Another PC oven surrenders to a PID ...

[OS OK]

It had to happen sooner or later.... thanks to Conditor22 and a generous surprise package that showed up this morning. He and I made a horse-trade for one of his spare Lee 10 pound furnaces. In that box he included a Rex C100 PID, a solid state relay, a thermocouple and a fuse enclosure...had no idea these controls were coming!
Thank you Jim, I appreciate this very much.

I decided to gut all the controls but the 'ON - OFF - Timer Set' switch and the pilot light. I removed the 'thermostat & dial temp. setting' and the 'selector switch' that selected the upper and lower heat elements and controlled the fan. I cut the lower set of elements out permanently and wired it back using the upper element only. It is a small oven, the upper elements are all I needed.

Everything tucked in nicely to the vented control area of the side panel...vents are bottom, side and back...



Only one test so far...as it is empty, 180ºC = 400ºƒ...



the thermocouple is in the rear on the right side 1.5" above the tray...



Heated air is drawn into the fan across the top of the tray on the right at the same level the thermocouple is mounted and is blown out from the top slots between the elements and that is the circulation. Heated air also blows out the bottom slots between the now defunct lower elements to heat the tray from the bottom...



There was plenty room in the back area of the enclosure for the thermocouple and the solid state relay...



In the front is the PID...fan in the middle...



Only thing left now is to take another PID I have and put the thermocouple in the control area now that's now closed up and monitor the temperature there while in operation. I think these controls are rated at max. 75ºC/167ºƒ. If the control area exceeds that I will insulate the oven wall side of the enclosure and add a small fan to the rear to pull in fresh cool air. This should take care of any overheating of the controls.



After that, I'll load the tray full of 230 gn. 45 casts and find out how long I need to set the timer for a single batch starting from a cold oven.
I think I've pretty much covered all the angles but if one of you fellas see something I've overlooked, please bring it up in a comment.

[kungfustyle]

Nice job.

[Valley-Shooter]

"wired it back using the upper element only. It is a small oven, the upper elements are all I needed."

So you no longer have an oven, it's just a broiler now.
Not sure if you enough heat to warm the bottom of your baking tray/screen .

Sent from my Pixel 4 XL using Tapatalk

[joe leadslinger]

Geuss you didn't catch the fan part.

[Valley-Shooter]

Guess you didn't catch the fan part.

Yes, I read that part, but where does it blow?
Across the top?

Sent from my Pixel 4 XL using Tapatalk

[OS OK]

Yes, I read that part, but where does it blow?
Across the top?

Sent from my Pixel 4 XL using Tapatalk

(copied from the first posting...)
Heated air is drawn into the fan across the top of the tray on the right at the same level the thermocouple is mounted and is blown out from the top slots between the elements and that is the circulation. Heated air also blows out the bottom slots between the now defunct lower elements to heat the tray from the bottom...

Take a look at a convection oven sometime, the fan system works the same in every one. I used a cigarette to determine this. Smoke drawn in at the center and ashes blown off at the extreme slots top and bottom, between the heating elements where the air increases heat before it once again is drawn in across the top of the tray.

My BROILER as you call it will do just fine as it used to cycle too much during a batch and overshoot the setting using both elements top and bottom. You might notice again, I've tested it once already...less than 5 minutes the PID was up to temp. from a cold oven...



Before I run a full tray and get the timing correct, I am waiting on an insulation blanket and a cooling fan I ordered off Amazon.
I'll post results then.

[oley55]

With the PID controlling the temp, what was/is the down side of keeping both heating elements? My PID will cycle almost continuously once up to temp while the two elements quickly get my oven/boolits up to temp. Have you noticed a longer heat time?

[Valley-Shooter]

OS OK,

Thanks for posting all the pics. Never see someone mount the pid in the oven .

My toaster convection oven just went bad. thermostat not controlling max heat.

So I'm looking to rewire mine with a pid.

Sent from my Pixel 4 XL using Tapatalk

[OS OK]

With the PID controlling the temp, what was/is the down side of keeping both heating elements? My PID will cycle almost continuously once up to temp while the two elements quickly get my oven/boolits up to temp. Have you noticed a longer heat time?

