Duel 240v 12v water heater element

[mako]

OP you’re going to waste a lot of money buying specialty elements which are mediocre in performance, or a specialty water heater.

You’ll lose about 12% in the inverter. Big deal. Just stick with something that works well.

[motion30]

I am heating water through my inverter.. I changed the heating element to a 1000 watt 110 volt unit. it consumes 85 amps through the inverter which my solar panels can easily carry. The thermostat on a hot water heater turns it off after approximately an hour

[motion30]

a friend told me about a setup where he installed a 1-inch tee with two lengths of pipe to accommodate two different hot water heater elements in this hot water heater

[swampbush]

The Australian Duoetto 10litre hot water has 12 and 240v. They list a replacement element here. https://ausj.com.au/product/duoetto-...ement-12-240v/
I will probably buy ine of these hot water systems when i need to replace mine. I use the inverter to heat mine now. You can also order lower power elements. 600 to 750 watts is fine and easier on the batteries than the standard 1500w element. Inverter losses are small compared to the load.

[Capt. Ray]

The OP is obviously looking for a heater that has two separate elements, one for 12v and one for house AC. I agree in this application it is more logical to use an inverter and have a simple AC heater element.

Originally Posted by SwellGuy

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.

[smac999]

if your inverter is on anyways (for other things) there is really no loss. the main loss is simply having it turned on. generally a few amps.

if you normally shut the inverter off. and the HWT is the only thing you need to power, then you' have some gain by going to a 12v one.

but there is no loss from the batteries weather its coming direct from solar or via inverter while solar charges the batteries.

[john61ct]

As long as the total loads are less than what the panels are producing at that time

[Pete7]

Interesting video on using 12v to heat water:

https://www.youtube.com/watch?v=x3iCnkNTy-I

[mako]

So is a 12VDC water heater/element that much cheaper and more reliable and efficient than a $40 Harbor Freight MSW inverter driving a "normal" water heater? Obviously not.

I think this aversion to 120VAC is sorta like the aversion towards having any electricity onboard, back in the 70's.

[leftbrainstuff]

We heat our hot water using our inverter when we have all three 350W solar panels deployed.

We switched from a 1300W 110V element drawing over 10A to a 240V 2400W element which has 600W of heating power on 110V. This equates to around 6A draw.

On solar and our house batteries we see around 70A draw for heating hot water. Our 1050W solar panels just exceed this demand in full sun. As it only takes 1- 2 hours to fully heat our 6 gallon hot water this works well in full sun.

The above is much less complicated than trying to heat hot water with multiple voltages.

Interestingly our clean 2400W element (600W on 110V) is almost as quick to heat than our old crusty 1300W element.

FWIW my $0.02 is that 12V hot water heating, dump loads for wind generators and other low voltage hot water heating options are not worth trying. The calculations validate that argument and availability of low voltage heating elements is sporadic.

Solar is cheap, inverters now work well and solar mppt controllers are able to respond and optimize power generation really well. BTW avoid PWM solar controllers they lose nearly half your generating capacity. As measured by me on our earlier configuration. Avoid all household solar advice as this sector peddles cheap PWM kit.

We use a separate victron mppt for each panel, we have a 400Ahr carbon foam battery bank and oversized high amp cable a on the 12V side. All panels can operate independently, are redundant and we use all our existing DC and AC infrastructure.

Hot water from solar always brings a smile. Even if its not full sun our 400Ahr carbon foam bank can heat the hot water. These batteries don't suffer from low state of charge empirically seem much more stable than FLA or AGM. We also avoid the ridiculous costs of lithium systems which all fail the cost benefit analysis.

[leftbrainstuff]

Originally Posted by leftbrainstuff

We heat our hot water using our inverter when we have all three 350W solar panels deployed.

We switched from a 1300W 110V element drawing over 10A to a 240V 2400W element which has 600W of heating power on 110V. This equates to around 6A draw.

On solar and our house batteries we see around 70A draw for heating hot water. Our 1050W solar panels just exceed this demand in full sun. As it only takes 1- 2 hours to fully heat our 6 gallon hot water this works well in full sun.

