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

[E350]

I was going to be a smart a$$ and say "Wow you can't even see anything left of the van in those black and white photos taken in the 1800's!" But then I read the entire Nachi electric water heater explosion thread and thought holy crap!

Post #33 says this:

"Kenton ... calculated the foot-pounds of energy released when 30 gallons of water is exposed to atmospheric pressure. It approaches the power of a 16-inch gun on a USS Iowa class battleship, which produced a 7,500,000 foot-pounds of energy. That's why there's so much destruction."

Which probably explains the photos of the hole in the garage roof, side wall, and double garage door blown off and the water heater in a school yard two blocks away and the garage door on the neighbor's roof.

The thread states that it was not a gas explosion, there was no fire. It was a waterheater explosion...

boywonder: The thread also says:

"The electric ones have an overtemp cutout also.
For an electric one to catastrophically blow would you not need two failures?
1. Bad overtemp sensor cutout
2. Stuck, blocked or missing TPR feature."

So, you confirmed you are leaving the Temperature Pressure Relief valve. But does the water heater you are using have a overtemp cutout also?
Is that the red reset button?

Edit: https://www.youtube.com/watch?x-yt-t...yer_detailpage

[daveb]

BLEVE is more of a correct answer. Seen a household water heater fly 2 lots over before it landed. Nice to have that come through your roof or on your head. That said, those are a bit bigger and an industrial unit is larger yet!

[boywonder]

E350: Yes the red button is the overtemp cut-out. I'm still not quite clear why the thermostat has two sections, perhaps another layer of redundant safety features......

Pretty much all high-severity failures are mitigated with a least two features. For example, all of the control surfaces of a typical commercial jetliner have at least triplex redundant hydraulics/controls; some even are "quad redundant".....they have 3 or 4 independent hydraulic circuits so that you can have 2 (or 3!!) failures and still land the thing.

The T/P valve is a last line of defense, but works well; you don't see many water heaters exploding these days. So the take-away here is never tamper with, remove, defeat or over-ride the T/P relief valve.....

The fundamental principal here is the energy in a pound of superheated steam is far greater than the energy in a pound of liquid water.......that's how steam engines work.

Again, the 12V 300W element should be very safe, assuming everything goes as planned.

[boywonder]

Originally Posted by boywonder

I'm still not quite clear why the thermostat has two sections, perhaps another layer of redundant safety features......

well.......it just occurred to me why the thermostat has 2 sections..........

To meet both boiler code (USA) and IEC (Euro) requirements, the water heater must have an overtemp cutoff and that is required to be manually resettable, ie it cannot reset by itself.....much like a circuit breaker, it let's you know that you have an issue. That's the red button in the upper section of the thermostat. This is most likely an over center latching type bi-metal, once it pops it stays that way until you push the red button. It probably opens around 160-170F or so (I'm guessing here) to be comfortably above the max operating temp of the water heater. If it designed to trip too low, it will generate nuisance trips and unhappy customers.

The lower section of the thermostat is the temp control thermostat. It's a bi-metal that opens and closes the circuit to stay at the set temperature. These are wired in series along with the element for redundant safety. If either thermostat opens, the element gets no juice.

[Chance]

Originally Posted by boywonder

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

.....cut.....

Yes, semantics. The technical definitions I've used usually describe this type of event:

"a violent expansion in which energy is transmitted outward as a shock wave."

The failure of pressure vessels caused by simple over pressure, regardless of how violent the results, were not considered true explosions. Not in the technical sense which is what I was referring to.

I get that many use "explosion" to describe many events including a tire failure. In any case I know what you guys mean.

[JWA]

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.

Ya know guys (and girls if applicable ) this ^^^ sort of nonsense contributes absolutely nothing, not even remotely. If I'm in or near anything that potentially can "explode" or "rupture" what that event is called would NOT be any consideration I'd made before, during or after said event. If bodily injury is the danger labeling it this or that is completely irrelevant.

I've been near explosions and ruptures along with once upon a time being charged with safely & significantly lowering the chances of either event occurring. Those that did happen left the same sort of damage and injury which I'm sure wasn't a concern to those affected either.

Just IMHO ya understand..............

[Chance]

Originally Posted by JWA

Ya know guys (and girls if applicable ) this ^^^ sort of nonsense contributes absolutely nothing, not even remotely. ....cut.....

I completely disagree with you. If the goal is to discourage people from trying to install equipment because it's too dangerous, then I'll call it the BS that it is. There is a difference and people should know that it's not the same as driving around with with a bomb in their van. That's just ignorance.

And for what it's worth, why make a big deal about one statement instead of pointing out a page full of pictures of boilers that "blew up". Can you seriously compare an industrial fired boiler from over 100 years ago to a tiny modern electric water heater? Let's get serious, it's not the irrelevant nonsense you object to.

JWA, please knock it off. This is the second time I've asked you nicely. You can disagree all you want with me, but don't make it personal.

[BroncoHauler]

From Merriam-Webster online dictionary:

Explosion: ex·plo·sion (\ik-?spl?-zh?n\)

the sudden, loud, and violent release of energy that happens when something (such as a bomb) breaks apart in a way that sends parts flying outward


Herb

[boywonder]

Chance: We are disagreeing with you because modifying water heaters can be very dangerous business. The fact that you are downplaying the potential things that can go wrong is worrisome to me.

I am presently working on a project that involves designing a small pressure vessel that operates between .5 torr and 1200 psi at 680 deg F, so I am quite familiar with the potential failure modes and relevant safety requirements of this sort of stuff. I remind the engineers working on this project almost daily about the potential dangers of this sort of energy.

Your comments about just using the water heater as-is and plugging into an inverter are good ones; that is a very safe approach......and it won't void the warranty!


.......also the 12V 300W element has arrived, I just need to find some time.....gotta fix the garage door opener this weekend.

[E350]

If boywonder's pictures can be worth a thousand words, then this youtube video can be considered priceless:

MythBusters--Exploding Water Heater

https://www.youtube.com/watch?x-yt-t...yer_detailpage