Electric boiler?

[ddmckee54]

I've got a defunct steam sanitizer, think small(ish) hand-held steam cleaner, that I'm considering using to build an electric steam generator - similar to the Mamod electrics only slightly larger.

I know I'll need a bunch of safeties for this, both electrical and mechanical, with a GFCI at the top of the list. The safeties part doesn't worry me - I design industrial control systems for a living. I'm just wondering if anybody's already gone down this path or if I'd be blazing my own trail. I'd like to have some idea if this will work, preferably without wasting my time or materials to find out.

I haven't ripped it apart yet to find out how big the heating element is, just going by the size of the power cord I'm guessing it's maybe a couple hundred watts. I've got no idea what this thing looks like on the inside and whether of not this idea is even feasible. I'll try to take it apart this weekend and see if it's do-able. If it looks like this just might be possible I'll take some pictures - otherwise I'm not going to waste everybody's time.

Don

 

[Blogwitch]

Don,

Jenson, a US model steam boiler and engine maker uses an electric blanket heating system for their boilers.

Maybe by reading a bit of their info can point you in the correct direction for wattage inputs to raise useable steam.

http://www.jensensteamengines.com/

John

 

[dave-in-england]

What is a GFCI ?

 

[10K Pete]

What is a GFCI ?

Ground Fault Circuit Interupter

Pete

 

[ddmckee54]

Well, I finally got a chance to tear the defunct steam sanitizer apart to see if it was usable. Nope, not gonna happen - had a couple of problems.

First, the heating element was die-cast into a rather large alloy block. It felt too heavy to be aluminum, substitute your own spelling if you're on the wrong side of the pond. I'm thinking it's probably a zinc/aluminum alloy. I might have been able to deal with the big lump is some form or another, but when I started checking the electrical components I found that there was no continuity through the heating element, it was a completely open circuit.

That defunct steam sanitizer really was DEFUNCT, the only thing worth salvaging out of it was the power cord. Oh well, on to the next idea.

Don

 

[ddmckee54]

It's been a while since I've done anything here, but I have been busy. Besides that pesky day job, I've been looking for alternative heaters and I'm really liking the tubular heating elements. You can get them in a variety of diameters, lengths and wattages. My next challenge, "How do I know I've got enough watts?" After all, it's always nice to have something that you design/build actually work.

I set out to find a way to convert steam usage into Watts. Here was my train of thought:
1) Determine the volume of steam per hour required by the engine in cubic feet per hour - yeah that's right I'm an Imperial kind of guy!(Your units may vary!)
2) From the saturated steam table, at the desired steam pressure, convert the volume of steam per hour into Lbs./Hr. of steam.
3) I found formulas to convert from Lbs./Hr. of steam to BHP and then from BHP to BTU, so that's what I did.
4) I've got a converter that goes from BTU's to Watts, so that was a no-brainer.
5) I've now got the Watts required to run the engine at a desired RPM. The only problem is these calculations assume 100% efficiency. We all know that isn't going to happen so I included a way to factor in my best guess at boiler efficiency.

I put these calculations into a spreadsheet that allows me to enter the following values and it will spit out the required wattage:
1) Number of cylinders(All cylinders are the same size, no compounds)
2) Whether the engine is single or double acting
3) Bore
4) Stroke
5) Desired RPM
6) The correct value from the saturated steam table at desired PSI
7) The expected efficiency of the boiler.(I use LOW values, usually less than 50%, because really I have no idea what this should be.)

From the Mamod forum I knew that their electric boiler used a 200 Watt heating element. Entering the bore and stroke for a typical Mamod engine, and 1000 as the desired RPM, I played with the boiler efficiency and found that my calculations showed I would need 191 Watts for a 35% efficient boiler at 1000 RPM and 20PSI steam pressure.

Since I know that a lot of people that have these electric boilers use a Variac, or the equivalent, to regulate their heaters I think my numbers are at least in the ballpark. I can now use these calculations to start and actually design the boiler.

I know that there is a LOT of variables that I have left out in my calculations, but at least I've got some minimum values to start with.

Don

 

[Dave Sohlstrom]

I needed some sort of test boiler to run a pair of engines I was building for the model of the W.T. Preston. A stern wheel snag boat that removed snags to navigation in the puget sound. It was retired in 1982.

I did not have the vessel boiler it was with the vessel at the builders house. I also did not have time to build a proper boiler.

I was in a goodwill store and spotted a Mr Coffee maker with a steam port for heating your milk for your lotte.

I bought it for a few bucks and brought it home. Tested it before I spent any time making mods. It worked so I replaced the nozzle with a valve and made it so I could hook it up to the engines.

It worked great for all the bench testing I had to do on the engines.

Once the engines were done the owner of the model brought it down to my shop and I installed the engines, did all the plumbing and testing and then the owner took the model home.

The complete build thread for the model is in the scale boat section of RCgroups. Look for W. T. Preston it will be a few pages back the model has been complete for a while now.

Dave

 

[ddmckee54]

I remember that build thread, it built into a great model. I don't remember the testing with the modified Mr. Coffee though, I'll have to review the thread again. Your testing solution is pretty much what my intention was with this investigation. I'm not building anything yet, at this point it's just another engineering problem to be solved.

Don

 

[KM6VV]

I remember finding/seeing a model boiler with an electric heater. Always wanted to build one. I now have an immersion heater coil from a commercial coffee brewer (expensive coffee by the cup brewer. Now I'd like to find the photos or plans. I might even have it. But with over 2500 PDF files (if it was a PDF), I haven't ran across it yet.

Anyone remember seeing plans/photos? It might have been 10 years ago, for all I know.

Thanks,

Alan

 

[tornitore45]

Regarding safety. It is one thing to generate steam at low pressure with an open nozzle/vent like a pressure cooker, a cappuccino machine or the image of Hero steam turbine we all know.
It is a different thing to operate a boiler that generate steam and is capable to hold some 50-100 psi.

A shirt steaming appliance generate stem at a pressure hardly sufficient to spit out a stream of saturated steam, I would not want to think what happen after plugging the nozzle if it it was not for the mandated safety valve sure to be equipped.