Kill A Watt = Hunk of junk?

[Jeff7]

Nope. Nichrome has a high cold resistance.

Ah, well that's good then, at least with respect to inrush currents.

I'm working on a sort of heater control board, that pulses a small array of heater elements on and off using some TRIACs. Some other designs which use timed duty cycles (33% would have the elements on for 20s, and off for 40s, and of course a 60s cycle time) use large contactor relays.
This controller's cycle time is 10 seconds and allows for slightly finer control.
Plus a contactor is $400, though that could control several elements at once.
The TRIAC of choice controls only one element, but is also only $10. And of course, no moving parts.

 

[Rubycon]

LOL at using a contactor for cycling...

KER-KLUNK-KER-KLUNK...

KER-POW!

Hey! What happened to the lights?:biggrin:

Reminds me of a fridge with a shorted start winding bouncing off the klixon for days until the klixon's contacts weld shut...MMMMMMMMMMMMMMMMMM.

60 ways to leave your lubber.

 

[Jeff7]

LOL at using a contactor for cycling...

KER-KLUNK-KER-KLUNK...

KER-POW!

Hey! What happened to the lights?:biggrin:

Yeah, that's pretty much what they said it's like when the thing is running, a loud clang/thud each time it cycles. It's not a particularly elaborate system at this other facility, but I guess it works.

I have a feeling they might want to try this solid state controller though, if it works. I'm working on the hardware controller, which is linked via wireless communication to a PC. Someone else is writing a GUI which will let an operator control various stages of heating, as well as give instructions to each heating array.

I just hope it works right.

Reminds me of a fridge with a shorted start winding bouncing off the klixon for days until the klixon's contacts weld shut...MMMMMMMMMMMMMMMMMM.

60 ways to leave your lubber.

Sounds fun.

I've also heard that these contactor things can fail rather spectacularly, complete with the whole "bursting into flames and blowing some fuses" scenario.



And now back to your regularly scheduled thread. :awe:

 

[Rubycon]

I've also heard that these contactor things can fail rather spectacularly, complete with the whole "bursting into flames and blowing some fuses" scenario.

They can last many years if sized and installed properly. As a matter of fact most failures in outdoor equipment occur due to rodent/insect/nasty critter intrusion! Most larger loads' protection cuts power to the contactor coil. But if the plunger is stuck regardless of whether or not the coil is energized interesting things happen. Just as a secondary load on a pole pig often runs amok with the primary fuses holding, motors can smoke for hours popping along the way until their windings short dropping the impedance and raising the amperage into trip range of the main branch protection. Sometimes there's a fire, sometimes not.

Another failure is when the contactor for resistance heaters (strip heaters) is stuck and the blower stops. The high limit switch snaps open killing the coil voltage but the plunger remains down. The coils get hot and glow - red, then orange, then yellow. The wires stretch, sag and may suddenly break open with a nice arc. If they fall down in the collar and ignite dust a fire is usually born.