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Panther256 · Aug 13, 2017, 10:25 PM

Hi all,
I am working towards creating a home coffee roaster for personal use. Here is my electrical information and question(s):

I have a 240 VAC, 30 Amp circuit.
I have purchased a 240 V, 22.5 A dryer element.
I would need to control the element with a dial (Infinite Switch or Variable Voltage controller?)
My question is: What components will I need between the outlet and the element to safely handle the 240 VAC @ 30 Amp and be able to control the level of power to the element?
Researching online I found that Infinite Switches are usually rated 15 Amps or under. I then found Variable Voltage Solid State Controllers which sound like what I may need. Then I started thinking that I would probably need to convert to DC... So here I am!
Thank you in advance for anyone who can guide me in the right direction to make this happen!
-- Panther256

ma0641 · Aug 14, 2017, 12:07 PM

Why would you need to convert to DC? The dryer element ran on AC. Resistance loads don't care if they are AC or DC. How big is the roaster? I might have gutted a wall oven for the elements and used the thermostat from it. Dryer elements are coils that would require an enclosure and a fan to keep them cool or they can burn out without direct air flow. Because of the design of an oven element, the wire itself is in ceramic insulation, it can be heated in open air without burning out. A 240VAC controller with that Amp rating is going to be pretty pricey.

Panther256 · Aug 14, 2017, 06:10 PM

That's exactly why I came here! Thank you for letting me know that AC/DC doesn't matter for the Resistance load.

The coffee roaster will have an air intake using an inline duct fan which will blow across the dryer element. The dryer element will be enclosed in ceramic eventually but for now I may just make do with fire brick. The dryer element will duct up to a bean chamber (mesh bottomed steep-walled metal funnel). There will be a vent hood to catch any debris and chaff and throw it outside.

The concept of a fluid bed roaster is to push enough air through the bean chamber to create a smooth convection. (Google: Sonofresco or Artisan 2.5 for commercial product examples)

So to recap: Wall outlet to Power Switch. Power Switch to Variable Voltage Controller (I found one that meets specs for $115). Variable Voltage Controller to Dryer Element. Everything else is simple COTS (consumer off the shelf).

Thanks for information! Roasting 1 pound at a time, taking 35 minutes sux! The goal here is to roast 10 - 15 pounds an hour which can be done. If anyone else is curious, this is based on the two aforementioned companies roasters. Artisan has a good video on using their product and if you pay close attention, just about all components are mentioned.

--Panther256

Stratmando · Aug 18, 2017, 08:38 AM

I would look up Temperature controlled relay. I have had good luck with Love Controls, About a 2"X2"X3" package with digital control, It used a "J" Type Thermocouple,
Then a 30 or 40 Amp Solid State Relay.
Can provide Links or additional help if needed.

Panther256 · Aug 18, 2017, 11:21 AM

Thanks, Stratmondo! I'm definitely going to incorporate something like that in "version 2". I'm just about set with parts for the first attempt now. Ultimately I'd like to go with full computer control so I can do profiling but for now I want the experience of building it so I can refine my next attempt. I will definitely bring my questions here when I am ready to proceed!