Variable power consumption for immersion heater?

[Kinsale373]

Youre correct Rogershaw! Its obviously too early in the morning for calculations for me ! I,d stay away from adding controls or transformers anyway when there is no need.

Kinsale 373

 

[lw395]

You are wrong

The element is a resistor and the resistance stays the same I (current ) = V(oltage) / R(istance) so as the voltage reduces the current will decrease and W = V * I so the if the current halves the wattage will be half

That would suggest 1/4 of the power.
The element is unlikely to be a very good resistor, I'd expect it to run quite hot at 230V and increase its resistance significantly.
So, I'd expect the current to drop by less than half, and the power to be maybe 1/3?
A water heating Eberspacher is a good answer IMHO.

 

[rogerthebodger]

That would suggest 1/4 of the power.
The element is unlikely to be a very good resistor, I'd expect it to run quite hot at 230V and increase its resistance significantly.
So, I'd expect the current to drop by less than half, and the power to be maybe 1/3?
A water heating Eberspacher is a good answer IMHO.

Yes you are correct as in theory both the voltage and current will be half, so an adjustable supply would be the best.

Gas is file but if you can heat water with engine heat which is free.

In my case the shore power electricity is included in my mooring fees so again no additional cost unlike gas

 

[[3889]]

A water heating Eberspacher is a good answer IMHO.

OK, to clarify my circumstances, I will be cruising for 6 months and don't want to use marinas more than once a week as a) I don't like them and b) they are expensive on a per night basis
So, last year I spent about 100 nights at anchor and did indeed use the engine for heating water but, as I have a small genset, I'm looking at a way not to run the engine for short periods whilst not under load. I detest Ebers/Webastos and think they are completely unsuitable for sail boats with their ampage demand and fickle reliability. I have had 3 including one in my current boat (space heating only) which I thought seriously about removing when I bought the boat and now regret that I did not. I accept that many people find them wonderful but each to their own: I speak from experience, not prejudice.

Yes you are correct as in theory both the voltage and current will be half, so an adjustable supply would be the best.

Gas is file but if you can heat water with engine heat which is free.

In my case the shore power electricity is included in my mooring fees so again no additional cost unlike gas

The item I linked to in post 18 is 'infinitely ' adjustable. Apparently it skips varying number of cycles in the 50Hz AC input, thus reducing power demand. I don't pretend to fully understand this explanation so I stand to be corrected.

 

[rogerthebodger]

The item I linked to in post 18 is 'infinitely ' adjustable. Apparently it skips varying number of cycles in the 50Hz AC input, thus reducing power demand. I don't pretend to fully understand this explanation so I stand to be corrected.

The one I posted chops a section out of each wave form and is quite old tech.

The one you have looks like it has some micro that will trigger the SCR to switch off after a variable number of cycles.


I have an instant gas water heater for use when I don't have shore power.

 

[lw395]

...



The item I linked to in post 18 is 'infinitely ' adjustable. Apparently it skips varying number of cycles in the 50Hz AC input, thus reducing power demand. I don't pretend to fully understand this explanation so I stand to be corrected.

If you click on the datasheet linked i nthe RS item, you will see mention of controlling the conduction phase angle from 30 to 160 degrees. It sounds very much like the Triac circuit as Roger suggested.
So, it delays switching on, on every half-cycle.
I do not know how the inverter in your generator would cope with that, but the peak current will be much the same at half power as it is at full power.
If you can remove the calorifer, adding a second fitting for a lower power element should not be expensive?

 

[[3889]]

If anyone's interested I fitted the device linked to in post #18 and it works perfectly.

 

[RJ1963]

In case others come across this thread, Bristoljim kindly pointed me in the direction of this which seems to do exactly what I want.
United Automation CSR2-10E Linear Voltage, Voltage Regulator 10A, 230 V 3-Pin | RS

I am looking at exactly the same challenge. Could I ask how you implemented the linear voltage regulator?

Thank you.

 

[RupertW]

I left the element as it is and put in a 240-110V portable transformer as used on UK building sites so rugged and cheap. That changes your element to 300W from 1200W. I also added a DPDT 10Amp rated switch to the element for 230, off, or 110 supply. I did a whole load of other gubbins so it all runs automatically off spare solar but that’s another story.

 

[RJ1963]

Thank you for the fast reply! A transformer, that's a heavy solution though I can understand why. Nice idea. Was certainly hoping to not have to change the immersion though I only have a 20l calorifier and am happy to wait for the water to warm up. It'll be a difficult job to change and yet I'd like to avoid the transformer. That adds weight I'd prefer my 34ft yacht not to have to carry. Thank you for the fast reply and I'll have a think. Why a 1Kw, in my case, immersion was installed to heat on 20l is something I can't quite fathom though probably a cheap option. There is now a gennie that will provide 1.2kw or 1.1kw constant that may just be the alternative and is no bigger than the 1kw that I have access to.

Thanks again!