The downside was two fold...first, the bimetalic strip/contacts that ran the two elements was very sensitive to staying put where it was set. It was very insensitive to keeping a constant temperature as it would open the heat circuit and allow the oven to drop to around 365 ~ 375ºƒ before it would close again. When closed it would open as much as 20 ~ 25ºƒ above the setting desired, 400ºƒ. A never ending battle to keep it right, many times having to watch the cycle to make sure things were OK in the oven.

Second..having two elements top and bottom create a heck of an overheating 'radiation' of the heat when they were on, too close and you can feel the searing heat. Those suckers would glow red as the thermostat cycled. In the end my PC'd cast were being cured from say 375ºƒ anywhere up to 425ºƒ, not hardly a constant oven environment. Several times I've caught it as high as 450ºƒ because the temp. adjusting knob got bumped and I didn't know it.

My tray used to be placed on the slot above where it is at in this picture...



That way it was about midway between the two raging red elements as they heated. The way it is now the tray is lowered away from the upper element and subject to a little less harsh temp. swings as they heat up.
The intention is to make less harsh the temp swings using the PID...it will bring the oven up to temp (empty) in less than 5 minutes, the elements above do glow red but I can't avoid that other than dropping the tray farther from them. Sorta like standing a couple feet farther from a campfire where you don't feel the searing heat yet your still warm against the cold night air.

When the PID is up to temp. it will sit there and flicker on and off in very short duration as it maintains the oven at 400ºƒ. This type of cycling is fine by me because the elements never are on long enough to glow red. The old system had too wide of 'on and off' variation and allowed the elements to glow red every time it was trying to maintain the set temp.
One element should, I think be better...may take a few minutes longer to bring a full batch of casts up to the temp. where the PC melts and the true timing would start but this is not important to me.

I am in no hurry as while an oven of PC'd cast are curing, I'm on one of the pots casting.

People get used to what they are doing with an unmodified oven and then start thinking that their way is the only way when in actuality, many of them have no idea what is going on inside the oven as far as temperature swings or temp. values are...all they understand is the markings on their knob, set to 400ºƒ and walk away...there's plenty proof of this floating around, I don't imagine too many are honest enough to post their mistakes and fess up to it.





All I am trying to do is coat my cast and do a fine job of it...if it takes a little longer...so be it.
Once I have the other parts-n-pieces here and the final work is done, I'll be casting and coating again and I'll post to this thread the time it takes. If one set of elements won't do the trick, I have the bottom elements I can put back into the circuit. No harm no foul.

[OS OK]

OS OK,

Thanks for posting all the pics. Never see someone mount the pid in the oven .

My toaster convection oven just went bad. thermostat not controlling max heat.

So I'm looking to rewire mine with a pid.

Sent from my Pixel 4 XL using Tapatalk

If your controls are on the side of the oven be fore-warned that this compartment will get almost as hot as the oven inside. You have to insulate that oven wall between the control compartment and the oven. I am also adding a computer cooling fan.
It would be much simpler to put your PID in a separate box, this way you can use the same PID for oven or pot.
I am doing it this way only to keep the controls within the oven, in my old'demented view of things, it looks better and I don't have more equipment to deal with in an already overcrowded shop.
This is what I've ordered to insulate that side of the oven and as a little extra insurance, I'll install the cooling fan too.

[cwlongshot]

Thats awesome Charlie!! Great writeup too. Did ya do a video??

Willie Bulletman made me a PID last month and I finally got it installed yesterday. (Video is up)

Love ta see!

Im ordering a couple
More thermo
Couplers as I run three pots and two ovens.

CW

[OS OK]

Thats awesome Charlie!! Great writeup too. Did ya do a video??

Willie Bulletman made me a PID last month and I finally got it installed yesterday. (Video is up)

Love ta see!

Im ordering a couple
More thermo
Couplers as I run three pots and two ovens.

