Now one of my batts overcharging!

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badnewswade
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Now one of my batts overcharging!

Postby badnewswade » Mon Mar 14, 2011 10:10 pm

Watered VRLAs, put dummy loads on them, discharged, recharged with scoot charger and then applied equalisation charges to three of the batts. There's still a fair bit of water in them, but I think it is starting to get soaked up by the mats.

Applied the dummy loads again today and made sure to discharge them to the same voltage (as much as possible). Got them all to within .03 of a volt of each other and sealed them up with superglue.

Batteries 1,2, and 3 are fine, but battery 4, (one of the ones I equalised earlier) got up to 14.7 volts during charging! Now they're on float, and battery 4 is at 13.7v while the rest are around 13.35v.

Am I in physical danger if I put these batts in my bike? One of them has to go right under the seat! (It was going to be #4 too, as it seemed weak and flakey & I wanted to get to it easily) AND I've had electrical problems with overheating wires too... so if any of them vent while I'm riding I'm in double trouble.
34 Watt Hours per mile, or > 700 MPG. What, me, smug?

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Jeremy
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Re: Now one of my batts overcharging!

Postby Jeremy » Tue Mar 15, 2011 9:25 am

14.7 sounds OK to me, that's about the top end of charge for a wet lead acid battery. A car electrical system generally runs at around that voltage whilst being charged. If the cells aren't gassing excessively and getting hot then they're not being over charged, as a general rule. Wet cells are generally pretty tolerant of a little bit of over-charge, as long as they are free to vent.

My guess is that the slight variations you're seeing are down to the lack of good mixing between the water on the top of the cells and the more concentrated electrolyte deep in the mats. It will take some time for the electrolyte to become uniform, in terms of strength, I think, so I'd carry on as you are for now; I'm sure they'll settle down before too long.

Jeremy

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badnewswade
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Re: Now one of my batts overcharging!

Postby badnewswade » Tue Mar 15, 2011 9:38 am

Well I've decided to discharge them for half an hour and and do number four more than the others to make them equal. Only by two or three minutes though - along with using the slower charger it seems to be working so far....
34 Watt Hours per mile, or > 700 MPG. What, me, smug?

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badnewswade
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Re: Now one of my batts overcharging!

Postby badnewswade » Tue Mar 15, 2011 11:52 am

Now I've got three of them gassing and one not. I can change that back though - what do you say?

I'm REALLY worried about the danger of a hydrogen explosion now. One of the wires to the motor gets very hot indeed and its very close to where the batteries go. I can't discount the danger of sparks either.

Am I safe?
34 Watt Hours per mile, or > 700 MPG. What, me, smug?

JonSpence
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Re: Now one of my batts overcharging!

Postby JonSpence » Tue Mar 15, 2011 2:35 pm

badnewswade wrote:I'm REALLY worried about the danger of a hydrogen explosion now. One of the wires to the motor gets very hot indeed and its very close to where the batteries go. I can't discount the danger of sparks either.


Hydrogen is only produced during the charging cycle as far as I know. I doubt that the motor will be running at that time to get the wire hot or for brushes to spark. You might want to think about possible burns using the bike though if that wire gets that hot.

Obvious safety rules apply. Charge in a well vented area. Have a tub of sodium bicarb* handy (home baking section of the supermarket) and try to use eye protection while working on or near batteries. Try to ensure that isolating the batteries from the charger is done remote from the batteries so that any spark is a good distance away.

*In case of a acid spill or burst battery.

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Jeremy
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Re: Now one of my batts overcharging!

Postby Jeremy » Tue Mar 15, 2011 5:25 pm

True, you don't get hydrogen produced during discharge. Battery heating when discharging is solely due to resistive loss, but if you have a wire that's getting hot it indicates that it might not be man enough for the job, or, perhaps, it may have a dodgy. high resistance, connection that's causing the wire to heat up by conduction.

The golden rules when charging are to turn the charger off before you remove any leads (to prevent sparks) and to ensure you have good ventilation in the area. Hydrogen is exceptionally light and will float up to the very top of any enclosed space very quickly - it won't hang around for long if you're charging with a door or window open nearby.

Jeremy

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badnewswade
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Re: Now one of my batts overcharging!

Postby badnewswade » Tue Mar 15, 2011 6:21 pm

Got them all charging at around 14.5 now, not sure how long that will last after I put them in the bike though...

Seems pretty good. No chance that the sloshing around of electrolyte during riding might cause any venting then? Also, I did experience some spontaneous venting when atmospheric pressure dropped recently just prior to / during some crummy weather, there was a definite acidic pong around the batteries and the rubber caps started to pop off... I think it was fairly low pressure venting but venting nonetheless.
34 Watt Hours per mile, or > 700 MPG. What, me, smug?


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