Heating calorifier by inverter?

Tim Good

Tim Good

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Summary:
I want to heat my 2kw calorifier using my 2kw inverter but it won't work.

Details:
This season I've been using the inverter a lot more as we are able to generate way more power on solar than we can consume now that we're on the coast of Portugal. We always boil the kettle now on the inverter and I'm looking for more things to use.

For hot water, when the engine hasn't been run we fire up the webasto. However, I figure we could use the inverter. However the calorifier is rated at 2kw and so is out inverter. When I switch in the calorifier it simply doesn't activate when the inverter is on. I assume this is because the inverter just says "no it's too powerful".

I doubt the calorifier needs a pure some wave, which my inverter doesn't have.

So my question is can I buy some kind of in line resister that I install in the positive lead to the calorifier which will reduce its power to something like 1.5kw?
 
Adding a resistor to the positive lead won't decrease the heaters power, it will increase the load of the complete circuit making it harder work for the inverter.

There should be no reason that the inverter won't run the heating element, it's a purely resistive load and will only work at the power rating that the inverter can supply.

Is the heating element definitely working?
 
If the immersion element has failed I suggest putting in a lower powered one. If I remember correctly the one in my calorifier is 900 watts, and it heats the water quite fast enough when on mains.
 
northcave said:
Summary:
I want to heat my 2kw calorifier using my 2kw inverter but it won't work.

Details:
This season I've been using the inverter a lot more as we are able to generate way more power on solar than we can consume now that we're on the coast of Portugal. We always boil the kettle now on the inverter and I'm looking for more things to use.

For hot water, when the engine hasn't been run we fire up the webasto. However, I figure we could use the inverter. However the calorifier is rated at 2kw and so is out inverter. When I switch in the calorifier it simply doesn't activate when the inverter is on. I assume this is because the inverter just says "no it's too powerful".

I doubt the calorifier needs a pure some wave, which my inverter doesn't have.

So my question is can I buy some kind of in line resister that I install in the positive lead to the calorifier which will reduce its power to something like 1.5kw?
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In theory yes you could fit a resistor in series with the immersion heater element but it would be ineffeicient and impracticable due to the heat that would be produced and wasted.

Assuming it is a 240 volt system a 10 ohm "resistor" would be about right to reduce the load on the inverter to 1500 watts but BUT BUT, the current, although reduced from 81/3 amps to 6¼ amps, would still produce nearly 400 watts of heating in the resistor. A beefy resistor would therefore be needed and 400 watts of heating would have to be dissipated and wasted.
Approx 1100 watts would be produced as useful heating by the immersion heater element

A lower power heating element as Norman E suggest is the simple solution
 
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VicS said:
A lower power heating element as Norman E suggest is the simple solution
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Without me lifting my floorboards and checking, do calorifiers a tend to have interchangeable / replaceable elements or does one tend to just change the entire tank?
 
The other option that might be attractive would be a 110v inverter for the water heater. You would retain the full heater capacity when connected to shore power. The heater would be 2kw on shore power and 1kw on the inverter. Perfect.

I have never heard of anyone doing this, I am just thinking outside the box, but I cannot see a snag for a resistive load.

There would be some side benefits such as the 110v inverter serving as a backup for multivoltage appliances such as a laptop. This might get you out of trouble if the main, 240v inverter failed. Both inverters could be used at the same time increasing the available capacity (if your batteries can tolerate the high load). I am not sure how the costs would compare but inverters, especially non sine wave models, are not expensive these days and it would be easier than trying to find a low wattage element that fits your heater.
 
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noelex said:
The other option that might be attractive would be a 110v inverter for the water heater. You would retain the full heater capacity when connected to shore power. The heater would be 2kw on shore power and 1kw on the inverter. Perfect.

I have never heard of anyone doing this, I am just thinking outside the box, but I cannot see a snag for a resistive load.
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No! . If you halve the volts you halve the current so the watts is only a quarter

it would only be about 420 watts on 110 volts.
 
VicS said:
No! . If you halve the volts you halve the current so the watts is only a quarter

it would only be about 420 watts on 110 volts.
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Yes you are correct Vic. Sorry, I should have realised that. But this is probably better when powering the heater from solar/batteries. Slower, with a lower current draw is a good solution. The full 2kw capacity would still be available on shore power without changing the element.

The other side benifit is the 110v intverter can be small (500w) reducing the cost.
 
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A lateral thought here, have you tested the immerser on shore power SINCE you found that it was not working on the inverter and got it to work? The reason I ask is that there are now usually two circuit breakers built into the immerser thermostat. The first is the usual one to prevent it overheating. It resets automatically. The second is a fail-safe one which operates if something causes the water to reach a higher level. It does not reset. On some thermostats there is a very small button that will reset it. On others you need to renew the thermostat.
 
It is common practice to keep the calorifier supply separate from the inverter circuits, so it's quite probable this is why it's not working.

This is done for good reason, a 2kw inverter at full output will draw about 200a.

Out of interest, what make and model of inverter do you have ?
 
Graham376 said:
All the ones I've come across have been just like domestic ones but although the same fitting, boats usually have much lower power elements. Typical Vetus one here - https://www.asap-supplies.com/vetus-whel110-electric-heating-element

OOOPS, WRONG VOLTAGE but they no doubt stock 240v as well.
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My calorifier used an element with the same thread size as UK domestic ones, but some makes use a much smaller thread size, so you have to check both thread size and length as well as wattage.
 
PaulRainbow said:
It is common practice to keep the calorifier supply separate from the inverter circuits, so it's quite probable this is why it's not working.

This is done for good reason, a 2kw inverter at full output will draw about 200a.

Out of interest, what make and model of inverter do you have ?
Click to expand...

You may be right there. The inverter is built into Heart Freedom system. Sends ac to all the sockets which are also used by shore power and generator.
 
I might be missing something, but it seems to me you're trying to draw 166 amps out of the battery, assuming 12V. That's a lot of current, and you better be sure the wiring, connections and battery are up to it, or else you're doomed to failure.
 
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