Hi guys.
Got one of these AC dimmers:
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THB131.62 | AC 220V 2000W SCR Voltage Regulator Module Dimmer Motor Speed Controller Thermostat Electronic https://a.aliexpress.com/_oBUF6h5
And tried to hook up to this 600W hot plate:
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THB410.42 | Ptc Heating Plate Soldering Station Demolition Hot Plate Chip Aluminum Desoldering BGA LED Lamp Remover Welding Station https://a.aliexpress.com/_oFXoNoR
It didn't work as was unable to control temp and upon closer inspection the Triac had shorted. Replaced Triac. Tested fine with an incandescent bulb. Thought maybe it just a dodgy Triac fitted and tested the hot plate again and popped the Triac.
Its a BTA16-800b Triac and the listing for the dimmer claims 2000W.
Maybe using with a heater is just not advisable.
For the record I have some BTA24-800 Triacs but not really sure I want to blow another just for fun!
That measurement or nameplate is wrong. You are getting just under 200 watts. for 600 watts you need to be at about 80 ohms and that would take about 2.75 amps. It sounds like maybe you have a short in the hotplate or an unknown ground.
@gilshultz
You are correct. I just did the maths.
Strange things are afoot.
220/450 would give me 0.48A, so only 107W.
The heater is sort of jammed into a slot in the aluminium extrusion that makes the hotplate, so going to have to use the cunning of a fox and extreme violence to liberate it and check the resistance again.
Will report back.....
Matt
450 ohms is the cold resistance, can you measure the AC current being drawn when you connect the heater to your AC mains power ?
The Vac / current = Hot resistance.
BTW, please confirm the heater wire leads are isolated from the heater metal surface.
If you get this working, add a fuse in the circuit.
Hum , maybe use this on a ground fault circuit too.
Are you sure resistance is 450Ohm @31°C and 52ohm @230°C?
That resistor inside the plate should be a ptc so its resistance should increase with temperature ( to reach an equilibrium at certain temperature 230°C in your case ).
If It is a ptc it could have a very lo resistance when cold, so maybe it safer to start the dimmer low then increasing it in a few steps.
Also when did the triac popped ( initially when triac was cold ) or after some work ( when triac was hot, how hot, dissipator seems very small, verify if dissipator is isolated from mains )?
@rsmls
Thanks for your reply.
And thanks for the link, but I do already have a 200mm x 200mm controllable hot plate. I also have a little 50mm x 50mm one.
I got the hotplate that I showed in the original link just because it was cheap as chips and sometimes the 50x50 is not big enough and the 200x200 is a bit cumbersome. And seeing as I've had that AC dimmer kicking around for ages I though that I'd see if it would control the temp. But no joy unfortunately. At least not yet.
On the flipside, I modified my laminator so that I could control the temp when making toner transfer PCB's, and that uses an OMRON SSR that I control with PID from an Arduino Nano, and works rather well. The temp is measured with two 100K thermistors (same as used on my 3D printer) and the PID seems to keep it within a couple of degrees. So maybe I should consider something like that instead of this AC dimmer circuit.
Buying stuff is easy, but modifying and making stuff is far more satisfying
Anyway. Onwards and upwards!
Cheers for all the help. We'll figure it out somehow.
@davidefa
Definitely 450ohms when cold and 52ohms when hot.
When cold, and with multimeter hooked up measuring resistance, if I put my hand on the plate to essentially warm it up above ambient, then the resistance starts to reduce.
I can't really say when the Triac died. Maybe I should throw another one in there and stick a scope on it. Purely educational at this point. Might help us all understand what's going on.
But first I think that I'll see if I can liberate the heater from the extrusion. It was only a couple of bucks, and I like to pull things apart
Matt, I understand and can relate. I still have one of those small hot plate/heating elements tucked away somewhere for similar reasons. It's quicker, easier and more energy efficient to use it instead of the big 800W unit for small PCB's and/or stuff that doesn't have to be heated up as far. However, I've not yet gotten around to building a temperature control for it. I would have followed a similar approach you're following, with a TRIAC-based circuit.
However, if I compare the time & energy needed to get this done vs. just unboxing the big unit and turning it on, the latter is still the quickest route to get the job done. I guess that's where my project got stuck. There's always much more to do so I don't get round to DIY-ing the smaller machine.
Ok definitelo not a ptc, so disregard the consideration I've made.
If you are hoking the scope to the 220Vac circuit be carefull, if you have a bench scope powered by the 220Vac ( without transformer/dc supply ) you could have the gnd connected to one phase of the main ( and when you connect the gnd alligator... you won't be happy, I learned the hard way ).
If the scope is battery operated or isolated, no problem.
@davidefa
On the scope. Thankfully never used my mains powered scope on a mains powered circuit. I use the battery powered handheld in such situations. Seen enough YT vids to know that it's a recipe for disaster!
But thanks for the warning!
Matt
, maybe use this on a ground fault circuit too.