Building my 120vac oven

The welder was a harbor freight 90amp and it was awful. It actually got too hot during this project and i couldnt screw the nozzle off to clean the tip or change it or anything so i got my money back. I will buy a lincoln before my next project. With that HF welder, i could get decent welds sometimes, but most ended up like the one on top. It literally had only two power settings, and this was at max power. Part of it could be me being inconsistent, but i swear sometimes it would just pop around for no reason sometimes. I mean i could one good weld and then immediately do another and it would just pop like crazy and i couldnt get a bead started worth a crap.

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I will switch off the element before reaching in, but of course that has a human element and i cant be distracted or i might possibly forget. With the system unplugged i did reach in with my tongs and try to bump the coil and it is difficult to do accidentally i think.

I am finding this oven to be pretty sensitive. It has been running awhile and it hasnt achieved the +/- 1 degree at all. It tends to run a little hot. It may drop 1 degree below what it is set for, then the element kicks on and it can go as high as 10 degrees over and drop back down and hover around 3 or 5 degrees hot a bit and then either slowly drop some more or jump up about 10 degrees.

Still 1000x better than a coffe can forge and plumbers torch!
 
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If you know the average temp runs a bit above the set point, use that information. For example, if you the oven overshoots by about 5° and you want to austenitize at 1475°, then set the PID for 1470°.

It can take a PID a while to "learn" the control parameters, and some don't have the programming to do it completely.
 
With your setup, I HIGHLY recommend adding a door interlock. It is just a limit switch ( roller switch) that is turned on when the door is closed, and open when the door is opened. It is placed in one of the low voltage DC lines going from the PID to the SSR
 
When an ssr fails, it is usually in a way where the ac terminals conduct and so i would think any switch in the dc circuit between the pid and ssr is not failsafe.
 
I started heat treating my first blades. I had a 2 blade joint i was making and i did the spring with the coffee can forge and then messed up the blades when trying a new nail nick cutting idea. So i will finish it up and see how it does.

My oven hot 1475 in 4.5 minutes which is pretty nice.
 
That has been my experience: most of the SSR failures that I have seen have been "fail closed".
When building HT ovens, I use a contactor in the AC supply line and energise the contactor through the door switch. I am in the UK, where we have 230V line-to-earth/ground, and there are obviously many differences between our wiring practices and those in the US. Most of them seem reasonable, but the door switch in the SSR switching is one I have never been able to understand.
 
Well, this is the most uniform blade i have ever pulled out of oil!

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I will rig up a door switch soon, it cant hurt having a manual switch and an automatic switch. I dont want to get deaded!
 
When i turned it on this morning at set it to 1475, it stayed a little low, around 1455 to 1465. Then when i opened the door and stuck the first blade in, it dropped a 100 degrees and then climbed and stayed right on the money. Then after quenching that blade and sticking the other in, it dropped to 1300 degrees and climbed to 1500 and stayed there awhile and slowly dropped to 1475 to 1485.

I think i should probably let it maintain 1475 for awhile and let it learn and stabilize.
 
Most of them seem reasonable, but the door switch in the SSR switching is one I have never been able to understand.
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I speculate it comes from Homegamers who ”saw on internet” or manage to rig up something ”that works” but fail to understand or care about its limitations.
 
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An SSR is basically an optoisolator paired with a triac that switches the mains either on or off. A breakdown where the triac would fail and conduct would only happen if the voltage across the triac on the live AC end is close to or has surpassed the breakdown voltage of the triac or SCR inside (which does not happen when using mains supply).
The only realistic condition where a SSR would fail in this case would be insufficient heat sinking capabilities and overheating, and it would no longer conduct.
The door interlock switch is pretty much essential when dealing with mains power. It's a very rudimentary low voltage DC switch that hooks onto the optoisolator low voltage side of the SSR in series. It basically turns the SSR off and it no longer conducts. Also, I agree that if an SSR does fail somehow due to crossing the breakdown voltage, the door interlock switch wouldn't be useful to kill power. Which is why I have indicator lights and an element kill switch in series with the elements.
You really can't take any chances with dealing with potentially deadly voltages.
 
I agree with the above. If an SSR fails, it will normally just be an open circuit, as what generally fails is the internal LED. I have worked on a lot of electronics carrying everything for 120AVAC to very high energy RF. Almost every piece I worked on had a door interlock that shut off the energy if the door was opened. The most common type was a roller type limit switch configured in NO.

For those who don't know the term "limit switch", this is what they are:
https://www.ebay.com/itm/10-pc-TEMC...74AAOSw~uJaTpe7:sc:USPSFirstClass!23454!US!-1
 
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