Dual Voltage (12v dc / 120v ac) Small Electric Water Heater - Page 5

E350 · 01-27-2015, 09:12 AM

It is my understanding that the number one reason water heaters don't explode in homes is that any excess pressure pushes the cold water column back down toward the street, well, etc.

The second would be that household water heaters have a pressure release valve. I can't remember, are you or tecnodave removing the pressure relief valve? Couldn't one be installed, if not in the water heater vessel itself, in the hot water line running from the vessel to the faucet (with separate piping to vent release under vehicle?).

Chance · 01-27-2015, 09:56 AM

Quote:

Originally Posted by E350

....cut.....

chance: Here's the original thread:

http://midniteforum.com/index.php?topic=2140.0

The Midnite Kid MPPT solar charge controller will top off the batteries then divert photovotaic power to another device. tecnodave converted a water heater to run on 12v/24v/120v so he uses his extra pv power to heat his water.

I see the how but not the why. I don't follow the advantage of why it wouldn't be easier to connect the 120 Volt water heater to the main electrical system, assuming there is an inverter for the house. Even if house inverter is at capacity, a second cheap small inverter can work fine with a heater -- no need for expensive pure sine or the like.

I guess it comes down to camping style. I wouldn't mind looking at battery charge level before switching water heater to on position. At that point wouldn't excess power flow from panels through batteries to water heater?

E350 · 01-27-2015, 10:14 AM

I think tecnodave's "why" is because it is automatic, not attended. Because his rv is used as a remote cabin. So the pv diversion to the water heater is automatically controlled by the pv controller so that he does not need to attend/check the battery charge level and manually switch on the water heater.

In my case, what boywonder is doing is interesting because whether or not my mini-rv is remote or parked in front of my house, I wouldn't need to think about it. I screw up a lot of things when the design requires me to think about/attend to something. The pv controller would automatically divert excess pv power to the water heater. And if it were parked in a sub-freezing environment, in my experience anyway, it only takes a little current to keep a tank type water heater from freezing, which might allow me to use my Webasto Dual Top Furnace/Water Heater for its water heater function without the need for constantly draining it. I am thinking putting an electric water heater in series before the Dual Top, or using it completely separately. (Although the Dual Top drain/purge function is electrical, I have had so much stuff freeze in the past - not in my van - that I am paranoid of ruining a very expensive furnace.)

Chance · 01-27-2015, 10:22 AM

Quote:

Originally Posted by E350

It is my understanding that the number one reason water heaters don't explode in homes is that any excess pressure pushes the cold water column back down toward the street, well, etc.

The second would be that household water heaters have a pressure release valve. I can't remember, are you or tecnodave removing the pressure relief valve? Couldn't one be installed, if not in the water heater vessel itself, in the hot water line running from the vessel to the faucet (with separate piping to vent release under vehicle?).

Technically water heaters can't "explode", they rupture. There is no way for an electric water heater to detonate -- hence no explosion.

Pressure vessels can and do rupture, but it's extremely rare. When a residential water heater ruptures there is a release of energy, but nothing of the magnitude to level a city block, or a building. It can still injure or kill a person if standing near it. A quality relieve valve practically eliminates this from happening unless the vessel is corroded to the point of catastrophic failure.

By the way, I have thought about an engine-heated water heater for my next van. To control water temperature I would set it up so water heater's temperature switch would actuate a solenoid valve in the engine's coolant supply. There are many safety issues to consider though.

Scalf77 · 01-27-2015, 10:55 AM

Boywonder,
This has been a very interesting thread, you are doing some nice work here. You do have a typo in your color code explanation, it would be gray not gold, silver and gold are use for tolerance but not part rhyme.

Quote:

Originally Posted by boywonder

.....and for the non-electrical types, daveb's abbreviation above is for determining the resistance value of a resistor by it's color bands.

The colors are black, brown, red, orange, yellow, green, blue, violet, gold & white.

I used to have a 110 water heater in my van and the pressure relief valve was routed down through the floor.

Chance,
I guess the why was to harness the unused power of your solar setup, the positive of the dump load concept is that your keep your batteries charged and in float and any excess would go to the water heater as needed. It is taking advantage of a feature of the controller, once implemented it is pretty much done. Since it is not hooked to the battery, there will be no worry when you are not producing enough to keep the water heater going. I do tend to agree that it might not fit our rigs so well, but if you had enough panels to make it worth it, what the heck. Boywonnder's approach is different, and he has a specific use case in mind, it may not work for others. Heck, it might not even work out how he wants it to, but I'm sure he is having fun getting there, and we get to come along for the ride.

-greg

Chance · 01-27-2015, 04:14 PM

Thanks Greg. I guess excess capacity is key. I'm not sure what to make of his signature (copy below), but suggests some really heavy duty hardware. I personally view needs a little differently. When I want hot water I want hot water -- even if some of the energy had to come from batteries which may temporarily leave them under 100 percent charge. If indeed there is additional capacity it can always charge the batteries back up.

FROM JUST BELOW HIS POST:

sys1: Classic 150 w/WBjr 2240 watts 72 cell poly PV 70v. strings 24volt L-16 800a.h. Brutus and Cotek SK1500 Onan NH-3
sys2: Two Kids/WBjr. sharing 1020 w. 72 cell poly PV, 70v. strings 24volt L-16 400 ah. Surette S-530 Exeltech inv. Onan Emerald 4
sys3:Trace C-40 36 cell parallel mono PV 12v GC-2

boywonder · 01-27-2015, 06:15 PM

Quote:

Originally Posted by E350

I can't remember, are you or tecnodave removing the pressure relief valve? Couldn't one be installed, if not in the water heater vessel itself, in the hot water line running from the vessel to the faucet (with separate piping to vent release under vehicle?).

No I'm not removing the temperature/pressure relief valve and I don't think technodave is either, and PLEASE DO NOT EVER REMOVE A T/P VALVE FROM IT'S LOCATION ON A WATER HEATER.

Installing it in another location would significantly compromise the safety of you and your loved ones......I cannot stress this enough.

boywonder · 01-27-2015, 08:03 PM

Quote:

Originally Posted by Chance

Technically water heaters can't "explode", they rupture. There is no way for an electric water heater to detonate -- hence no explosion.

Perhaps it's semantics........you say rupture I say explode.....violently.....

http://inspectapedia.com/plumbing/BLEVE_Explosions.htm

Here are a few pics of the aftermath of boiler explosions.........This is why the ASME developed the boiler code.

boywonder · 01-27-2015, 08:20 PM

...and a couple of water heater explosions....

http://www.nachi.org/forum/f13/water-he ... ion-31722/

https://www.youtube.com/watch?v=iQK6McNdyXE

boywonder · 01-27-2015, 08:32 PM

.....OK, back on topic.....

JWA's comments about the thermostat prompted me to investigate further.....the thermostat is rated for 40A for 120-277VAC service and 25A/480VAC service, so we should be good to go here. The juice that I will be pumping through the unit is well within (below) spec. These thermostats are trademarked as "therm-o-disc" so I suspect that they are a bi-metal type thermostat.

The red button in the pic is the manual reset button, another safety feature that let's you know that you have a problem before bad things happen......it forces you to manually reset the heater.

.......now I'm just waiting for the 12V element to show up.............

.....and thanks for the resistor color correction Scalf77, I fixed the original post.......another senior moment....