12 volt water heating ?

wizard

wizard

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Whilst watching the solar charger clicking on and off last weekend as the batteries charged and then off, then on again as the fridge needed more power I wondered if it was possible to heat the water in the calorifier using a 12v element rather than let the power being generated by the solar panels go to waste.

An amp or two for some period of time would certainly take the chill off the stored water and maybe over long periods using the wind generator as well might bring the temp up to shower levels of heat.

I just wondered wether anyone has pondered this idea or better still found an economical way of doing it.

Your thoughts gentlemen would be appreciated.
 
Given that 1 watt is equal to 1 Joule per second , that 4.1868 J is equal to 1 calorie and that 1cal will raise the temperature of 1 gram (call that 1 cc) of water by 1 degree C. if you estimate the volume of water you want to heat and pick a temperature to which you want to heat it you should be able to calculate how long it will take to heat the water to your required temperature, assuming no heat loss, if all the available power from the generator is used. If that is many hours then I'm afraid the actual heat loss will win and you will never get it warm enough but if it works out to a much shorter time then you are in with a chance. Better thermal insulation will help of course.
 
Thanks for the theory VicS that will make the calculations easier.

I was thinking of getting a 12v element from somewhere (yet to be found) and plumb it into the existing calorifier which is already insulated.

There used to be a heater element for cars years ago to put into the bottom hose leading to the radiator to both stop the water freezing and to warm up the water to make the engine start in the depths of winter. Some worked off the battery and some with mains transformers - but with modern cars all this sort of thing has become redundant.

Still I shall keep looking...
 
You used to be able to get little heater elements designed to pop into a teapot so you could brew up in your car. Probably withdrawn due to Health & Safety or some such b*ll*cks. Will try to post a link if I can remember where I saw them.
 
I have a 12V kettle for use underway. I only run it with the engine on. Takes about 20min to make water hot enough for not quite hot enough tea. Ditto electric filter coffee machine, although this is usually used when on shorepower.

Water has a specific heat of 4.2kJ/kg/K. To get 100cc of water to boil for 20deg is
4200 x 80 x 0.1 = 33.6kJ. In 1 second this would require 33.6kW (!), in 10 seconds 3.36kW (big domestic kettle) and in ten minutes 33600/600 = 56W. At 12V this would be 4.67A.

However, lets think losses. How efficient is your solar panel? How long are your cabkes between panel and heater element? What sort of heater element are you using? And what use is 100cc of warm water when SWMBO wants a shower?
:-)
 
and thats for 100cc. Multpiply by 45 to get whats required for a gallon and you are talking 400 or more amp hours. With a fairly typical good output from a set of solar panels of say 4 amps (convenient how all these numbers involve a 4 isnt it?) suggests you would need to run your solar panels continuously for 4 days. But of course there is night, when it cools down and the sun goes to bed.

What this boils down to (sorry!) is size. Yes it can be done but to do it in a sensible time scale requires an array of solar panels that wouldnt disgrace a cruise ship.

One of those med type black plastic shower bags is much more effective. There's a thought.
 
had toyed with the idea of plugging a solar panel into the existing 230v calorifier/immersion heater, the element will convert voltage of any type into heat, it is not voltage sensitive. but as others have said will the heat losses in the calorifier let the small amount of heat generated escape rather than raise the temperature of the water, the idea was to leave it attached whilst away from the boat during the week so that it took the chill off the water so that the engine could warm the calorifier up quicker. thats a thought as well i suppose it would be heating the block up as well. given that the 56 watter i have gives 2 - 3 amps per hour measured during the day what do the panel think?
 
No sorry Stu it is not going to work. The current flow will be so low that the heat produced will be negligible

To quantify that:

The power produced is proportional to the volts squared. Taking 240 volts rather than 230 in order to simplify the arithmetic, since 12 is 1/20th of 240 the power disipated will be a 1/20 squared when run at 12 volts which is 1/400th of the original rating of the heater.

