I have found the ultimate batteries for any EV!!!

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ha123
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I have found the ultimate batteries for any EV!!!

Postby ha123 » Thu Aug 14, 2008 9:20 pm

I do not understand why people are shelling out loads of money for crappy lithium ion batteries when you can just get the Nickel-metal hydride batteries used in hybrid cars. One of these batteries produces a whopping 201.6 volts and has a power output of 21 KW, now thats power!! I have two running my mini and it flies!!!

If your wondering where you get them from I got mine of ebay out of two toyota prius. :D

GregsGarage
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Postby GregsGarage » Thu Aug 14, 2008 9:38 pm

Very nice,

Please post some more details, links, pics, short description, problems encountered?

Greg

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retepsnikrep
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Postby retepsnikrep » Fri Aug 15, 2008 6:04 am

Hmm

Sadly they are/were made out of 6.5ah nimh cells, and yes are high voltage with a decent punch, but don't contain much actual stored energy.

If you are using two strings/packs thats a lightweight 13ah pack at whatever voltage it produces. I bet it goes well, but for how far?

Nimh also have a horrible self discharge rate and don't like getting hot.


Please tell us more.
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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Jeremy
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Postby Jeremy » Fri Aug 15, 2008 6:42 am

There are some problems with using Prius cells in a deep discharge application. The NiMH cells in the Prius pack are optimised for very long life and very low cycle depth. They are unable to recombine effectively if charged above about 95% and will gas. Several people who have tried using Prius cells have discovered that they are quite tricky to charge and fairly fussy about being charge limited the instant that they reach about 90 to 95% SOC.

They are only 6.5Ah, so you need quite a lot of them to make a useful pack. The other problem to overcome is that the BMS is built in to one of the cars MCUs, all that is in the pack is the main contactor and the sub-pack wiring. The battery MCU in the Prius does all the management, so for reliable operation without it you need to find a way to ensure that the sub-packs remain balanced.

Finally, second hand Prius packs seem expensive. I saw one sell on eBay a while ago for around £600 and was offered a 5 year old pack with some damaged cells a few weeks ago for £300. That's probably more per watt hour than I paid for my LiFePO4 pack, so it isn't that good a deal. Add in the fact that the usable capacity of a Prius pack is less than half the cell capacity (if you want them to last) and they start to look seriously expensive.

For comparison, I paid around £800 for a 2000 watt hour LiFePO4 pack. The Prius pack is theoretically about 1300 watt hours, but only has a usable capacity (if run within design limits) of 40% of this, so just over 500 watt hours.

If you can get Prius packs for less than a couple of hundred pounds each then they start to get close to LiFePO4 prices, but are still bigger and heavier.
Jeremy

TESLACOIL
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high selfdisharge for nimh ??

Postby TESLACOIL » Sat Aug 16, 2008 3:44 am

I know they go flat after a day or two with smaller cells - that could be a drag

any views to back this up with bigger packs ?

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Jeremy
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Re: high selfdisharge for nimh ??

Postby Jeremy » Sat Aug 16, 2008 7:49 am

TESLACOIL wrote:I know they go flat after a day or two with smaller cells - that could be a drag

any views to back this up with bigger packs ?


I'm not quite sure what you mean above. The self-discharge rate of NiMH is fairly high, but usually less than about 1% or so per day.

The useful range of a couple of 1300 watt hour packs, most probably with a usable capacity of only around 1000 to 1500 watt hours for the pair if long life is desired, depends on the weight, size and overall efficiency of the vehicle they are used in.

A Toyota Prius in EV mode has a range of about a mile or two at speeds below 28mph. Extrapolating from this would seem to indicate that if two packs were used range might increase to maybe 4 or 5 miles (the losses would be slightly lower with two packs in parallel).

Adding more packs would definitely increase range, but the complexity of the wiring for all the BMS channels needed would also increase, plus the weight would go up as well. Additionally, Prius packs are big, even the cells modules are large for their capacity, so finding space for multiple packs gets to be a challenge, especially as they need active cooling/warming to work well (the Prius has a temperature controlled fan that feeds cabin air to the pack to maintain it at a good working temperature).

Jeremy

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arnolde
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Postby arnolde » Mon Sep 08, 2008 9:24 am

6,5Ah doesnt sound like much, but it's really not a good number to compare. I really dont understand why everybody measures battery prices in price/Ah instead of price/Wh which is really what you want.

At 200V thats 13kWh, 2 packs are 26kWh, now that is not small at all, if your car is anywhere near efficient you can go 100 miles on that. If you can get a pack for 500 GBP that would be 38 GBP per kWh, Li-Ions cost 300 GBP per kWh. I'd grab those packs anyday for that price, I want 3 of them!

microman
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Postby microman » Mon Sep 08, 2008 12:46 pm

Before you buy them, check your arithmetic! A factor of ten seems have crept in.

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arnolde
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Postby arnolde » Mon Sep 08, 2008 1:00 pm

microman wrote:Before you buy them, check your arithmetic! A factor of ten seems have crept in.


You're right, 6,5Ah at 212V, thats only 1.378 kWh, not 13kWh. Thanks!

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Jeremy
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Postby Jeremy » Mon Sep 08, 2008 4:43 pm

arnolde wrote:6,5Ah doesnt sound like much, but it's really not a good number to compare. I really dont understand why everybody measures battery prices in price/Ah instead of price/Wh which is really what you want.


Curiously I did refer to the watt hour capacity of these packs in my post, rather than just the Ah capacity of the cells...........................

Jeremy


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