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Old 23-08-2015, 19:19   #46
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Re: 12 volt hot water

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Originally Posted by bene505 View Post
I measured the draw of our water heater while on shore power at 240 watts. Then did some calculations and fugure a small inverter then 2:1 step down transformer would mean 60watts for a 5 amp draw at 12 volts -- actually 6 or 7 amps with inefficiencies. Our 540 watt array would handle that no problem.
240 watts seems a bit small. The water heaters that I am familiar with (Quick) have elements that range from 500W to 1200W.

Your calculations are unclear. If the element was rated at 240 watts at 240 volts then if you connect it to 120 volts the draw will fall to 60 watts, but that will not be good enough to heat water for a shower.
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Old 23-08-2015, 21:03   #47
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Re: 12 volt hot water

The thermostat is built into the element head
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Old 23-08-2015, 21:05   #48
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Re: 12 volt hot water

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Originally Posted by svlamorocha View Post
240 watts seems a bit small. The water heaters that I am familiar with (Quick) have elements that range from 500W to 1200W.

Your calculations are unclear. If the element was rated at 240 watts at 240 volts then if you connect it to 120 volts the draw will fall to 60 watts, but that will not be good enough to heat water for a shower.
I would assume that brad meant 240 volt not 240 watt on the heating element.
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Old 05-10-2015, 20:22   #49
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Re: 12 volt hot water

Just an update, we replaced our seaward 18 gal unit's OEM heating element (1800W 120V) with a grainger (2000W 240V) which I calculated should run around 500W 120V. About a week into service and my seaward tank failed with major leaks. It's an old unit and they self destruct when they get old, so it's hard to say if it's related, but I went with an Isotherm to replace it. Only 750W so I'm happy with that current draw. Seems like a much better designed unit.
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Old 05-10-2015, 21:27   #50
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Re: 12 volt hot water

Thanks for the update keep us informed how it goes
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