# Inverter's how long to they provide power for



## Mrplodd (Mar 4, 2008)

OK I am sure this a really stooopid numpty type question but.......

I am picking up a new (to me) MH this Friday (yes I am dead excited !!!)

It has an inverter fitted so I was wondering is there a simple formula for working out how long it will provide power for before the leisure battery gives up ??

A bit like the formula for working out how many 240 appliances you can power off a 10 amp EHU before it trips out !!

Answers please !!!


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## AberdeenAngus (Jul 26, 2008)

Dead easy but you need to know how many Watts the appliance uses and then work out the Amp Hours

Watts = Volts x Amps
or
Amps = Watts/Volts
or
Volts = Watts/Amps

Same equation just swapped about.

So a 100watt telly on 240v takes 0.4 Amps (i.e. Watts/Volts = 100/240)
Now...
the same telly on 12v (via your inverter) will take the same power (100 Watts) but, on 12v, will now be pulling 8.3 Amps (100/12)

So, if you have it on for an hour, running through your invertor, it'll pull 8.3 Amp Hours. In 2 hours it'll use 16.4 Amp Hours etc

If you have an 85 Amp Hour leisure battery, then you don't really want to take much more than 50% out of it or you can damage it.
So that gives you about 40 Amp Hours to play with.

So 40 / 8.3 = 4.8 Hours (say 5 hours)

There are losses by using an inverter as they are not 100% efficient but the above will give you a rough idea.

A good idea is to do a list of what you a likley to want, and for how many hours.
e.g.
Telly, 2 hrs per day
Lights, 4 x 4 hrs per day
etc
Add up all your amp hours and, if it come to more than half the capacity of your battery, you should consider getting an extra battery.
Course, none of this matters if you are on hook up.


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## Mrplodd (Mar 4, 2008)

Boy now that was quick and very comprehensive answer, thank you !!

So as a rough guide I could get an evenings TV watching without too much trouble. This which was pretty much what I was wondering as I cannot think of any other 240V appliance that I would use. Unless of course her indoors wants a hair drier but that would be mega watts !!

I assume that the wattage of the inverter indicates the maximum wattage of any appliance that is connected to it ??


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## AberdeenAngus (Jul 26, 2008)

"I assume that the wattage of the inverter indicates the maximum wattage of any appliance that is connected to it ??"

You are correct.

I would say that, so long as you are not powering anything that gets hot (like hair drier etc) then you will get an evenings telly & lights from a bog standard leisure battery. If not then bin it and get a decent one.

If you are going to be away from hook up for a number os days then I would suggest you consider changing your lights out for LED's as that is the single best thing you can do to save power.
After that think about an extra leisure battery.
After that, think about a solar panel.

But that's only when you are going off hook-up for a good few days.


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## Mrplodd (Mar 4, 2008)

Thats very handy information, and very much appreciated !!

I am aware that some of the lights in the new one are already LED and I have removed all the LED lights from the one I am trading in (they cost a few quid so I am hanging on to them!!) . It really is amazing how much less power they use !!

The new MH also has a generator built in but I dent really want to use that unless necessary. I dont like noise when I am on site so am always careful that I am not p*****ng someone else off with my noise !!


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## AberdeenAngus (Jul 26, 2008)

There are differing opinions re gennies on this site but, I know, they are not for me.


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## clodhopper2006 (Aug 13, 2006)

The trouble is calculating battery endurance is not as easy as that. It should be on paper but there's another law you need to consider, Peukerts Law.
Basicaly a 100Ah battery will provide 1 amp for 100 hours. The trouble is the higher your current draw the less Ah you get and it falls off exponentialy the higher the current drawn. 
This means that you won't get say 100A for 1 hr with the same battery, it will be more like 10min.

Bob


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## AberdeenAngus (Jul 26, 2008)

Agreed, but based on typical consumption rates (say) 5 - 10 amps, I think the 50% advice is reasonable.

I find that understandable approximation is better than confusing accuracy.

Of course some people just don't do pragmatic, do they ?


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## clodhopper2006 (Aug 13, 2006)

AberdeenAngus said:


> Of course some people just don't do pragmatic, do they ?


I agree with you too. Just added some extra info that might help others understand how Ah capacities change. Shame you felt the need to get sniffy about it.


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## CliveMott (Mar 10, 2008)

More headaches below

For each 100 watts of mains equipment allow 10 amps from your battery to the inverter and you won't be far out.

C.

http://www.motts.org/HOOKUPS.htm


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