8fun conversion kit

[KirstinS]

Just a comment - my 8fun cuts out at 32v - wether designed that way or not !

Ignore me, I tested a good half hour after I off the bike

I expect it was voltage bouncing back a little after constant use for 7/8 miles

 

[andycoh]

That doesn't look good. It should be at least 41.5v straight off the charger. If you want to fix it yourself or check what's wrong (or right), you have to take the top off the battery (3 screws),then unplug the wire that's still connected to it. On top of the battery is the BMS. You'll see one or two multi-pin plugs to it. These are the sense wires from the cells. Put your black probe on the BMS where a thick black wire from the cell-pack is joined. It should be marked "B -", then with your red probe, check each pin on the sense wire connections to get the incremental voltages, something like 4.1, 8.2, 12.3, ....etc. Write them down and post them here.

If you don't understand where to check, take a photo of the BMS and post it here. Make sure it's clear.

Ok finally got the better cover off. Red and black wires are soldered to a board in the top, so could not disconnect. With black probe on plug with two black wires and red probe on various colored wires in plug on opposite side of BMS my voltages are:
black - 3
brown - 7
red - 11
orange - 15
yellow -19
green - 23
blue - 27
purple - 31
grey - 35
red - 39
(two more yellow, also 39)


Not been charged for 3 or so weeks, so may be a little lower than usual.

 

[Deleted member 4366]

You need go to a lower scale so that we can see tenths of a volt. From what you've shown, cell 1 looks dodgy, but we need a more accurate measurement to confirm.

 

[andycoh]

You need go to a lower scale so that we can see tenths of a volt. From what you've shown, cell 1 looks dodgy, but we need a more accurate measurement to confirm.

oops sorry my bad. Switched down to tenths now:
3.5
7.3
11.4
15.5
19.6
23.7
27.8
31.9
36.1
40.2

 

[Deleted member 4366]

The first two cells don't look healthy at 3.5v and 3.8v. The rest are all over 4.1v. I suspect water came in and drained them down a bit. It might be worth rebalancing them, which can be done through the multi-pin connector in the BMS. If you want help with that, you need to post a clear picture of the BMS so that I can see which one you have, but basically, you connect a 5v phone or USB charger to the positions you probed with your multimeter. You must monitor the charging so that it doesn't go above 4.2v. It'll start to accelerate upwards when it gets past 4,1v, so be careful.

 

[andycoh]

Heres a photo of the BMS. Have plenty of USB chargers, but not sure how to connect them. Thanks for your help.

 

[Deleted member 4366]

You need to butcher a USB cable. Cut the connector off the end, then use your voltmeter to figure out which two wires give 5v.If you have an old 5v phone charger, there's probably only two wires, so it's easier. Whichever method you use, you just connect the two wires to where you measured the cell voltage -plus to plus.

That's a nice BMS you have.