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Old 12-04-2019, 10:09   #16
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Re: 12 volt heating element

You can also use heat from the engine to heat water when you are running it anyway
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Old 12-04-2019, 10:10   #17
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Re: 12 volt heating element

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You can also use heat from the engine to heat water when you are running it anyway
Most raw water cooled engines like the 3GM30 operate at a lower temperature than freshwater cooled ones and so aren't really suitable to add a heat exchanger.
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Old 12-04-2019, 11:11   #18
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Re: 12 volt heating element

80A a light load ROFL.

Especially for an extended period. We're not talking about using a whole big bank of panels and dedicated batteries just for the daily shower.

Yes a bigger boat's system PV/DC system **can** be designed to heat water.

This thread is about just adding a DC element to the tank in an existing setup, for the purpose of reducing ICE runtime.

The OP has rightly concluded it's just not **practical**, and that would be true 99+% of the time.
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Old 12-04-2019, 11:22   #19
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Re: 12 volt heating element

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Most raw water cooled engines like the 3GM30 operate at a lower temperature than freshwater cooled ones and so aren't really suitable to add a heat exchanger.
Running saltwater through the block is preferred?? I have to question this logic.
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Old 12-04-2019, 11:42   #20
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Re: 12 volt heating element

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80A a light load ROFL.

Especially for an extended period. We're not talking about using a whole big bank of panels and dedicated batteries just for the daily shower.

Yes a bigger boat's system PV/DC system **can** be designed to heat water.

This thread is about just adding a DC element to the tank in an existing setup, for the purpose of reducing ICE runtime.

The OP has rightly concluded it's just not **practical**, and that would be true 99+% of the time.
Light enough for a 675ah bank to run for 45 mins. I'm not saying do it, but it's simple enough. Maximum continuous discharge is usually rated around C/3 or if you want to be super cautious C/5. Most liveaboard cruisers I've met have banks ranging between 450ah and 900ah.

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Originally Posted by Shrew View Post
Running saltwater through the block is preferred?? I have to question this logic.
Where did you get preferred from? Engines like the Yanmar 3GM30 are raw water cooled. It runs up to 10c cooler than the 3GM30F that is freshwater cooled.
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Old 12-04-2019, 11:52   #21
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Re: 12 volt heating element

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Originally Posted by Scubaseas View Post
Google "300 Watt 12 Volt DC Submersible Water Heater Element"


But you need a huge battery bank or big power source. How much power depends on how much water and to what temperature. You need to look at amp/hours to BTUs.



Having said that I can get hot water from a wind generator if it's blowing 30 knots for a day or two. My set up has a shunt or dump to a water heating element and after the batteries are full all the energy goes to the water heater.
I've been thinking about the same thing- diverting excess wind-turbine power to the hot water heater instead of to the dump resistor bank. Do you have an automatic thermostat switch that diverts back to the dump resistor bank when the hot water is at temperature? I'd be very interested in the details of how you implemented this.
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Old 12-04-2019, 12:07   #22
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Re: 12 volt heating element

Yes **wind** power, where the excess loads must be dumped anyway would make this option more useful.

Also a eutectic holding plate fridge system.
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Old 12-04-2019, 12:46   #23
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12 volt heating element

To give an idea of how much power is required to heat water, it takes an hour of generator time for my water heater to heat water that is 80 ish to start with, that is 12 amps at 125 VAC, that is 1440 watts for one hour.
To generate heat by any means requires a tremendous amount of power, or said another way, heat contains a huge amount of power.
For example to stop an automobile you convert the huge amount of kinetic energy into heat, and yet the brakes dont melt.
To move heat like a heat pump does is much more energy efficient, much more, and yet our refrigerators are usually the big energy user.