CW

No CW'b, no video...I am burned out on shooting/editing videos. Today a picture is what you get from this old'Lazybones.
I thought I saw your video when it first came up, nice package...portable and all.
Question...? Is the SSR connected to a heat sink. I think they will go out prematurely if they can't bleed off the heat. I thought that box the PID is in was plastic is why I asked.

Here is the video we are talking about...

[fivegunner]

Wow thats a great job, I think I will build one like it, Thank you for sharing

[Cast10]

Wow! Super custom install! I like it!

Fixing to build mine for melting pot.......

[OS OK]

Wow thats a great job, I think I will build one like it, Thank you for sharing

Please see post number 10 and my warning regarding building controls into the side of the oven...

charlie

[Hossfly]

The most accurate way I’ve found to sense the temperature of a boolit is a way another member showed, (Slide)IIRC. Take the boolit you intend to cure and drill a hole to the center, place the thermocouple tip into it, close with glue or epoxie, or just smash to hold in place. I use several of these and a separate thermometer to monitor the temp of boolits I’m curing. The PID units are 100% way to go, and are very inexpensive. You did an excellent job on converting yours.

Just another way to check temp and monitor that process. Some convection ovens come with pretty good controls. Mine controls at 400 when set at 425, with all original equipment. I would convert if it didn’t. I have melted ingots on my hot plate thinking I was just keeping them hot for adding to pot.

[OS OK]

The most accurate way I’ve found to sense the temperature of a boolit is a way another member showed, (Slide)IIRC. Take the boolit you intend to cure and drill a hole to the center, place the thermocouple tip into it, close with glue or epoxie, or just smash to hold in place. I use several of these and a separate thermometer to monitor the temp of boolits I’m curing. The PID units are 100% way to go, and are very inexpensive. You did an excellent job on converting yours.

Just another way to check temp and monitor that process. Some convection ovens come with pretty good controls. Mine controls at 400 when set at 425, with all original equipment. I would convert if it didn’t. I have melted ingots on my hot plate thinking I was just keeping them hot for adding to pot.

THANKS FOR THE TIP's.

You know, I got this oven back when I joined up here on CB's site and PC was already the 'new-thing' and developing. Like others I was happy with lube-sizing but this PC thing looked awful good to me. I go to K-Mart and buy the cheapest 'convection oven' they had...it was small also so I am limited to say 180, 45cal, 230 gn. casts...small batches like this is not really a problem.
BUT...
If I had it to do over again I would have spent the extra money to find a digital oven, If I had I wouldn't have had all the trouble I have been through up to now. Sometimes the right tool in the long run...is not the cheapest.

Something I've seen some friends do is locate an electric wall oven that is being pulled from a remodel in a kitchen and put that on a small piano type dolly, wire it with a welding 230VAC single phase plug so they can use an already existing outlet in their shop and use the wall oven for PC work.
They often fabricate various parts and pieces in their welding projects and they like the option of having them PC'd rather than a rattle can of paint.
You can coat a pretty good size object in an old wall oven.

[OS OK]

The Ceramic blanket and the cooling fan came in today, got a little more done towards an end.

Had to remove the PID & SSR & thermocouple to install the insulation...



It will probably be next week before the heat sink & thermal paste for the SSR gets here, then I can put it all back together.
Never used this type insulation before, spun ceramic or some such...



feels weird to the touch so I followed precautions and wore the whole safety thing ~ eye, breathing & hands. I guess I'm getting too old to flirt with having any more ailments than I have already.

More to come soon.

[Hossfly]

OS OK, you are wise to head those cautions, I’ve worked with that insulation doing boiler work for 30+ years and still do. When I just look at it I start coughing. Still have several rolls of it in my shop. Very good high temp insulation, was used on back doors of boilers for turn around of flue gasses.

[jsizemore]

Recovery time is greatly improved with the 2nd element running. I use insulation like you but on a large Oster. I mount the SSR directly over the vent slots at the back. I've got 2 shelves so my 8" thermocouple probe is through the opposite wall from the convection fan. With all the insulation I haven't had cabinet temps in the control area be a problem but that circulation fan for that area will add a much longer life to your PID not to mention more accuracy in your oven temps.