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Amperage - related question

Old 06-20-2010, 12:13 PM
  #1  
DanooshDesign
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Default Amperage - related question

Is there any problem if I use for example 30000 mAmp/h instead of 15000 mAmp/h
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Old 06-20-2010, 12:51 PM
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Insomniac
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Mah only refers to the capacity of the cell... it is the amperage in milliamps that you would need to draw from the battery in order to deplete it in exactly one hour. So a 1500mah battery can supply 1.5 amps (1500ma) for one hour, and a 3000mah battery would be able to supply 3 amps for an hour. Further, a 3000mah pack would be able to suppy 1.5A for two hours.

This means a few things for battery selection. Firstly, a 3000mah pack will be heavier than a 1500mah pack (all other things, such as cell configuration being equal) and physically larger.

Secondly, and most importantly, the capacity of the pack partially determines how many amps it can safely supply. How fast you can safely discharge a battery is measured in C, which stands for capacity. A typical value is a 20C discharge rating. This means that you can safely draw 20 times the capacity of the battery in amps from that battery.

So, a 20C 1500mah battery will be rated to supply (20 x 1.5A), or 30 amps. A 20C 3000mah pack will be able to supply double that, (20 x 3A), or 60 amps.

So the only things you need to consider when dealing with battery capacities is the size and weight of the battery, and how many amps it's rated to supply. It's ALWAYS ok to substitute a capacity with a lower discharge rating with a battery with a higher rating, but it's not always OK to replace a battery with a high discharge rating with a lower one.

Hope that helps.
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Old 06-20-2010, 02:06 PM
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billintn
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Excellent explanation Insomniac. Sometimes it is difficult to clearly explain the ratings.
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Old 06-20-2010, 03:46 PM
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Lieutenant Loughead
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Think of the "mAh" rating as the size of your "fuel tank".

If you double the size of your "fuel tank", you double your weight and the physical size of your battery.
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Old 06-20-2010, 04:39 PM
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DanooshDesign
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hmmm... very thank you guys! You are really helping me,but could you come here to answer this question?
http://www.wattflyer.com/forums/showthread.php?t=56398
I'm sorry that I am asking too much... .
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Old 06-20-2010, 04:51 PM
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philipa_240sx
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Originally Posted by Insomniac View Post
This means a few things for battery selection. Firstly, a 3000mah pack will be heavier than a 1500mah pack (all other things, such as cell configuration being equal) and physically larger.
Don't forget that swapping in a larger battery is going to increase overall weight, affecting stall speed and handling.

More weight = more lift required to stay airborne = plane has to fly faster

Generally I end up with the lightest pack I can get away with and still get decent 10-20min flying times.

For example:

I have a 5oz foamy. The motor draws 4.5A at WOT. I use a 2S 350mAh 20C pack.

1) The battery fits in the plane.

2) The pack only weighs 21g which the plane handles fine.

3) At 13C (motor amps/pack capacity in amp hours), I am not exceeding the maximum C rating of the pack.

I get 10 min flights with this pack which is plenty.

If I went larger: More flight time but more weight and I would lose the great vertical performance this plane has.

If I went smaller: Less flight time, slightly less weight, I would be pushing the C limit of the pack.

Last edited by philipa_240sx; 06-20-2010 at 06:25 PM.
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