Formula for Calculating Battery Runtime? - RC Groups
Nov 21, 2006, 03:08 PM
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# Formula for Calculating Battery Runtime?

Hey guys,

I was wondering if there are any online calculators or What the Formula is for Calculating the amount of Runtime for a battery, at a Certain Amp draw, at a certain voltage.

For example, a 3cell Lipo 1500mah capacity, being drawn at 10amps would last how long until the recommended voltage cut-off?

Simple math makes me think that the answer would be 1500mah capacity/10,000mah amp draw= (.15hrs * 60)= 9mins

How wrong am i guys?

Luis
 Nov 21, 2006, 03:26 PM Registered User Simple math is all it takes. You've answered your own question . BTW voltage doesn't make any difference, it's only current draw and capacity that count. Steve Last edited by slipstick; Nov 21, 2006 at 05:59 PM.
 Nov 21, 2006, 05:15 PM Registered User Sweet, GoldStar for me! haha
Nov 21, 2006, 06:40 PM
Registered User
Quote:
 Originally Posted by slipstick Simple math is all it takes. You've answered your own question . BTW voltage doesn't make any difference, it's only current draw and capacity that count. Steve
Why is voltage irrelevant?
Nov 21, 2006, 06:46 PM
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# Flight time calculator

Quote:
 Originally Posted by GWSLAWNDART Hey guys, I was wondering if there are any online calculators or What the Formula is for Calculating the amount of Runtime for a battery, at a Certain Amp draw, at a certain voltage. Appreciate your info Luis
Try Here:http://www.bphobbies.com/view.asp?id=A0320048&Nav=7
Bob
Nov 21, 2006, 06:59 PM
Registered User
Quote:
 Originally Posted by bob2005
I was looking for the theory behind this, not a link to a web calculator. Somehow I recall Ohm's law as having three variables and I didn't think it was possible to leave one out.
 Nov 21, 2006, 07:34 PM Senile Member Actually, two variables are left out, voltage and resistance, so Ohm's law is not applicable here. The only applicable factors are the current draw and the battery capacity in ampere hours. A 1500 mah battery can be just one cell or made up of several cells in series. Regardless of how many cells there are in the pack it will still deliver only 1.5 amps in one hour or 10 amps in 0.15 hours, or 9 minutes. Where voltage comes into play, is that as the voltage increases, the load, i.e. prop size, has to decrease to maintain the 10 amp current flow. But, as long as the 10 amp draw is maintained, the time to deplete the battery remains the same regardless of the voltage. Larry
 Nov 21, 2006, 08:47 PM Registered User Here ya go Luis, & its FREE! HTTP://brantuas.com/ezcalc/dma1.asp I have used this program many times to calculate; What Motor, What Prop, How many Batteries, and you will get your run time, Amp draw, and amount of Thrust. Fast Fly Last edited by Fast Fly; Nov 22, 2006 at 12:02 AM.
 Nov 21, 2006, 09:21 PM Registered User FastFly, Thanks for the link, i have been using p-calc for a long time, but it doesnt have the newer motors that are out. P-calc is really good, but lacks in motor selection.
 Apr 12, 2009, 05:04 AM Registered User BP = Battery pack (in amps) AD = Amp Draw (in amps) X = time to deplete 1000mah pack BPX = time to deplete battery pack 60(minutes) / AD = X X * BP = BPX