Roaster PID II

After using my roaster PID for a while, I decided there were some things I wanted to upgrade.

That PID worked fine, but it was too much work to setup.  I was using a variac to control fan power, and the PID to control heater power.  I was also monitoring Bean Temp (BT) and Environmental Temp (ET).  ET is the temp of the air, right when it enters the roast chamber.  In my air popper, I have the ET probe mounted in between the slots, so it is just at the edge of the roast chamber.

So, I had to plug in the PID and variac, then plug the heater into the PID, fan into variac, and connect the ET and BT probes.  I also had to connect the PID to my laptop, and the meter I used for BT to my laptop.  When I was finished, I unplugged everything, and stuck it in a box.

I was looking for a bigger box, where I could mount outlets.  I also wanted to replace the variac with a boast transformer and a fan dimmer.

First, I needed a bigger box, and for a different project, I was making an order from surplus sales, so I also ordered a Nabu Case.
I already had my PID, from the previous version.

Here is the schemtic for this version of PID

My parts list

Nabu Case at top of page
24V-20VA transformer (used to boast the AC for the fan)
150VAC Panel Meter
Fan dimmer made by Lutron from Ebay
D2440-10 40A Solid State Relay, made by Crydom
Ebay RS-485 converter
Two On-Off switches I had in my junk drawer
One more on-off switch (single pole, single throw) I bought
2 AC outlets I had in my junk drawer
Various Wire
AC plug


The main electrical difference between this and my first version was I added fan power.
I picked a 24V, 20VA surplus transformer.  Transformer input is wired across 115 VAC line and neutral.  One line of the output is also connected to 115 VAC line.  I tested which line to connect.  If you connect the wrong output, it will subtrac from 115.  Of course, the first time, I picked the wrong wire, and ended up with around 90VAC.  So, I reversed the connection, and then got around 140VAC at the remaining secondary.

That secondary is then connected do a fan dimmer, then to a switch.  From the switch, it goes to the fan outlet. I also connected a panel meter across the outlet, so I can see the fan voltage.  I am glad I added that meter, it's nice to see the fan voltage.

Here is a picture of the power side of the PID.  The AC comes in on the left, transformer is in the middle, and the dimmer is on the right in this pic.

Rear of box.
The wire below the fan outlet is for the RS-485 communication link between the PID and my laptop.

The other side of the rear.  The thermocouple connector is connector is next to the heater outlet

The thermocouple connector is epoxied to a angle bracket, which is screwed to the chassis.

Here are some pics of the rest of the inside.

The front.

With the cover on.

Here it is, with my popper on top, ready to roast.  I have velcro to hold the meter down.

I can just leave everything connected now.  I roast on a table in my backyard, so I just have to carry this out to the table, along with my laptop, and the plug it in, along with the RS-485 and USB connectors to my laptop, and I'm ready to go.

It is also nice to have switches to turn off and on things, I used to have to unplug the heater to stop the roast, or unplug the PID to reset it.

The one problem I have is that the fan power fluctuates when the heater turns on.  I used larger gauge wire, and star wiring for neutral, but still see the power fluctuate.  It did get better when I increased the wire gauge, but still happens.

Building a Roaster PID

This blog describes the PID I put together to control the heater in the Popcorn Pumper I use to roast coffee with.  The Popcorn Pumper has been modified to seperate the fan and heater power, with a standard AC plug for each.  So, I just needed to put together a PID that I could pluf the heater power into.

I got lucky, and got a good deal on this PID, made by automation direct, on ebay
Automation direct SL4848_Series / SL4848-VR


My parts list was

SL4848-VR PID by Automation Direct
D2440-10 40A Solid State Relay, made by Crydom
Metal chassis from a local surplus electronics place
Ebay RS-485 converter
16 gauge, 3 conductor wire from Home Depot
Fuse holder from my storage box
Misc wire from my storage box
Type K thermocouple wire and female thermocouple connector from Mcmaster Carr

Here is the assembled unit.



Here is a simple schematic I made, shows how I connected everything.



I had to cut a square hole in the front of my box, to mount the PID in.


In the pic above, you can alse see the yellow thermocouple connector sticking out of the top.
I used this connector, from Mcmaster
Female, Type K mini thermocouple connector
This is compatible with the Type K thermocouples you can buy from Ebay.

I drilled a few holes in the back.
One for the fuse holder. Fuse is not shown in the schematic, but connected to the Line of the AC input plug.
Another hole is for the AC power line coming in.
Last hole is for the AC socket line, which is what the heater power from the roaster will plug into.



This is the RS-485 converter I bought from ebay.
The PID has a RS-485 output. I just connected the data-, data+ and ground wires from the converter to the PID, and plugged the convertor into the serial port of my laptop, and then I can use my laptop to control the PID.

The software required is at the very bottom of this page

http://support.automationdirect.com/demos.html

Here is a pic inside the PID, showing the back of the PID, the SSR, and the AC in and out wires.
The twisted white wires, and grey wire are the RS-485 wires, going to the converter.

Heres a pic of the thermocouple installed in the Popcorn Pumper, to measure bean temps