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Mah To Kwh Conversion I Need Some Help


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#1 cowsgonemadd3

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Posted 08 June 2007 - 08:15 PM

Okay so I could find nothing on this. I was hoping google would have a conversion or something but I could not get it.

I want to know how many mAh hours are in a Kwh hour.

Like how many AA batteries as 2500mAh equal 1 Kwh.

Thanks

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#2 bilko

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Posted 08 June 2007 - 08:31 PM

You cant really make a direct conversion, but try this link. I think it explains pretty well why.


http://www.powerstream.com/Amps-Watts.htm

### Edit ###

Dont know if you know, but the mAH = milli Amperes per Hour, kWh = kilo Watts per Hour, if you dont know your milli's from your kilos ive put a link from wiki in to show you. Sorry If you already know, not trying to insult you, just making sure you get all the info.

http://en.wikipedia.org/wiki/Milli

Edited by bilko, 08 June 2007 - 08:37 PM.

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#3 Animal

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Posted 08 June 2007 - 08:35 PM

According to a chart I read, which I will include. Using your reference of 1 AA battery @ 2500mAh = 3Wh. Therefore doing the math I calculate 833mAh = 1Wh.

Hope that answers your question.

The chart I used for my assumption is here: http://www.technick.net/public/code/cp_dpa...ide_bpw2_c17_02

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#4 cowsgonemadd3

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Posted 08 June 2007 - 08:39 PM

So like its 1000 watt hours in a Kwh (kilo watt hour)

#5 Animal

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Posted 08 June 2007 - 08:41 PM

Yup, which calculates to 333.2 AA batteries to 1 Kwh

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#6 cowsgonemadd3

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Posted 08 June 2007 - 08:45 PM

Great thats what I thought. I learned my kilos and milli's in like 3rd grade. Something I still remember them.

Thanks

#7 bilko

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Posted 08 June 2007 - 09:53 PM

Hmm, Ive thought about this a bit more, my Electrical knowledge is a bit rusty, but i will do my best and try and keep this simple. It really is a lot more complex, you have to take into account the internal resistances of the bateries, the resistance of the load, weather you would wore the batteries up in series or parallel.

Any Electronic grads that can correct me or explain it simpiler please do.

The 2500mAh is its Capacity, or maximum drain. So if you had a 1.5V 2.5A light bulb it would work for 1 hour, or a 1.5V 1.25A bulb would work for 2 hours.

Watts = Amps x Volts

So your single AA battery (assuming 1.5 V)

1.5V x 2500mA = 3750 mW

This means at maximum drain it could supply 3750mW for 1 hour.

When connecting two batteries in Series you are doubling the voltage while maintaining the same capacity rating (amp hours). ie 3V at 2500mAh

When connecting two batteries in Parallel you are doubling the capacity (amp hours) of the battery while maintaining the voltage of one of the individual batteries. ie 1.5V at 5000mAh.

Next you need to know how many Volts your 1KWh device will be running at.

As an example I will say 12V. So to supply 12 V you will need to have.

12/1.5 = 8

So you will need 8 batteries in series, however these 8 batteries still only give you 12V at 2500mAh, but

12 x 2500 = 30Wh

But you are now 970Wh short.

To find out how many banks of batteries you need, devide the total by the amount per bank. 1Kw =1000W

1000/30 = 33.3333

So you would need 34 banks of 12. 33 would leave you slightly underpowered.

So in total you would need 12 x 34 = 408 batteries

Hmmm, this doesnt seem like a lot, maybe i messed up with the maths.

Anyways, this is very basic as the are still lots of other things to take into account, and is only a rough estimate.

I hope it gives you some insight into the complexities of electrical theory.
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#8 ddeerrff

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Posted 08 June 2007 - 10:46 PM

Animal used a NiCd battery at 1.2 volt. An alkaline cell puts out 1.5 volts.

2500 mAHr x 1.2 volts = 3 WHr
2500 mAHr x 1.5 volts = 3.750 WHr

So you are both right.
Derfram
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