DIY Temperature Controller for Heating Blankets

[Robbie Collins]

I'm thinking about building a temperature controller using a PID unit off of eBay. Does anyone have experience doing this?

[Keith]

[Eric Steven Johansen]

Diagram please.

[Keith]

also this might help

very simple to operate. i'm sure the unit your getting will be similar 

[Keith]

the units are very easy to program 

many different types of thermocouples out there or use an RTD

degrees f or c

i set mine for 300 f the first time left it there for ten minutes with heat then over night to cool down

i'm sure you could place the bent side in the mold while you do the other side,then place them both in the mold over night to cool

[Keith]

[Keith]

[Robbie Collins]

Nice job! A few questions: One black wire is ac supply and the second becomes white wire going to blanket? The silver mesh wire coming out below the PID controller is the thermocouple? If so, what is attached via the yellow connectors? Those connectors are usually for type-k thermocouples, if I'm not mistaken.

[Robbie Collins]

Here's my preliminary circuit diagram:

I have everything ordered except for an aluminum enclosure and a k-type panel connector for the thermocouple. I scavenged an aluminum heat sink for the relay from my box of old computer junk.

I did the circuit a circuitlab.com...check it out.

[Keith]

first q  yes the black wires are as you said. an old computer cord sliced in half 

the heating blanket has the mating connector to the cord

second yes silver wire is thermocouple  

and yes the yellow connectors are type K

this unit will work with many different types of TC

now i believe you should have the heating blanket (HB) being fed buy the output of the SSR

most of these units can't handle that high a current load 

when i get some time at work i'll draw up a schem.

later 

keith

[Robbie Collins]

Correct me if I'm wrong, but the SSR only switches the Hot off and on while the neutral comes directly from the wall (which is how I have it in the schematic).

The yellow are k-type connectors...but what are they connected to?

Here are two schematics I found this morning. The first is for a kiln and the second is the one JC Clark used in his Guitarmaker article in 2006. He seems to have the relay wired differently.

Of course, I don't have the relay and manual in hand, having just ordered it so the schematic will change.

Also, I will add two power lights, move the fuse after the on/off switch, and possibly run a 12v fan on the heatsink with the SSR trigger circuit. Also, a metal oxide varistor (MOV) across the SSR's load terminal for surge protection. I'm guessing that the relay gets hot from resistance when it's switched off, in which case, the fan will be of minimal use since it would come on with the relay.

[Robbie Collins]

Oops...the additional schematics:

[Keith]

Robbie,

the heat sink from a computer should be more than enough to cool down the SSR

no need for a fan when you only use for ten minutes at a time

the SSR circuit should only be used for the SSR 

when you turn on your controller it will light up like a xmass tree, no need for on light.

it also will have indicators to show that power is at  the heating blanket

do not use the relay inside the controller to drive the heat blanket it will not handle the high current

you can wire your light indicator to that

i hope i'm not boreing you

hope this helps

keith