# NIMH 7.4V prius cells



## evolutioneng (Jun 29, 2011)

Im going to start off small .im looking at the prius cells that have 7.4 volts.each. how many of these would i need for a 2k car that i would like to go 200 mile distance and about 65-80 mph. else is involved? i know i would need a transmission but is there another way out with using a trans.im trying to make it less maintenance free.


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## PhantomPholly (Aug 20, 2008)

We have established that it takes somewhere in the vicinity of 8Kwh +/- of battery power to equal the propulsive capacity of 1 gallon of gasoline. However, since the weight for NIMH batteries is somewhere in the vicinity of 40-50 times heavier than gasoline (LiIon is around 30x), adding more "gallons" becomes an exercise in futility at some imprecise point. 

Thus, if at a given weight and speed the vehicle gets 20mpg using an ICE, you would need around 8Kwh worth of batteries to go 20 miles. You would then think that you would need 80Kwh of batteries to go 200; but now you're probably talking about 1,500 lbs of batteries, which will impact your "mpg."

The best that money can buy right now is probably the Tesla with the maximum range battery pack (supposedly around 150 - 200 mile range). Using LiIon, the battery pack is a substantial proportion of the gross vehicle weight. With NIMH, that weight would be nearly doubled for the same capacity.


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## frodus (Apr 12, 2008)

I know you keep asking about different setups, batteries, motors, cars, etc, let me simplify this so you can do this over and over and over again for different batteries.

For a compact car, estimate ~250wh/mile at 55-60mph. This could be as low as 200, and higher than 300. Use 250wh/mile for a good estimate.

*To calculate how much energy needed to go 200 miles:*
Take the number of miles and multiply by the amount of energy you need per mile. 250wh/mile * 200 miles = *50kwh*, give or take.

*To calculate battery pack size:*
You want your pack to be larger than that (i.e. don't discharge all the way).... so lets say 50kwh is 80% DOD, so (Pack size) * 80% = 50,000kwh.
50,000kwh / 0.80 =* 62,500Wh*, give or take.

*To calculate the Energy in each battery:*
Prius 7.4V cells are 6.5Ah. Now, under load, they'll sag a little, so lets say they sag to about 6.5V under load (another estimate). 6.5Ah * 6.5V = *42.25Wh/cell*

*To calculate how many batteries you need:*
Take the Battery Pack Size and divide by Energy in each cell.
62,500Wh pack / 42.25Wh/cell = *~1480 of these.*

*That's bare minimum.*


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## EVfun (Mar 14, 2010)

I estimate that would take 80 to 90 of the large 400 amp hour LiFePO4 cells. If you really want to use Prius cell blocks I estimate it would require 2000 to 2200 of the 7 volt blocks.


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## Tm PV1 (Jun 5, 2010)

It's reading a thread like this that makes you miss the old EV-95 NiMH batteries. The 2002 Rav4-EV uses 240 of these (10 cell bricks, 24 bricks in series for ~27 kwh) for about a 100 mile range. Since Chevron owns the rights to these batteries now (have since October, 2000) nobody can get ahold of these cells unless they dismantle a Rav4-EV. Would that be considered cannibalism (one EV killing another EV for batteries)?

Maybe what you can do is buy RC battery packs (12 volt, 10 ah for $150) and wire them in series. The advantage of this is you're only making connectors and not messing with cells at all. Judging that you would need 62 kwh of battery storage, this would amount to 517 packs, costing $77,550. The EV-95 battery would do this with 55 packs, or 550 cells, a little more than double the Rav's battery. This would have costed $21,700.

A set of LiFePO4 batteries would cost $27,160 and consist of 97 cells. The fact that lithium's are much cheaper than NiMH's today is the fact that no large-format cells are made, no one is allowed to make them.


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## MN Driver (Sep 29, 2009)

"The fact that lithium's are much cheaper than NiMH's today is the fact that no large-format cells are made, no one is allowed to make them."

That's not entirely true. If you are an OEM and are willing to throw the right amount of money down, the patent has been worked past and its a matter of cost, demand, and availability now. I discussed this with someone who works closely with battery manufacturers, nobody wants to put the money into large format prismatics anymore. For example, you can pull up large format NiMh details on SAFT's site. They aren't interested in the automotive industry though. It's mostly an energy density against weight issue, power density not excluded. NiMh has really hit a limit to how much you can pull from them. The EV-95 cells get a quite warm when you work them hard and even the most recent and common smaller format NiMh in Honda and Toyota vehicles are proving to not last as long as many feel they should. Honda decided to abandon NiMh for their next generation Honda Hybrids. Hyundai/Kia are having nothing to do with NiMh and going to LiMn. Chevy is leaving NiMh to go to LiMn in the Volt, maybe LiFePO4 in future vehicles. Honda's statement about leaving NiMh was almost entirely based on their power density, it's actually cheaper to build a Lithium pack than it is to build a NiMh pack because they have to size the pack to get the desired power density. With NiMh Toyota only uses a very tiny SOC band of the cells to make them last longer and Honda uses a little more keeping it between 20-80% but mine seems to love hanging at 75-80% always, which is almost 18-20 bars on a 20 bar gauge. Since it uses a pack size to get almost 100 amps, they can really use a pack under 300Wh or even less now instead of having about a kwh.


