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Air Conditionar on battery??

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Posted by Alubukhara on May 5, 2009, 7:38 am
Everybody knows you dont run heavy loads (Iron, AC etc) on batteries but

A normal one ton Air Conditionar (AC) requires 1500 Watts so the current
(amps) required if the mains voltage is 220 should be 1500/220 =  6.8 Amp

A 100 Amp hour battery can provide 100 amperes for 1 hour right?

That means it should be able to run about 14 AC's  (100/6.8) for one

I know its nonsense but what am I missing here?

Posted by RamRod Sword of Baal on May 5, 2009, 8:11 am

Several things

First it is recommended that you only discharge batteries down to 50% or
they pack up earlier.

So depending what voltage your battery is, is it 12 or 24 volt

Now these are simple calculations and I am not bringing any other factors in

If it is 12 volts and 100 amps, that is in watts (no extra losses taken into
consideration) 1,200 watts (12 volts x 100 amps = 1200 watts)

If it is 24 volt system it is 2,400 watts

Now if you only discharge the battery down to 50 % it equals 600 watts and
1200 watts.

Let us look at your air conditioning unit.

Using your numbers.

220 volts; 1500 watts and 6.8 amps

IE 1500 watts (220 volts X 6.8 AMP)

That would mean on a 12 volt battery that has a possible 600 watts of power,
it would run less than 1/3 of an hour (1500 watts into 600 watts)

On a 24 volt battery with 1200 watts the air conditioning unit would run for
say 3/4 of an hour (1500 watts into 1200 watts)

Of course this is with you using an inverter to convert the DC (Battery
Power) to 220 volts AC house power.

The inverter would not be 100% efficient, around 90% is the one I have, so
the actual running time would be less than the numbers I have shown.

Other numbers can be factored in but this is a very basic explanation of the
question you have asked.

On a practical note, running the battery flat to get more power out of it
you would find that the inverter would properly shut down on its low voltage
safety before you could get everything out of it.

Posted by Jim Wilkins on May 5, 2009, 9:45 am
You also need 220V from the batteries.


Posted by RamRod Sword of Baal on May 5, 2009, 10:14 am

The power supply for the A/C  needs to be AC (Alternating Current) as from
an inverter.

220 volts DC will not run a normal everyday Air Conditioner.

Posted by Eeyore on May 5, 2009, 10:14 am

Alubukhara wrote:

NO. High rate of discharge lowers the capacity and also reduces the battery
lifetime. It's complicated and varies between battery chemistries. You ned to
find the discharge rate at which the battery was rated.


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