Powerpack time length

[steve_bham]

Does anyone know of a formula that i can use to work out how long my 10ah power pack will last for (i.e. if i know wattage / current rating of device)

Just working out how long my battery pack will last for at Sailsbury as i dont of electric hook up!

[MikeP]

In theory 10aH means you can supply 10amps for 1 hour or 1amp for 10 hours or any other combination that multiplies to 10. However in practice you can't or should not run the powerpack to zero, so assume (say) only 80% of that capacity.

Obviously you need to know how many amps you are supplying in total. You can get this information from each of the devices you hook up - it will either say it in amps eg 500mA (half an amp) or in watts eg 18 watts. If it is quoted in watts, divide by 12 (the voltage you are working at) to get the amps 18watts at 12volts is 1.5amps.

I know nothing about electricity but I believe the above is true. If not someone will come along and correct it.

Mike

[brianb]

I believe the above is true.

It's perfectly true as far as it goes. But the actual voltage of a fully charged 12V battery pack is approx. 13.8V so the power drain may be a little faster than you calculated.... by the time the voltage is down to 12V the battery pack is pretty well drained.

Also, unless the batteries are known to be of the "deep cycle" variety (these are more expensive), reckon on 50% rather than 80% of the rated capacity. Normal cells simply do not like being discharged close to empty, they rapidly lose capacity and storage life if they're treated that way.

[Whippy]

I think the best thing to do is to take it charged, use it on a session and the try and 'borrow' a socket and re-charge it again during the day. As Brian has mentioned, if you drain it fully then the battery does go downhill quite quickly.

Tony..