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## Tm PV1 (Jun 5, 2010)

Interesting. The EV-95 battery seems to be a favorite among the NiMH batteries being that it has been tested in the real world. They are still getting 80-110 miles per charge after about 100,000 miles of driving (heard of some approaching 200,000) and have had little failure. I just read an article a little bit ago saying that Chevron doesn't own the rights anymore. I figured that one of the car companies would start out using NiMH to get a low-priced EV on the road capable of 100 miles a charge, but that won't happen now because of lithium being on the market. What would be nice though is if Chevy would open up more of the Volt's battery. They only allow 60% of the battery to be used (probably the top 20 or 30 and the bottom 30 off-limits) to extend the life. This is probably where NiMH is superior in that much more of the battery can be used without a huge decrease in cycle life. 

What makes comparisons like this is difficult is that I don't have an EV powered by either battery chemistries, but I do know that I am on my second Li-ion laptop battery in 6 years, yet have 12 year old NiMH rechargeable batteries still going strong.

What would be a good comparison, having two Nissan Leaves, one with NiMH, and the other with its Li-ion, and run them in almost identical ways for 100,000 miles and see which one did better. Or probably a more realistic comparison, the old Rav4-EV against the new Rav4-EV. (Glad to see it return)

I was surfing Saft's website and i found this:
http://www.saftbatteries.com/Produit_NHE_329_24/Language/en-US/Default.aspx
This seems to be close to the EV-95 battery. It is just a touch bigger and stores 5 Ah more energy with 5C discharge at 10 seconds. I would like to see how difficult it is to get these and how expensive they are.


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## athlon (Feb 27, 2012)

This are a little different , are not Ni-Mh but Ni-Zn http://www.powergenix.com/?q=technology/technical-documents there are prismatic for 80Ah , 40Ah and 8 Ah , but is the first time I see battery of this type .. do you know how this battery work in real life? or building a pack from Thundersky still the cheapest option ?


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## FWD (Feb 3, 2012)

7,4 volts? or 7,2


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## ga2500ev (Apr 20, 2008)

Actually I want to get back to the original poster's specifications. The bottom line is that with current battery technology and prices, the battery pack is equivalent to a gas tank with 2-4 gallons in it. This gasoline equivalent page shows that 1 gallon of gas is equivalent to about 33 kWh of energy. Right now in lithium the cheapest thing going is the gray market A123 20Ah prismastic pouches. They have a usable energy capacity of a bit more than 50 Wh of energy. So to get the equivalent of one gallon of gas you'd need 33000/50 = 660 of them. They are running just about 20 USD each. So 660 * 20 = 13200 USD. And that's the equivalent of one gallon.

Now it really isn't that bad. Gasoline is so powerful an energy source we can afford to burn 75% of it as heat and use the remaining 25% of the energy for motive force. Electricity will put well of 90% of the usable energy directly into the wheels. So you can expand that one gallon tank to a 4 gallon one and be in the ballpark. That's where the 8 hWh number above came from (33kWh/4 = 8.25 kWh).

The problem really isn't batteries. The problem is infrastructure. Owning an electric car today is sort of like having a gas car in a world where no gas stations exist, or more exactly where the only gas station is at your home and you only have a 4 gallon tank. Thinking about taking a 200 mile trip under those circumstances just isn't in the cards. If electric cars had the appropriate infrastructure, and there are a number including battery swapping, flow batteries, electrifying the road, and even some farther afield such as liquid nitrogen as a hybrid technology, then the size of the tank wouldn't be an issue. Frankly there are some ways that the electric car infrastructure could be superior to gas. Consider a world with no stations and never having to stop to refuel. Unlike gas electricity can be efficiently transmitted without wires. Magnetic resonance coupling projects such as Witricity could set up cars that charge all the time, or at stop lights for example.

But it's going to take a while. In the meantime, unless money is no object, you may need to scale down your expectations...

ga2500ev


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## Tm PV1 (Jun 5, 2010)

They have systems in development that can wirelessly transmit up to 10 kw to an EV in the road. This would double the range of the LEAF and Mitsubishi I at highway speeds. Since NiMH batteries production isn't as developed as lithium right now, having enough NiMH batteries for a decent range is going to be more expensive than, say, LiFePO4. 

Athlon, I think the batteries that I have linked are true NiMH, not NiZn. The data sheets make no mention of zinc. The ones you have linked are NiZn. Both would be nice to have more marketshare to drive down prices of all batteries. If the 100 Ah cell packs can be purchased by the individual, they could be drop in replacements for the Rav4-EV's when their batteries finally give out.

