Immersion heater running from inverter

[plumbob]

No experience with this situation, so, have 4 new 120ah AGM batteries just fitted. Will a say 2kw inverter sensibly run the 1.25kw immersion heater for 45 minutes which is how long it takes to get the hot water up to temperature? I guess logically it looks as though it should but no idea if that's a real world thing Thanks

 

[wonkywinch]

Should be no problem at all. How will you put the charge back into the batteries?

1.25kw for 45 mins is 78AHr at 12v. Allow for some system inefficiency, you'll use something like 90 AHr or 40% of your usable capacity (AGM shouldn't be discharged below 50% capacity for max lifespan, which is 240AHr in your case).

 

[PaulRainbow]

Should be no problem at all. How will you put the charge back into the batteries?

1.25kw for 45 mins is 78AHr at 12v. Allow for some system inefficiency, you'll use something like 90 AHr or 40% of your usable capacity (AGM shouldn't be discharged below 50% capacity for max lifespan, which is 240AHr in your case).

Ball park figure for inverters is to divide the inverter output, in watts, by 100. So a 1.25Kw immersion element will draw 125A from the batteries which = 94Ah in 45 mins, so your figure of 90A is close enough

As you mention, getting that back into the batteries needs to be a consideration. It's going to take 4 - 5 hours to fully charge the batteries and using the inverter suggests that mains isn't available, so unless the OP has a substantial solar array he's need to run the engine/s, which would be a massively inefficient way of heating water, it would be much better to run the engine to heat the water.

 

[plumbob]

Ball park figure for inverters is to divide the inverter output, in watts, by 100. So a 1.25Kw immersion element will draw 125A from the batteries which = 94Ah in 45 mins, so your figure of 90A is close enough

As you mention, getting that back into the batteries needs to be a consideration. It's going to take 4 - 5 hours to fully charge the batteries and using the inverter suggests that mains isn't available, so unless the OP has a substantial solar array he's need to run the engine/s, which would be a massively inefficient way of heating water, it would be much better to run the engine to heat the water.

Thanks for that. I have shore power, 175amp solar panel and on a single 135 diesel. I've always used the engine for hot water, but if staying put for a day or two it would be nice to have another way to heat the water. Running the engine out of gear achieves nothing except recharging the batteries. My solar works well.

 

[wonkywinch]

Thanks for that. I have shore power, 175amp solar panel and on a single 135 diesel. I've always used the engine for hot water, but if staying put for a day or two it would be nice to have another way to heat the water. Running the engine out of gear achieves nothing except recharging the batteries. My solar works well.

An ICE is so inefficient that if it's not heating your water just idling in neutral, I'd check that the thermostat isn't stuck open.

Some engines need c 1500 rpm to kick the alternator into life for simultaneous battery charging (no point wasting those engine hours).

You should feel the pipes from engine block to the calorifier get hot before the heat exchanger does.

An old remedy to get home in a car with a broken (stuck closed) thermostat that caused overheating was to put the heater and blower on full as the heater is plumbed before the thermostat and could act as a mini radiator.

 

[PaulRainbow]

Thanks for that. I have shore power, 175amp solar panel and on a single 135 diesel. I've always used the engine for hot water, but if staying put for a day or two it would be nice to have another way to heat the water. Running the engine out of gear achieves nothing except recharging the batteries. My solar works well.

Are you saying the engine does not heat the water ? If not, you should look into getting that to work.

If you heat the water for 45 mins, as you said above, it will take the solar panel about 2 days to replace that energy (if it's sunny).