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Glad I found Sailnet
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Discussion Starter #1
All summer long we don't hook to shore power. It would be nice to have even warm water for showering. And we have 540 watts of solar power, more than we need, actually.

Does anyone know if Raritan hot water heaters can be powered by 12v instead?

After doing some measuring, it looks like the 1100 watt heating element is a 13 ohm resistor. I could invert 12v to 120v AC and then step down 2:1 to 65 volts AC to drive the heating element at 277 watts. But solar panels can drive even low resistance loads, so it would be much simpler to go direct from panel to heater (or charge controller dump load to heater).

How about it, anyone know if there's a limitation that precludes this?

Regards,
Brad
 

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islander bahama 24
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It would work on direct 12v however I would think rather poorly just like the old travel mate coffee pot I had in a truck had an adapter that the 120ac cord plugged into and went direct to he old CIG lighter it worked but rather poorly the may answer your questions better and provide an alternate that would work better 6 Inch 12 Volt DC Submersible Water Heater Element
 

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Master Mariner
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There are 12 volt water heater elements made specifically as dump loads for windgens which might serve your needs. A quick search should find you the info.
 

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Mermaid Hunter
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Brad, someone posted a conversion formula for 120<>12v resistive heating loads, either here on on a certain other forum, a week or three ago. Basically, it is NOT just a matter of driving loads and resistance, the heating element wants to see a certain wattage and if you drop the voltage, you've really got to up the amps in order to still get heat out of the heating element.

In practical terms, you either want to apply the rate 120V or ideally, find a 12V heating element for it. There may be one, targeted for the RV market, that bolts right up. Raritan might know. If not, you might be able to have an adapter threaded up to make one fit.
 

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One of None
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build a solar water plate to heat the H20 should be easy enough :) Or just route black tubing in a loop. but fill it to the top, it should move via gravity/temp difference. It won't "Flow" if there is air in the plate or tubing.
 

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Was going to express my concept but thought ,'no ,they wouldn't be interested' But Denise is on a similar tract. My plan is to bypass the hot shower water up thru the deckhead into a black solar tank on deck. Tank heats and overflows back to shower head mixing with cold for optimum temp control. This assumes a pressure water system and a desire to wash.
 

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islander bahama 24
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1,842 Posts
Brad, someone posted a conversion formula for 120<>12v resistive heating loads, either here on on a certain other forum, a week or three ago. Basically, it is NOT just a matter of driving loads and resistance, the heating element wants to see a certain wattage and if you drop the voltage, you've really got to up the amps in order to still get heat out of the heating element.

In practical terms, you either want to apply the rate 120V or ideally, find a 12V heating element for it. There may be one, targeted for the RV market, that bolts right up. Raritan might know. If not, you might be able to have an adapter threaded up to make one fit.
Here is a dedicated direct replacement 12 v heating element that meets all of Brad's requirements and a lot cheaper han a new heater 6 Inch 12 Volt DC Submersible Water Heater Element
 

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I use an tankless propane heater. They're common for RVs and easy to install. Going from DC to AC etc etc seems to have a lot of complexity and efficiency loss. Takes a lot of watts to make heat.
 

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Isn't your diesel cooling loop routed through your hot water tank? Every boat I've chartered has this feature, and running your motor for awhile would give you hot water for a few hours.
 

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Closet Powerboater
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I use an tankless propane heater. They're common for RVs and easy to install. Going from DC to AC etc etc seems to have a lot of complexity and efficiency loss. Takes a lot of watts to make heat.
Be aware that if it's mounted below, it's not ABYC compliant and your surveyor will have a seizure when he/she sees it. Basically it's a big carbon monoxide risk. Propane, when completely combusted in the presence of oxygen (as in your galley stove) doesn't produce any CO, but the instant hot water heaters produce tonnes of the stuff because they are forced to heat too much, too fast, and don't combust the propane with enough O2.

Personally, I think they're safe enough, but bottom line, be aware of the risks, make your own risk assessment, and at least have a working CO monitor nearby.

MedSailor
 

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Glad I found Sailnet
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Discussion Starter #14
Isn't your diesel cooling loop routed through your hot water tank? Every boat I've chartered has this feature, and running your motor for awhile would give you hot water for a few hours.
We have this, but we don't run the engine that much.

Went for a nice sail on Saturday. Ran the engine just to nudge the boat upwind a few yards, so the electric anchor windlass wasn't pulling the boat forward. And then later ran the engine when the channel was into wind.

Regards,
Brad
 

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How about a dedicated solar water heater panel. I've seen a couple examples made commercially for boaters. Permanent system that taps into the hot water tank to keep it warm without shore power or 12v heating elements.
 

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That would need a 12 volt circulating pump to bring the solar heated water back down to the tank.and a system of valves to keep it from losing heat back. A flat ,black tank on deck can hold heated water a while and overflow back to sink or shower when refilled with cold water.
 
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