit a wall

Both the battery and the charger are from em3ev.

The battery is 36v and 20 Ah.

The charger is 42V and 2A. It doesn't have a voltage selector switch

When I took the battery out of the box, the indicated had only 1 flashing red light. This means it's not charging and it has 0% - 10% charge. I plugged in the charger, but the charger has a light that means "Disconnected or full charge." I left the charger plugged in for an hour and a half, nothing changed.

The battery won't stay on for more than a few seconds unplugged.

I tested the charger with a multimeter, I measured 42V which matches the spec, and It put out brief spikes of 2A. The rest of the time it's 0A. I'm guessing those spikes are how it determines if it should charge or not.

I tested the battery and got around 35V for a fraction of a second before the battery turned off. When it's off, I get a reading of 3V. I tried connecting it to the bike and got a similar result. The screen turned on for a fraction of a second, then the battery turned off.

I'm not sure what to do now. This is my first ebike, so I don't have a lot of experience to draw on.
Please help.

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amberwolf   100 GW

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Re: New em3ev battery not working.

Post by amberwolf » Nov 08 2018 10:30pm

diffcamp wrote:
Nov 08 2018 8:19pm

The battery is 36v and 20 Ah.

The charger is 42V and 2A. It doesn't have a voltage selector switch
It doesn't need one. 42v is the full charge voltage of a typical 36v pack.
When I took the battery out of the box, the indicated had only 1 flashing red light. This means it's not charging and it has 0% - 10% charge. I plugged in the charger, but the charger has a light that means "Disconnected or full charge." I left the charger plugged in for an hour and a half, nothing changed.

The battery won't stay on for more than a few seconds unplugged.

I tested the charger with a multimeter, I measured 42V which matches the spec, and It put out brief spikes of 2A. The rest of the time it's 0A. I'm guessing those spikes are how it determines if it should charge or not.


It sounds like the battery has a problem internally--the most likely thing is that at least one cell is so low that it is causing the BMS to shutoff pack output.

The charger turning on and off could indicate the BMS is trying to allow charge, but that a cell (or several groups) is hitting the HVC (full) point very quickly, and shutting off charge until it is drained a bit by the BMS balancers. This commonly happens to unbalanced packs where most cells are very full, but one group has a problem and is very low or empty.

You could leave the pack on the charger until it begins charging normally; this could take days to weeks depending on how badly imbalanced the pack is.

But since its a new pack, it shouldnt' have this problem, so I'd recommend first contacting EM3EV to see if they have specific things they want you to check first, but it sounds like you've done everything you can without opening it up.

If you open it up you can measure all the individual cell groups (at the balance wires to the BMS), but I don't know how this affects their warranty.

diffcamp   1 µW

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Re: New em3ev battery not working.

Post by diffcamp » Nov 08 2018 11:39pm

When I say voltage selector switch, I mean for 110V and 220V.

I've contacted em3ev. I was just hoping to get a quicker diagnosis.

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Re: New em3ev battery not working.

Post by neptronix » Nov 09 2018 12:19am

Yeah that's a warranty claim.
Did you get a model with a bluetooth BMS? Because if so, you'd be able to do some basic diagnostics with their app.

But maybe the BMS is just faulty or there's a wire loose. Paul will help you figure it out.
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diffcamp   1 µW

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Re: New em3ev battery not working.

Post by diffcamp » Nov 09 2018 12:47am

I haven't been able to connect fully with the app. It shows up on the scan, but it hangs while trying to connect.

Sounds like the best course is to wait for a response from em3ev.

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Re: New em3ev battery not working.

Post by Thomsontouring » Nov 09 2018 3:02pm

I recently had the BMS fail in a brand new 52v em3ev battery. They sent a new one and it also failed within a week. The second replacement appears to work. So maybe they got a batch of faulty BMS boards? They will definitely replace it under warranty, and it's much cheaper and faster to air freight a BMS than to ground ship a whole battery.

I was also using the ST brand 2A charger they sent, and I noticed right away that it got a lot hotter than the 5A switchable chargers do. So after the last time I fixed the battery I stopped using that suspicious 2A charger.

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Re: New em3ev battery not working.

Post by 999zip999 » Nov 09 2018 3:20pm

Does the battery have fuse on the side ?

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Re: New em3ev battery not working.

Post by diffcamp » Nov 09 2018 5:07pm

999zip999 wrote:
Nov 09 2018 3:20pm
Does the battery have fuse on the side ?
It does have a fuse. Does it sound from my description like that might be the problem?

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