Immersion heaters

[Roger Chapman]

Hi all. I am back for a brief visit and some advice so please don't try to wind me up. Last looked in before Xmas so I have just marked 79,000 headers as read without reading a single one. :-(

I am under the impression that back in the dim and distant past you could get immersion heaters where the load could be set at 1, 2 or 3 kw. A quick google has led me only to 3 kw nominal (well one was 2.7) heaters so do such animals still exist? If so where available or if not is there some sensible way of reducing the power consumption of a 3 kw immersion heater to the levels referred to above?

[Andy Burns]

Turn it on for 1/3 the time?

[Andrew Gabriel]

I do recall seeing a 1kW one about 40 years ago. You may find they're still used in situations with limited power, like on a boat. I also recall seeing switched power ratings but it was done by switching 2 immersion heaters.

Connecting two in series will get you 1/4 of the power.

I suppose you could connect a diode to half-wave rectify, which is half power, but you would need to mount it safely (could use the bottom of the cylinder as a heatsink with suitable insulation), and if you are doing this to limit current draw rather than power consumption, then you still have the full current draw every half cycle and the power factor will be less than 1.

[Roger Chapman]

Sorry if I did not make myself clear. What I want to do is limit the instantaneous power consumption.

[harry]

In days of yore, immersion heaters could have new elements fitted (or ones of any size). They are virtually all 3Kw now and disposable..

You can get electric elements for water heaters of various sizes. This is probably your best chance or some sort of electronic voltage control device.

Alternatively why not get two and connect them in series or use a three heat switch? They were used in days of yore on electric cookers. There were two elements that could be connected in series, parallel or just one element.

[Martin Brown]

Why? Usually if you need to use an immersion heater you want it on max. It still takes a while to heat up from cold even so.

Unless your wiring is not up to 3kW current requirements. I can't see why you want to do this. Two in series will get you one quarter power.

There are no obvious advantages of taking longer to heat up the cylinder full of water unless it is *exceptionally* badly insulated or you do not have sufficient mains power. There are vastly overpriced 1kW "solar" immersion heaters offered to cater for that latter scammarket (prices start at about 10x that of normal 3kW units).

[harry]

One advantage ie to tailor the immersion heater to the output of a Pv panel (ie not to imort electricity. There is apparently a device that does just this. I am checking it out now.

[harry]

Here it is.

[Roger Chapman]

To take advantage of 'free' electricity from PV panels without constantly monitoring cloud cover. Heating the DHW with bought in electricity is some 3 times as expensive heating with gas so it makes no sense to use an immersion heater unless there is a minimal chance of the imported electricity demand exceeding 1 kw for any length of time.

But as I only have one immersion heater boss that is a non starter.

I didn't come across any such 1 kw units during my search and I don't think £200 would be a cost effective solution. But that sum is much less than a wireless gizmo that purports to avoid importing electricity but retails ITRO £1500.

[harry]

How about this?

[Roger Chapman]

snip

Interesting!

Several different items on offer including low input immersion heaters. Not sure yet which is the right course of action.

[brass monkey]

Bung it onto a 3Kw dimmer.

[Archibald]

Thyristor power controller. You could get them for drills & similar, as most power tools have built in controllers look for a motor speed control. I bought a biggish one [20A] for about a tenner from Ebay.

Why waste energy? Providing your wiring is adequately rated you will loose more energy through the tank insulation during the extended warm up time than you will from the resistance change due to the higher current flow.

Have you looked into fishtank heaters BTW?

Or even fish on their own, they will heat up water over time, but a shower would probably involve a spreadsheet application relating to ant's eggs, local temperature and breeding. I believe kippers are noted for their tolerance to heat BTW.

HN

[Roger Chapman]

How much power would the dimmer dissipate if it was halving the output of the immersion? The link Harry gave includes a a power reducer that runs hot which I presume works on the same principle. Might work out as an expensive and possibly unwanted space heater if the values are significant.

[brass monkey]

At a guess maybe 10 watts.

[Roger Chapman]

That looks like the cheap option then. I assume it would cost substantially less than the £49 power reducer.

[Bill Wright]

If you read though all the messages under all 79,000 headers you'll find the answer to your question.

Bill

[Tim Watts]

Relatively little if it is a chopper dimmer (eg triac based).

[The Natural Philosopher]

My 400W dimmers get perceptibly warm. I'd say a watt or so at full chat

[John Rumm]

Well that covers both the suggestions I was about to make, so, what he said ;-)