Electrical diagnostic help

pjvenner

Finding my (electric) wheels
Mar 20, 2011
24
0
Hi folks. My bike suddenly died on my way to work. I've managed to cure the symptom, it's now running again, but I need help finding the cause so it doesn't happen again.

It runs on 3x12v SLA batteries. I connected the wires by feeding them through the holes in the tabs & securing them with the silicone sheaves provided with the batteries.

When I opened the battery compartment up there were 2 areas of concern: A small amount of clear odourless liquid which I thought was water, but after wiping there was light erosion to the plastic battery box so I'm assuming it's battery acid. Secondly (and what caused the breakdown), The silicone sheaf on the '+' terminal of the 1st battery in the series had melted. The wire was still hooked onto the tab but obviously not securely enough to keep a good connection.

My main questions are:

If a battery has leaked would that be a likely cause for the overheating terminal?

If this is the case, how can I tell which battery has leaked? There's no visible sign of damage on any of them, and the amount of seepage was tiny - much less than a teaspoonful so I don't think weighing on normal scales will be an option.

Assuming I find a faulty battery, I have an unused spare. If I were to use the spare would it need charging separately to match the charge of the other 2 or do they balance themselves out?

Any help would be greatly appreciated. I'm in a new job so being late for work isn't good. I'm wary about using the bike again until I can fix the cause of the problem, even though it costs £2 a month to run - £73 less than a bus pass! Even more importantly it has reduced my daily travelling time from 2-3hrs (depending on shift) to under an hour, so for obvious reasons I would like to feel confident about using it again ASAP.

PS: It looks as though somebody has tried to steal the batteries. The battery box locks into the footplate & has folding plastic handles. Both handles have snapped at the hinge on 1 side. I can't see how this would damage the batteries inside but I thought I should mention it in case it is relevant.
 

Blew it

Esteemed Pedelecer
Jun 8, 2008
1,472
97
Swindon, Wiltshire
If the wires are connected to the battery tabs using spade end terminals, then make sure the spades are gripping the tags tightly. Personally, I prefer to solder the cables to the battery tags.

Gel batteries are generally fitted with vents to release any pressure build-up within the plastic casing, particularly those referred to as Valve Regulate Lead Acid. Internal pressure is usually caused by overheating as a result of the batteries being shorted, perhaps this happened when the attempt was made to steal them. The liquid that vented from the batteries is highly corrosive and should be carefully washed away with plenty of water.

There is a possibility the plates and seperators in the battery were damaged as a result of the shorting, so it's possible they may have lost some of their capacity.

Regards
Bob
 

pjvenner

Finding my (electric) wheels
Mar 20, 2011
24
0
Thanks Bob. My batts are VRLA. I'm going to get a soldering iron in the morning to make the connections more resillient. Is there any way to test the batteries' capacity individually with nothing more expensive than a multimeter?
 

Blew it

Esteemed Pedelecer
Jun 8, 2008
1,472
97
Swindon, Wiltshire
No not really, if they still have enough capacity to complete the trip then all is well. Lead acid batteries have a short life anyway, fortunately inexpensive to replace.

Have fun
Bob
 

banbury frank

Banned
Jan 13, 2011
1,565
5
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pjvenner

Finding my (electric) wheels
Mar 20, 2011
24
0
Thanks for the tip Frank. I'll look for a high rated Iron & hope that the batts are OK. . I got my current batteries from batterybay & no complaint with them personally, but if I have to spend another £100 on batteries my bike is going to break speed records for an ebike - albeit vertically off a cliff edge.

After 9 months unemployed I need something cheap AND reliable. TF it's a long weekend so I have time for a test-ride. I'm still guna cry if I don't make it home!