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Old 04-04-2009, 10:52 PM   #1 (permalink)
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Another n00b question: NiMH batteries and me...

So I got to thinking about something someone said a while back about the advantages of more, lower voltage batteries vs fewer higher voltage and it got me thinking.

What if I were to buy (let's say) 100+ of this : # 250mAh-9v-NIMH

It's a very small battery that weighs hardly nothing so I figured I could buy 100+, solder them together and have X amount of power to power an electric motor. Now my thinking is probably way off and I know the amp rating is very low but would a set-up like this yield any power for a decent time? If so what could you move with it?

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Old 04-04-2009, 11:06 PM   #2 (permalink)
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Doing further research I find this: "3.7 Volt 2200 mAh Li-Ion 18650 Battery" I could get 100 of these for about the same price as the NiMH listed above.

I'm not sure about the "mAh" rating though. Do I want higher or lower? 100 of the above battery packs would give me 220Ah and 370V is that correct?
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Old 04-04-2009, 11:13 PM   #3 (permalink)
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ok you have 100 9 volt bats. . .One issue I could forsee would be overcoming the batteries maximum voltage. If you plug too many together the voltage becomes great enough to "jump" short-circuit between the terminals in your battery using the molecules as a bridge that causes them to heat up very rapidly and fries the battery.

You're going to want 220 volts output to power some equivalent systems(e-motors) and you have 900. you can split it(lets pretend you have 98 instead) into 4 220 volt systems. This gets you to the right voltage for your electric drive functions.

each cell has roughly 24 units in it that can supply 6 amp hours each for a total of 24 amp hours at 220 volts.

In otherwords you've got 220 volts at 1 amp for 24 hours or 220 volts at 24 amps for one hour. I can't find any electric motor specs at the moment or I would be happy to tell you the other answers.

I'm pretty sure though the problem would be the overload voltage. Also charging becomes a little dangerous or you can burn out the cells because the charge rate of one cell might be different based on temperature and cause a domino effect blowing out others.
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Old 04-04-2009, 11:20 PM   #4 (permalink)
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Am I crazy or does this sound like something that could be done if we figure out a few snags? These packs look a lot like cell phone batteries (NiMH) and the LiON look like AA rechargables. I don't know which would be better but the are about the same price.


sorry, I was mixed up... the 9v NiMH look just like regular 9V batteries. The LiON look like standard AA's. I was looking at a different battery that looked like a cell phone battery,

Last edited by Electric Frenzy; 04-04-2009 at 11:27 PM..
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Old 04-04-2009, 11:46 PM   #5 (permalink)
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You are correct in the Ah and volts you get.

The problem is those batteries probably do not have a very high tolerance for either amperage or voltage.

I would gamble the 3.7s are around 12 volts and the 9s are around 14-16. You have to put them in series like you do in a tubular flashlight. Slide one battery in and then the next. This causes each successive battery have to support more strain. What makes the expensive packs expensive is the cells have high tolerances that can reach that 220 volt mark without burning out.

In my example there is no way you could get 24 of those things in series and not fry half of them. Also I don't think their amperage gets high enough. You need at least a solid 2-3 amps to do anything and I think thats outside their tolerance. Once again you would cook them and then the others would burn out twice as fast.

Thats why car batteries are expensive. They have a relatively high voltage tolerance(12 volts continous up to 16) and they can do 200 amps for very short periods and 50-60 long enough to start your engine. An equivalent stack of those would scorch a hole in your battery box from heat transfer and never work again.
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Old 04-04-2009, 11:47 PM   #6 (permalink)
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This happens to be the way the prius battery pack works. Looks like anywhere from 168-240 of them. You can find out more about the prius setup here: Toyota Prius - wikipedia
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Old 04-05-2009, 12:18 AM   #7 (permalink)
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ok, it says they used a 38 module NiMH pack supplied by panasonic.

What I was looking for was smaller batteries I could link in series to create my own MiMH pack for a project vehicle. Does anyone know where I could find proven/solid NiMH batteries for this? Everyone does 12v or 6v golf cart batteries but I thought I could save weight and space kind of building my own.
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Old 04-05-2009, 01:24 AM   #8 (permalink)
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amps times volts, simple simple math, you would get less then a mile of range on flat ground with a light weight ev like mine, if it worked at all!
I put "D" cell nimh batteries on my electric bike, BIG waste of money, they could not handle the draw of a bike motor, 10 amp hours at 36 volts, for sale, cheap!
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Old 04-05-2009, 09:40 AM   #9 (permalink)
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12 Volt SLA 12 V 32 or 33 AH Sealed Lead Acid Batteries, Chargers and Adapters at PlanetBattery.com.

This is more the amp hour rating you would need for a golf cart in which half its weight is batteries(I'm pretty sure the Ez-gos I've been in were more like 75% because you could carry them if you put the cell on the ground.) Also it will be able to go for maybe 45 minutes at ~20 mph carrying two moderately sized people and nothing else.

Now that I am awake the easiest way to consider it is to convert to power. 370 volts 220 Ah is 81 KWHrs or. . .like 110 HPhrs. so you can run 55 hp for 2 hours. Not quite though, it will hold steady for the first half and then rapidly drop off. Not to mention its a bad idea to get your expensive batteries below say 20%. Why people rate the charge time from 20-100%.
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Old 04-05-2009, 02:03 PM   #10 (permalink)
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I'm looking for NiMH bateries for an actual EV car, not golf cart. The only reason I mentioned carts was because people kept telling me that 6v cart batteries were good for EV conversions.

I'd like the bigger power and longer life of the NiMH batteries.

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