What do you think???

[rowdenboyz]

I am in the process of building my second oven (first one is too small). I found a great deal on some prefabbed oven panels (measurements 32"Wx9'6"Lx4" thick). I bought enough of them to do a 20' long oven (20x5x6). At $3 per panel, I sure didn't get hurt! What I would like to hear opinions on is this: Would it be wise to build a "BurnBox" and stack 8-3000watt electric elements inside the burnbox and pull air from the oven compartment, across the elements and back out into the oven compartment? I plan to build a "Duct" channel along the top center with holes the entire length to pull air from the top, back into the burnbox (just like conventional batch ovens). The air coming from the burnbox to the oven compartment will go down each side in similar duct channels, mounted lower to the floor. I have access to all the electrical supplies I need, like wire, etc. My main concern is this: Can you control two SSR's with one PID controller? I will likely use two 90A SSR's and split the elements into two groups of four (parallel of course).

I have a 200Amp service in my shop, so that's not an issue. Anybody have any ideas similar to this? I plan to start on the control panel first, and see what else I might run into. Thanks for your time!

[ed_denu]

Most pid's can control two ssr's ok, you just need to look at the specifications. My pid(TC-408) can support an ssr output of 40ma at 8 vdc. My ssr(Fotek) requires 7.5ma at 3-32 vdc. In theory I could probably control 4 of these ssr's with this pid.

However I think there is a bigger problem that you need to look at closely before proceeding. In my opinion 24000 watts isn't anywhere need enough to heat a 600 cu. ft. oven. Most all the ovens I've seen this size are heated with gas. My guess is it would take a couple of hours to heat this space with 24000 watts, if at all.

As a reference, my oven is 27cf and with 5200 watts takes about 30 minutes to heat to 400(the first time). The oven size you are proposing is roughly 22 times larger than mine but you are only increasing the wattage by less than 5.

[ed_denu]

Here's another way of looking at the size versus wattage question. The oven you're proposing is 600 cu. ft. with 24,000 watts. This computes to 40 watts per cu. ft.

I might be making a false assumption that wattage requirements can be computed in a linear fashion based on oven size, but if other members would like to share their oven measurements and element wattage it might make for interesting comparisons.

My oven is 27 cu. ft. and has 5,200 watts, or 192 watts per cu. ft. For my needs the heat-up cycle time is acceptable at around 25-30 minutes.

[JTW37]

I'm no arithmetician, but if I did this right I'm at 150 watts per cubic foot. My oven is 3x3x6. I'm assuming that you divide total wattage (8150) by cubic ft (54) and you get the answer (150.925). And like you I don't know if that has anything to do with price of tea in China, but I'm game for anything.

I'm pulling 34 amps (33.9) when it's first starting up.

[baz]

mine is 63 cf and 11 kw= 174 watts per cubic inch takes about 25 minuteson the first run.
but we all have to remember that wattage is not the only thing that affect the warm up time ,insulation and also the gage of steel used inside has to sink in the heat so a thicker gage will take longer to sink to temp but will stay warmer longer . also bing able to bring an oven in a short time when empty is something
but getting a heavy mass of steel might take much longer in an oven that is on the low side of the watts per cubic feet.
an example my oven with 25 minutes to get to 400 with 11 kw is fine for regular parts but if i fill it with 300 pounds of 1 inch thick steel plates in there it takes
too long to heat up tht why i am looking into adding a few more kw s to give it a boost

[baz]

juat for your info .
i had a look at different electric ovens (real industrial ones )
one of them as an example is 5x5x5 450 degrees 65 kw
another one about the same size and temp 45 kw.

[ed_denu]

Interesting data baz. That oven with the 65000 watt rating would compute to 520 watts per cu ft and pull about 270 amps!!! That's industrial strength.

[relethg]

rowdenboyz would like more info on the panel you got. like what are they off of? Where did you get them? Any other information you could provide on how I could find some. Any pictures of them?

Thanks Glenn

[baz]

Originally Posted by ed_denu

Interesting data baz. That oven with the 65000 watt rating would compute to 520 watts per cu ft and pull about 270 amps!!! That's industrial strength.

hey , check your mailbox

[rowdenboyz]

Originally Posted by relethg

rowdenboyz would like more info on the panel you got. like what are they off of? Where did you get them? Any other information you could provide on how I could find some. Any pictures of them?

Thanks Glenn

Glenn, I actually got really lucky in finding them. My father-in-law works in a factory that builds transformers. They have large ovens that are used to back paint etc. They were replacing one that was HUGE and he was able to buy them at salvage cost. The panels look a little rough, but are well insulated and snap together like a tounge and groove. Hope you can find some!