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Old 20-08-2015, 20:51   #31
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Re: 12 volt hot water

Also discussed here and this company sells what you need to.
http://svhotwire.com/tag/diversion/

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Old 21-08-2015, 02:15   #32
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Re: 12 volt hot water

Or just let the solar charge the batteries and buy a marine 12 volt water heater.

25 amps for one hour will heat the tank.

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Old 21-08-2015, 04:59   #33
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Re: 12 volt hot water

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Originally Posted by EllisElectric View Post
We need to find the resistance of the element @ 120 volts because that's the actual rating. Take the actual wattage of 1500 and divide by the amperage squared will give us the resistance. The amperage is wattage (1500) divided by voltage (120) equals 12.5 amps. Now take the wattage (1500) and divide by amperage squared (12.5 X 12.5)=156.25. 1500 divided by 156.25 equals the resistance 9.6 ohms. Now take the 12 volts and square it to equal 144 and divide by resistance of 9.6 ohms to get the wattage 15 watts.
Exactly.
Wattage varies as the square of the voltage (or amperage).
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Old 21-08-2015, 05:27   #34
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Re: 12 volt hot water

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Originally Posted by mitiempo View Post
Or just let the solar charge the batteries and buy a marine 12 volt water heater.

25 amps for one hour will heat the tank.

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That would be awesome if it had the ability to utilize heat exchanger water to heat it as well, but I guess the point could be argued, you dont need the heat exchanger if the engine is running and producing amperage.
I like it has a built in overheat protection, and switch.

Found this also dual voltage heating element, but still need to buy a switch and turn it on and off,

https://www.emarineinc.com/Water-Hea...ement-12V-300W
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Old 21-08-2015, 09:03   #35
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Re: 12 volt hot water

We've got a Seaward S1800, where do I find a 500W or 600W 120v AC heating element? I don't want to mess with DC and having to buy huge cables to wire it up.
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Old 21-08-2015, 09:41   #36
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Re: 12 volt hot water

Is it possible to put a rheostat or something on the stock 120v 1500W element to lower it's power output? Or modify the 1500W unit some how?
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Old 21-08-2015, 09:58   #37
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Re: 12 volt hot water

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Originally Posted by GJori View Post
Just because I am an engineer....
When the 825 Watt is the listed power of your solar panel you should consider yourself lucky if you can get 30-40% of that. Similar to 35 Miles per gallon listed on your car sticker.
So lets say you are in Latitude 0 during the equinox, 12:00 AM on a crystal open sky day. Your solar panel is perfectly flat, aligned with the horizon and are no waves. You will be able to get 200-300 watt from that panel. Please deduct the efficiency of your resistance heater and the wiring transmission losses and you will get 50-100 Watt in the water. Now you have to deduct the heat losses on the tank insulation and the result will be similar to the temperature increase in New York when you lit a candle in Boston.
Please buy a "solar shower bag" and don't drop the soap.
This could not be farther from truth.
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Old 21-08-2015, 23:58   #38
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Re: 12 volt hot water

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Originally Posted by autumnbreeze27 View Post
Is it possible to put a rheostat or something on the stock 120v 1500W element to lower it's power output? Or modify the 1500W unit some how?
The problem with the 1500 watt 120v ac unit is on 12volt DC would only have an output in the range of 15 to 20 watts better to get a 12 voltdedicated element
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Old 22-08-2015, 14:42   #39
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Re: 12 volt hot water

So a replacement 1500W 120V heating element for my S1800 is under $30, but these 12v setups are $100... wth?

I checked mine, I didn't want to drain it and pull the heating element but it looks like it's a 1" NPT, right?

Looking at Grainger, it looks like I can get this 2000W 240V element for $20, which I could wire up to my 120v system and it would run at 500W/4.2A, so about 42 amps through the inverter?
http://www.grainger.com/product/GRAINGER-APPROVED-Water-Heater-Element-2E299?s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/2E756_AS01?$smthumb$
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Old 22-08-2015, 16:32   #40
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Re: 12 volt hot water

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Originally Posted by autumnbreeze27 View Post
So a replacement 1500W 120V heating element for my S1800 is under $30, but these 12v setups are $100... wth?

