Kws to amp hr conversion

[T1 Terry]

Here's the question from Greg

If you have an appliance that uses 3.6 kW per 24 hours, how many amp hours of battery is required to run this, using 12 V batteries through an inverter?

This will get technical..... it always does eh
3.6kWh per 24hrs is the average use over the 24hr period. The instantaneous load measured in amps x volts is referred to as watts, the instantaneous amps @ 12v is critical for battery type/capacity.
An example,
Scenario (A) A light circuit drawing 150w continuous will draw 3600Wh or 3.6kWh per 24hrs at a rate of 12.5 amps continuous. A lead acid battery (agm, gel flooded cell) has a C20 rated capacity, 5 amps continuous load for each 100Ah capacity. The above load would require 600Ah of lead acid batteries to power it and limit the discharge to 50% and stay within the C20 rating so all the 300Ah to 50% SOC were available if the battery was in really good condition. Not completely accurate as the discharge rate would be less than a C20 rate so technically the battery could supply more than the 300Ah before it reached the 50% SOC mark
Eyes rolling yet? Now it gets real techo
Scenario (B) The same 3.6kWh load drawn on a 50% duty cycle will see bursts of 25 amps and periods of no discharge from this load, the same 600Ah lead acid battery will power this 50% duty cycle type load, but it will do it harder with a discharge of 4.1 amps per 100 Ah capacity and less capacity will remain in the battery bank.
Scenario (C) Same load on a short cycle, say 4 times per 24hrs so the load would be 900w or 75 amps 1 hr from the 12v battery. To get the same 300 Ah required at a C20 rate the battery capacity now would need to be 1500Ah, not gunna happen, so a C5 load will require more than 800Ah capacity to still have the 50% SOC after 24hrs due to the Peukert losses.
Scenario (D) The load is an electric kettle rated at 2400w instantaneous load. 10 boils of 9 min each, the same 3.6kWh but now bursts of 200 amps instantaneous current, that would require 30 x 105Ah Fullriver AGM's at a C5 discharge rate (from the Fullriver site 17.2 amps) They don't list a C1 discharge rate any more as I'm guessing it is beyond the batteries capabilities to do it very often without damage.

The same 4 scenarios from a quality Li battery, 300Ah will do any of these loads and supply the 3.6kWh required.
If your eyes haven't rolled back to the point you fell off the chair means you didn't really read it all did you

T1 Terry

[GregnDee]

I've just read this out to Greg

He said, and I quote:

"I need a piddle"

[Mrcoolabah1au]

Sh*t

[jon_d]

Greg,

What is the device?

jd

[T1 Terry]

Greg,

What is the device?

jd

You shouldn't ask such things Jon, but needless to say at 3.6kWh a day it's a heavy duty unit

[Dot]

I think Greg is still piddling!!!

[Jon and Kay]

At least 400 ah batteries 400 watt solar on top of anything else being used.
And of course Lithium batteries are best.

[Dot]

He said it is a Dometic 3 way fridge of 117lit The 3.6kwh pr 24hr figure comes from the spec chart in the manual.

[T1 Terry]

He said it is a Dometic 3 way fridge of 117lit The 3.6kwh pr 24hr figure comes from the spec chart in the manual.

Then scenario (A) applies, but add 10% to the 3.6kWh for inverter losses, not really viable as a replacement inverter fridge would be cheaper than 100Ah of Li batteries.