"It worked when I got it"....0.9 cu ft vacuum oven hack

According to NPR, the most popular song in Nigeria is a ballad called “It worked when I got it” which refers to Chinese goods.
So, I got one of these nifty 0.9 cu ft vacuum ovens discussed in this thread.
Vacuum Ovens are Commoditized
It worked when I got it…:laughing:
Then the control system locked up and the temperature headed to the moon.
Sometimes I could get it to control but usually it just heated and heated.
Taking off the side panel revealed the problem and this is what drives me nuts about Chinese stuff.
The mechanics of this thing are pretty good but the electronics have a big issue.
They used a naked Triac with no heat sink as a relay to control the heater power.
The Triac overheats and locks on resulting in overheating until the Triac cools down.

This is an easy fix.
I replaced the Triac with an AC solid state relay rated at 25 amps.

Now it controls fine but overshoots on initial heatup.

That could probably tuned out if I knew how to adjust gain, etc on the PID controller but there is no documentation.
Still, it works and what can you expect for a $500 vacuum oven.


Just found an instruction manual for the REX C900 controller.
It is not a PID controller but you can change other parameters.
REX C900 controller manual

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I’ll read the rest of the post later but please post a link to the song


Wish I could.
I heard it on the NPR show “Afro Beat.”
Google can’t seem to find it either

hy broo i have same problem can you send me a full pic of the wiyeuring on yeur SSR 25 pleas

The wiring in those things is a mess.
The triac terminals are like this.

The solid state relay terminals are like this.

The wires that go to the two main terminals of the triac go to the output side of the SSR in no particular order.
The gate wire for the triac goes to either of the input terminals of the SSR.
Then you need to hook a line ground to the other input terminal from somewhere.
When it is done it looks like this.

tacks to you i got mine fix i cant balive how much that cheapt out on this part but it steal over chut it every time ovencholy levels of but now end then temp whouls just start going up end up end up not a thing a could do about it glad i sold it get a good 8 shelv BVV 0.9 oven