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Old 07-31-07, 04:15 AM   #1
kirtley
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NiMH vs. Lead-acid battery?

I've decided to buy a folding electric bike for a short (6-7km each way) commute (+train) in Australia. I have basically two options:

IZIP EZGO Folding Bike - Lead-acid, Australian$1,000
<http://www.bicyclestore.com.au/Izip-Ez-go-Power-Assisted-Bike-pr-22764.html>

Sherpa MK3 Lithium, Australian$2,000
<http://www.currietech.com.au/Sherpa%20MK3%20Lithium.shtml?openmenu=5>

Doe anyone have experience of either of these? Is it worth paying twice as much for Lithium?

I'm also a bit worried that, like my laptop battery, the lithium will lose it's charge over time. is that a problem usually?

Thanks,

Chris
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Old 07-31-07, 06:29 AM   #2
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I think you'll find that lithium polymer batteries have a long life in terms of charge / discharge cycles - vastly better than NIMH which is quite low in that regard. LIPOLY also has a higher energy density than the other technologies - vastly better than lead acid. This means you get twice the range for the same weight. Lead acid also needs to be charged at once when depleted or they die through sulphation. LIPOLY seems by far the nest battery technology around at the moment.

Take a look here for more info on battery technologies:

http://batteryuniversity.com/
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Old 07-31-07, 07:36 AM   #3
cerewa
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You can get a whole lot of lithium batteries for $1000. If that is the only important difference, then the $1000 bike is probably by far the better deal. Buy the cheap bike and spend some of the savings on better batteries?
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Old 08-01-07, 06:50 AM   #4
kirtley
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Thanks for the advice everyone. So there's no problem switching batteries, then? I guess the only thing might be finding one the right size.
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Old 08-01-07, 07:35 AM   #5
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The Li battery could cost $300-400 more than the SLA Acid battery and is at least 10 lb lighter.

Sherpa MK3 has 7000 Aluminum frame which is stronger and lighter than 6061 Aluminium frame of IZIP EZGO. This will make a few hundred dollars difference.

Sherpa Mk3 has 6 pedal-speed gear which is very helpful in pedal-only and pedal-assist speed upto 30 km/h.

With only one pedal-speed, it is extremely difficult to pedal-only and pedal-assist for speed over 20km/h.

I have an Schwinn AL1020 which is identical to IZID EZGO. As an second thought I might trade-in it for the Mk3 or its Limited Edition model with rear and front suspension.

Last edited by The7; 08-01-07 at 07:55 AM.
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Old 08-01-07, 10:23 AM   #6
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You will also need a different charger if you swap out lead acid batteries for lipoly types. They have different charging characteristics.
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Old 08-09-07, 01:52 AM   #7
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I am for Evilv's comment:
Lithium polymer batteries have a long life in terms of charge / discharge cycles
No dout it is better than NIMH
The lead acid is found to have more defects and the price of lead seems to increase these days.
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Old 08-09-07, 01:58 AM   #8
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You can get a whole lot of lithium batteries for $1000. If that is the only important difference, then the $1000 bike is probably by far the better deal. Buy the cheap bike and spend some of the savings on better batteries?
Yes, also a good ides.
36V LiFePO4 Battery (2C) PLUS a charger only cost around 440 USD.
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Old 08-10-07, 10:53 AM   #9
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I really don't get much advantage between NiMh/SLA - they both heavy. SLA can be abused more and require less complicated BMS so it becomes a very narrow margin of improvement compared to the cost and added complexity of NiMh chemistry. I've used both for about 2 years.

Hi-power Lithium is where you get BIG improvements for your trouble and money. Both in weight, longevity and performance. I built mine from A123 Systems developer kits and using them for over a year now. 250-300 cycles so far and still storing power like new. Cells are very stable to date.

If you don't have the money for Lithium - start with small SLA's and concentrate on getting a good ebike working while saving for serious batteries, BMS and charger. NiMh ain't enough benefit IMO.

In this day and age it's fairly easy to find older/used ebikes with bad batteries for sale locally. There've been some good designs over the past few years. Some bad ones too but almost all use inadequate NiMh/SLA battery packs. Get a good eBike, upgrade those packs and you can have a great eBike for much less than current complete turn-key choices in the marketplace.
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Old 08-10-07, 12:25 PM   #10
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I
Hi-power Lithium is where you get BIG improvements for your trouble and money. Both in weight, longevity and performance. I built mine from A123 Systems developer kits and using them for over a year now. 250-300 cycles so far and still storing power like new. Cells are very stable to date.
Glad if you could tell us a bit more about your A123? Volt? Ah? Cost?
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Old 08-10-07, 12:45 PM   #11
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Shouldn't be any problem in swapping batteries if they are the same voltage. (I hope) Be sure the new battery is compatible with the old motor. Discharge characteristics of a lead-acid battery (SLA) are different then other battery types and a motor designed for SLA might be damaged by other battery types.
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Old 08-10-07, 01:48 PM   #12
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Glad if you could tell us a bit more about your A123? Volt? Ah? Cost?
Took me a total order of 5 developer kits for 30 cells @ about $550 plus s/h. From that order I built 4qty 7-cell packs for about 24V @ 2.3AH. Two packs in parallel deliver almost 5AH but with this chemistry that's about like 8-10AH SLA for my application. Unlike SLA, when they're empty, they're empty, can't squeeze any more out of 'em.

I often use just one pack for quick errands around neighborhood but my normal commute requires 2qty 7 cell packs to cover about 10 miles r/t. At the end of day, still plenty in reserve for a couple miles more if needed.

Note - that's with a very efficient Panasonic drive alloy bike, barely tipping the scale at 45lbs with 2qty 7-cell packs. On my heavier hub motor w/throttle, steel frame bike, about 1/2 that range with the same 24V packs. Anyway, one, two, three or four packs is how I discharge 'em in parallel depending on the need.

2qty 3A modified NiMh chargers supply CC so I can charge each pack at a time in under an hour if temps are okay at beginning of the bulk charge cycle. I watch cell balance from time to time with individual cell taps but haven't noticed anything weird yet. Knock on wood...

Originally I was gonna use 8 cells per pack but that peak voltage was just too much for my polite Panasonic unit. It wouldn't turn ON with freshly charged packs and I can't find squat about the Panasonic controller so I dropped the packs down to 7 cells and called it a day.

This project was a year ago and today I think the DeWalt route is the best way to go for cells. Especially since I read about tool service centers giving away warranty exchanges! LOL...

Last edited by BroadwayJoe; 08-10-07 at 04:04 PM. Reason: typo...
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Old 08-10-07, 03:55 PM   #13
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Thanks Boardwayjoe for your sharing.
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