After running across a couple of water tank heating elements I had replaced earlier, I was about to toss them out and THEN…I wondered…could I possibly use them for something like a plastic strip heater? I know that normally they have to be kept submerged in water in the tank or they can short.
So, is it feasible?

 

Do they have their thermostat on them?

If yes, you can plug and use them immediately for heating any liquid with similar heat characteristics to water, because the thermostat will shut down the heaters at .. I dont know, 50 degrees C?

If you want to use them not submerged in liquid you would have to remove that thermostat and build your own control (another type of thermostat, PWM, PID...)...

 

OK last part of my answer is complete garbage because the heaters are AC and I wrote PWM and PID, but the other stuff remains.

 

Heating elements will run just as well from AC or DC.

 

Heating elements will run just as well from AC or DC.

Is AC heat or DC heat better for bending plastic? Does it matter for acrylic or polycarbonate?

[Don't answer! Totally silly question based on reading too many Facebook comments recently! I couldn't help myself.]

 

If they are 230V 3kW then they are 18Ω, so connected in parallel would make a near-enough-8Ω audio dummy load.

 

If they are 230V 3kW then they are 18Ω, so connected in parallel would make a near-enough-8Ω audio dummy load.

Ideal for 24h stress-test of a tube amp with 1kHz sine signal, it would also emulate real-life ambience of a death metal gig in a garage in Tampa, mid August

 

Feed with 120VAC or a few in series and will warm your plastic bender. Just observe the distance/time that works well.

 

A couple of years ago I managed to cobble together a strip heater so I could finally bend “plastic glass” (Lexan, plex, acrylic—I don’t remember what it was for sure but it worked great for my 4-wheeler trail wagon.) It worked real well—maybe around 32” long. I had tried that nichrome wire from a few things I found, and even the wire loops from an HVAC strip heater, but not great results. But THEN, I managed to run across one of those old floor heaters I remembered from the 60s as a kid—you know…had the wide strips wound vertically behind the grille and would turn red-hot and glow. Got me a length of that and mounted in a jig…perfect! These tank elements I thought surely there’s another use for them, and you guys are putting out the ideas Many thanks.

 

I know that normally they have to be kept submerged in water in the tank or they can short.

They don't short. They Open. That is to say they burn out, just like an old style light bulb. My concern would be three fold: How do you handle them while they're hot? And out of water, how hot will they get. Finally, they could become a fire hazard.

Heating elements will run just as well from AC or DC.

Yes, they will. And given that they can be run from either AC or DC, you might start your first experiments with a 12 volt car battery. Not likely to get hot, but warm at the very least. Two 12V batteries (24VDC) would do a lot more. You may find that a variable power supply capable of some serious amperage would give you plenty of control and not end up with a giant light filament in open air. In fact, do all your testing outdoors. No need to run the risk of burning the carpet or the bed sheets - depending on where you do your experimenting.

 

If they are 230V 3kW then they are 18Ω.

Assuming they are 18Ω elements. On 24VDC, 18Ω would equal 1333•••mA or 32W. 48VDC would be 128W. Twice the volts, four times the wattage. Ever unscrew a hot incandescent light bulb? A 40 watt bulb can be hot to handle. 60W is where you have to drop it from hand to hand. A 100W bulb - well you need gloves for that one. So 128W can burn the skin. Imagine how quickly you'd have to drop it at 120VAC. That would be 800 watts.

Moral of the story - be darned careful.

 

Moral of the story - be darned careful.

This is.... ahhh.... was.... a 6KW water heater element in a commercial dishwasher. It measured open. It consists of three u shaped elements mounted to a circular plate. Simple replacement, just removing 3 screws and pulling it out....

It pulled out 3 inches and refused to move further. Turns out the dishwasher had been operated with no water in the tank – the element had literally exploded!

Much cussing, poking a screwdriver through the opening, bending or breaking off the shrapnel, and the mess pictured below came free.

 

So 128W can burn the skin. Imagine how quickly you'd have to drop it at 120VAC. That would be 800 watts.

Maybe. Depends on how big they are. 128W spread over any element that's almost a metre long wouldn't.

 

Post#12 describes exactly the problems that I would predict! The power density versus the surface area tells me that out of water these heaters will get much hotter than the designed maximum, and do it very rapidly. THAT is why there are the warnings often found on replacement heater elements.
Consider the watts per surface area ratio and it becomes very clear that they will overheat if they are not submerged in water.
Using one as an audio amp load resistor will still require some evaluation.

 

Yep…after some serious “soul searching”, I have decided there isn’t much worth in them, and sadly, I’m forced to send them away (trash) It was just another of my “hey—what if?” moments…thanks to all of you for your usual great ideas and comments.

 

They could make a great dummy load if one was testing power outputs. Stack them in a water cooling circuit. Air cooled resistors need a lot of space.