# Prius battery in a EV Challenge



## Rok Kocevar (Jul 4, 2010)

Hi everyone

I am currently 6months in a EV conversion. I am converting a 1996 Opel Corsa B to electric power using the classic Dirt cheap( TM ) Forkenswift model. Proboably becouse i am flat broke I used a 5kw series wound forklift motor and since the forklift was rebuild, it came with a 72V ZAPI controller.After ALOT of improvisation i finnaly got to battery part. I really didnt want to use lead acid battery technology ( becouse it sucks ) or Lithium ( becouse expensively sucks also). I wanted to get those improved chinese Ni-Iron battries with recombination plugs, but lost my job beffore i could save enought money to buy them. Well i got lucky and found a good deal on a prius battery pack from a crashed Prius ( 2007 ). Since the battery is 201V and my controller is 72V i need to reconfigure the battery pack. Here i see two options:

- Connecting 10 cells in series to get the 72v adn connecting the rest 18 cells in paralel to the 100ah for range

-Or make 3x 72V battery packs for 3 EVs from 1 Prius pack. Here i would be using 10 prius battery modules to get the voltage and some traction lead-acid batteries from forklifts for range connected in paralel. The lead acids would be working like a ''slave battery'' providing the Ah. Is this doable?


Thanks

Oh BTW how do you add photos to posts? I made a nice one of the suggested Ni-mh / Lead-Acid Hybrid battery.


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## Anaerin (Feb 4, 2009)

Rok Kocevar said:


> - Connecting 10 cells in series to get the 72v adn connecting the rest 18 cells in paralel to the 100ah for range
> 
> -Or make 3x 72V battery packs for 3 EVs from 1 Prius pack. Here i would be using 10 prius battery modules to get the voltage and some traction lead-acid batteries from forklifts for range connected in paralel. The lead acids would be working like a ''slave battery'' providing the Ah. Is this doable?


I think you're misunderstanding how series and parallel packs work.

18 cells in parallel (as you described) would give you a pack with a voltage of 7.2v and a capacity of 100Ah. This would be incompatible with your 10-cell 72v string of cells in series, and attempting to connect them together would give you a nice chemical fire as the 72v string attempted to push their combined voltage through the paralleled cells. If you made 3 10-cell series strings, then connected those in parallel, all would work just fine, giving you 72v and 19.5Ah. It would leave you with 8 cells over, however. Your Prius pack should be set up for 273.6v, and have 38 7.2v/6.5Ah cells in it.

As for combining NiMh and Lead-Acid, you're looking at a world of trouble. They have different power and charging profiles, and you would probably end up blowing up at least half your pack.


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## Rok Kocevar (Jul 4, 2010)

Hm, as you can see i am still a bit confused about batteries. The prius pack has 28 cells inside since its past year 2004. So i cant combine two seats of batteries with different voltages? Pack 1: 72V/6.5Ah + Pack 2: 7,2V/100Ah.

I guess it wont work with the Ni-Mh( 72V/6.5Ah )+ Lead acid( 12V/100Ah ) combo then to?

But if the voltages match in both packages, it will work then?

Oh and i know about charging Ni-mh connected with lead-acid accidents. I would be charging them seperately.

I am splliting the prius pack into smaller voltage strings becouse of the charger. I cant get a charger fo this chemistry in high voltage model. Thats why i am gona have to build it from scrach. I found a schematic on the net that uses LM2576 in the circuit and has 2 temperature sensors- one for ambient temperature and one for battery temp.

Does anybody have a good circuit design for ni-mh?


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## jwr813472 (Jun 1, 2010)

You kind of have the right idea.

Prius packs have 28 modules. Each module is made up of 6 cells that are sealed inside. Each module has a nominal voltage of 7.2v. (1.2v X 6 cells).

10 modules in series would give you 72 volts. To increase current capacity you would need to put several strings in parallel.

DO NOT MIX LEAD ACID WITH NiMH. You will have a fire.

Many people in the industry also say that trying to charge NiMH in parallel doesn't always work so well. Reading some of the blogs on Endless Sphere so people say it isn't a problem.

I currently have two Prius packs. For my pack I am considering four strings of 14 modules for 120 volts. Each string will have their own separate charger. I will have a contact for each string to put them in parallel.

These batteries aren't used much fir this application because of the challenges. The guys with the E-bikes love them.

Good luck and do more research. 

John


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## jwr813472 (Jun 1, 2010)

OOps!

My math is wrong. I plan to use 4 strings of 14 but the nominal voltage is 100v and the charge voltage no more than 120v.

John


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## DavidDymaxion (Dec 1, 2008)

Unlike some other chemistries, I heard it is better with NiMH to make the long strings first, and then put the long strings in parallel.


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## EVfun (Mar 14, 2010)

DavidDymaxion said:


> Unlike some other chemistries, I heard it is better with NiMH to make the long strings first, and then put the long strings in parallel.


and then charge them separately if at all possible! The problem is that the terminal voltage of a Nimh cell does *down* when it reaches full charge. When in parallel the fullest cell hogs the amps -- and bad things happen.


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## Rok Kocevar (Jul 4, 2010)

Ok thanks 

Now for the charging. If i have a battery pack with 72V nominal voltage, then i need to charge it with 84-85V DC? Just hooking 85V from a power supply and putting a timer on it proboably isnt a good idea?

I would like to buy a charger with temperature cutoff, does anybody know where i could get a high voltage Ni-Mh charger? Or several cheap small voltage ones?


Here are some circuits of DIY Ni-mh chargers with the before mentioned temperature regulation:

http://www.solorb.com/elect/tmpchrg/index.html

http://www.national.com/an/AN/AN-946.pdf

http://www.maxim-ic.com/datasheet/index.mvp/id/1666

Did anybody build this? Is there a DIY out there on the net?

They dont look to expensive to build, but i wonder if these IC chips are still on the market?


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