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post #21 of 66 Old 11-27-2017
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Re: Solar heating element for water heater

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If the batteries are frequently topped, the idea of a heat sink into the hot water heater is a great idea. Of course, that requires a smart controller too. The real trick is how could you have both the 110v element and the 12v. I think the best the 12v is going to do is get you a good start.
Why would you need two elements? They are both just resistors, granted when running on dc you would produce less heat as the power of the element puts out would be reduced by 64 for a 120v element being heated by a 12 v, only by 16 if using a 24 v dc system. One would only need to isolate the two voltage sources via a relay or an isolation circuit.


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post #22 of 66 Old 11-27-2017
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Re: Solar heating element for water heater

Dual elements allows for more efficient elements for each, as well as simpler wiring - you keep your present AC wiring on one element, and just add the DC wires to the other element (no internal brains required). But they are pretty pricey. Relaying or otherwise isolating 120VAC to/from 12VDC on the same end point seems like a recipe for future disaster to me.

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post #23 of 66 Old 11-27-2017
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Re: Solar heating element for water heater

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Hopefully the OP is in a tropical cruising location.
San Francisco Bay - cold even during the warm months.

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post #24 of 66 Old 11-27-2017
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Re: Solar heating element for water heater

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Originally Posted by colemj View Post
Dual elements allows for more efficient elements for each, as well as simpler wiring - you keep your present AC wiring on one element, and just add the DC wires to the other element (no internal brains required). But they are pretty pricey. Relaying or otherwise isolating 120VAC to/from 12VDC on the same end point seems like a recipe for future disaster to me.
Intuitively, I would agree. But, how do you attach two elements to the same water heater?


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post #25 of 66 Old 11-27-2017
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Re: Solar heating element for water heater

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Intuitively, I would agree. But, how do you attach two elements to the same water heater?
The same way they attach one. Two feed throughs instead of one on a big plug with standard threads. https://www.emarineinc.com/Water-Hea...ement-12V-300W

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post #26 of 66 Old 11-27-2017
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Re: Solar heating element for water heater

How about a short length of 3"? copper pipe, vertical and outside of main hot tank. DC element is in top cap and plumbed both ends to high and low on hot tank. Run dc wire thru thermostat strapped on.Insulate but red buttons on thermostats should be accessible. Anybody with a wood stove hot water can tell you why.
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Re: Solar heating element for water heater

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Originally Posted by colemj View Post
The same way they attach one. Two feed throughs instead of one on a big plug with standard threads. https://www.emarineinc.com/Water-Hea...ement-12V-300W

Mark
Assuming the AC and DC are fully isolated, I like it!!


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post #28 of 66 Old 11-27-2017
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Re: Solar heating element for water heater

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Assuming the AC and DC are fully isolated, I like it!!
Yep, totally and completely. Two different elements and wiring. All insulated and isolated from each other in a single screw in fitting.

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Re: Solar heating element for water heater

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San Francisco Bay - cold even during the warm months.Mark
I think it highly unlikely that the OP, if in Frisco, would have a large enough surplus of solar power to raise the water temperature in a 6 gallon water tank even a few degrees, on all but a few days a year. He'd have to have a monster array.
I don't know the exact figures, but even down here in the tropics with a fixed and relatively unshaded installation, I doubt that we average 60% efficiency over the daylight hours.
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post #30 of 66 Old 11-27-2017
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Re: Solar heating element for water heater

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Originally Posted by colemj View Post
Dual elements allows for more efficient elements for each, as well as simpler wiring - you keep your present AC wiring on one element and just add the DC wires to the other element (no internal brains required). But they are pretty pricey. Relaying or otherwise isolating 120VAC to/from 12VDC on the same end point seems like a recipe for future disaster to me.

Mark
How is it dicey? Multi-source battery chargers do the exact same thing, take voltage from multiple sources and route them to your battery for charging. The only issue is that you must size the relay to handle the AC voltage and Current for the water heater as that side will normally be the one with the most wattage running through it. Relays of this type using 12v to excite them and latch them are common. This would keep the two voltages isolated as only one at a time would be connected to the water heater. In other words, one would be heating the water by AC or DC and never both as the relay would only route one voltage to the water heater at a time.


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