Is there a difference in SLA vs NiMH ah?

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alanpo
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Is there a difference in SLA vs NiMH ah?

Are the ah ratings on NiMH different than SLA batteries? For example, in an EV bicycle or scooter, would a 10ah NiMH give the equivalent of 20ah SLA battery pack? I didn't think so, but my field tests appear to show otherwise.

I've got a 24v Bladez powerboard scooter with 2 12v 12ah UB brand SLA batteries. I've increased the scooter voltage to 30v by serially adding 2 NiMh 3.5ah RC battery packs, both wired in parallel, to the 24v pack. The scooter runs fine at 30v.

After about 30 minutes of riding, the 24v batteries are drained almost to the point the motor is ready to auto-cutoff, if I were to cut-out the extra 6 volts (I have them on a switch). When I go and recharge the 3.5ah NiMH packs, about 2.5ah is typically charged into them. The SLA charger doesn't indicate how much juice is put back into the SLAs during their charging, but given what I'm seeing, it appears the 3.5ah NiMh pack is equivalent to the 12ah SLA pack. I've repeated this scenario many times.

The SLA batteries are broken in and appear to be fine and are giving the same performance as the original pair of SLAs I'd used.

alanpo
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Re: Is there a difference in SLA vs NiMH ah?

Correction: The 2 3.5ah NiMH are wired in parallel, giving 7ah. So it appears 7ah NiMH is roughly equivalent to an 12ah SLA.

LinkOfHyrule
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Re: Is there a difference in SLA vs NiMH ah?

Yeah, SLA suffers from something called the Peukert effect. It basically means that the faster you discharge them, the less capacity they have, so it doesn't take as much NiMH/NiCd/lithium to match the actual capacity of an SLA.

Also: is that 30V NiMH pack wired up directly to the SLA cells? Doesn't seem like it (since the SLA cells aren't destroyed), but I thought I'd ask.

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dogman
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Re: Is there a difference in SLA vs NiMH ah?

You must ride like me, allways full throttle. I get about 7ah worth of watthours out of 12 ah sla's too. So I get maximum voltage sag. I find I get 3 times the ride out of 20ah lithum that I get out of 12 ah sla.

Be the pack leader.
36 volt sla schwinn beach cruiser
36 volt lifepo4 mongoose mtb
24 volt sla + nicad EV Global

alanpo
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Re: Is there a difference in SLA vs NiMH ah?

I'm not sure what you mean by 'directly'. I've got the 2 NiMh packs connected in series to the 2 SLA batteries via a toggle switch. The NiMh packs connect to the toggle switch. I can toggle the switch to use the full 30v or just the 24v SLAs. I was told that was OK and they seem to be OK.

alanpo
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Re: Is there a difference in SLA vs NiMH ah?

Yep I mostly ride full throttle on the Bladez, because I get 13mph on 24v and 17mph on 30v w/ a 175 lb load. That is not too fast in either case.

To the other reply...thanks for the "peukert effect" tip. That explains alot.

LinkOfHyrule
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Re: Is there a difference in SLA vs NiMH ah?

Eh...so you're using them sort of like a boost pack (swaps them in and out of the series string with the toggle switch)?

Not necessarily such a good idea. If you rode a while on just the SLA packs and then rode a while with the NiMH pack in the string, you could drain the SLAs badly or even drive them into polarity reversal (instant death for any battery).

I'd take out the switch and just ride with the whole pack, if I were you.

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alanpo
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Re: Is there a difference in SLA vs NiMH ah?

Yep it is a boost pack. I'm careful to prevent the condition you mention. I don't use the SLAs for a while and then kick in the boost. Based on what you said, I will avoid using the NiMh to boost a depleted SLA at any cost. I always ride w/ the boost the whole time. I've found out that around my area, w/ mostly flat roads, I can ride 25 minutes with a good safely margin, running on the SLA and NiMh packs. I'm into electric RC boating, so I know some things about NiMh batteries but little about SLAs.

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