DC water heater element?

GLC

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Has anyone tried these? Just wondering if they actually work. I was wondering what to do with extra energy from the panels I have.

 

GLC

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Thank you, I had heard that you could only use DC elements. Do have any specifics with a thermostat that you could suggest?
 

snoobler

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Excess power into a water heater is a "maybe one day" thing for me. No experience with it. You need some kind of alternate means of control if you're using it for "excess", i.e., you only want it to come on when your battery is in float and your panels can produce enough to store it.

A simple thermostat would allow it to come on whenever the thermostat says so.
 

GLC

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Excess power into a water heater is a "maybe one day" thing for me. No experience with it. You need some kind of alternate means of control if you're using it for "excess", i.e., you only want it to come on when your battery is in float and your panels can produce enough to store it.

A simple thermostat would allow it to come on whenever the thermostat says so.

Thank you, I was looking at my MPPT controller and it can be programmed on the load side to turn off and on within certain perimeters but i may just use other panels to to drive the hot water heating production.
 

snoobler

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The current ratings of your charge controller load terminals may prove to be too limited to be able to run a significant heating element.
 

tazmann

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I have been experimenting with them took a 6 gallon aluminum rv hot water tank and welded in a 1-1/4" coupling and installed a 150 watt 12 volt element. Took about 5 hours to get hot, cant tell you temp but hot enough to burn hand, It pulled about 12 amps, tried a 300 watt and it took 2-1/2 hours and pulled 24 amps so I would say they work good just have to size them for what you want. I cant remember the spec at the moment but there is a formula for how many watts to raise the temp of 1 gallon 1 degree
 

snoobler

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Converting for Gallons/°F:

kWh = (4.2 * 0.264 G * (32+9/5*T) / 3600

Once you have the total energy required, kWh, you can compute the # of hours it takes for a given wattage.

This all assumes perfect insulation.

kWh = (4.2 * 0.264 * 6 * (32+9/5 * 50)/3600 = 0.205kWh

So 205W would raise 6 gallons of water 50°F in 1 hour.

50°F assumes starting at 75°F and ending at 125°F - typical water heater temp.

My RV water heater element is 1400W IIRC, so...

4.2 * .264 * 10 * (32 + 9/5 * 50) /3600 = .376kWh

.376/1.4kW = .27 hours or 16 minutes. It tends to take about 35 minutes, so there's definitely some inefficiencies in there.
 

gnubie

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Pt = ( 4.2 x litres x differential C ) / 3600

6 US gallons is about 22 litres.
Raising heat from 75F to 125F is close enough to a differential of 28C to call it that

4.2 * 22 * 28 / 3600 = 0.72kWh. At a rate of 205W it would take 3.5 hours to do it.
 

gnubie

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In this house Lisa Snoobler, we obey the laws of thermodynamics!
 

tazmann

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Yep lots of variables . 2.4 watts to raise 1 gallon 1 degree +or- a little so my 150 watt element would raise 1 gallon 62 degrees in an hour and that is pretty close to what I got with bare aluminum tank sitting outside. I am using the rv tank because it has air gap in the top for thermal expansion so I dont have to add a expansion tank. Following the kiss rule
 

GLC

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Well, I ordered one a week ago. Should be here in a another week. Snoobler is correct, it will not work off of of my controller. Will try wiring direct to PV on a couple of panels on the ground to test it out and see what happens.
 

efficientPV

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Just what did you order? I don't know why, but nobody selling "DC" heater elements will tell you the resistance of them. I have to assume they are multiples of 14.5V. A fixed resistance has to be matched to the array and even then it is only for current calculated. Just 70% of rated amperage is a dramatic power loss. Expect only marginal performance without a heater controller that keeps the panel near power point. Just buying a random heater element is like buying any tire and hoping it will fit your car.
 

GLC

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24 volt - 400 watt adjustable heating element. Think of this as one of Will's "experiments". May work and may not. Will not know till I try. For me and my wife we use a little over 5kW daily just on hot water heating and that is just for two of us. Over 60% of our electricity is consumed by Oven, AC, Heating, Dryer and Hot Water Heating. One way or the other I will find ways to cut that 60% down to a manageable level.
 
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