Its why I get tickled when people start talking about cooking with electric power, sure you can, but it takes a large amount of power to do so, likely way more than a fridge.
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Old 12-04-2019, 16:11   #24
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Re: 12 volt heating element

In a nutshell, all the posts said before: "t is possible, but is it advisable?"
Davidhoy and later John61 added something like: "By all means do, if you have a wind generator". You then can divert surplus energy into a water heater, instead of heating up air with resistors.
Don't expect instant hot water. And how often does a boat have surplus power? Here are some links to such water heaters:
https://www.amazon.com/Watt-Submersi.../dp/B00KLKGJ1I
https://www.hurricanewindpower.com/d...ersion-heater/

Disclaimer..... when I have a chance I will get some of those elements, and install them as dump resistors for wind generators. However this job is very low on my priority list. It might take several years.... as I am able to get a hot shower after running the engine for 10-15 minutes. Actually I time my showers when I have another need to run the engine.

Last comment: there are some other options as well, like this:
https://www.ebay.com.au/i/264186031416?chn=ps
And there are many variants on such 'instant' hot water system.
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Old 12-04-2019, 16:59   #25
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Re: 12 volt heating element

Quote:
Originally Posted by Shrew View Post
Running saltwater through the block is preferred?? I have to question this logic.

I have to question your conclusion...


Apart from that, the topic was "12 V heating element".


As mentioned, at 12V you need lots of Amps to heat water and the OP already decided it's not a good idea for his boat.
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Old 12-04-2019, 17:07   #26
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Re: 12 volt heating element

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Originally Posted by HankOnthewater View Post

Last comment: there are some other options as well, like this:
https://www.ebay.com.au/i/264186031416?chn=ps
And there are many variants on such 'instant' hot water system.

That heater looks neat, however, looking at the specs, it takes 25A at 12V. A 300W element will take several hours to heat up this 10 l tank.
When I tested it with a similar 12V water heater, it took about 40 mins to heat just 2 l of water from 25C to 65C. That was in a small esky for my sous-vide tests.
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Old 13-04-2019, 06:04   #27
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Re: 12 volt heating element

I am considering the same (12 V additional water heater) but have som reasoning which has not been mentioned I think:

No doubt generally it is not a feasable solution to use 12V heating from various points of view.

But when I am on the hook for one night and want a shower in the morning, the water temp could be A BIT low.

Then I could run the engine but the engine would not produce hot water for a while until the thermostat opens - you must first run the engine hot before it makes your shower hot. A 12V x00 W heater driven by the battery which is simultaneously charged by the engine alternator will start heating immidiately and should be sufficient to increase the temp a few C-degrees/K which is the difference between "a bit low" and comfortable.

On my boat, I moved the safety (excess pressure) valve from the tank to the headrom for better accessability and drainage control. Thus I have one threaded connection available which can be used by for inst https://www.ebay.com/itm/Water-Heati...w/323236257400

I have no genset and only a minor inverter.
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Old 13-04-2019, 09:17   #28
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Re: 12 volt heating element

To answer the OP's question directly - yes we have a dual voltage water heating element. 120 / 12 volt; single unit with 2 elements, so only one hole in the water heater. We got it specifically to avoid putting in a heat shunt for the wind generator since we only had a small space left in which to install the shunt. We ordered it from eMarine systems:

https://www.emarineinc.com/

We got it about 2 years ago but I no longer see it on the site. The element has a reduced wattage for the 120 volt side

Quote:
Originally Posted by Davidhoy View Post
Has anyone ever used a 12VDC water heater element as a dump load for when you have excess amps? It would seem like a handy way to not let those amps go to waste. Assuming you have any excess amps, that is...
David - I have yet to see any noticeable increase in heat at the tap from the 12 v water heater. We have used the 120 volt side when we are on shore power, but since the element is smaller, that takes longer to heat the water than a "normal" 120 volt only element.

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Old 13-04-2019, 09:41   #29
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Re: 12 volt heating element

To calculate the wattage required to heat water in a tank:
Watts = 3.1 x Gallons x ΔT (in F) Heat-Up Time (in hrs)
Hence, to heat 6 gallons of water 45F (from 75 to 120F), in 1 hour:
Watts = (3.1 x 6 x 45) 1
= 837 Watts (≈ 67 Amps @ 12.5 Volts for 1 hour) (or 837 W/Hr)
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Old 13-04-2019, 09:55   #30
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Re: 12 volt heating element

If you already have propane on your boat, look into a propane fired tankless heater.
They're inexpensive, efficient, and take up little space. You do need a thru deck stack (chimney) for the exhaust.
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