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Old 15-05-2019, 03:46   #1
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Duel 240v 12v water heater element

Does any one know where I could get one?

The only thing google has turned up is a water heater for RVs with one built in from SureCal but they don't even list the element as a spare.

I have 1000w of solar and a 2kw inverter which I use to heat water when at anchor through the 240v element but obviously its much more efficient to have the spare power from the solar directly heat the water by 12v than have losses from inverter and draw on the batteries at 80A ...

So the best solution should be a dual element that I can run from shore power on 240 when needed (or if needed in a hurry through the inverter) but can run on 12v every afternoon once the batteries are full - normally that's by around midday so I am "wasting" 6 or 7 hours or power that could come from the 30A load of Morningstar MPPT in to a 300w 12v element
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Old 15-05-2019, 04:16   #2
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Re: Duel 240v 12v water heater element

http://mwands.com/store/9-3-8-inch-d...eating-element
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Old 15-05-2019, 04:25   #3
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Re: Duel 240v 12v water heater element

Thats just a 12v one - I am looking for one with both 240v AC and 12v DC as I said above
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Old 15-05-2019, 04:29   #4
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Re: Duel 240v 12v water heater element

Ive researched setting up dump load to my hot water heater. You can run 12V thru your 220V element and it will heat just not as much. Maybe test it out of tank to verify performance.

You just need to be careful how you wire it...dont want to introduce 220V into your 12V system! Also, you need to verify existing thermostat will work w 12V.
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Old 15-05-2019, 04:47   #5
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Re: Duel 240v 12v water heater element

Sorry, yes dual in multi-voltages but only up to 48V.

Looks like an inverter is the way to go.

But thousands of watts, and will still be slow, you really have that much DC excess energy available?
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Old 15-05-2019, 05:09   #6
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Re: Duel 240v 12v water heater element

We run a 1040 w of solar at around 38vdc - the MPPT coverts this in to enough to run a domestic 240v fridge, separate freezer, fans, computers etc and all the 12v dc boat loads and we wake up each morning to around 60% discharged batteries and they are full by midday in summer - we can make 200AH easily in that time; so yes, afternoons through to sundown is pretty much wasting another 200-300 AH of power and dumping all that in to a hot water system seems the most logical thing. A 300w 12v element will heat the 20L tank in around 3 hours to a nice shower temperature so theoretically we could get two tanks per afternoon out of power that now goes to waste in summer. However, in winter or if we are at the dockside with shore power I still want to use the 240v if I need to heat up quickly - so I either need to find a dual element or just accept the shorter life on my batteries by using my inverter in the afternoons on 240v (drawing 80A which just can't be good for the batteries every day)
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Old 15-05-2019, 05:14   #7
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Re: Duel 240v 12v water heater element

Running 12v through a 240V element will take something like 400 times longer to heat due the resistance in the 240v element - and cooling losses even in an insulated tank outweigh that so its not really possible to run the 12v load to a 240v element successfully
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Old 15-05-2019, 05:21   #8
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Re: Duel 240v 12v water heater element

Yes dual heating elements are available. The are widely used as “dump loads” for wind generators.

They replace the existing heating element. In a wide number of water heater models.

Here is one. They are cheap, too....
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Old 15-05-2019, 05:39   #9
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Re: Duel 240v 12v water heater element

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Originally Posted by billknny View Post
Yes dual heating elements are available. The are widely used as “dump loads” for wind generators.

They replace the existing heating element. In a wide number of water heater models.

Here is one. They are cheap, too....
Once again that is NOT a dual voltage element - it says quite clearly its a 12v only not a dual 12v and 240v

I appreciate people contributing but I have specifically stated what I am looking for a DUAL 240 VOLT AC and 12 VOLT DC element - that is a fitting that has two power inputs going to two separate elements on the same fitting - one AC one DC
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Old 15-05-2019, 05:42   #10
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Re: Duel 240v 12v water heater element

Quote:
Originally Posted by billknny View Post
Yes dual heating elements are available. The are widely used as “dump loads” for wind generators.

They replace the existing heating element. In a wide number of water heater models.

Here is one. They are cheap, too....
Ooop... my bad! That was 12v only element. Try svHotWire – Energy for Home, Boat, and RV for a dual voltage unit!

Although, you might find it better to use 12v only if you are going to the trouble of wiring 600 watts to the water heater. The dual voltage units usually have half wattage elements for each voltage.
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Old 15-05-2019, 06:57   #11
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Re: Duel 240v 12v water heater element

Quote:
Originally Posted by billknny View Post
Yes dual heating elements are available. The are widely used as “dump loads” for wind generators.

They replace the existing heating element. In a wide number of water heater models.

Here is one. They are cheap, too....
That one you linked is listed as a DC, ie 12v 600w. I cant see any AC ie 110 or 220V listed. Maybe I missed it?

Im pretty sure the OP is asking for both an AC AND DC capable element. So he can run it at the dock or as a Solar DC dump depending on where he is.

I suspect most of those advertised DC water heater elements are in fact really just regular AC elements being 'passed off' as DC elments to try and capture the demand for DC elements from off grid a d RVers etc.

In fact if you have a look at a physical example many have the manufactures AC rating still in the plastic insulated base. Some of the more 'sophistcated' vendors try and smudge this out with a soldering iron. Very few are actually designed as DC. The one John linked is actually manufactured as DC.

As said by others a resistive load like a heating element doesnt care if it is AC or DC. But as others have said it gets down to trying to get a useful power at different voltages by finding a suitable resistance.
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Old 15-05-2019, 07:30   #12
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Re: Duel 240v 12v water heater element

Get a unit with room to fit two separate elements.
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Old 15-05-2019, 08:58   #13
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Re: Duel 240v 12v water heater element

If you have enough surplas solar to be able to heat water why are you worries about loosing a few % in the inverter, should be running around 96 - 98% efficiency under those loads. It is quite likely that even if you can get a duel ellement you will loose more power in the wiring than you would in the inverter, high load DC transmission is pretty inefficient even over short distances.
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Old 15-05-2019, 09:17   #14
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Re: Duel 240v 12v water heater element

Strictly speaking, a "dual" 12V / 240V element isn't really possible. A water heater element is just a loop of metal with some resistance, and you run current through it to heat the water. Such a device will behave dramatically differently with 12V vs 240V. One designed for 240V will hardly get warm with only 12V, and one designed for 12V will draw so much current at 240V it'll either explode or pop a breaker.

This doesn't mean you can't find what you are looking for. Who knows, someone might make a single gizmo that is, internally, composed of two separate elements: one designed to produce a useful amount of heat at 240V, and another designed with much lower resistance to produce a useful amount of heat at 12V. Finding such a gizmo that is appropriate wattage for the size of your tank might be difficult, though, since demand for such a gizmo is almost nonexistent.

I think it would be a lot easier to just have two completely separate, standard, ubiquitous, readily available everywhere, 12V and 240V heating elements in your water heater.
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Old 15-05-2019, 11:29   #15
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Re: Duel 240v 12v water heater element

What I was looking for was a single fitting that has one 12v element and one 240v element - not one element for both as that won't as you say work. I thought if you can get a dual element in 12v or 240 v (which you can to to get more power in short elements ) then surely you could get one with two separate voltage elements and wiring - it seems not

I can continue to use the inverter but that requires manual intervention - turning it on when batteries are full and off before it uses too much power and of course it will reduce battery life with regular high amp discharges...
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