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Old 02-14-2019, 07:22 PM   #1
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12 volt hot water

I am installing much larger solar panels and expect to have XS power. I want to install a 12-volt heating element in my hot water heater and send the diversion load there. My question is what do you do about the thermostat on the hot water heater? Will it run on 12 volts?
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Old 02-14-2019, 07:47 PM   #2
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Use the 120 VAC element and run it through an inverter.

Ted
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Old 02-14-2019, 08:00 PM   #3
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[QUOTE=O C Diver;741151]Use the 120 VAC element and run it through an inverter.

Ted I am considering exactly what you say I was just trying to maximize the efficiency, knowing that the inverter uses some power
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Old 02-14-2019, 08:21 PM   #4
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Do a google search on 12v for water heaters in RVs. There's more and more overlap between RVs and boats these days. The consensus I got was it's a lot less trouble to just use AC. Especially if you're powering this with excess wattage.

If you really wanted to be efficient for hot water it's better to just use a loop of tubing through a solar water heating panel. Much better energy transfer straight from solar to the tank. But that's not likely practical on a boat.
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Old 02-14-2019, 08:23 PM   #5
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That'd take a lot of watts. How about this? Heliatos Solar
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Old 02-14-2019, 08:27 PM   #6
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Originally Posted by wkearney99 View Post
Do a google search on 12v for water heaters in RVs. There's more and more overlap between RVs and boats these days. The consensus I got was it's a lot less trouble to just use AC. Especially if you're powering this with excess wattage.

If you really wanted to be efficient for hot water it's better to just use a loop of tubing through a solar water heating panel. Much better energy transfer straight from solar to the tank. But that's not likely practical on a boat.
My buddy installed that system on his sailboat. He only has one water heating panel and it works well in the summer oh, but it's not quite enough in the winter time in South Florida. I think the installation of another water heating panel would be enough. on my boat routing the plumbing from the hardtop to the bilge would be problematic
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Old 02-14-2019, 08:29 PM   #7
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Do a google search on 12v for water heaters in RVs. There's more and more overlap between RVs and boats these days. The consensus I got was it's a lot less trouble to just use AC. Especially if you're powering this with excess wattage.

If you really wanted to be efficient for hot water it's better to just use a loop of tubing through a solar water heating panel. Much better energy transfer straight from solar to the tank. But that's not likely practical on a boat.
The biggest obstacle for running the hot water heater through the inverter, is you have to remember to turn it off and on. To just leave it on would certainly kill the batteries. in the early morning and the late afternoon
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Old 02-14-2019, 08:41 PM   #8
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http://mwands.com/store/adjustable-w...eating-element

12v, built in adjustable thermostat.
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Old 02-14-2019, 08:58 PM   #9
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[QUOTE=motion30;741157]
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Originally Posted by O C Diver View Post
Use the 120 VAC element and run it through an inverter.

Ted I am considering exactly what you say I was just trying to maximize the efficiency, knowing that the inverter uses some power
Wouldn't worry about the inverter penalty. If I were doing it, it would be through the inverter with either a mechanical or electrical timer. With some experience, think you could figure out how much stored power you could afford to convert to hot water and still recharge the bank. Then set the timer and walk away. I'm thinking a commercial grade spring driven timer should be able to handle the load.

I can envision a more sophisticated setup that is triggered by bank voltage, runs the water heater, draws the bank down to a set point, then waits for the bank to attain the high voltage set point to repeat the process. Thankfully, those complexities are beyond my engineering capabilities.

Ted
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Old 02-14-2019, 09:03 PM   #10
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Ted
you may be onto something there probably could turn the hot water heater off and on with current from the diversion load. There is only power on the diversion load when the batteries are in float
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Old 02-14-2019, 09:11 PM   #11
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Ted
you may be onto something there probably could turn the hot water heater off and on with current from the diversion load. There is only power on the diversion load when the batteries are in float
I have no idea what you're talking about, but I hope it works for you.

Ted
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Old 02-14-2019, 09:58 PM   #12
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Quote:
Originally Posted by motion30 View Post
I am installing much larger solar panels and expect to have XS power. I want to install a 12-volt heating element in my hot water heater and send the diversion load there. My question is what do you do about the thermostat on the hot water heater? Will it run on 12 volts?

Thermostat does not care if it's 12 / 120 or 240 Volts It's just a switch.
At 12 V and if you want to maintain the wattage of the element, the wire size will need to be substantially upgraded ( 10 X in my opinion ) Is it worth it ? Maybe run through an inverter as was said elsewhere, maybe install a timer in that heater circuit.



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Old 02-15-2019, 12:33 AM   #13
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You can buy a cheapo inverter from Harbor Freight, dedicated to your water heater. Do not wire it into the battery bank, just powered from solar. Then either switch it on manually as stated above, or a simple relay can be triggered by a signal from your charger when the batteries enter float. In float you only need minimal electric, then the bulk is absorbed by the water heater. Might be a fun project to play around with.

Also if you're thinking of replacing your water heater, and don't need an engine loop, then a small domestic unit from Home Depot is the cheapest solution.

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Old 02-15-2019, 02:52 AM   #14
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All good advice. Inverter best choice, but makobuilders has good idea also, but I question if it's really worth it.

How much excess energy do you have? and why? If you are are living on the boat, then you have a nighttime draw that must be replaced the next day. At what time, do your batteries enter float on any given day?
If you are not on the boat at night, why do you even need hot water all the time?

I'd be a little concerned that you are stepping over dollars to pick up nickles.
If you batteries are not kept fully charged, then you put them at risk to save what??
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Old 02-15-2019, 05:58 AM   #15
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Pacific Yacht Systems a leading authority on marine electric and electronics installations (and wiring redo’s) adamantly says that inverters used to create heat are a waste of power and a big NO NO, as also suggested in an earlier reply to the OP. There are a lot of good YouTube videos on the subject of marine wiring on this and many other wiring topics . . . Great rainy day “watch and learn”.
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Old 02-15-2019, 06:10 AM   #16
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" adamantly says that inverters used to create heat are a waste of power and a big NO NO"

For normal folks they probably are , and certainly not a system to build in and hope to live with,

BUT the poster claims a huge oversupply of power , very rare indeed , but why not?

Backwoods Solar has 12v and 24v DC water heating elements.
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Old 02-15-2019, 06:44 AM   #17
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Hook up your water heater element to 12v and measure the amp draw. With that number, decide from there.
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