Voltage after charging

[Andy]

Hi, I have just fitted three new Panasonic 15ah sealed lead-acid batts from Powabyke. I notice that when they've finished charging they're only about 41 volts or so, should they be higher? And if so how urgent is it that I change my charger?

I'm using the charger that came with the bike, an old Sakura running on 14ah batteries - should I get a special charger for the 15ah ones? Or will a generic 36v 2ah charger off of Ebay be OK (as long as it uses staged charging obviously)?

 

[flecc]

That's perfectly ok Andy, well over 13 volts per unit is fine.

The Ah rating doesn't affect the charger to use within reason, only the charge time. That tiny increase in capacity will just increase the charge time by 1/15th.
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[Andy]

I don't know - someone told me that 42.4, at the very least 41.4v or I'll run into "balance issues and early failure."

 

[flecc]

News to me Andy, and as long as the three batteries start off as reasonably well balanced when new, there should be no trouble with an average of 13 volts per battery.

It's worth rechecking after the second and third charge and use anyway, since all batteries settle in after the first charges. You might find a higher charge level then.
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[Andy]

Oh, absolutely - I check after every charge (not individually though; that would be going too far)


According to Battery University one should leave it on overnight!

 

[tony18m2001]

Hi Andy

I hope the following bit of technical information helps you see about the way batteries charge. I used to own a Powabyke, and because of the monitoring connector on the battery, I used to do tests on charging and discharging the battery. Attached is a typical set of curves of charging voltage against time recorded from a data logger. I can't quite remember, but I believe the battery was being charged with the standard Powabyke charger (I'm a bit vague because the charger blew up somtime around then). The 3 12V batteries were of various vintages and you can see how the batteries were showing the same rising voltages for about 200 minutes, then the end-point voltages of the different batteries began to tell, with battery 2 rising fastest and then dropping again before charging ended.
By adding up the 3 battery voltages, you can see that an endpoint of 45V total was appropriate for these particular batteries - perhaps your new ones wouldn't need to go quite so high. In any case, I dont believe the last minutes add much to the charge - perhaps Flecc might comment.
Tony

 

[flecc]

I agree Tony, the latter part of the charge won't add much.

I think Andy should complete at least one use and recharge to see if the voltage rises then, since these paste electrolyte cells benefit from conditioning in the same way as some other chemistries.

Seeing the poor performance being reported for these newer bikes now, I am beginning to wonder about the battery type supplied. You may know these SLAs come in two varieties, one for deep cycling, the other for long life low current use with permanent trickle charging, as used in burglar alarm backup and the like. The latter type are very reluctant to issue high currents and are unsuitable for our usage.
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[Andy]

Well mine are definitely from powabyke. I see from your graph that they end up at around 13.75 each, the same as mine. The voltage while charging is over 14v though, which is to be expected. Looks like I probably don't have a problem but I'm going to try getting a different charger anyway as mine is quite elderly. As long as the batts last at least a year I'm fine with it, in fact with my usage of the bike they'll probably last a lot longer as I rarely do over 10 miles in it without charging.


[quote[I think Andy should complete at least one use and recharge to see if the voltage rises then, since these paste electrolyte cells benefit from conditioning in the same way as some other chemistries.[/quote]

Are you saying that I should deep-cycle them? I am using the new batts; the bike is often used every day or every other day (Although giving it a rest now) so I've already charged it a couple of times.

Re: partial charges. If I'm on a long run and stop somewhere, is it worth putting a partial charge in even if I don't strictly need it, or will a partial charge place undue stress on the battery?

Thanks for all your help btw!

 

[flecc]

If you've already done a couple of fairly full charges, no need for more Andy. Lead acid likes charge cycling so topping up will never harm them.

Personally I'd be entirely happy with 13.75 volts per battery, and can't see any reason why they shouldn't last well.
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