Any sparkies/electrical engineers here?

[freddofrog]

What is the simpliest/safest way to control the temp of these heating elements? It’s in a Behmor coffee roaster and the control panel only allows increments of 25/50/75/100%. I need it to be infinitely variable.

I was thinking of setting up a timer to pulse the voltage which is how it currently works. Eg 50% power cycles the elements on/for 7.5sec at a time. While I have created timing circuits based on a 555 IC timer chip it is still a relatively complex solution.

Other roasters have used Solid State Voltge Relays (SSVR) which seems to be a glorified dimmer switch on steroids but given these seem to be very hard to source I’m thinking there must be another way. But it does seem easy, simply connect inline to the heating elements and mount on a heat sink.

And I’ve pulled apart a few toaster ovens and bar heaters and they work on some weird variable resistor trim pot thing which I can’t figure out.

Ideas?

http://www.behmor.com.au/

 

[Aussie_Ryder]

Do you have a circuit/wiring diagram?
10k ohm potentiometer might be what you're after. If you have the circuit diagram it should be easy to enough to work out then again I haven't stuffed around with a coffee machine.

Sent from my SM-G900I using Tapatalk

 

[SF Trailboy]

Solid state dimmers should be easy to source. Contact your local electrical wholesaler.

http://www.tobins.com.au/DisplayPro...name=Solid+state+relays,+dimmers+&+heat+sinks

We sell the 10amp (Srr2510) version for $65. Strongly recommend getting the heat sink to suit which adds about another $15.

Will it work??? - I am not a sparkie, just a wholesaler....

 

[freddofrog]

Sorry no circuit diagram

Isn't that SRR2510 is $117?

 

[SF Trailboy]

Sorry no circuit diagram

Isn't that SRR2510 is $117?

If you buy it direct off tobins it is. Most local wholesalers will do heaps better, hence the other pricing. It is only rated to 10amp though so not sure what your machine is rated to?

 

[link1896]

How many watts does this roaster draw? There should be a compliance sticker somewhere on the back or bottom.

 

[chicko]

You could just use a commercial simmerstat with the suitable current rating. You only need to drill a hole to mount it. I would suggest get an electrician to look at it if your not sure about wiring.

http://www.stokesap.com.au/ROBTS0007/SIMMERSTAT-_and_-GRADUATED-KNOB/pd.php

 

[freddofrog]

The unit is rated at 1600 watts so I'm guessing each heating element is 800W.

Not sure about the current draw though I have read it people have measured it to 7.5 Amps. So theoretically 10amps is enough but doesn't leave a whole lot of room for error. Mind you there are one rated higher so possibly those would be ok.
I'll look up some specs on solid state dimmers and see what I find.

Looked up potentiometers and seems others have tried it but doesn't last all that long. Not sure why.

I did find this 555 based solution http://makezine.com/projects/adjustable-temperature-controller-heating-elements Dimmer seams easier if I can find one at a decent price.

 

[link1896]

A basic triac dimmer like this is perfect:

https://www.ebay.com.au/itm/140375889476

 

[link1896]

Make sure the heatsink is bolted to the triac (unlike the photos) with some silicon heat transfer compound. Beware the triac's tab might not be isolated and so the heatsink will have 240vac on it

 

[cokeonspecialtwodollars]

Are you intending to completely replace the original controller or install something additional inline? There are a couple of pitfalls that can be associated to either method.
1. If you bypass or replace the original controller you may loose integrated overcurrent and overtemperature protection leading to a potentially unsafe scenario.
2. If you place a switching type device e.g. Triac as suggested inline with the existing controller assuming that the existing controller has some kind of PWM output to control the temp the new component may go out of sync with the output leading to unreliable control, i.e. the old output is off while your controller is on and then in the next cycle the old output is on but your controller is off thus giving lower than expected power or potentially no power.
3. You could install a large potentiometer inline but this is fairly crude and just dissipates unwanted energy as waste heat, also careful consideration would need to be given to the power rating to prevent overheating.

 

[freddofrog]

Wish I'd seen that triac based dimmer before. Very late last night ordered a digital controller and a solid state relay . Not sure if it will work but it should. My input voltage is 15VDC so more than enough to trigger the SSR. My only concern is I don't know that the frequency the controller works at. Hopefully it's not too fast for the SSR.

https://www.youtube.com/watch?v=2Eoa95TJAKU

I am connecting inline with the existing pwm controller so still maintain all safety features/thermal protection etc. I will set it to 100% power/duty cycle and then use my DIY controller to reduce the power from there.

I've looked into potentiometers and found others have tried this method but with only varying degrees of success.