Replacing SLA with Li or NiMh

[Daravon]

I have an electric scooter that runs on two 12V 9Ah batteries in series. The batteries are toast, and replacements are close to $100. I'm looking into the feasibility of going lithium instead of replacing the SLA's. I also see that D-cell NiMh batteries are something like 4Ah, but I would need like 40 of them which would be way too expensive at over $10 each.

Where should I look for cheap cells for doing cost comparisons? Is there any companies that will build packs for you?

 

[Norm]

Li-ion will be far more expensive than the SLA batteries you are using currently, you should be able to replace the existing batteries for well less than $100. Don't forget that if you change battery chemistry you will also have to buy a new charger. Universal Battery UB1290 (12V, 9AH) Battery
Norm

 

[lctorana]

I would recommend staying with SLA. By FAR the cheapest option, and it's what your charger and drive controller circuitry were designed for.

The alternative, for this heavy traction use, would be 20 x NiCad "F" cells, but we are talking US$300, plus shipping.

And Lithium traction batteries are even dearer, even though you need less of them.

I wouldn't promise anything else to last very long in service.

Just remember the SLA golden rule. Shallow discharge, quick to recharge. Try to avoid running the batteries down completely, and always recharge ASAP, however little you have used the machine.

 

[Gazoo]

I have an electric scooter that runs on two 12V 9Ah batteries in series. The batteries are toast, and replacements are close to $100. I'm looking into the feasibility of going lithium instead of replacing the SLA's. I also see that D-cell NiMh batteries are something like 4Ah, but I would need like 40 of them which would be way too expensive at over $10 each.

Where should I look for cheap cells for doing cost comparisons? Is there any companies that will build packs for you?

Do a search on google and ebay for LifePo4 batteries. They are more expensive initially, but over time they pay for themselves. They are much lighter and have more capacity than an SLA with the same amp hour rating. It's like comparing an alkaline battery to a NIMH battery. And they have a 2000+ cycle life which blows away SLA's.

Compare them to SLA and I don't think you will ever look back. I don't personally have any hands on experience with LifePo4's. But I have done enough research on them to know how much better they are than SLA's and plan on using them in future projects.

 

[alpg88]

I have an electric scooter that runs on two 12V 9Ah batteries in series. The batteries are toast, and replacements are close to $100. I'm looking into the feasibility of going lithium instead of replacing the SLA's. I also see that D-cell NiMh batteries are something like 4Ah, but I would need like 40 of them which would be way too expensive at over $10 each.

Where should I look for cheap cells for doing cost comparisons? Is there any companies that will build packs for you?

ebay.

take above advice stay with sla, d nimh are 9-10 bucks a pop everywhere.

 

[evenchaos]

Just remember the SLA golden rule. Shallow discharge, quick to recharge. Try to avoid running the batteries down completely, and always recharge ASAP, however little you have used the machine.

You know, the problem with that rule is that you don't get useful utility from a SLA if you do that. Like with the OP application - it means cutting down the range of the scooter. You buy thinking so and so rated batteries that you get x km out of the pack, but then you get so few recharge cycles and cut the range down real quck. I have a real problem with the way SLAs are advertised. ....

 

[alpg88]

if you really want to go nimh route use aa, you can get 10-12 of them for the price of 1 d cell, you,ll have 2,5x capacity,

 

[mdocod]

Hi Daravon,

An SLA doesn't deliver it's full rated capacity unless it is discharged at a pretty slow rate. I'd imagine that an electric scooter hauling a human around is not an easy load on these batteries.

Capacity de-rating for 1 hour discharges is about 40% for SLA. meaning that if your scooter runs for 1 hour, then the actual capacity you got from your cells is ~5.4AH each.

In lithium chemistry, both LiMn and LiFeP04 would be worth a look, NIMH would also work. To get the same runtime you have now, you may only need a pack built to ~60% of the label capacity of your SLA pack, since the ratings on those Nickel and lithium chemistry cells will hold pretty true for discharge rates ~1 hour.

You mentioned thinking you would need 40 x $10 D cells to match it... Hold on a minute there...

There are plenty of quality NIMH D cells out there that have a true 9-12AH rating for ~$7-$14 each. 20 of said cells would match your needs for voltage and actually result in more runtime than your SLA pack.

After taking De-Rating into consideration, $150-$250 would cover the cell costs for a 24V 5AH LiFeP04 pack.

----

More information would be needed to really know for sure if the above information can be taken as 100%, especially the runtime you normally get from the scooter with new SLA batteries. The less the runtime is on the SLAs, the less capacity you actually need to match in building an alternative chemistry pack to replace it.

Considering the improved cycle life of LiFeP04, I think it would be more than worth the investment if you intend to use the scooter long term.

