Question About sheet metal

[eclipsespeed]

Hi, im new around here and to PC'in and am attempting to build an oven out of an old refrigerator/freezer unit. I have it stripped out and am currently installing the sheet rock beams. I was planning on using 2 3000watt oven elements, and R13 or R15 insulation from home depot. If anyone has any comments or concerns about anything said so far please feel free to chime in.

My question is what kind of sheet metal do i use. Stainless steel sheet metal is crazy expensive and ive also been told galvanized is poisons once heated. Im having a hard time locating a local supply around my area so i resorted to online dealer. I found one that sells Cold Roll Mild Steel Sheet A366/1008 20ga and 16ga at a good price. They however will not give me any help on whether this will work or not. So I figured I would ask since you guys seem to know a lot about this type of stuff. So will this work or do I need something and where can I look to find it.

Any info is appreciated

Thanks,
Keith

[ed_denu]

I used 24 ga galvanized sheet on my oven. Once you go thru an initial heat cycle the oven does not release any further fumes. Most galvanized sheet is actually zinc plating which has come to be known as electrogalvanizing. Zinc tends to melt at around 1200 degree, much higher than what your oven will be heated to.

Check your local phone listing for metal supplies or possibly hvac contractors. I found 4X10 sheets for around $50.

[FigureLLC]

galvanized fumes are a problem when welding, and there are even mixed stories about the dangers of those besides feeling nausious, but you won't have a problem with an oven. i used 20ga (i think) galvanized. i think i paid $26 a sheet for 4x8 from an hvac company. the company i called before that one wanted double, so it's definitely worth it to call around. i used R15 fiberglass insulation and it seems to be working great. one note: remove the kraft paper backing before installing. i used 1/8" aluminum rivets, which also seem to be holding fine after about 6 months.

[eclipsespeed]

Oh well thats good to know. Do you or anyone else know if i could strip an old washer and dryer of its sheet metal. I have one of each laying around. Between the two of them there should be plenty to skin the inside of a fridge. Also is 2 heating elements enough for that space. Its maybe 5X3 and maybe 2 1/2 deep. Sorry i dont have exact mesaurments but its about the same size of a standard fridge with a freezer on top. And one last question. Is the only reason people push other people to use rivits, to help prevent warping as the metal expands.

Sorry for all the questions, but i guess i have to start somewhere and would prefer to get it right the first time so i dont burn the house down.

Thanks.
Keith

[ed_denu]

Your around 35 sq ft of heating space. The (2) 3000 watt elements should heat this ok. Could take 30 minutes or so depending on how well your oven ends up being constructed. Your at 25 amps so you will need a 30 amp circuit.

I used rivets where I needed a flat surface to attach another stud or sheet metal over. All other exposed areas I used self drilling screws. Panel warping should not be a problem if you have reasonable stud spacing.

[eclipsespeed]

Well then in your experience would you say that it would be worth the extra cash to add a third element? Maybe 3 2500watt elements.

These are the elements i was looking at. They are cheap so its really just extra cash for the ssr, and the sheet metal to mount.

http://www.electronicsporium.com/ind...S&Category=290

Also

this is the PID i was looking at. Does this seem appropriate for what i am trying to do?

Thanks,
Keith

[ed_denu]

(3) 2500 watt elements will put you over 30 amps. That will require probably a 40 amp circuit. If this isn't a concern for you then add the 3rd element.

I'm using 5200 watts on a 27 sq ft oven. It heats to 400 in about 30 minutes which is fine for me. It all depends on how quick you want it to heat.

There's no link to the controller you reference. Ed

[eclipsespeed]

Oops my fault

I was looking at this one

http://auberins.com/index.php?main_p...d3ce7debf2fb4c

but i also found this one by delta. They had a few different types in the 1/16 din controller but i didn’t really know what specifically i needed to have.

http://www.factorymation.com/s.nl/sc.2/category.2/.f

The biggest thing ive seen people say to make sure is correct when choosing a PIC is that the amp and ma output is high enough to drive the SSR/SSR's

The differences im seeing between the pids though is whether its DC current, pulse voltage, or linear voltage. Im just not sure what the difference is and what I would need.

Sorry for all the electrical questions but im more of a wrench turner than an electrician

[ed_denu]

Originally Posted by eclipsespeed

The biggest thing ive seen people say to make sure is correct when choosing a PIC is that the amp and ma output is high enough to drive the SSR/SSR's

Yes, you need to make sure that the controller is compatible and capable of driving the SSR/contactor you chose. That is the major consideration. Other than that it depends a lot on how simple or complex you want the controls. Either of these manufactures PID's would work fine in an oven environment.

I'm not sure why a controller used to maintain oven temperatures would need to generate a pulse voltage As PID's use a relay of some type to control element power I would assume all of these would supply linear(fixed) voltage on their output terminals. As for DC voltage, SSR's can have either AC or DC input voltage requirements so again you need to match the SSR to the PID. Most of the newer PID's however are capable of supplying either DC or AC output power to drive a relay.

[eclipsespeed]

Alright, well ive been reading more and more and i feel like im getting a better understanding of this. I guess what i will do is start ordering my supplies and see if i cant come up with a wiring diagram to run by you guys before i do the wiring.

But as of now this is what im going to shoot for based on you comments and some other reading ive done

If you see anything you think should be changed please feel free to chime in.

And once again thanks a lot for helping me out with this

Keith.

2-1/2X3X5 refrigerator, with high temp 2inch insulation from McMasters,
Skinned with 24ga galvanized sheet

3 2585watt elements
http://www.electronicsporium.com/ind...OD&ProdID=3606

1/16 PID
http://auberins.com/index.php?main_p...&products_id=1

75A SSR
http://auberins.com/index.php?main_p...products_id=29

50 CFM Air Blower
http://www.surpluscenter.com/item.as...tname=electric

360lb Door Latch
http://www.grainger.com/Grainger/items/5E651

High temp wire to get from the element to the other side of the insulations. Then regular wiring to the controle panel

Ceramic fixture with high temp oven bulb.

Tad pole fiberglass rope