Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

Photowhit · June 2013

Well, I'm off grid again! It took way too long, due to work going nuts.

I wanted to run my converted 240V breaker box by you; I Combined the Hot connections with a jumper, and disconnected (and labeled) all the 240V Breakers except the water Heater. I've been told by enough people I can run the 240V heating element on 120 (running at 1/4 the wattage) That I'm comfortable with that for the time being. I'll batch heat for 1 1/2 -2 hours during the day and see how that works for a while.

The water heater is a 30 gallon 3500 watt heater, so we're looking at it drawing around 900watts, I don't know that it will fully heat in 2 hours, but I'll also conserve a bit more, just installed a .5 gpm shower head. I'll try to keep the water somewhat warm before it heats the water.

This appears to be an original hot water heater to the 'Tin Can' (Mobile home) so guessing a 2000 model. I has somewhat thin wires (I can't read a gauge) going to the Breaker box 16 gauge or 14 gauge at best. The white wire appear somewhat discolored.

Questions are do I just run the white wire (they didn't mark it as a hot wire!) to the neutral bonded wires? As it is in a bonded pair of breakers, I would guess I can just use the breaker as is?

Photos of my newly converted Breaker....
Attachment not found.

In the second photo you can see the discolored white of the water heater coming down on the left.

I guess I should ask if they make 4/0 wire nuts of caps of some type? Hope no one goes nuts on my taping off the old incoming wires, they are disconnected at the pole!

BB. · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

Normally, the 240 VAC water heaters are wired for a single element across 240 VAC.

If you want to power with 120 VAC, you will have to disconnect one of the wires to the water heater (say the white one) and connect it to your neutral bus--Otherwise, you will have 120/120 (same phase) across the water heater and no current will flow.

You could cut the fuse back to 1/2 -- But that does not matter. Your wiring is all sized (I hope) for the larger breaker (that white wire is looking a little unhealthy, but that can happen with older wiring).

The other thing, most home electric hot water heaters have two elements. One at the top, and one at the bottom. Usually they are wired that the top element gets power first until the top 1/3rd of the tank is hot, then the bottom element turns on and the top element turns off. The bottom heater now heats the rest of the tank. This keeps the overall power of the water heater lower (for smaller wiring/panels).

In some water heaters, you can rewire them (they have the instructions on the wiring diagram) so that both heater turn on at the same time.

You could instead, disconnect the bottom heater and only keep the top 1/3rd of the water hot if you don't use much water for showering/etc... And save a little energy (and/or insulate the whole tank). (this disconnecting the bottom element is an untried suggestion--being the issue of electric hot water on off grid power--It may not keep the water at the correct temperature--not sure if the thermostat for the top element switch over is adjustable or not).

-Bill

Photowhit · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

Thanks Bill, It is a single element water heater, 30 gallons, 3500 watts. I suspect it'll work OK until I get some cloudy days and have to run the water down to cold, then I bet it takes a 'month of Sundays' to heat the water with 900watts heating. or it might be on of those 'Oh sh!t moments as the shower turns cold, and I forgot to run the water heater. I really need to get the opportunity load going, through the Classics going(waste not?), so I don't have to watch it...

ChrisOlson · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

The Classic's Waste Not works the best, and that's what I use. You can figure that if you convert a 240V element to 120V that it will take 4x longer to heat the water to the same temp. 900 watts is a little low IMHO to get water heated in reasonable time. Basically you're going to raise the water temp by at least 75 degrees to have a comfortable shower but it depends on your well water temp. Ours is normally 50 degrees F.

But anyway, 30 gallons of water is 250 lbs and it takes one BTU to heat one pound of water one degree F. So to heat 250 lbs 75 degrees F requires roughly 19,000 BTU. For all practical purposes electric water heating is so close to 100% efficient that you may as well use 100% efficiency at the element. There's a little loss in the wiring. 1 kWh = 3412 BTU. So I just use 3,400 BTU = 1 kWh input and that comes out "close enough for goverment work".

