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Compression Oven/PID Wiring (240v)

This topic contains 3 replies, has 2 voices, and was last updated by  Chris 1 year ago.

Chris id-trojan

Compression Oven/PID Wiring (240v)

09/09/2019 at 19:10

In the schematics provided by precious plastics “PP” (thank you by the way), the wiring diagram shows a switch only on one hot leg.  The other hot leg is wired directly to the oven/heating element.  I think this is very problematic.  With this wiring you have to have a seperate manual shutoff switch or at the very least a wall plug, then plug and unplug every time you use your oven (United States Electrical Code Requirements).  If you don’t you’re oven will essentially allways be hot.

In my case I tried the wiring shown in the PP schematic and I find that when I flip the switch, my oven actually continues to have power, but only 120v not 240v.  So it is not heating up but the PID is still powered and so is the SSR.  I suspect this is because the 120v on the nonswitched line is still sending power to the elements on the one side and backfeeding to the other hot leg that was just switched off.

Has anyone else had this issue?  I am installing a double pole 30 amp switch today and then both legs will be switched, but I thought I’d ask the forum how you handled 240v power?  Maybe it’s different overseas?

One other note on the PP schematic.  In future renditions, I’d recommend putting a note on there that every PID does not following the same numbering.  I used an Inkbird and it was completely different.

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09/09/2019 at 19:21

Hey @id-trojan,
nice to see a new committed user on board. That’s right, the thing is essentially hot and one solution would be to double the amount of SSRs per PID. I don’t know even the regulations for the EU but I haven’t seen 2 pole SSRs either. One DIN rail SSR alone is already 30 – 100 Euro (or 8 from China) and recently I figured I need actually 8 of them to make it alright for an extrusion alone.

Other than that, PP wise, I think it was meant for ‘build-cheap and improve yourself’ or so.  No idea, I am still puzzled 🙂

Happy to see more input on this too.

btw. and whilst at it, pulling up old topics in mass makes it a little hard for the other veterans here but no worry, nothing we can’t deal with  🙂

09/09/2019 at 20:04

I had an electrician friend review my plans.  He indicated that yes, you can leave the second leg hot as this is actually pretty common when wiring industrial motors and other heavy 240v equipment but only if you have an emergency shut off close by OR it is a plug in/plug out appliance.

I’m going to wire both hots into a double pole switch, but I should not have any need for second PID or SSR.  When switched on the hot 120v lead does actually energize a heating element because the elements required 240v to run.   However, I do want my switch to completely shut off power, not just one side.  I’ll try to remember to take pictures and post of my frankenstein looking compression oven ($10 oven + $50 PID, SSR and wiring + one day of welding).

09/09/2019 at 20:12

Here’s a link to the best resource I found on the web for PID wiring.
George with Barley and Hops Brewing

He explains everything in pretty simple terms and has videos for each of the most popular PID models, both 110v and 220v.  Only thing I wished he added was how to add an indicator LED to show when the oven is calling for heat … something I can see from a distance with old man eyes!  LOL

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