-Eric

 

[rmteo]

I use 10AH NiMH cells and they are about $5.50 each. You would need 20 cells for a total of $110.00.
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=711

 

[alpg88]

I use 10AH NiMH cells and they are about $5.50 each. You would need 20 cells for a total of $110.00.
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=711

wow, that is cheapest d's i've seen so far,

 

[lolzertank]

+1 to LiFePO4.

Another benefit of LiFePO4 over SLA is that they can be charged really fast. For example, A123Systems lists their 26650 cells as being able to charge at 10A, which results in a 15 minute charge time. You'll need a pretty powerful charger to do that though, especially since you'll probably have to wire cells in parallel.

 

[lctorana]

I still stand by what I said.

For traction use, I would use nothing smaller than NiCad F cells.

Or stick with SLA.

 

[Daravon]

I think I'm going to stick with SLA since I can get those ones listed above for $60, shipped. Looks like NiMh would be $120 just for the cells and a lot of work. LifePo would definitely be the best way but that's looking like $200 or more. I got the scooter for free, I just need batteries. I've heard of people using like, dealextreme cells in big packs for electric bicycles, but I didn't realize that SLAs were still so cheap-per-Ah.

By the way, what's the best way to charge SLA batteries? I don't have a proper charger but I do have lots of electronics and leftover DC power supplies. Could I just take a LM317 set for 13.9v, hooked up to a leftover laptop PSU, and leave it hooked up for a "long time"?

 

[Gazoo]

I can highly recommend this ebay seller for SLA batteries:

http://cgi.ebay.com/RBC32-APC-UPS-R...34.c0.m14.l1262&_trkparms=|301:1|293:1|294:30

I ordered a 4 pack of 6 volt 4.5 AH batteries from him and the shipping was very quick. The batteries have been in use for only a couple of months but so far so good.

 

[lctorana]

By the way, what's the best way to charge SLA batteries? I don't have a proper charger but I do have lots of electronics and leftover DC power supplies. Could I just take a LM317 set for 13.9v, hooked up to a leftover laptop PSU, and leave it hooked up for a "long time"?

Yes, that is a good approach.

But might I suggest two small refinements?

1) When your batteries arrive, change the 13.9V figure to the lower of the charging voltage figures printed on the actual battery. This is often 14.4V. Give yours what it is asking for.

2) SLAs don't like being rapid charged, so I like to hook up a current-limiting resistor upstream of your voltage regulator. Again, the aim is to limit the current into a flat battery to the maximum printed on the battery.

 

[TakeTheActive]

I have an electric scooter that runs on two 12V 9Ah batteries in series. The batteries are toast, and replacements are close to $100...

[Thinking-Out-Loud Mode]

12V 9Ah reminds me of my UPS batteries - 12V 7.5Ah, IIRC. I have ~10 APC UPSs that use that cell and last year (or was it the year before? :shrug I researched and replaced them all (MANY were OVER 7 years old!). IIRC, via eBay, I found them for less than $10 each - shipping was the killer.

I wonder if four (two in series twice, then the pairs in parallel -> 12V 15Ah) @ ~$40 would work for you?

[/Thinking-Out-Loud Mode]

...I'm looking into the feasibility of going lithium instead of replacing the SLA's. I also see that D-cell NiMh batteries are something like 4Ah, but I would need like 40 of them which would be way too expensive at over $10 each...

IMO, lithium requires too much 'supervision' and NiMH is intolerant of deep discharge, leaving you with SLA or NiCD.

...Where should I look for cheap cells for doing cost comparisons? Is there any companies that will build packs for you?

Gruber Power is the name that comes to mind for my UPS SLA packs. Maybe not exact, but enough to GOOGLE on. IMO, I wouldn't look for CHEAP - maybe INEXPENSIVE. CHEAP always seems eventually to bite you in the A$$.

As for re-building packs, I remember seeing something in the CPF Archives regarding 'Drill Battery Pack' rebuilding - maybe Batteries Plus? It was a 'Nation-Wide' chain. :thinking:

 

[Mr Happy]

SLAs don't like being rapid charged, so I like to hook up a current-limiting resistor upstream of your voltage regulator. Again, the aim is to limit the current into a flat battery to the maximum printed on the battery.

The traditional current-limiting resistor for this application was a bulb, such as a 6 V or 12 V automotive bulb. Bulbs have the useful property of changing their resistance as the voltage changes, so as to produce an approximately constant current supply.

Also, place the current limiting bulb downstream of the voltage regulator, between the voltage regulator and the battery.

 

[alpg88]

you can revive dead nicd's, if you kill them by overcharging.
i did it few times it worked wery well, strobe circit from disposable camera, i zapped each cell 3 times. my drill pack was not taking charge, now works as good as new, well almost as good. don't think it'll work on nimh or li ion cells

 

[marschw]

All-battery.com has 14Ah F-cell NiMHs for $10.91 in quantities of 20 (which you'd need for the 24v here). Not that I'd actually suggest NiMH for this.