So basically, 19,000 BTU/3,400 = 5.6 kWh to heat your water from well temp to 125 degrees F. At 900 watts you're looking at over 6 hours to heat up your water heater. That's too long. Why? Because if you have to use the generator to heat water when RE don't work you want to be able to do it in less than half that time.

Over many years of fiddling with methods to heat water with off-grid power, I've determined that 2 kW is about ideal for the water heater load. It is large enough so that if you have to resort to generator power it can be done efficiently. And at 2 kW input input to the heater(s) the time required to heat the water is about double (most dual element water heaters come with 4,500 watt elements) of what the heater is rated at for recovery time.

Again, not that you can't do it with 900 watts. It will work. As long as the RE can do it. If you have to use the generator it will be bad.
--
Chris

ChrisOlson · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

Here I was going on and on about this, and forgot to mention how I would do it.

I would pull that 3,500 watt 240V element and swap it with a 2,000 watt 120V. The Classic's Waste Not will regulate that element to whatever the RE system can put out. If there's only 400 watts extra that the batteries and other loads don't need, that's what will be sent to the water heater. You can adjust the offsets so it don't overload your inverter.

But IF you have to use the generator to heat it up, you can walk up to the Classic and simply turn on the AUX port and then the element will draw the full 2000 watts. This has the benefit of using the water heater to keep the generator at full load while you're topping off your battery. And if everything is sized right, both the battery charging and water heating gets done at the same time. So you make maximum use of your gen fuel.

This has worked well for us for over 2 years now. I know every system is different, and I don't know what you have for a generator (or if you have one). But about a 2,800 watt generator would be ideal for the above. If you want to use a smaller generator like a EU2000, then reduce the size of the element to 1,500 watts so you have about 300 watts left over for loads and trickle charging the battery.

In the absence of generator power, you could be taking cold showers for a few days

RE works good when it works to heat water with off-grid power. But over time I've been forced to throw huge RE generating capacity at the problem to make it reliable. And even then the days come when we have to use the generator to heat water up

--
Chris

Photowhit · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

No generator, I didn't realize the waste not feature was that sophisticated, I'll have to read more. Thanks Chris.

ChrisOlson · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

Well, I assume you intend to use a AC SSR on the AUX2. It works so awesome that you can't believe it. The manual does not explain it well. But there are two voltage offsets that you can adjust to vary the output to the heater element, and when it comes on. And you will find that if you use, say, a 1,000 watt heating element that you will never get 1,000 watts to it with Waste Not due to the difference in the freq between the PWM control and the fact that zero cross SSR's don't shut off when the PWM tells it to. So you need to use a larger element and use roughly 90% of its watt rating for the peak that you could get if the batteries and other loads take zero amps and it all can go to the element.

If this is a permanent off-grid installation, and you intend to do long term heating of water with electric power, I think I would at least consider getting a small generator if you don't have a propane backup

--
Chris

Photowhit · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

The idea is to be 'overpaneled' enough to not worry about it. I will be selling my cabin and may end up with that 2Kw array and I was adding 2.6 Kw to what is there all ready.

I may dedicate an array to cooking water by it's self, but like the Midnite system.

I'm not big on burning gas, looking into the future and see 'peak oil' as a reality, with us near the peak. We have become dependent on cheap oil and it has driven the industrial revolution. With greater demand and less oil produced or more expensive oil to recover, I want to use as little as possible.

ChrisOlson · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

The peak oil thing doesn't bother me too much. Most engines can be readily modified to run on homebrew fuels. The reason I don't mess with it much at this point is because of the guvverment. They treat you like a terrorist with all the inspections and licenses and permits, and filing of IRS forms. Once the guvverment collapses, which shouldn't be to far in the distant future, then we'll go out to the woods, load up the still, bring it home and set it up in the front yard.

They could completely quit producing petroleum fuels and my generators would still run - guaranteed.
--
Chris

Photowhit · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

Well the sun broke through after a rainy morning, and I flipped the water heater on, it does draw about 900watts. When I get to float, I'll run it more than the 15 minutes I had it on. Water still running hot even though I've taken 2 showers, the .5 gpm shower head I think makes a good bit of difference. I'm guessing I'll be fine, but then again I admit to being an odd duck!

