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Possible cell sag or bad BMS

Old 12-18-18, 06:35 PM
  #1  
Gneux01
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Possible cell sag or bad BMS

I would first like to mention, that I've had a Ebike kit for about 8 years, and dealt with and fixed every problem that was thrown at me, or the very least. I figured out what the problem was. I've also had my share of problems with batteries in the past. I had tabs come loose from a pack and was able to fix it, and have it running just fine again.

I finally got my new ebike kit up and running after my last bike/kit was stolen, and I've had non stop problems with the battery. When I first got the Golden Motor Black Pie 5 Vector with Sinewave Controller kit, I plugged the battery into the charger I had left over from Ping Battery. This is when I first noticed problems. The charger kept cycling on and off, but eventually brought it up to a full charge.

Not only that, the battery was giving me very inconsistent voltage readings. When I originally took a reading. It read 45.7 V. I found this odd, as it should of been charged up. I checked it later on and this time it read a little over 53 Volts. I figured, maybe I got a wrong reading. Shrugged it off. Checked again It was @ 45.7V.

I tried with a different meter and I get 52v. Tried my good meter again, and back to 45.7v. I'm like what is going on here. Why is this battery all over the place.

So I put it on the bike and use the bike for a little bit. I got MAYBE 8km out of it, before the BMS tripped @ 48v. Charged it again overnight. Ran it again, and it seemed fine. I had to take it to the bike shop for a wheel fix, as I got loose spokes and such.

Let it charge once again overnight, and when I got the bike back. I went to take it out for a test ride, and soon as I apply and sort of load. The BMS on battery will trip. I can have the bike upside down, and throttle on auto throttle and the motor will keep going for as long as I let it...

It seems to be only when a load is applied, and I draw a large amount of power at once from the battery, that the BMS trips. I'm leaning towards a bad battery, or bad BMS at this point. I've never seen a battery behave in this way before.
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Old 12-19-18, 10:30 AM
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New batteries for the voltmeters. Always need a good baseline.

Your problem sure sounds like battery. By the way, didn't ping sell LIfeP04 batteries? Less likely to blow up but lower voltage (3.2V nominal instead of 3.6V for lithium 18650). You might want to check the voltage on the Ping charger.


.
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Old 12-19-18, 11:02 AM
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Originally Posted by Doc_Wui View Post
New batteries for the voltmeters. Always need a good baseline.

Your problem sure sounds like battery. By the way, didn't ping sell LIfeP04 batteries? Less likely to blow up but lower voltage (3.2V nominal instead of 3.6V for lithium 18650). You might want to check the voltage on the Ping charger.


.
The ping charger is 59.6v
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Old 12-19-18, 08:51 PM
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That 59.6V is a odd voltage. A 14S charger for a 52V battery should have a max voltage of 58.8V. A 13S charger for a 48V battery is 54.6V max. Typo?

I still agree with your thinking. Bad batteries spin the motor all day with the wheel in the air and bog down when you sit on the bike.

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Old 12-19-18, 09:43 PM
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Originally Posted by Doc_Wui View Post
That 59.6V is a odd voltage. A 14S charger for a 52V battery should have a max voltage of 58.8V. A 13S charger for a 48V battery is 54.6V max. Typo?.
No typo. That's what is listed on the charger.

Charger is DC 59.5V
Charger Model: KP4805AL
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Old 12-20-18, 09:34 AM
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I would check the output. Too high if not a misprint The battery BMS would protect the cells, but that can fail.
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Old 12-20-18, 11:08 AM
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Originally Posted by Doc_Wui View Post
I would check the output. Too high if not a misprint The battery BMS would protect the cells, but that can fail.
It worked for years on my old 15ah 48v pack.
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Old 12-20-18, 09:54 PM
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Originally Posted by Gneux01 View Post
No typo. That's what is listed on the charger.

Charger is DC 59.5V
Charger Model: KP4805AL
Was the charger originally for a 48V LiFePO4 pack? I have a charger that came with one of my LiFePO4 packs that put out 60V and I never had a problem, even though recommended charge voltage for those is 3.6V/cell or 57.6 for a 16s config.
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Old 12-20-18, 10:14 PM
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Yes it was meant for a 48V LiFePO4 pack and was used for years without any problems.
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Old 12-26-18, 03:51 PM
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Regardless of your battery issue, that 59.6V exceeds the max voltage of a 13S or 14S Lipo pack. If that is the type of battery that you have, and its BMS overcharge protection ever fails, you got problems.
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Old 12-26-18, 03:55 PM
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I only charged it once with thst chargercharger, and still hot a normal off charger voltsge reading. The pack was not behaving normally before I, even charged it.
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Old 12-26-18, 10:38 PM
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But you never clarified whether you have a LiFePO4 or Lipo battery or the max charge voltage..Your charger may be perfectly acceptable for what you have. ,

I believe a 16S LiFEP04 battery is called "48V", but comes off the charger at 58.4V, but quickly drops down to 52.8V when you start riding. If it's reading 48V, it's way way down, or maybe never got fully charged.
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Old 12-26-18, 10:50 PM
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I thought I did, seems I didn't. Odd... Anyway, it is a LiFePO4 battery. Specs are as follows:


48V15AH Battery LiFePO4
Built in BMS
C-rating 3C (45A)
Weight 8.5 kgs
Life cycles >1500 Cycles


Size without bag 25cm x 18cm 12.5cm
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