Bad Battery Cell

[adamsavage79]

I just started having a problem today, and possibly the other day, where the pack will just cut. It soon only did this when going over a bump. I checked out the plugs and one looked like it needed to be replace. So I spliced in a new one, took it for a 2km test run and it was fine. Had it on charger for about 2 hours earlier, then went to work. It sat outside in about +5 Celsius weather. I was able to get up two hills and then on the last hill, I was about 1/2 km on the flat stretch, before going into a downhill. Then it just kept dying on me. So I pedaled the bike home. Got it up to speed and going downhill I was able get the motor going. However, once the road flattened out and the power increased, the pack died again. I checked the voltage once I got home and it was reading 51.6v. Still plenty of juice left.

So I sit on the bike and use the throttle. Bam, the power is cut. If I left the back end of the bike up, and use the throttle the motor will spin just fine, and this because there is much less power being drawn from the battery. I then put it back on the charger for a hour, and tried again. This time the battery didn't cut. Will charge it overnight and see if it's the same. If it is, then I have a reduced range. It seems I have a cell that is weak ? Not sure why the pack is cutting out @ 51.6v. Never seen the behavior before. Typically with a weak cell, the pack will go down past 48v before cutting out. Not sure what is going, but honestly getting fed up with the neverending issues with this Golden Motor Kit..

 

[goatman]

id open it up and check voltages before putting it back on charger

 

[adamsavage79]

I'm thinking of doing that. See if I get a imbalance. Might be best to drain it till it cuts off, then check.

 

[goatman]

are you using these sla batteries?
https://endless-sphere.com/forums/viewtopic.php?f=14&t=106546

 

[adamsavage79]

Nope. I got rid of that Ebike. I have a golden motor e-bike kit. Here is the Battery pack I'm using: https://goldenmotor.bike/product/48v15ah-lifepo4-battery-in-free-eco-pack-bag-2/

 

[goatman]

look at the battery connections on the case where its contacts are to make sure theyre pinching the cradle prongs, a bump in the road will cause power to cut out and also what youre experiencing



so will a melted fuse holder like this, if you have one inside. 1500 watts continuous melted the plastic but didnt blow the fuse just made a bad connection

 

[adamsavage79]

I didn't even realize that my battery is now discontinued and that the link is broken… the closest I could find to what it looks like is this: https://goldenmotor.bike/product/24v10ah-lifepo4-battery/

However my battery is 48V 15ah, with Anderson black and red connectors. As for the bump in the road I resolve that problem by splicing in a new connector. This is a brand new problem.

 

[goatman]

i dont know anything about lifepo4

 

[adamsavage79]

I can confirm this is a now DEAD cell. This one cell was discharging faster than the rest, dragging the pack down. Today it died at around 52.6v roughly give or take .10 of a volt. Kept riding it to work. Left it sit outside for my shift. Checked the voltage again, and just sitting there with battery disconnected from the bike. It now read 44v. It was at this point, I knew there was definitely something going on with the pack. So I cracked it open and un screwed a few cells. Then started to check them. I got to the 2nd cell and I got a reading of 1.5v while the rest of the cells are giving me 3.2v - 3.1v, which would be a normal reading for them. 1.5v however, is NOT a normal reading. This means I have dead or dying cell.

 

[fatty]

Is there a BMS that was disconnecting the pack due to bad cell(s) hitting cell LVC?
Or were the bad cell(s) sagging the whole pack enough that the controller was hitting pack LVC?

 

[adamsavage79]

I checked all the cells and there's only one bad one and that was causing the BMS to hit low voltage cut off. In fact when that cells removed from the pack the voltage of the entire pack jumps up to 50. When you return the bad cell the pack voltage goes down to 44. I think that's the BMS doing a partial disconnect to protect the rest of the pack ?