I will set up the waste not feature, I can't really understand why it won't allow for 900 watts going to the water heater, but I'll read more at the Midnite forum. I want to have the battery module installed, and setup the 'follow me' first, so the charge controllers understand what's going on... there I go wanting to communicate to a machine...

animatt · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

In an offgrid house in a somewhat moderate climate to me make sense to solar heat water via something dark in color rather than pv. Although it depends on many things. Kind of like how chris admits to spending a fair amount to do solar heating. If you could hook an array directly to elements it probably not be bad. But getting into things like charge controllers, inverters and such to do the heating can add up. For those of you who are handy building something black to absorb heat does not seem like a bad idea.

Obviously each design has its pros and cons. But you can build really cheap solar hot water heating system if you do not have to worry about inspections.

Either way heating with pv or thermal solar you probably want to have a solar buffer tank that feeds into your main tank. I believe chris has a fairly decent size buffer. This is especially helpful with solar thermal as having a panels operate at lower temps can have panels running really good efficiencies Probably into 70 % range. Much better than say the 15% of pv.
Something like a 200 gallon tank that is kept at a minimum of say 90F. Then you can have your small 30 gallon primary tank do the final bump up to temp went needed although bumping from 90F to 115F not going to use a terrible amount of electricity. ~1.8kwh And that is only on the days without good solar input.

But it does depend on many factors. I built a system in a non freezing climate for $200. And it would provide more than 50 gallons of over 125F water a day. This included panel and storage tank and insulation.

Also built a solar panel out of electrical pvc for roughly $300 and it provided roughly 125kbtu / sunny day for a Jacuzzi. Pvc can make a cheap collector but has some extreme limitations.

Matthew

Photowhit · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

There's a thread here somewhere about the pros and cons. I'm in a freezing area sub 0 degrees Fahrenheit, so a system that would be year round would cost a good bit of money and involve a heat exchanger. My peak energy use is in the summer, I should have plenty of electric for water heating in winter. As stated I also will be 'over paneled' so I'm comfortable with my choice.

I agree, a 'bread box' water heater where temps don't get below 20 or so is cheap and effective. For me the extra space taken and the plumbing involved in adding a buffer tank and an expansion chamber makes moving a wire inside the breaker box and attractive proposition. Now if I had a family or others who would need to worry about having hot water, I would likely go ahead and do a gas or some variant of a solar water heater.

Time will tell, I'm not too proud to let people know what hasn't worked so stay tuned!

solar_dave · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

I would think that using the fully battery configuration and the water heater as a dump load would be a good idea.

Perhaps you could add a solar thermal DYI setup next to the heater with a drain back system to pre-heat and supplement your needs.

ChrisOlson · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

Photowhit wrote: »

I will set up the waste not feature, I can't really understand why it won't allow for 900 watts going to the water heater

It will if you set the low voltage offset deep enough. But then what happens is that the water heater comes online before the battery gets to absorb voltage and on a poor day you'll heat water but not charge the battery. If you set the offset closer to charge stage then you'll get to absorb but the element won't go to full power due the anomalies with AC SSR's.

That's why you use a bigger load than what you actually need, and let the Waste Not throttle it.

Dave is right that having a buffer (we have dual 55 gallon heaters) is necessary to make this work. Like you say, most times in the summer you'll be fine. If you go into winter with this system it's probably not going to work very well unless you use drastically less hot water than most folks. On the really good days we can dump up to 18 kWh into the water heaters trying to get them up to 160 degrees. If we can do that we can go five days without putting a single watt in them and still have 125 degree water coming out. However, about 75% of the time we end up someplace in between with the primary heater at full 160 deg and the preheater anywhere from well temp to luke warm.

I do like the electric water heating because once the electrons leave the inverter on their way to the heaters it's almost 100% efficient. RE power, once you own the equipment to harvest it, is virtually free. You have no problems with freezing in the winter, don't have plumbing running all over tarnation with heat exchangers and pumps - it's a very simple system. And like all electric appliances for off-grid living, it's "dual fuel" - you can either heat the water with "free" RE power, or you can do it with a fossil fuel thru a generator. And if you tune the system and design it to use a generator, the efficiency isn't all that bad compared to propane water heating.

