Convert mains power consumtion to 12volt a/h

[The Maestro]

I have a meter which measures the consumption of all my 240 volt gear - The TV is 20 watts and the SKY+ box about the same. They are usually both on together.

 

I hope someone can tell me how to convert these numbers to amp-hours drain on 12 volt batteries, through a 1800 watt inverter, perhaps assuming 100% efficiency in the first instance.

 

A separate estimate of efficiecy losses would also be helpful!

[jodansgang]

That's numberwang.

[GBBS]

Hi inverter efficiency dependant upon make but probably 80% as a guide

 

Watts are watts voltage irrelevant

 

So 2 x 20 watts @240v = 0.2 amps if left on for one hour = 0.2 ah ( watts / volts = amps)

 

2 x 20 watts @12 v = 3.3amps one hours use = 3.3ah. If 80% efficient then 3.3 x 1.2 = 3.96 - say 4 amps

GBBS

[BlueStringPudding]

That's numberwang.

 

[Tony Brooks]

or for simplicity divide the mains wattage by 10 to get the 12V consumption (assumes an 80% inverter efficiency).

[Paul C]

P=V x I

 

P being power in W

V being voltage in volts

I being current in Amps

 

Your power monitor is no doubt showing W being consumed in real time, you need to know how long it runs for to convert to eg kWh which is a unit of energy. For example 1000W consumed for an hour is 1kWh. I reckon your energy monitor will do this cumulatively for a day, week,month etc too.It probably also has a p/kWh figure (which you can change) and show energy in £/p and CO2 produced.

[Richard10002]

Hi inverter efficiency dependant upon make but probably 80% as a guide

Watts are watts voltage irrelevant

So 2 x 20 watts @240v = 0.2 amps if left on for one hour = 0.2 ah ( watts / volts = amps)

2 x 20 watts @12 v = 3.3amps one hours use = 3.3ah. If 80% efficient then 3.3 x 1.2 = 3.96 - say 4 amps

GBBS

+1 4A

[jonathanA]

As Tony said 40W/10 is about 4 amps at 12v

 

which means that in your case, for one hours TV+Sky you will need 4 amp-hours (AH) of capacity from your battery.

 

you can expect to get better than 80% efficency from your inverter, but what you get will depend on inverter make, load, battery voltage etc etc

[smileypete]

A DC clamp ammeter will give you the right answer, £40 from Maplins, more info here:

 

http://www.canalworld.net/forums/index.php?showtopic=43603&p=1180439

 

Will also tell you the idle current of the inverter, and the current for your DC loads too.

 

cheers, Pete.

~smpt~

Edited November 19, 2013 by smileypete

[bottle]

See post #5 for a good estimation

 

and if you want to really know, exactly

 

see post #9

 

[PeteS]

What meter are you using to measure power used?

[The Maestro]

What meter are you using to measure power used?

 

Its a 5-socket mains extention lead with a meter built in. Maplins sold them for a while although I haven't seen one recently.

 

Thanks to everyone who has replied with very helpful information!