How to calculate your electricity usage

[jayjay]

Have been doing some electrical stuff today, and in the course of finding out how, came across this really easy way to calculate how much power your electrical stuff uses and how much power in hours a leisure battery has before it's flat! So I thought I'd post it here. Of course, I'd still need a calculator to do the maths, especially division !

Battery Power Calculations
Load (Watts) ÷ Voltage (Volts) = Current (Amps)

Current x Time (Hrs) = Capacity needed (Ah) Then add 25% on to Ah Capacity for reserve.

i.e.
Lighting (30Watts) + Fridge (30 Watts) + Water Pump (10 Watts) + TV (Black & White 50 Watts) = 120 Watts.

120 Watts ÷ 12 Volts = 10 Amps

For 6 hours = 60 Amps Then add 25% = 75 Ah

So a 75Ah leisure battery will last for 6 hours using all these things... Now that doesn't sound right to me, I always thought that just having a fridge on a leisure battery would flatten it in around an hour or so! Correct me if I'm wrong!

[lunnie]

Dont think your fridge will work on the leisure battery, only on ehu, but it will run on your gas.

plus remember you will not have the lights on that much, long nights, candles and led lamps help the battery out. plus your water pump, if you keep your water in a 5 litre bottle it saves again.

I went 2 weeks on no hook up but gas for fridge and didnt use the pump.

[playallday]

My fridge runs on 12v, but only off the van battery, when in transit. Didn't I read somewhere in the manuals that the fridge shouldn't be connected to the leisure battery?

[jayjay]

Apr 18, 2008 20:42:12 GMT lunnie said:

Dont think your fridge will work on the leisure battery, only on ehu, but it will run on your gas.

plus remember you will not have the lights on that much, long nights, candles and led lamps help the battery out. plus your water pump, if you keep your water in a 5 litre bottle it saves again.

I went 2 weeks on no hook up but gas for fridge and didnt use the pump.

Great bit of info for when in Scotland and wild camping, thanks Joan! I never thought of just using the water pump to fill up a container occasionally and use the water from there.

I never use my fridge except on gas. Don't even know how it works on the battery - I think mine is connected the van battery rather than leisure as well as I was warned not to switch it to 9v unless the van was actually running and switch off whenever I stopped the engine or face the consequences! So I just don't bother with it all.

When in transit, I just fill it up with those frozen blocks that are used to cool coolboxes, fill it with frozen stuff (more frozen blocks!) and that keeps it cold until I can overnight stop and connect the gas. It works really well on gas, on highest setting for an hour or so will freeze the blocks again, ready for travelling the next day. I only have a two way fridge, gas or 9v, so EHU isn't an option!

Any more words of wisdom? I need all the help I can get! LOL! ;D

[lunnie]

I never used the pump to fill up containers, I found a water tap and fill up pop bottles and my 5 litre bottle. on the Isles, water was readily available at visitor centres, the disabled loo had two door a door which you used from inside the building but at night this was locked and you used the outside door, and there usually had a drinking water tap there as well, and on the fishing quay, usually hot showers for 50p and sinks with HOT HOT water were I washed my smalls, these are in place for the fishermen, but anyone may use them.

My fridge in Freda 1 was either engine when travelling or gas on site, it did not have mains hook up. but my lights never failed. Fridge used a bit of gas, but all was well, but make sure you have gas and fuel as they are very expensive on Harris and Lewis, you can get gas on Lewis near the ferry terminal, but expensive.

Have a good trip, I am off to Turunc, on Friday until 12th June, and it is 74degs at the moment!!!!!! but I still come on site as there are plenty of internet cafe's in the village.

[ant]

Hi jayjay. The formulea are right but the values are not right for the fridge. If you could run the fridge from the 2nd battery ( which you can't or shouldn't be able to) it will use between 8 and 12 amps depending on the size of the element fitted. Also the calculation assumes the battery voltage remains at 12volts, which of course it doesn't, as it is used the voltage goes down also. so the effect is like having more amps.
So to conclude if you run the fridge directly from the battery without the engine running you'll flatten the battery very quickly.
Ant

[jayjay]

Hi Ant - that's what I thought. I think it was from a VW site, maybe wild camping, can't remember now!

[jayjay]

Apr 20, 2008 17:44:18 GMT lunnie said:

Have a good trip, I am off to Turunc, on Friday until 12th June, and it is 74degs at the moment!!!!!! but I still come on site as there are plenty of internet cafe's in the village.

Thanks for the tips, Lunnie! Which harbour is it that has the showers and all?

Have a wonderful time in Turunc! Don't forget your sunhat and swimmin' cossie, you lucky person, you! ;D

[lunnie]

That was on Bernaray, but I am sure you will find the same on Lewis and Harris. except the loos are locked on Sundays!!!

8 swimming cossie's to Turunc, but will leave a couple there for my October break of 3 weeks!

Suncream and hat already there, as well as the Bailey's and Brandy!

But I am taking my favourite cheese that I have just found after looking for it for 2 yrs. White stilton with lemon! found it in Derby market, it was new to them, then my cousin said that morrisons are now selling it! feast /famine comes to mind.

I am really looking forward to it, Freda 2, has been tucked up safe and sound, she has been washed and waxed, in readiness for my return, she will only need a quick wash and will shine!!

I know that you will have an absolutely fabulous time up North! whether the sun is shining or not, as it is just soooooooooooo beautiful.

Hope you c u on my return. - Joan