# Prius Batteries?



## Gnigma (Sep 20, 2007)

Just out of curiosity, since there are a few crashed Priuses (Prii?) now, has anyone tried using the NiMH pack(s) in a conversion?


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## EVBug (Aug 19, 2008)

The story I've heard is that they are of too small a capacity to be very useful. Plus you need some kind of BMS to keep them balanced and prevent damage.

Personally, I'm curious and would like to try.


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## sailfish11 (Sep 15, 2007)

I owned a 2005 Prius for about three years and had modified it so it would work in 'EV only' mode. I can tell you that in Ev mode, the Prius woud only go about 1 mile at 30mph before the ICE had to kick in to save it. I think the computer's programming had the ICE turn on pretty quickly (meaning, while the battery was still in a fairly high state of charge), but still, not a lot of energy in those packs. You'd have to use several of them to get anything close to an acceptable range. Plus, as mentioned earlier, you'd have to design a battery management system sophisticated enough to handle 'used' batteries (different age, cycle, etc.).

Interesting idea, but I think more trouble than it would be worth.


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## bblocher (Jul 30, 2008)

The Prius batteries are only 6.5 AH batteries. They are however 200+ (they've changed between versions of the prius) volts but that's still only over 1k wh so yeah you'd need like 10 of these at least to get range comparable to the lead acid. Do the math for comparisons of different lead acid packs of course, but unless you can get them for free or very cheap it's not worth it. You'd be better off just looking at lithium since new these packets are like 3k from Toyota if I recall from other posts.


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## TX_Dj (Jul 25, 2008)

Exactly as the others have mentioned... the Prius stock pack is designed with "microcycles" in mind.

Due to the fact that they are rarely deeply discharged before the ICE kicks in to replenish them, they rarely become imbalanced. Using them in a full EV mode for long distance will increase the chances of individual cells becoming imbalanced without a proper BMS/regulator setup.

Scale up that 200-ish volt 6.5Ah pack to something that you could use for 30-40 miles in full-EV mode, and you compound the issue with every extra "brick".

It is possible to use NiMH in a full EV, as other mfr's have shown (Rav4EV, EV1, and so on) but those systems are specifically designed for 100% plug-in EV-only use, and have the required safety systems in place for charge/discharge regulation.

Trust me, you do NOT want to see what would happen if you were powering your car with NiMH without proper charge/discharge regulation and either demanded too much current, or over-discharged or over-charged the modules.


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## fevoris (Sep 22, 2008)

I have 2 Prius's on the road now ('08 and an '03) and one ('02) I am putting into a kit car to see if I can make it full EV out of it. The batter pack life is very short---2hr when sharing the load with the ICE but the recharge is very fast---so would not be good for an EV


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## Evan (Feb 20, 2008)

Has anyone though about a Honda Insight pack? The Insight used 144V 9AH. 

What I can't wait for is someone to just make it up to say 20 or 25AH. You could use 3 packs made of those independently. One for each phase of an AC motor. Impractical I know but hey they don't make large format packs any more so a 60 or 75AH pack is not possible.


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## Gnigma (Sep 20, 2007)

Well, let's see.... The reason the Prius pack is only @ 6 AH is because the Prius setup is for the microcycling. The batteries are never let to fall below 60% capacity and never charged above 75%. I suspect that keeping them in this narrow range eliminates the need for a battery management system. And yes, NiMH batteries have had a few incidents of thermal runaway, in single-cell applications without BMS. When you consider the tens of thousands of single cells that are actually in use, though, that's still pretty good. In the EV1, with a BMS, GM had no heat failures in the 500 vehicles they leased. And the projected life of the EV1 packs was around 100,000 miles, with many decomissioned packs functioning as well as new. You can get packs from wrecks at anywhere from $200 up to $1000, depending on how much the seller thinks they are worth. Sure, it would still take quite a few packs to actually run a vehicle, but I think the price will come down. When GM announced the Volt, they promised a 40 mile range per charge. They also stated they were betting on improved battery technology in the near future, improving the range. Is that because the patents on the NiMH batteries are going to expire in the next couple of years? Is it because Chevron/Texaco, owners of Ovonics, who make the NiMH batteries, are also major shareholders in GM? They seem to have an (inexcusable) ace in the hole. I don't see why they haven't been charged with breaking the antitrust laws, myself. Anyway, I still say if they weren't trying to shaft the American driver, they'd produce 12volt NiMH car batteries that would last the life of the car--- oh, yeah, if they did, we could just purchase several and do our own conversions for cheaper than the car they intend to sell at inflated prices...


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## Rolls Kinardly (May 30, 2008)

TX_Dj said:


>


For the sake of clarity, I want to point out that this is NOT a battery pack from a hybrid car in the above photo... The Prius battery looks like this: http://www.autobeyours.com/gifs/inventory%20prius%20parts/Prius%20battery%20cells.jpg



Evan said:


> Has anyone though about a Honda Insight pack? The Insight used 144V 9AH.


Actually the Insight's pack is 144V, 6.5AH. The BMS keeps the SOC between 20% and 80%, so the usable capacity is 4AH. The Prius, Insight and Civic Hybrid have the same capacity but different voltages. And the Prius uses prismatic cells while the Hondas are cylindrical. Subpacks of 6 cells are interchangeable between the Insight and Civic Hybrid.



Gnigma said:


> Well, let's see.... The reason the Prius pack is only @ 6 AH is because the Prius setup is for the microcycling. The batteries are never let to fall below 60% capacity and never charged above 75%. I suspect that keeping them in this narrow range eliminates the need for a battery management system.


Actually I'd say keeping the battery in this range absolutely requires a BMS. The voltage curve of NiMH batteries does not indicate its capacity until it approaches maximum or minimum capacity (i.e. outside the 20% - 80% range). So the BMS must do amp hour counting and subpack voltage/temp monitoring to look for imbalances.

See this forum topic about an open source BMS system for LiPo batteries for a PHEV Insight conversion: http://www.insightcentral.net/community/viewtopic.php?f=4&t=7665


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## Evan (Feb 20, 2008)

Gnigma - The heat failures should go down if you make the cells larger. There are expansion related issues when you charge the cells too. We are all frustrated at the lack of available batteries. Yes GM is not my favorite car company at the moment but there is not a lot other than writing letters to our public representatives about the need for restoring our antitrust law.

Rolls Kinardly - Ok my idea won't work. The things you are talking about the BMS having for required functions are really things all EV's should have.


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## TX_Dj (Jul 25, 2008)

Rolls Kinardly said:


> For the sake of clarity, I want to point out that this is NOT a battery pack from a hybrid car in the above photo... The Prius battery looks like this: http://www.autobeyours.com/gifs/inventory%20prius%20parts/Prius%20battery%20cells.jpg


To my point though, the physical form factor of the cells is irrelevant, NiMH is what NiMH is. Treat it properly, and it's greatness. Treat it improperly, and it's a timebomb waiting to happen. The same is true for other chemistries as well, but I digress.


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## Evan (Feb 20, 2008)

Well there are different NiMH chemistries. Some are better for this kind of thing than others.


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