Wednesday, Apr 16, 2003 at 19:12
A 12V item drawing 1 amp would drain a 30A/H battery after 30
hours - yes. At these lower currents, this equation applies - however
it is unlikely that the same battery would supply 30 amps for 1 hour.
Probably more like 40 - 50 minutes. They usually aren't designed for
long periods of high discharge and, indeed, you have to apply a
fudge factor which will vary according to the purpose the battery
was designed for.
You are on the right track when you mention Power (as opposed
to voltage (volts) or current (amps)).
The power (in watts) you are using is calculated by multiplying the
voltage-drop across the appliance by the current flowing through it.
Thus your 12V item drawing 1 amp is consuming 12 watts of power.
Your 240V item drawing 1 amp is consuming 240 watts of power.
Thus an inverter would have to supply 240 watts at 240 volts.
In theory, the 30AH battery would need to supply 240 watts of power to the inverter at 12 volts
Working the equation backwards, 240 watts divided by 12 volts =
20 amps. Thus the battery would be supplying 20 amps at 12volts
into the inverter.
Again, another fudge factor. No inverter is 100% efficient - probably
70% - 90% depending on the design (and how much $$ you spent!)
You would probably be drawing around 25 amps (using the thickest hookup cable practical to minimise losses) from the battery.
I would hazzard a guess that you would get around 30 - 40 minutes
from this set up. The best way to find out is to test it. Remember
though that regularly cycling a 30 AH battery at a 25A discharge rate
will quickly destroy it unless it is purpose designed for this.
Hope this is clear & happy flying! Err, I trust that this is a, ahemm, 4WD
plane! :-)
Rob
AnswerID:
17795