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Homeroasters - Home Roasting Coffee Community » BUILDING A ROASTER » Fluidbed Roaster

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Current draw pulses using SSR
Jwheld	#1 Posted on 06/20/2023 8:59 PM
Newbie Posts: 15 Joined: November 28, 2019	I have been controlling my home built roaster with SSVRs + Rheostats. One for each the heating element and blower motor. The way I have it wired, there is one power 120V going to a main switch before splitting off to the blower SSVR and secondary switch then to the heater SSVR. Depending on the heat setting I have to adjust the fan due to current draw. I currently use TC4+ & artesian to log roast profile. Recently I've tried to modify a little more with TC4+, connected to SSR, to heater so i can eventually try PID control. This seems to be working, I'm able to adjust the heat power through the software. Problem: The fan now pulsates low/high with the on/off of the TC4+ controlling the SSR/heater. Thoughts on how to rewire this to prevent? Is my only option to use two separate circuits for each the blower and heating element? Thanks for all your expertise in advance!


btreichel	#2 Posted on 06/20/2023 11:15 PM
1/4 Pounder Posts: 182 Joined: May 07, 2007	You are basically doing PWM, and the frequency has to be above the response of the thing you are trying to control. Also, I've seen this reduce heater coil life.


renatoa	#3 Posted on 06/21/2023 12:55 AM
Administrator Posts: 2744 Joined: September 30, 2016	Please, can you give an example of the SSVR used ? Is TC4 doing any control of heater/fan ? The only place where are produced pulses in such setup is the TC4 heater control channel, known also as OT1, when TC4 sketch is compiled for CONFIG_PWM mode. But the TC4 outputs are designed to drive SSRs, not SSVRs... that's why my initial question...


Jwheld	#4 Posted on 06/21/2023 11:43 AM
Newbie Posts: 15 Joined: November 28, 2019	Quote renatoa wrote: Please, can you give an example of the SSVR used ? Is TC4 doing any control of heater/fan ? The only place where are produced pulses in such setup is the TC4 heater control channel, known also as OT1, when TC4 sketch is compiled for CONFIG_PWM mode. But the TC4 outputs are designed to drive SSRs, not SSVRs... that's why my initial question... You are correct. For clarity, I replaced the SSVR controlled by Rheostat (for heater), with a SSR controlled by OT1 on TC4. I still have SSVR controlled by Rheostat for the fan motor. Before now, TC4 was only used as thermocouple interface with artesian. The control with artesian on heater is working, but producing the pulses in fan as earlier described.


renatoa	#5 Posted on 06/21/2023 12:31 PM
Administrator Posts: 2744 Joined: September 30, 2016	This means the fan SSVR is not wired to mains, but to heater... thus following the on-off pulses of heater PWM control.


Jwheld	#6 Posted on 06/21/2023 5:41 PM
Newbie Posts: 15 Joined: November 28, 2019	Here is how I have it wired. Should I separate them to two separate plugs? Do they need to be on their own circuits? Jwheld attached the following images:


randytsuch	#7 Posted on 06/21/2023 10:37 PM
1/2 Pounder Posts: 394 Joined: June 20, 2009	If you put a meter on the AC at the fan, does the voltage drop when the heater kicks in? Heaters pull a lot of current, so it can cause a voltage droop, maybe that is what you are seeing. What gauge wire did you use? I use all 12 gauge wire for my heater wiring. When I had a fan, I could still tell when the heater was kicking in as the fan would slow down a bit.


renatoa	#8 Posted on 06/22/2023 4:12 AM
Administrator Posts: 2744 Joined: September 30, 2016	The diagram is confusing for me, I don't know how to read the mains switch, with 6 poles... Probably you mean a double pole single throw switch, and the heater switch wiring coming from the main switch output, same circuit as the fan, but before the SSVR. As sketched in the attached. I would check the wiring again... renatoa attached the following image:


Jwheld	#9 Posted on 06/22/2023 6:40 AM
Newbie Posts: 15 Joined: November 28, 2019	Quote renatoa wrote: The diagram is confusing for me, I don't know how to read the mains switch, with 6 poles... Probably you mean a double pole single throw switch, and the heater switch wiring coming from the main switch output, same circuit as the fan, but before the SSVR. As sketched in the attached. I would check the wiring again... Your diagram is correct. I figured something would be incorrect, I’m a chemical engineer not electrical engineer.

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