12v batteries & inverters

[Jimmyb]

Does anyone have any info/formuals to work out how long a battery will last on a inverter if you know the load that will be connected to the inveter

thanks inadvance

 

[MarkieSparkie]

This can only be calculated approximately because you probably will only know the nominal battery capacity, nominal output voltage, nominal load wattage, typical inverter efficiency and for simplicity assume the load is purely resistive:
Load Current(A)=Load Power(W)/Load Voltage(V)

Load Time(hr)=(Battery Capacity(Ahr)/Load Current(A))x%Efficiency Inverter/100

A better plan might be to determine things empirically, especially if you don't know the efficiency of the inverter:
1) Fully charge your battery.
2) Connect battery to the inverter.
3) Select an appropriate load, eg. 100W tungsten filament lamp.
4) Switch ON the inverter and START your stopwatch.
5) Run the inverter until it automatically switches OFF the load, at this point STOP the stopwatch and note the time elapsed.
6) Disconnect your battery from the inverter.
7) Recharge your battery.

With a bit of simple formula transposition and using the nominal battery capacity, you should then be able to plug the numbers into the formula to calculate an approximate inverter efficiency. Having done so, you now have the means to calculate approximate times for other loads.

 

[Jimmyb]

Im trying to work out what i need but think im never going to do it as i will need about 6 batteries, its a burger van and uses about 4amp an hour am i right in think to last 6 hours i will never to able to do it

 

[Knobhead]

I take it’s 4A at 220V. So assuming a 6Hr day, it’s 220X4X6=5280Ahr. Assuming 85% efficiency for the inverter it’s 5280X1.15=6072Ahr. To prevent battery damage an overhead capacity is needed of say 33%, we then get to 8075Ahr. Or 8 X 100Ah leisure batteries.

Have you got a Scammel tractor unit to drag this lot around?

 

[Deleted member 26818]

I think perhaps a generator, or bottled gas might be in order.
Do they still make those gas lamps and mantles?

 

[Knobhead]

Do they still make those gas lamps and mantles?

I’m buggered with my new lighting if they don’t

 

[Bitslice]

I take it’s 4A at 220V. So assuming a 6Hr day, it’s 220X4X6=5280Ahr. Assuming 85% efficiency for the inverter it’s 5280X1.15=6072Ahr. To prevent battery damage an overhead capacity is needed of say 33%, we then get to 8075Ahr. Or 8 X 100Ah leisure batteries.

Have you got a Scammel tractor unit to drag this lot around?

It was my understanding that you never discharge a battery more than 50% and preferably less than 25% if you want it to last a few years, so your 33% overhead seems off to me ? I think he is looking at 1200 Ahr.

Better to get or convert a generator to run on propane I think


Edit
Hah, yes slight typo there, I meant 1.2KAhr, lol

 

[Deleted member 26818]

12kAhr, how big is this battery, does it have it's own post code?