Direct solar water heating is more efficient, but it don't work for everybody. If you already got over-capacity in solar panels, and wish to keep the system simple, then it's a no-brainer even if it's "inefficient" when looking at it from the outside.
--
Chris

NorthGuy · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

ChrisOlson wrote: »

And if you tune the system and design it to use a generator, the efficiency isn't all that bad compared to propane water heating.

My tankless natural gas water heater is 85% efficient. They now sell 95% efficient models. I'm sure propane models are available too.

The generator running on the same fuel cannot get anywhere close to this in terms of efficiency.

Photowhit · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

ChrisOlson wrote: »

...On the really good days we can dump up to 18 kWh into the water heaters ...

I suspect I'll use maybe 4 Kw a day in winter, if that, I'd like to have the additional array of 2.6Kw setup by then(he says confidently)... 6.6Kw array we average 2.5 hours of sun in January (I think) I gotta do something with the extra...

For now I think I'll buy a quality timer and run through that so I don't forget to turn it off. I guess I'll need to setup 'follow me' now or at least address the Classic Lite's via network. I had one stay in float all afternoon and one that would drop back to bulk when I ran the water heater. Late afternoon sun I was pulling 37Amps at a voltage of 26.8 at the inverter and one of the classics refused to drop back.

ChrisOlson · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

NorthGuy wrote: »

The generator running on the same fuel cannot get anywhere close to this in terms of efficiency.

It is when you factor in that better than 95% of the time the electric water heating is totally free, powered by RE. For the few times that we have to run the generator to heat water I have things sized and designed so that the generator stays at close to full load at all times that it runs.

I will venture a bet that our electric water heating system powered mostly by RE and sometimes by generator is at least as efficient as your natural gas or propane fired tankless heaters in operating cost. It's not as cheap overall because of the equipment required to do it with off-grid electricity. But the only real input in fossil fuel is quite small for the hundreds of gallons of water we heat every year. I've never actually measured it - but my gut feeling is that even with the occasional use of the generator it's efficiency is pretty darn good.
--
Chris

NorthGuy · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

ChrisOlson wrote: »

I will venture a bet that our electric water heating system powered mostly by RE and sometimes by generator is at least as efficient as your natural gas or propane fired tankless heaters in operating cost. It's not as cheap overall because of the equipment required to do it with off-grid electricity. But the only real input in fossil fuel is quite small for the hundreds of gallons of water we heat every year. I've never actually measured it - but my gut feeling is that even with the occasional use of the generator it's efficiency is pretty darn good.

I would certainly take the bet if there was any chance to accurately estimate it.

For a dollar in fuel cost, my heater can heat up 220 gallons of water (with 40 C temperature increase) and it takes just slightly over an hour.

I understand that RE heating is free, but when there's no RE ...

Can you tell me how much would it cost to heat up 220 gallons (same 40 C) with your Honda generator (fuel only)?

waynefromnscanada · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

Makes me realize how lucky I am. Direct solar heating with convection circulation to the 60 gallon storage tank supplies all my hot water from early Spring to late Fall, and costs me not one cent for fuel. I don't waste hot water, but I definitely use what I need, and more. Today is the 3'rd day without sun and the water temp at the top of the tank is still hanging at 127F.

ChrisOlson · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

NorthGuy wrote: »

Can you tell me how much would it cost to heat up 220 gallons (same 40 C) with your Honda generator (fuel only)?

Not really, because I've never done it, or never used the generator only for water heating. When ever it runs it's always powering multiple loads.

We use roughly 30 gallons of 125 degree water per day (we got one of those thermostatic mixing valves on the primary heater so only 125 degree water comes out). I don't have a separate kWh meter going to the water heaters (something I've intended to do but never got done). But just off the top of my head there's maybe 8-10 times that the generator ran last winter and it was heating water while it was running. The reason it starts is due to low battery voltage when that happens so it initially charges at full load, then when the bank gets to absorb the Classics kick the heaters in and it splits duty between water heating and charging, as well as running normal house loads.

