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Power-User

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Overvolting 12v 300 Watt Immersion Element

04/28/2014 2:40 AM

I got this element here to use for boiling eggs and stuff using my solar panels and deep cycle battery. In my previous experiment where I was using bare nichrome to boil water, each end of the element went a different colour and brown stuff was beginning to appear in the water after a few hours of operation.

http://www.ebay.co.uk/itm/291113900125?var=590265209334&ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

The element is labelled as 12v 300 watts and the seller is selling a few different power ratings. It has a resistance of 0.48 ohms. If I was to run it directly from my solar panels which are capable of 40 amps in the height of summer, it would output around 600 watts. Would this be likely to damage it? The seller seems to think that the element will pull my 800w worth of panels down to 12v. They have a maximum power voltage of 17.9v and an open circuit voltage of 21v.

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#1

Re: Overvolting 12v 300 watt immersion element

04/28/2014 5:18 AM

Short answer:- Dunno.
Long answer:- the resistance of the heating element prob' goes up as it heats so a resistance measurement is futile (a petite star trek borg jokette reference).
Does the heater have a thermal cut out (many do to avoid the dry kettle thing) It could well be ok, but I'd suggest maybe the easiest way is to use an inverter to get yourself up to a 'standard' 240v.

Sorry if that's all a bit vague and unhelpful. Often with this sort of thing, you have to become your own expert.

Del

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#2

Re: Overvolting 12v 300 Watt Immersion Element

04/28/2014 10:48 AM

If it is rated for 600 watts at 24 volts and 300 watts at 12 volts, the rating can be thought of as 25 amps.

.

Exceeding 25 amps by a little bit occasionally probably won't make much difference. Exceeding 25 amps by a large about or regularly by a moderate amount might shorten the life, especially if any problems develop that limit heat transfer or compromise the integrity of the protection for the conductor.

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#7
In reply to #2

Re: Overvolting 12v 300 Watt Immersion Element

04/28/2014 6:18 PM

From his link, it looks like there are 4 models available with different voltage and wattage. His is 12v, 300W.

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#12
In reply to #7

Re: Overvolting 12v 300 Watt Immersion Element

04/29/2014 9:24 AM

That makes more sense.

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#3

Re: Overvolting 12v 300 Watt Immersion Element

04/28/2014 2:21 PM

Is this element fully immersed under the water? The typical application would have a threaded header on the side of your water 'pot', at the bottom, and the element would be horizontal. This is how it would be installed in a hot water heater. If any part of the heating element is exposed to air (not including the electric terminals), the internal temperature may climb to a level where the insulation (high temp electrical) is damaged, and the heating element may exceed maximum operating temperature, which typically results in a meltdown.

Relative to each end changing colour of the bare nichrome, there will be a current flow through the water and electrolysis will occur. This will result in some of the metal ions of the heating element being deposited in the water.

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#4

Re: Overvolting 12v 300 Watt Immersion Element

04/28/2014 3:07 PM

At 12 volts, your 300 watt heater draws 25 amps making the resistance 0.48 ohms (as you said).

In the summer, your photovoltaic array produces 40 amps and 600 watts. That works out to 15 volts. If the open circuit voltage is 21 volts, 40 amps drops 6 volts. Its internal resistance is 6/40 or .15 ohms.

If you draw a load line for the photovoltaic array and the heater, you get the graph below. The intersection point is at 16 volts. The power dissipated in your heater would be proportional to the square of the voltage or 533 W. So you will dissipate almost twice as much power as the heater was designed for.

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#5

Re: Overvolting 12v 300 Watt Immersion Element

04/28/2014 3:19 PM

This does not seem to be an efficient use of solar power....check out this video

https://www.youtube.com/watch?v=24TJCfJLzMI

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#8
In reply to #5

Re: Overvolting 12v 300 Watt Immersion Element

04/28/2014 7:15 PM

More efficient and a lot cheaper!

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#6

Re: Overvolting 12v 300 Watt Immersion Element

04/28/2014 3:40 PM

Get a second element and run it in parallel with the first during summer months. Problem solved, no extra load banks required and no wasted power which could be better used to heat the water.

In my previous experiment where I was using bare nichrome to boil water

I wouldn't recommend it, use a sealed element unless you want to make yourself sick.

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#9

Re: Overvolting 12v 300 Watt Immersion Element

04/29/2014 12:50 AM

Water cooled resistive load is all it is. Go for it. Just don't boil dry.

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Power-User

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#10
In reply to #9

Re: Overvolting 12v 300 Watt Immersion Element

04/29/2014 6:17 AM

That is what I was thinking. He is selling a 600w element the exact same shape and size so it should be fine if all goes well.

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Member

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#11

Re: Overvolting 12v 300 Watt Immersion Element

04/29/2014 6:25 AM

Over voltage is not ok as you will have doubled the wattage of the element (0.48 ohms @ 18V = 675W). And you will have doubled the "loading" on the internal resistance spiral inside the element and the loading on the elements surface. Scale and lime build up on the surface will increase drastically too, hindering the heat transfer from taking place and causing the element to fail, thats if the internal resistance spiral doesnt superheat itself first and blow through the elements sheath.

A resistance spiral (taking into account, wire size, coil OD and pitch etc etc) is normally designed to be as safe as possible or MSW (maximum safe wattage) to suit that medium to be heated. If its safe to run in air then its safe to run in water, but not the other way around mostly.

Under voltage is ok as 8V @ 0.48ohms = 133W, which probably wouldnt boil anything.

Your element will fail shortly is the short end of it. Rather have him or another element manufacturer make you the correct element for your voltage.

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#13

Re: Overvolting 12v 300 Watt Immersion Element

05/02/2014 6:00 PM

If you wish to cook eggs at night (it happens), then you will be drawing from your deep-cycle battery. What is its voltage? If 12V then draw from your battery day or night.

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#14
In reply to #13

Re: Overvolting 12v 300 Watt Immersion Element

05/02/2014 6:08 PM

The battery is 12v. I had the element running directly on the panels today and it was running at 600w so far without damage. I boiled some eggs with it.

Here's a video of it working but it was on the battery at that time.

https://www.youtube.com/watch?v=FMeBZ5QRxBM

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#15
In reply to #14

Re: Overvolting 12v 300 Watt Immersion Element

05/02/2014 7:21 PM

Hey that's great - until you're distracted by something and let it boil dry. 300 W or 600 W, either way it's going south except that, at 600 W, things could get interesting much faster.

Why not run it at its rated voltage? You're charging the battery (hopefully through a regulator) during the day, and you can run the element day or night off the battery, charging or not, so why not run it at spec? Running it straight off the panel does not make a helluva lot of sense quite honestly, not when you've got 12V available 24/7.

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#16
In reply to #15

Re: Overvolting 12v 300 Watt Immersion Element

05/05/2014 8:15 PM

There is no VGA button, so a GA will have to suffice.

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