Faulty battery, 20ah/36v shrink wrap.

Alan Quay

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So I have a new battery from BMS battery here, and its faulty.

If I ride the bike for about 5 mins or so, the battery cuts out, and will not restart until it been disconnected and reconnected. Also have to wait a bit.

I have just taken it for a spin, and got it to cut out. Rode it home, opened it up and checked cell voltage at BMS connector. All around 4.0 (+/- 0.05), so I'm pretty confident it's a BMS problem.

Anybody know how I can check that the BMS is the 36v version, not the 48v one?


(Note: have started a new thread from the one about p5 parameter, as thats proven not to be tha case)
 
D

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You should send an email to BMSB. Tell them that you think that they've fitted a 48v BMS because it cuts out at whatever voltage. Ask them to send you a new 36V BMS. See what happens.
 
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banbury frank

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Jan 13, 2011
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Hi It is a 36 volts you can see the 10 balancing resistors not 13

Simple the BMS is to small you are taking out to many amps and it is doing its job cutting the battery out you need a more powerful BMS

The BMS they fitted is 15 amps continues MAX 30 amps for seconds only

Frank
 
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Alan Quay

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You might be right Frank. Now I look at the website, the 20ah battery is listed at 15a continuous. I thought they were 20a continuous.

If that's true, then BMS battery do not supply batts big enough for the controllers they sell.

The weird thing is that I have a 6 month old, seemingly identical battery, and it performs without cutting out on the same bike. I'm wondering if they have changed the spec at some point?
 

103Alex1

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New BMS needed by the looks of it. :rolleyes:. I'm sure mine has the 20-40 fitted because it still supports 30A continuously for a considerable time

The web listing has always said 15A continuous for that battery but in practice the BMS fitted didn't cause cutout like that during continuous running over 15A.

Perhaps they swapped the BMS to the smaller one when they started listing high discharge rate batteries - to create more of a tangible difference between the two ? It's a pain whatever way because although $20 is neither here nor there, having to disassemble the shrinkwrapped batteries and reassemble with a higher capacity BMS fitted is a PITA :mad:.
.
 
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D

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They've clearly made a mistake in their listing. You can see from the photo that at least 6 output FETs, maybe eight, compared with an average of two on a 15 amp BMS.

Frank's right about it being a 36v BMS because it only has 10 channels installed, ut clearly it has the three empty chanels for the 48v version. I'm not sure whether it's microprocessor based. The smaller ones are. Is there one on the back? If so, it could simply have the wrong software in it, otherwise there might be a voltage divider somewhere with the resistors for 48v.

This is the 15 amp BMS that they fit to the 36v 10aH shrink-tube battery. You can see the microprocessor and only two output FETs



This is the 36v high power BMS that they fit on the 20aH shrink-tube battery. It looks like they've changed it since then.
 
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Alan Quay

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Hmmm, I cant decide if its a faulty BMS or just that the new ones will only run at 15A. Either way, looks like I need to change it.

BMS Battery are being no help here, because they are saying that the battery is 15A continuous. They just keep telling me to keep current under 15A - not easily done with a 27A controller, which is labeled 22A!

Not sure I'll be using them again after this.

So, where can I get hold of a BMS that will fit without having to chop it around too much and will give me at least 20A?

And once again, thanks for all your input guys.
 
D

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That's definitely not a 15 amp BMS. A couple of things to try: can you temporarily use a 15 amp controller to test if it's the current that's tripping it?
If it is, you have three choices that I can think of.
1 Move your power output wire to the B- pad to by-pass the output control, which you don't need because your controller will limit current and look after LVC.
2 To limit the current, the BMS has to measure the current - usually by measuring the voltage drop over a shunt or FET. If it's a shunt, you can solder it. If it's a FET, it's a bit more tricky but still possible.
3. Replace the BMS. Try to avoid microprocessor based ones because they're open to programming errors.

Please let us know if there is a shunt. I can't see from the photo.

Conhismotor do 48v BMSs, but the one I bought didn't seem to have LVC, in which case you'd be better off using your present one with output control by-passed.
 

Alan Quay

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I have just come back from testing the battery on my trek, which runs at a peak just over 15A. I did a moderately hilly 8 mile trip, with no cutouts. I used about 3.5ah, and I used about 2ah yesterday on the Butler (when it cutout).


So, it does look like a current limiting problem.

I double checked the BMS, and I cannot see a shunt, unless it's on the back. The board is bonded to a GRP plate and won't come off.

I guess I could just leave it like that, however I may want this battery for a future project.

If I bypass the BMS's output control, will it still serve any purpose at all?
 
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You take the output directly from the cells, so there is no current limiting. You leave the charging through the BMS, so you still get the cell balancing and over-charge control. Your controller will cut-off when the LVC is reached, so you can't over-discharge. There's only one unlikely theoretical risk: if a cell went low, the system wouldn't pick it up because it will only see pack voltage. You'd probably notice the drop in capacity if that happened, unlikely as it is. If it were mine, that's what I'd do. One minute and it's fixed by moving the wire from P- to B-. You can always move it back later if you want.
 

Alan Quay

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I think what I'll do is take two wires out from p- and b-, and stick an Anderson powerpole on each. I can then run it normaly, in the knowledge that if it cuts out on me I can connect up my bypass wire and get home.

I will also have one more attempt to persuade BMSB to send me a replacement BMS, although I'm not holding my breath on that.
 
D

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I've another thought. What controller are you using when it cut out?

I've been out on my trusted BPM Giant with 20aH Ping Battery. This is the first time that I've been more than 20 miles since fitting the S12S controller, and the battery cut out at about 6aH. There's a setting that might have something to do with LVC that nobody can understand. I'm wondering if that has anything to do with it.
 

Alan Quay

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I'm pretty sure it a battery problem, because it does not occur when I use my other, seemingly identical but 6 months older battery.

Also, when it cuts out my watt meter (connected between batt and controller) goes off.

...but I am using a very similar controller, the S12P.......and I suspected that first.....and the p5 parameter....
 
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