Heating element voltage woes

[GDorn]

I bought an ariston water heater to use as my boiler. It's 6 gallons, glass-lined, has a 3/4" threaded port on top that the column fits right into, and it's pretty light. Only one problem - it came with a 1500w element. I'm using only 1" copper tubing as the center column, so I knew that 1500w would be far too much. I figured, hey, no problem, I'll do what the forums and the books say to do - replace it with a 240v 3000w element and run it at 120v and end up with a 750w element.

Only the Ariston doesn't use a standard water heater element. I thought maybe the 'universal adapter kit' would be able to make it work, but no, the largest metal bracket just doesn't fit.

What are my options, here? Googling doesn't yield any alternative elements for that model, as far as I can tell.

I've read suggestions about dimmer switches (rheostats), but it seems like I'd need one rated for 13ish amps, and those aren't cheap.

I've read suggestions about autotransformers (variacs, powerstats) and that seems like closer to what I want. But again, they're rated for a certain amperage. Question: is the amperage rating on an autotransformer for the actual amperage after being knocked down 120v, or before? If it's after, I could get a 9amp autotransformer and run the whole thing at 80-85 volts, which yields between 650w and 750w...

Another idea I've had is to put another resistor in series with the heating element. I measured the ohms of the heating element (9.7 ohms) and did some math to determine that adding an extra 9.2 ohms in series would drop the amperage down to 6.25, yielding a 750w element. However, resistors are also rated, and finding one that'll handle 750w is not cheap - again, in the $100 range.

Yet another idea - a fixed transformer. You'd think a fixed transformer would be cheaper than a variable transformer... Doesn't seem to be the case. On digikey.com (great electronics supplier), a transformer to output 60v rated high enough to handle 6something amps (the closest such transformer) is $90.

Any other ideas? I'd thought about putting it on a 15-minute on/off timer, but it seems like the boilup/cooloff would be too pronounce and I'd probably have overflow and/or no reflux for periods of time.

[stoker]

having no other solution available yet, I would try it with what you have right now,

[fahdoul]

I sure as heck would ditch the 1" pipe and build a bigger column. Lot easier to build a bigger column than screw around with controllers etc.

Resistors aren't the way to go. They'd have to consume as much electricity, and create as much heat, as the element itself. Wasteful and possibly dangerous.

[pothead]

You could put a whole bunch of lightbulbs in series

Reall, I would keep looking for the proper element, and possibly a bigger column.

At one time I think I posted a link to a site that carries all kinds of heating elements. Do a search and see if you can find it.

[agl]

the cheapest and least atractive method is to get another 1500W heater element (small stove element for example- or a hotplate) and wire that in series.
better solution - make an adapter to fit a standard element to your boiler. How does the stock heater fit in? there might be an "off the shelf" solution that wouldn't require fabricating your own mount.

[GDorn]

the cheapest and least atractive method is to get another 1500W heater element (small stove element for example- or a hotplate) and wire that in series.
better solution - make an adapter to fit a standard element to your boiler. How does the stock heater fit in? there might be an "off the shelf" solution that wouldn't require fabricating your own mount.

Oof. In the summer, no less. You're right, though, what better way to find a resistor capable of handling that much heat?

The stock heater... Well, you know how most water heater elements are the screw-in variety? This one isn't. It has a square flange with bolt holes. There are adapter kits for standard heater elements to put a square flange on it, but the size doesn't match up - the flange is too small.

I think fabricating my own adapter is a bit beyond my means. That's gotta involve welding, I think.

[GDorn]

Another idea:

Put a heavy-duty diode in series with the element. AC power will then only run one way, dropping average power (wattage) in half. This is called a half wave rectifier and probably takes a hefty heatsink, but not as much of one as a resistor would.

Lamps that have two brightness settings often use this method. It's a bit lower wattage, but digikey seems to carry mega-diodes meant for much, much higher loads, still for pretty cheap. I'd get one rated for at least twice the voltage/amperage that I'd be using (at 1500w) just to be safe. And probably a heatsink.

[agl]

You are right about the diode, it would work... but (there's always a but with the easy solution isn't there?) at that current there would be a heavily unbalanced load on the mains. best case you wouldn't notice any problems and you get a heater of half the wattage, worst case you could have your lights flicker, or worse, blow fuses- it could even wreck sensitive electronics plugged into your houshold ac.
- but pessimism aside I have built circuits at work that did worse things to the electrical system. and we suffered no damage from it.
- as for fabricating the flange, if you had access to the tools you could make an identical size and bolt pattern flange, with a hole with the appropriate threads tapped into it to mate with a standard element.
good luck