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diy solar

Running 240V water heater on 120V?

Ok thanks. I would have seven 12ga wires since it's a 20A circuit. Don't know if I could use a single gang box for those and the switch. I'll check out your links.
I'd use a double if for no other reason than to make my life easier.
 
How will load dump work if the water is hot? Need two thermostat settings.

May need a separate pre heat water heater to be left cold and only power with 120v. Existing can stay at 240. Space could be an issue.
 
Here is maybe a better idea:

Leave your current water heater alone - that way your wife always has hot showers.

Add a second water heater in front on your water heater and this one runs off the solar dump load. It will always be cold water - and will heat the water up before going into your regular water heater.

Then you only need to program your dump load to turn on/off automatically - and you don’t forget to turn it off.

Good luck
 
Here is maybe a better idea:

Leave your current water heater alone - that way your wife always has hot showers.

Add a second water heater in front on your water heater and this one runs off the solar dump load. It will always be cold water - and will heat the water up before going into your regular water heater.

Then you only need to program your dump load to turn on/off automatically - and you don’t forget to turn it off.

Good luck
Sounds like a good idea. But. We live in a single wide, and the water tank is behind an enclosure inside a closet. So there's nowhere to put another tank.

This switch over would only happen during the day if there's to going to be lots of sun. So the rest of the time, the grid would run it. We use hot water for showers at the end of the day, and maybe washing some dishes in the evening. Don't use the dishwasher hardly ever. And we run our washing machine usually on warm for most loads, unless it's whites so we'd need hot water. In other words we don't use a lot of hot water.

So I'm guessing we'd have enough hot water stored when it gets switched over to the inverter. Will it save any money? In the long run, maybe? But, it would be nice to have the switch available for the rare occasion when we have extended grid outages so we'd have some way to heat the water.
 
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How will load dump work if the water is hot? Need two thermostat settings.

May need a separate pre heat water heater to be left cold and only power with 120v. Existing can stay at 240. Space could be an issue.
I guess the solar will run it until it gets hot. After that I suppose it just won't produce anything until a load is required. I am also considering adding a high efficiency window AC unit to soak up the power.
 
I agree, which is why I went to a 3-gang in my case for two switches.

THHN isn't too awful, it is slippery and flexible.
Solid NM-B at 10 AWG makes me bleed, 12 is tolerable.
This is solid 12ga THHN, so it's a bit of a pain, but not too bad. What was bad was running three 10ga solid THHN 60ft thru 1/2in conduit, but that's my fault for ordering solid instead of stranded..
 
Will likely work as you've described. If you can add a tempering valve to the hot water outlet then you could safely "overheat" the tank water, and the mixing valve would bring it back down to 120F or whatever you set it to for use. Effectively makes your hot water tank bigger.

If you decided to go that way, then you might also want to add a second hot water heater thermostat for the 120v side, so that you could set it for a higher temp. No reason not to heat that water hotter if you have the spare 120v power.
 
Sounds like a good idea. But. We live in a single wide, and the water tank is behind an enclosure inside a closet. So there's nowhere to put another tank.

This switch over would only happen during the day if there's to going to be lots of sun. So the rest of the time, the grid would run it. We use hot water for showers at the end of the day, and maybe washing some dishes in the evening. Don't use the dishwasher hardly ever. And we run our washing machine usually on warm for most loads, unless it's whites so we'd need hot water. In other words we don't use a lot of hot water.

So I'm guessing we'd have enough hot water stored when it gets switched over to the inverter. Will it save any money? In the long run, maybe? But, it would be nice to have the switch available for the rare occasion when we have extended grid outages so we'd have some way to heat the water.
At least in Australia, most HWS are rated for external use, so if yours are similar, then just run pipes outside to it (at worst you might have to built it a little 'leanto' to house it in...
 
Will likely work as you've described. If you can add a tempering valve to the hot water outlet then you could safely "overheat" the tank water, and the mixing valve would bring it back down to 120F or whatever you set it to for use. Effectively makes your hot water tank bigger.

