How to reduce power to a heating device.

[davesparks]

So you said :
"Looking at products that could be used for the power control you are looking for I have found that they exist more commonly than I had expected."
Are you now saying you're not willing to point me in the direction of some of them so I can have a look and a think about possibilities?

A little later in that same post I told you could look at the infrared heater dimmers being sold for use in vivariums, stables etc

 

[DaveV72]

Reducing the voltage to 110V won't reduce the power to 1500W it will reduce it down to about 600W and the current will be around 6A.

In basic terms the resistance of the element will dictate the current which flows for the applied voltage, this then dictates the power which dissipates. Its a bit more complex than this due to things like the change of resistance due to temperature.


The easiest way to achieve what you want is to use a solar immersion heater controller which is designed for this exact task, such as the solar iboost.
These use a current sensor on the incoming supply to detect exactly how much power is being exported to the grid and then regulate the immersion heater until there is near zero power being exported or imported.
This basically operates like a 3kW dimmer switch which is electronically controlled.

This is what I have been trying to figure out. I'm worried that the iboost will draw power from the grid if the power required for a 3kw element isn't met. So if only 2kw of solar power is being produced, the immersion will draw 1kw from the grid. Or does the iboost prevent that? And will the element still heat up the water at a reduced rate/lower temperature?

 

[w0z]

A 4kW dimmer in series with the (a resistive) heating element (as, FOR EXAMPLE sold by a well known chinese website) would work with a resistive load, you could set the current to be a specific value (if you're able to measure it safely).
It's a cheap manual solution, apologies if I've missed the gist.

 

[bill01803]

11” / 279mm 1.5kW Solar Panel Immersion 09899SP - https://www.backer.co.uk/products/11-279-mm-1-5kw-solar-panel-immersion-09899sp

 

[haysdb]

OK, this is a weird one!
I have a grid tied PV system which exports spare power to the grid.
The maximum it will export is around 2.5kW
Now I want to use around 1.5kW, but I want to use it to heat a 3kW element.
So it will be a slow long heating rather than the full 3kW the element normally takes.
I can send the spare power I have to that element no problem, but at the moment because it is 3kW it takes all the spare power and makes up the difference from the grid.
I want this 3kW element to just take 1.5kW of power.
It's much like the 3 position switch on a slow cooker. Low, Medium and High. Somehow different amounts of power are being supplied to that same element.
What device would I need to achieve that?
Would it be a voltage regulator? if I took the voltage down to 110 x 13A that would be around 1.4kW
I can find voltage regulators on the net, but not ones that would supply 13A there seems to be a load of them that convert 240V to 110V but only 300W which is only around 2.75A
Where do I find a voltage converter that will allow a constant output of 110V @ 13A ???
Before anyone suggests it, obviously the sensible thing to do is to use a 1.5kW heating element!
But for what i want, the heating element is a fixed thing. that can't be changed. I just need to be able to feed 1.5kW to a 3kW element.
Any ideas?

This is an old thread but I'm trying to accomplish the same thing and I don't multi hundred dollar solution, i just need to reduce the power supplied to the water heater. Why wouldn't a voltage regulator work? $25 from AliExpress, rated for 10000 watts. 180v would reduce 3000 watts to 2000. bad boom bad bing, no?

 

[Simon47]

I would be wary of basic electronic choppers, since the chopped waveform could well confuse things. It is possible to build a chopper running at a high frequency and then filter it, actually quite common these days - but not a DIY job.
Assuming changing the heater isn't an option, then an auto-transformer would be my next suggestion - that would allow you to drop the voltage efficiently, potentially with multiple taps. Finding the right transformer at a sensible price could be tricky.