Wiring for a three element oven?Element Help

[pappahenn]

Does anyone have a wiring diagram for a three element oven? I am building a 36x36x72" inside dimension oven. I would like a fan, contact, and a PID, electric box. Anything else? I am installing three 3400 watt elements as long as I can find them. Any good sites for that?

[pappahenn]

I need a website too to locate the elements at a reasonable cost.

[ed_denu]

I got my elements off ebay. You might not find exactly 3400 but I would just do a search to see what is available. PID and SSR also from ebay or check Auber Instruments.

With 3 3400 watt elements you are going to be drawing around 43 amps. I only run one SSR(rated 40 Amps) with 2 elements off my PID, but I don't see why you couldn't connect two or more SSR's to a single PID to run the 3 elements.

[grommit]

Helo Pappahenn, i am no good at wiring diagrams, but a lot of guys have helped me out and if they dont mind i can send you what i have if you PM me your email address.
i found it very daunting at first to build a oven, but i took the bull by the horns and started at the basics and that was find a large enough upright freezer, take out the foam which was the worst part,buy insulation which i have got rockwool,aquire a donor oven, strip and document all the leads and connections, if you hit on alright you should get a oven with a fan.the easiest part is if you know a friend is an electrician get him to do all the work that is needed on electrics.i got decent sheet metal and rivetted all my sheet in place.
decent door seal and i bought a infa-red thermometre for doing my checks.
as Chromo n the guys have advized is to do my first test outside just incase there is any of the foam etc still lurking in there,i will do tests on outside temps to confirm the reliability of the insulation and the sheet.there is alot of info out there but i got confused with all the technical stuff like PID SSR etc.so looked for my easiest and cost effective method.pictures to follol soon.
regards
Brian

[pappahenn]

I searched back a little bit and found some else diagram for a four burner. That will work too for a three. I did find three 3100 watt elements on ebay and ordered those. My next question is a 40 amp SSR ok now. It should draw 39 amps according to the calculator I found on this site. I am confused a little how to hook up the PID and SSR. But it does look fairly simple.

[ed_denu]

Most PID hookups are fairly straight-forward. The pid should have 2 connections for input power. Most accept either 120 or 240 vac. The pid will also have two output connections used to drive the SSR. Most PID's I've seen output dc voltage. Just make sure the output voltage range of the PID is compatible with the input voltage range of the SSR you are looking to use.

Two other connections on the PID are to hookup the temperature sensor. The other connections on the PID serve as connection points for high and low temperature alarms(not required).

As for driving 39 Amps out of a 40 amp SSR, I wouldn't do this. I would use 2 SSR's or lower the total element wattage. If you really want to try it this way, you definitely need a very good heat sink for the SSR.

[ed_denu]

One additional thought. The output or load side of the SSR typically only switches one leg of the 240 vac element circuit. Therefore i think it is advisable to have a master disconnect for the oven.

[pappahenn]

Thank You. I have decided to increase my oven size to 72" tall, 60" wide by 36" deep. I am adding another 3100 watt element. Would I need two SSR's? I am a little confused on this still. Also, I want to add a a fan/blower. What would be the best CFM for the oven. I will have it recirculate the air by building duct work from top to bottom.

[ed_denu]

If you are planning on using (4) 3100 watt elements you are going to be drawing about 52 amps. I have a Fotek SSR and I know they make these in up to 75 amp units.

If you are looking to use (2) 40 amp SSR's then you need to look closely at the specifications for the PID and SSR's you are planning to use. Specifically, on the PID I use, the output driving contacts are rated at 8 VDC and 40ma. This means that the PID outputs a DC voltage of 8 volts used to drive an SSR. However it is also limited to 40ma. The 40 amp Fotek SSR is rated to operate on 3-32 VDC and consumes 20ma. So you can see that the PID output of 8 VDC and 40ma load will match to the SSR I am using. However if I wanted to use (2) 40 amp SSR's, with (2) elements each, then I will be at the 40ma limit of the PID. Might work for awhile but you probably run the risk of destroying the PID.

You need to look closely at the specifications of the PID and SSR(s) to determine if these devices will work correctly together. If you want to post specific device information I'm sure someone would be able to help.

Keep in mind that a 52 Amp load will require a 60 Amp circuit using #6 wire or greater.

As for the fan, I don't have specific air movement calculations available. I believe someone posted these calculations recently. Recirculating the air from top to bottom via ducting is what I do and seems to work well. Other options would be a fan within the oven.

[GeneNewcomb]

I used a 60 amp contact block vice an SSR. Next time I will use two 30 amp. Cheaper and I minimize the #6 wire. Than stuff is tough to bend around in a box. http://stores.ebay.com/English-Wheeling-Machines its there.
You see where my fan is? I don't think ducting top to bottom is neccesary and I consider the fan for convection rather than heat destratification (for lack of a better term)
ie I am not trying to even out the temp top to bottom, that takes care of itself, I am trying to get the air that is nearest the powder coated object to circulate.
Gene