You don't say what power the heater is but for the sake of this argument suppose it is 1kw then 1/400th of 1000watts is only 2.5 watts.

That is going to be no good at all.

If the element is 3kw then 1/400th is still only 7.5 watts. It might be enough for frost protection but not much more. If you get severe cold weather and little sun shine then you are not going get even that much heating just when you need it most.
 
So VicS if we throw a wind generator into the equation which generally produce a good few amps (when its blowing of course) is this going to produce a result worth testing experimentally?
 
No sorry. The calculations apply for any 12 volt source no matter how many amps or watts it could potentially supply.

Except, that is, for things so small that they could not even supply that amount of power anyway. For example my 5w soalr panel won't give me 7.5w of heating if I connected it to a 3kw mains voltage heater. 5 w is its maximum output under optimum conditions
 
have never drained it in 4 years of ownership, one side is antifreeze anyway! and have never had a prob.
 
Being delighted with the solar charging on my westerly , I wondered about connecting a solar panel,maybe 75 w, on my home roof to the bottom immerser on the hwcylinder ; can i do this as you suggested in 2006 to a 240v element ? Regards , James
 
[ QUOTE ]
I wondered about connecting a solar panel,maybe 75 w, on my home roof to the bottom immerser on the hwcylinder

[/ QUOTE ] If you mean connect a 12volT 75watt panel to a 240 volt heater you can do it but it won't achieve anything worthwhile.

One of the formulae for calculating watts is V²R where R is the resistance of the "load" and V of course is the volts applied to it.

That means that the power produced is proportional to the square of the volts . So if you connect 12 volts instead of 240, ie 1/20th, the power produced will be 1/20th squared ie 1/400th If you had therefore started with a 3000 watt immersion heater and connected it to 12volts instead of 240volts you will only get 3000/400 = 7.5watts of heating. Not a lot of good.
 
Sorry -- never having done physics (zoologists were treated thus in the bad old days ) do I take it that the 75 amps (?) from the panel don`t enter into the equation ? And is 7.5 watts of heating , over say a long scottish summer , insufficient to pre-warm my hot water cylinder ? J /forums/images/graemlins/confused.gif
 
[ QUOTE ]
Sorry -- never having done physics (zoologists were treated thus in the bad old days )

[/ QUOTE ] You cannot study every subject. Personally I did physics, chemistry and maths consequently I keep well away from matters biological although I did a spell in a Biology research lab and as result was the co-author of a report on the "Trial Eradication of Hydroids with Hypochlorite Solution" Pesky things soon recover and after a while those that you'd nearly killed have caught up with the control batch. Probably as a Zoologist you'd expect that!

However the point about connecting a 240 volt immersion heater to a 12 volt source is that the current will be very small. You can calculate that the resistance of a 3000 watt 240 volt heater element is 19.2 ohms
<span style="color:red"> And I have just spotted that I typed in the formula wrongly before. It should be W=V²/R </span>

If that is connected to 12 volts then the current that flows will only be 12/19.2 = 0.625 amps and the power produced will only be 7.5 watts (You get the same answer by using the W = V²/R 12²/19.2 = 7.5watts)

1 litre of water requires 1.16 watts to raise its temperature by 1° C in 1 hour so 7.5 watts will raise it by 7.5/1.16 = 6.47°C however that is for only 1 litre. Domestic hot water tanks vary in size but for a 100 litre tank that amounts to only about 0.065°C per hour. Insignificant I think. Even if it were left running for a prolonged period once the temperature rises by much the heat loss will take care of such a small input.

(Before anybody points it out the figures will not be quite right for a solar panel as with such a small load the terminal volts will be much higher than 12V. 18V, maybe a bit more but we would have to get some basic operating figures for the panel to predict exactly what. If you take 18 volts and rework the calculation you still only get about 0.15°C per hour for 100 litres and that's with the panel getting maximum light and a tank losing no heat.)
 
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