The above is much less complicated than trying to heat hot water with multiple voltages.

Interestingly our clean 2400W element (600W on 110V) is almost as quick to heat than our old crusty 1300W element.

FWIW my $0.02 is that 12V hot water heating, dump loads for wind generators and other low voltage hot water heating options are not worth trying. The calculations validate that argument and availability of low voltage heating elements is sporadic.

Solar is cheap, inverters now work well and solar mppt controllers are able to respond and optimize power generation really well. BTW avoid PWM solar controllers they lose nearly half your generating capacity. As measured by me on our earlier configuration. Avoid all household solar advice as this sector peddles cheap PWM kit.

We use a separate victron mppt for each panel, we have a 400Ahr carbon foam battery bank and oversized high amp cable a on the 12V side. All panels can operate independently, are redundant and we use all our existing DC and AC infrastructure.

Hot water from solar always brings a smile. Even if its not full sun our 400Ahr carbon foam bank can heat the hot water. These batteries don't suffer from low state of charge empirically seem much more stable than FLA or AGM. We also avoid the ridiculous costs of lithium systems which all fail the cost benefit analysis.

Here's the engineering math for those with propellor hats


P=VI gives us power available to heat water
V=IR gives us ohms law and R of the element remains fixed
P=I^2R from P=VI and substitute V for Ohms law IR. It’s the I^2 that sees the quadruple drop in power when we halve voltage
For 240V let’s determine the fixed resistance of our 240V 2400W heating element
2400=240I therefore I=10A on 240V
Now calculate resistance of our 240V 2400W heating element. Using Ohms laws V=IR and substituting I=10A calculate R = 240/10 = 24ohms which is the fixed resistance of our element
Now lowering voltage to 110V from 240V and R stays same calculate I and then P
I=V/R therefore I = 110/24 = 4.58A and P = VI therefore P=110*4.58 and P = 504W is a little less than a quarter of the heating power available by using a lower voltage.
I couldn’t find 110V low wattage < 750W heating elements and so I used a readily available higher voltage heating element.

[motion30]

Leftbrainstuff
I was unable to find anything smaller than 1000 Watts for 110 volt heating element. but a 220 volt element can be used with 110 volt power. of course with a corresponding decrease in heating ability. a 4000 watt 220v heating element. Run on 110volt uses about the same power as a thousand watt 110 volt element

[mako]

Mr. Leftbrainguy, do you run 3 separate MPPTs just to reduce shading influences?

[leftbrainstuff]

Originally Posted by makobuilders

Mr. Leftbrainguy, do you run 3 separate MPPTs just to reduce shading influences?

We have 3 x 350W panels that are stacked. The top panel is always visible to the sun.


At anchor or in calm conditions we can deploy the other two panels. One slides forward of the top panel and one slides backward. We can have 350, 700 or 1050W generating. Deployment is currently a manual process that takes about a minute per panel. The intention is to have the panels deploy or stow based on sunrise, sunset and wind or roll / pitch / yaw.



Each panel has it's own mppt controller. This gives us redundancy as well. The real time data for each controller is visible in an app and we see that the panels are performing at the upper end of their published performance. We can also see that we have plenty of spare capacity, based on the amount of time the controllers are in float mode. Having extra solar capacity is key on a sailboat. Don't scrimp.


We don't have any appreciable shading because our panels sit atop our arch and our back stays terminate forward of the arch. We have a Liberty 458. Cutter rigged sloop that just happens to be ideal for solar on the arch.



Our antennas and numerous GPS sensors, weather station, etc are located each side of our top fixed solar panel. They do shade the panels but this impact is barely noticeable as the controllers respond very quickly.



We use commodity monocrystalline panels with the highest efficiency we can find. The Victron MPPT controllers easily double useful power double that of our old PWM controllers in real world conditions.


This is successful primarily due to the MPPT controllers. Our carbon foam batteries also are much more consistent in accepting charge. This is empirical but I suspect they alone are 10 - 15% more efficient at accepting charge than FLA or other AGM types.