VxA=W

[[2574]]

Inverters. Can someone confirm my (schoolboy) maths and physics that an inverter producing 600w (240v) will pull down 50Ah from the 12v battery supply. (And therefore would kill a 260ah battery bank used to 50% in about 2 and a half hours).

TIA

Rob

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[Oldhand]

A bit worse than you calculate because the inverter is not 100% efficient, you will find it produces a fair amount of heat, even off load.

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[davel]

Basic maths is OK but a couple of points
1. An inverter rated at 600W won't always consume that ammount of power. It depends on the load you're drawing (ie check the power consumption of the telly or whatever you're powering via the inverter)
2. Inverters are inefficient so you need to allow for that. I'd suggest allowing an additional 20% for that.

So assume your telly is rate at 120 watts 240 volts, the drain on your 12v battery would be something like 120/12 x 120% = 12 amps

<hr width=100% size=1>Dave L.

 

[Guest]

in fact

will likely pull about 55 - 60 amps due to losses / heat dissipation etc.

putting it simply - it would flatten a bettery pretty smartly !


<hr width=100% size=1>Nigel ... and of course Yahoo groups :
http://groups.yahoo.com/group/gps-navigator/

 

[Guest]

using an inverter shows that it doesn't draw in proportion to the required ..... daft I know - but fact. So now I look on an inverter as darwing near what it is rated for ..... palying safe !


<hr width=100% size=1>Nigel ... and of course Yahoo groups :
http://groups.yahoo.com/group/gps-navigator/

 

[Guest]

exackerly ..... nm

.

<hr width=100% size=1>Nigel ... and of course Yahoo groups :
http://groups.yahoo.com/group/gps-navigator/

 

[andyball]

More or less....well rather less time actually.

Watts does = V x A

But inverters operate at say 90% efficiency at best, some rather less & all less at lower powers.

Batteries are rated in Amp Hours based on a 20hr discharge & sadly, the quicker you discharge them, the less effective capacity you get....you could reckon on at least a 25% reduction in capacity of the bank you mention due to the high discharge rate, rather more if the bank is made of starter type batteries, less if they're pukka traction ones or spiral cell.

Also battery capacity is measured at 20C.....at todays temp. you might find 5 -10% less capacity.

So your figure is likely on the fairly generous side.

There's a good 1MB download "electricity on board" that goes into this & many other aspects of batteries & charging at
http://www.victronenergy.com/ . Click "technical info" on the left & you'll see it.


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[[2574]]

thanks all above for very helpful responses.

rob

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