If you decided to go that way, then you might also want to add a second hot water heater thermostat for the 120v side, so that you could set it for a higher temp. No reason not to heat that water hotter if you have the spare 120v power.
Thanks, sounds interesting, but don't know what a tempering valve is. I want to make this as easy as possible, and adding the switch above my critical loads panel would be easiest. Would just have to run 6 wires and a ground.

I'd rather not have to empty out the closet of all those clothes, and open up that wall to get to the tank.

Actually our outdoor A/C unit uses less power (3KW), than the water heater (3.6KW). But you can't run that on 120V.
 
Here's an example (not recommending this one, just the first to come up in a search):


I need one cause my solar hot water tank can get up to 160F on a sunny day, but it would work the same for any hot water source that is too hot and you need to bring down to a safe domestic temp. Many manufactures, and they come in various connection styles (sweat, threaded, etc). Caleffi is a good brand (and the one I used) but pricey. In any case, it will need to be plumbed into the hot water exit and a cold water source.

You would still need the electrical switch, to move the heating element from 240v lines to the 120v lines. Otherwise there will be big sparks as the 120v neutral is also a return for each of those 240v lines. But this way you can add another AC thermostat for the 120v and heat it up to whatever when the extra power is available, higher than your 240v grid thermostat is set to.
 
Here's an example (not recommending this one, just the first to come up in a search):


I need one cause my solar hot water tank can get up to 160F on a sunny day, but it would work the same for any hot water source that is too hot and you need to bring down to a safe domestic temp. Many manufactures, and they come in various connection styles (sweat, threaded, etc). Caleffi is a good brand (and the one I used) but pricey. In any case, it will need to be plumbed into the hot water exit and a cold water source.

You would still need the electrical switch, to move the heating element from 240v lines to the 120v lines. Otherwise there will be big sparks as the 120v neutral is also a return for each of those 240v lines. But this way you can add another AC thermostat for the 120v and heat it up to whatever when the extra power is available, higher than your 240v grid thermostat is set to.
Tempering valves are a legal requirement in Australia and New Zealand (and many other countries) as the HWS is required by law to remain above at least 60C for health reasons . but at those temperatures scalding becomes an issue, so a tempering valve is also required to bring water coming out of the tank down to a safe temperature...
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On that tank the top right outlet is the overpressure relief valve, the top left outlet is the hot water out, and the bottom inlet is cold water in... Like most HWS tanks in Australia it is mounted outdoors, and the tempering valve is the black 'knob' in the center, with hot water coming in the top, hot water leaving to go nto the house on the left, and cold water coming in the bottom...
The temperature required (45C normally) is set by that knob, and whatever the temperature of the water is coming into it, it will mix cold water with it until the water coming out is the correct temperature- this allows the tank to be run at a safe temp (sufficiently high to ensure any pathogens are killed) without risking scalding people if they turn the hot water tap on
These are now a legal requirement here after several outbreaks of Legionnaires disease back in the 1990's from people having their HWS temperature set too low
1716269494396.png1716269519651.png

1716269783289.png
From https://www.qld.gov.au/health/conditions/all/prevention/legionnaires-prevention
 
Update on this project, I ordered the DPDT switch last week, should be getting it soon. I ordered the Leviton 1288-w via Amazon, cost about $50, egads..

Another question, when switching the hot water from grid 240V to the inverter's 120V output, does it matter which of the HWT leads gets the 120V hot and neutral? Or does it matter? I'm guessing since it's just a simple resistive heating element, it doesn't care.
 
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Another question, when switching the hot water from grid 240V to the inverter's 120V output, does it matter which of the HWT leads gets the 120V hot and neutral? Or does it matter? I'm guessing since it's just a simple resistive heating element, it doesn't care.
It doesn't matter, however if your water heater has a black and a white conductor for 240v (sometimes marked with black or red tape), like mine does, just for sanity put the neutral on the white (no electrical difference). If you have two black conductors or a black and a red, your choice.
 
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