Ezee kit, bad battery?

[Nico]

I recently bought a second hand eZee kit, intended for a Yuba Mundo, to put on my xtracycle. The battery is 37V 14Ah, and according to the seller and the Cycle Analyst that came with it, it had 11 cycles.

One of my first tests, the battery gave up really quickly. It suddenly turned off and wouldn't come back on. I charged it overnight (measured 41.8V), put it on the bike and it worked normally. I thought maybe the hills around here were too much, so I set the CA to a 16A limit and was careful to keep it under 12ish amps on climbs.

Today, after two rides totaling about 15 miles but less than 2Ah, the battery gave up again on a hill. I was pulling about 10-12 amps, don't remember the voltage. As soon as I got home I measured about 11V and slowly climbing. I let it sit for a while and it stabilized at 37ish V. I tried it on the bike again, and the CA flashed on and quickly off. I measured the battery and got 9.5V , again, climbing slowly. Once it stabilized again I put it on the charger and there it is now.

I am new to electric bikes so I'm trying to make sense of this. It doesn't seem normal, but how bad is it? Could it be just an unbalanced pack or is it a sign of dead cells? Also, even though I set the CA to a 16A limit, it recorded peaks of well over 20. Is this normal?

 

[dnmun]

if the battery was drained to 9 volts under load it has already been ruined. it should have shut off the output mosfets in the BMS when the battery dropped under the LVC.

do you have a voltmeter? can you take pictures of the battery when you get it apart? and post them here so we can see.

 

[voicecoils]

The low voltage is just the BMS resetting.

You may have a faulty BMS, bad cell (or cell group) or just imbalanced cells.

Pop the battery open and take a photo to post here.

From there we can guide you where to check cell voltages etc.

EZee has used lots of different cells and BMS plus a few case designs over the years so a photo will help.

Do you have a multimeter? You don't need to be an electrical pro to do basic testing with some guidance.

 

[dogman dan]

That 12th cycle, the one where the battery sat for a long time is likely the problem. It may take significantly longer than overnight to get the low cell that is causing the bms shutoff to happen to fully charge.

If nothing else, put it on the charger and leave it on for a week, whenever you are not doing something else with it, like opening it up to check individual cell levels.

The peak amps is normal, the amps will spike higher before the CA or the controller has time to pull it back down. Too fast to see on the display, but the CA records it.

Hard to say at this point if you can bring the battery back, but hope is not lost yet. But unfortunately, it's a small hope, not a large one. One cell may have such low capacity now, that it sags badly under even 5 amps of load. And that one cell will keep shutting down the whole pack.

 

[d8veh]

Don't worry about the low voltage. That's only residual and leaking charge after the BMS has disconnected the cell pack. You have to find out why the BMS is switching off. Almost certainly it's because one or more cells are reaching LVC. You have to open the battery to confirm which one/s. The older Ezee batteries have Phylion cells that, when worn out, sag down to LVC under load, but then recover back to 4v when you take the load off, which makes it difficult to test what's wrong. you need a test rig of some sort to put the battery under load while you measure the cells.

 

[Nico]

Thanks, everyone. I took it apart this morning, here are some pics.





I do have a multimeter. I tested it right off the charger this morning, at only 20something V (unlike last time when it did charge to 41.8 ). It creeped up to 36, and then it went back to the charger. The odd thing is that both times the charger went to green (charged) within a couple of minutes.

That 12th cycle, the one where the battery sat for a long time is likely the problem.

That's what I'm thinking. I do believe it had been sitting for a while.

you need a test rig of some sort to put the battery under load while you measure the cells.

I'm close to Ebikes SF. If the home remedies don't work I can probably take it to him.

 

[dnmun]

you have to get that shrink wrap off the pouches and expose the other end of the battery. that is where the BMS and poles of the electrodes are where you need to measure. post up a picture when it is clear. or the BMS may be under this end next to the fuse.

post up a picture when the shrink wrap is off. you can wrap a piece of masking tape around it at the top and bottom to hold the pouches together but the shrink wrap damages the pouches where it squeezes them into distorting the corners.

but it prevents us from seeing anything.

 

[d8veh]

When you get those stange voltage effects, it's because the BMS is switched of, which prevents you from measuring the pack voltage. You have to measure the voltage where it goes into the BMS, not where it comes out.

The BMS is located at the top of the battery. I've disassembled a couple of those before.Cut the four corners of the shrink-wrap, and peel it back about two or three inches. Then there's wide tape that's reinforced with fibreglass over the BMS. You have to peel that off too. Now you can start measuring. You need to measure the individual cell voltages where the sense wires come in to the BMS. IIRC theyre marked B0, B1, B2, etc. Be careful not to short anything with your probes. Once you have those individual cell values, you'll know the cause of your problems.

 

[Nico]

Thanks everyone. I won't have time to open up the battery like that till this weekend, so in the meantime I'm leaving it in the charger in case it's just an unbalanced cell.