It has not run for battery charging or water heating since about the end of February right now. So over a year's time I think it's pretty cheap. But to tell you an exact number, I can't. I can only tell you that since March 1 we've heated and used probably around 2,700 gallons without spending a single dime on any sort of fuel.
--
Chris

Photowhit · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

Well I took my third shower this morning, and then did some dishes and water was becoming a bit tepid so about 12:30 I switched on the water heater, It shut off on thermostat between 2:30 and 3:30, I did shut it down while making lunch, running the microwave for a couple minutes and again while running the vacuum for 5-10 minutes.

Nice to know that the thermostat works! I'm off to pay my last bill to the electric company, and pickup some phone connectors to hook up the 'follow-me' feature on the charge controllers. Frustrated that one would always be in float, and needing to do an equalizing on the battery. I pushed the manual equalizing button on the one in float. The CC just changed places...lol

Eric L · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

FWIW, I have one spare 4500 watt, 240v element running at 120v, so about 1100 watts at full power. This is using Waste Not Hi and a 45 or maybe 50 gallon tank (not sure on size). I have the offset at -1.4 volts, which means the inverter comes on pretty quickly and, once the absorption voltage stabilizes, the output measures about the same voltage at the element as it does when the controller is just set to "manual on". So there's not an appreciable loss from having it on Waste Not Hi. But, this offset setting pulls the absorption value down; oddly, this happens even when there is more than enough pv power available to push the absorption up to the set point level. Consequently, I set my absorption and equalization levels .6 volts higher as well. This setting came about through observation and a bit of trial and error -- the .6 lift counteracts the slight reduction in absorption voltage caused by the Waste Not Hi kicking in, so that the batteries are getting up the manufacturer's recommended abs charge.

But the result is pretty good. It's not as ideal as having way too much capacity like Chris O. is recommending and then using a portion of it, but it is certainly making a meaningful difference as long as there is surplus sun power. For a time this spring, when we didn't need either heating or air conditioning, but had good sun, the thermostat on the tank was tripping off and water at the tap was just under 170 degrees F. When the heating or a/c opportunity loads are also on, the water heating is less since the system is nearer its limit, but still can hit 140 or so on a full sun day.

gww1 · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

Eric

Do you manually turn you air conditioning opertunity load on or is it automated?
Thanks
gww

Eric L · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

Do you manually turn you air conditioning opertunity load on or is it automated?

I have two. If we are home, we turn them on ourselves depending on sky conditions and battery state. If I and my wife are gone, I set up the timer on one of them so it goes on at a time when the batteries typically are into absorb. Even under partly cloudy conditions, there's usually enough amperage to support one unit and finish the charge cycle. One unit can go a long way to cooling and dehumidifying our house while we're gone. This unit is connected to an SSR that is controlled by one of my Classic's AUX functions to turn off once battery voltage hits a setpoint (about 49.8, in my case). So if it clouds up heavily while I'm away, it will turn off before the batteries are drained very far. However, I can't turn them on with this SSR function, just the timer.

gww1 · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

Eric
Thank you for your clear responce.
gww

ChrisOlson · June 2013

Re: Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

Eric L wrote: »

I have the offset at -1.4 volts, which means the inverter comes on pretty quickly and, once the absorption voltage stabilizes, the output measures about the same voltage at the element as it does when the controller is just set to "manual on". So there's not an appreciable loss from having it on Waste Not Hi.

I've never been able to get full power to the element (at least with the SSR's I'm using) with -1.4 offset unless the charge stage voltage is bumped up accordingly. At -3.0V I can get it to within a few watts of full rated element power without changing the charge stage set points. I attribute that to the fact that there's a mismatch between the PWM freq and the AC current freq, so the PWM can't turn the zero-cross SSR on and off at quite the speed it would like to.
--
Chris

Converting 240V Breaker box to 120, and running 240 Water HEater at 120V

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