I checked mine, I didn't want to drain it and pull the heating element but it looks like it's a 1" NPT, right?

Looking at Grainger, it looks like I can get this 2000W 240V element for $20, which I could wire up to my 120v system and it would run at 500W/4.2A, so about 42 amps through the inverter?
http://www.grainger.com/product/GRAINGER-APPROVED-Water-Heater-Element-2E299?s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/2E756_AS01?$smthumb$
Don't know where you are looking but I found a 600 watt 12 volt unit for 1" npt for 16 bucks
http://www.ebay.com/itm/12-VOLT-DC-600-Watt-UL-Low-Voltage-Submersible-Water-Heater-12V-HD-dual-coil-/231483640875
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Old 23-08-2015, 15:23   #41
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Re: 12 volt hot water

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Originally Posted by monte View Post
I occasionally plug the water heater into the AC socket to heat it from the batteries/solar ( so does Nigel Calder )
1500W waterheater, 1600W inverter, chews about 50Ah
Me too, except it's hard wired.
On our previous boat, I made a home brew water heater panel.
It worked nicely with a differential controller, so we always had hot water.
Trouble was though, the panel was at the high spot of the loop so I installed a valve at the panel inlet because it had to be burped every few days.
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Old 23-08-2015, 16:51   #42
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Re: 12 volt hot water

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Originally Posted by newhaul View Post
Don't know where you are looking but I found a 600 watt 12 volt unit for 1" npt for 16 bucks
12 Volt DC 600 Watt Ul®™ Low Voltage Submersible Water Heater 12V HD Dual Coil | eBay
Thanks, that's a great find. I try to avoid ebay as much as possible after getting burned on some solar panel cables... which wouldn't have bothered me as much as they censored my feedback as well... if you can trust ebay or the feedback, there is really no reason to shop there.

I'm going to try the Grainger one, I'd prefer to heat the water with AC when we have shorepower. Our battery charger only does 30A.
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Old 23-08-2015, 17:14   #43
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Re: 12 volt hot water

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Originally Posted by svlamorocha View Post
Still, if you want to heat water in the sun nothing beats a black bag full of water exposed to the sun. The question is whether you want to also use the bag to shower naked in front of a Greek taverna as some Scandinavian cruisers do

We have a dedicated shower across from the forward head. It has a small hatch directly above. If I lay my sun shower on the deck above, I'm able to run the hose down the hatch to where it does its job without my having to expose myself to ultraviolet radiation. Please don't divulge this trick to the Scandinavians.

I've been known to use the inverter to make hot water, but it's a hassle to have to remember to turn it off after 15 minutes or risk running the house bank down. I'd love it if someone would design a water heater that had two elements, 110v for when I'm on shore power, 12v for when my house bank is fully charged and I've got nothing else to do with the power.
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Old 23-08-2015, 17:16   #44
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Re: 12 volt hot water

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Originally Posted by Bash View Post
We have a dedicated shower across from the forward head. It has a small hatch directly above. If I lay my sun shower on the deck above, I'm able to run the hose down the hatch to where it does its job without my having to expose myself to ultraviolet radiation. Please don't divulge this trick to the Scandinavians.

I've been known to use the inverter to make hot water, but it's a hassle to have to remember to turn it off after 15 minutes or risk running the house bank down. I'd love it if someone would design a water heater that had two elements, 110v for when I'm on shore power, 12v for when my house bank is fully charged and I've got nothing else to do with the power.
They make them, I think somebody already posted a link to it in this thread, the only downside is they're $100.
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Old 23-08-2015, 18:58   #45
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Re: 12 volt hot water

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.

Question...

With the dual (12v/120v) heater elements, how is the 12v turned off?

I fugure that with a 120v water heater, there is a thermostat switch to make sure you aren't creating a steam explosion. Adding a second heating element would then mean you have to add another thermostat, right?

Maybe I don't understand how they work.

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