SLA Battery "Pack"

[dofbikes]

Hi everyone.

Recently, after quitting from GM batts (boring problems, faulty cells...) , I've took many old UPS batteries, charge them up and created a 4 batteries pack each one 12V 7Ah. Took excessive weight of the ebike by choosing the lightest old bike parts I had in my garage and then made the first test run.
I can tell you I'm surprised because I made 7 km including a very agressive climb, about 2 km from 20m above sea level to 280m above sea level and despite my help on pedaling the motor did not burn (as happened with the GM LiMn battery).
After that I've disassembled everything and checked every battery because I feared some kind of problem as long as I know these batteries can explode.
One of the batteries was a bit hot and it can mean danger.
The connection was done as you can see in the following pic:



The battery that is closer to the motor power cables was the one that was hot (the others weren't)
I think that it was due to very thin cables used so it caused resistance.
Do you have any different idea about that?

Many thanks,

Rui Santos

[Morgen 3Eman]

If the wires are too small for the current, the wire itself will get hot.  Since your problem is that one battery got hot, I would suspect that battery has a bad cell, and was being reverse charged by the other cells supplying motor current.  What is the output voltage of the individual batteries?


TTFN,
Dennis

[dofbikes]

Thanks Dennis for the reply.
Answering to your question. Right after the ride all the 3 good ones had 12,4V and the hot one 11,85 V.
I've bought bigger cables, new connection plugs (to fit the bigger cables) and today I'll try to replace the supposedly bad battery by another one..

Thanks again,

Rui

[Morgen 3Eman]

Bigger  and shorter power cables allow more volts to be developed at the motor windings, so that is a good idea in any case. Good Luck with your Pie.

TTFN,
Dennis

[skylinenitro]

Thats exactly what I did to get my battery packs.  They are all used old UPS batts wired the same way you have.  I would try those same 4 batts with the bigger cable, but this time don't try that huge hill.  Take em out for a cruze on mostly level ground and see if it gets hot again.  If it does, thats probably a bad batt.  I use all 8ga wire or bigger, and I soldered the wires to the battery terminals so they cant wiggle loose on the gravel trails 

If you have a volt meter that you can ducttape to your bike to measure the volts when you ride that would help too.  Connect the voltmeter to measure the 48v supply to the controller, leave it on when you ride.  If it drops below 46v when you floor it, but then goes back up to 50v-54v when your idle, then you might have a bad cell.  (Assuming all batts are fully charged when you start).  You might want to see if you can get a 48v charger, maybe from an old UPS?  I assume that you have to break the pack apart to charge them as 12v?