As for Prius batteries, I'm not sure how they are made, but the 1st gen Insight uses a bunch of D cells. I haven't studied alot on the hybrid batteries. They are probably built with a lower energy density to reduce costs and prevent them from being used in EV's.


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## TexasCotton (Sep 18, 2008)

Anyone know how to charge the 7.2v 6.5ah nimh prius bat module...


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## bangerla (Dec 11, 2008)

The prius battery charges just like any other Nimh battery. The difficult part is that Nimh batteries are difficult to run in parallel.


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## TexasCotton (Sep 18, 2008)

bangerla said:


> The prius battery charges just like any other Nimh battery. The difficult part is that Nimh batteries are difficult to run in parallel.


Yea I am looking for something more than "just like any other". I get they are "difficult" in parallel both run and charge.... 
So once again anyone with first hand experience that has charged a prius battery module, How many modules can be charged and a low cost charger...


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## bangerla (Dec 11, 2008)

As I said, they charge just like a regular Nimh battery. Buy an electrifly charger, and charge to your hearts content. Or buy an Nimh charging IC from Maxim, and build a charger for every 3-4 modules. Or stick with Toyotas idea, and only charge to 80%. This way you do not need to worry about charge termination voltage etc... Just dump the power in. But as I said in the other thread, frankly its not worth it. The energy density of the battery is low, they need active cooling, charging and discharging isnt easy. You are more than welcome to develop a Prius BMS system though, and see how well it works. I might even be able to find the old schematics for one I drew up.


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## TexasCotton (Sep 18, 2008)

bangerla said:


> As I said, they charge just like a regular Nimh battery. Buy an electrifly charger, and charge to your hearts content. Or buy an Nimh charging IC from Maxim, and build a charger for every 3-4 modules. Or stick with Toyotas idea, and only charge to 80%. This way you do not need to worry about charge termination voltage etc... Just dump the power in. But as I said in the other thread, frankly its not worth it. The energy density of the battery is low, they need active cooling, charging and discharging isnt easy. You are more than welcome to develop a Prius BMS system though, and see how well it works. I might even be able to find the old schematics for one I drew up.


Okay I got BMS issue resolved
My issue is charging 28 cell modules 7.2V 6.5ah 201volt with low amp of 1.5amp-5amp top end. All I see is 5amp charger and above with less cell count.


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## TexasCotton (Sep 18, 2008)

I do like the electrify Triton 2 comes real close for nimh. If you have 28 modules and each ONE has 6 cells. How are you counting cell to match charger


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## bangerla (Dec 11, 2008)

Nobody makes a charger for that many cells. You need to either make your own charger, use many small chargers, or only charge to 80%. Keep in mind that if you charge over 80% you must deal with the heat. And you must make sure all the cells are in compression, otherwise they will burst.


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## MN Driver (Sep 29, 2009)

You might want to look at the gen 1 forum of Priuschat for this, it's been done and there are links to peoples sites of the risks involved with them as its well known to their community that they don't terminate as easily off of -dV as cylindrical NiMh cells due because their prismatic structure will just swell up and they are destroyed.

Not sure what you are using them for but you can't safely charge them in parallel so it's a moot point. It really depends on how you plan to use them but IMHO it's not really worth it. I scrapped an ebike project because dealing with scrap NiMh is a PITA. I now use the NiMh in a B&D plug-in lawn mower connecting the battery through a DC rated switch to the 120v socket after some basic wiring and a DC rated fuse. I'm using cylindrical NiMh, the Honda stuff though and wouldn't touch the Prius stuff with a 10 foot pole in a project.


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## TexasCotton (Sep 18, 2008)

bangerla said:


> Nobody makes a charger for that many cells. You need to either make your own charger, use many small chargers, or only charge to 80%. Keep in mind that if you charge over 80% you must deal with the heat. And you must make sure all the cells are in compression, otherwise they will burst.


80% that what I am looking for with low amps


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## TexasCotton (Sep 18, 2008)

bangerla said:


> As I said, they charge just like a regular Nimh battery. Buy an electrifly charger, and charge to your hearts content. Or buy an Nimh charging IC from Maxim, and build a charger for every 3-4 modules. Or stick with Toyotas idea, and only charge to 80%. This way you do not need to worry about charge termination voltage etc... Just dump the power in. But as I said in the other thread, frankly its not worth it. The energy density of the battery is low, they need active cooling, charging and discharging isnt easy. You are more than welcome to develop a Prius BMS system though, and see how well it works. I might even be able to find the old schematics for one I drew up.


 Let me restate I need to charge my complete nimh prius battery pack 28 module 7.2 volt nom makes about 201volt . I want to charge up to 240vdc .......


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## bangerla (Dec 11, 2008)

As I said before. Buy 5 48V flatpac power supplies on ebay, or 1 megapac power supply, with 5-48V modules, and you will have yourself a charger.


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