Grounding 220 oven.. and SSR cooling

ScottRoush

ScottRoush

Joined
Jan 10, 2010
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I've been building my heat treat kiln controls with all the stickies here.. but I'm a little muddled on the proper way to ground. I have the 2 legs of the 220 plug wired to a DPST... and then ground. do I simply ground it to the metal enclosure that I'm using to house the SSRs and PID? I've read that I should also ground the frame of my oven to.. do I just extend a ground wire from the enclosure on to the oven frame?

Also... I have a 115v/10W cooling fan... would I wire that to the DPST? or say... to the toggle switch that is in this diagram
attachment.php


And... Where do I actually place the heat sink fins on the SSRs? To the metal plate on the bottom? And I saw where Stacy mentioned having the fins outside the enclosure... I didn't follow that. If somebody could explain how to orient the SSRs and heat fins for best cooling I would appreciate it. I'm basically using a large, rectangular tool box for my enclosure that will have a fan coming in at one end and an exit vent at the other...

So close!
 
The oven and electronics enclosure should both be grounded. Run a wire from one to the other, and connect that to the incoming ground wire..

You should be bringing in two hot leads ( black most likely) a neutral lead ( white) and a ground (Green).
The fan can run by connecting to one hot leg and the neutral. It would be best to do this at the power switch, so the fan runs anytime the power is on.

I can't read your schematic because it is posted too small. Perhaps putting it in as an attachment will allow expansion.
 
I'm just bumping this because tomorrow is the day I put the final touches on the box and just want to make sure I do it all right. So... what is the best way to handle the SSR cooling? I was originally thinking I would apply the heat sink fins to the SSR and that would be it.. but I've seen allusions to somehow placing the fins outside of the enclosure somehow. Does this mean mounting the ssr to the inside of the metal enclosure but placing the heat sink on the opposite surface?

Like I said.. I do have a fan that will be blowing air through the enclosure....
 
I mounted mine inside my enclosure with the flat side against the SSR with heat conducting paste between. But, I also run 40amp SSRs. and my enclousure has some room in it. To much stuff packed to tight will cause heat problems too. You could wire your fan with one leg to the downstream side of the main switch and the other side to ground. That waY ANY TIME THE UNIT IS ON THE FAN RUNS, LIKE sTACY SAID
 
Place the SSRs and heat sinks as far out in the box as possible.....away from the oven shell. The oven will get hot...trust me. It is a good idea to add a piece of 2" kaowool on the shell between it and the electronics. The fans should blow straight through the fins.
 
I don't think you can put to much insulation in when building an oven. I put an 1" of Koawool on the outside of my bricks and that helps. I have my control enclosure mounted bout 1 1/2" above my oven.
 
Okay my box was too small and I'm now making a larger plywood box. So I have my 2 leads (white and black) coming from the wall plug to 40amp buss fuses (one for each line) and then to switch. Where do I put the ground since I will no longer have a metal box to ground it to? Just send it straight to the metal frame on the kiln?

By the way... the enclosure will be located on a wall next to the oven so there won't be any contact with the furnace.
 
Also... If I wire as in the attached diagram (minus the door switch and LEDs .... for right now) when turning on the main DPST switch.. does this just turn on the PID? Or do the elements also come on (at whatever temp the PID is set at)?

I'm really struggling with this. I fired up for the first time today and one of the buss fuses (30 amp) in-line between plug and switch blew as soon as I switched the DPST switch to on. I've since switched to a 40 amp fuse.. but haven't tried yet. Still wondering where to place the ground wire from the plug!

View attachment Heat Treat Oven.pdf
 
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Before you try it again. There is no way that your oven should have blown a 30 amp fuse if wired correctly. Check your wiring to make absolutely sure it matches the diagram. one leg of the 220 should go to one SSR terminal #1 and the other leg to the #1 of the other SSR and the ends of the element should connect to the #2 terminals. You do have a 220 element. A 110 element would draw way to many amps and blow the fuse and if you put in a bigger fuse the element or the SSRs will blow.

You will need the white neutral in your control box if you plan on running the 110 fans. One leg of the 200 to neutral is 110v. But, more important is I don't think a wooden box for your controls is a good idea at all. Electronics create heat and possible sparks. That is why all the junctions in electrical wiring are required to be in a metal or plastic box. Metal boxes are not that hard to come by, please get one. the metal control box and the oven case should be bonded together by a ground wire to make sure that no differential can exist between the two.

If you have the toggle sw of terminal 7 0f the PID in the off position all that will come on is the PID. If no switch there or they are on everything will come on very quickly when you flip the dpst switch. As soon as there is power the PID comes on and if not up to temp it will instantly turn on the SSRs
 
Thanks a lot Jim. First... I will look into some kind of metal box then. Second.. I checked and re-checked the wiring a million times before firing it up. But now I'm wondering about the elements. How do I know for sure? The elements came from a 220 volt, 30 amp kiln. But two of the 3 elements on the original kiln were powered by a separate infinity switch and one on another and now I have all 3 acting as one. So it seems possible that I have 110 elements?

Also... I read that I need to have more fuse protection (25%) than the amp rating of the kiln. That is why I bumped up to 40 amps fuses. Should I go back to the 30 amp fuses or keep the 40?
 
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Okay.... just found this: "When ordering the elements, have both the model number and the electrical data available to assure getting the correct elements. The heating elements for any kiln design are available for either 110 volts or 220 volts. The manufacturer may design a kiln using only 110-volt elements so that with simple switch wiring changes, the kiln can be set up for either voltage. Crusader, for example, uses pairs of 110 volt elements wired in series to make one 220 volt heating unit. Wiring a 110 volt element directly to 220 volts will produce spectacular but disastrous results. "
 
If you wire 2 110 volt elements in series you would have a 220 element. That would be the end of one element to an SSR the other end to one end of the other element that has its other end wired to the other SSR. Running 3 this way would up your resistance, drop you amperage and get you less watts. If you wired 3 110 elements in parallel you would have a huge amount of amperage. 3 220 elements in parallel would work, but you would have a lot of draw (amperage) depending on the resistance of the separate elements. I suggest you buy a cheap VOM meter and check the resistance of the elements. If you measure the resistance (ohms or an upside down u with tails) and divided that resistance into the voltage you would have the amperage for that element. If 2 are ran in series double the resistance and 1/2 the amperage. Three of course triple the resistance. If 2 ran in parallel, 1/2 the resistance and double the voltage. Amperage X voltage = watts. 3 would 1/3 your resistance and triple your amperage.

A 4400 watt setup at 220v would take 20 amps and have 11 ohms of resistance. 30 amps at 220 would produce 6600 watts and have a resistance of a little over 7 ohms. Thing is you could power a 7 ohm element that was designed for 110 with 220 but, it would never survive the amps. Because a 7 ohm 110 element would draw 15 amps and produce 1650 watts, but the wire would be so thin that it would burn up at 30 amps of 220. The gauge of the wire dictates how many amps it will handle. The heaver the wire the longer it needs to be to get the same resistance as lighter wire.

Examples (lengths are for straight uncoiled wire)
I could make a 11 ohm element with 8 ft of 22 gauge Kanthol A1, but it would burn up at 220v and probably at 110 too
I could make the same 11 ohms with about 16 ft of 19 gauge and burn it up quickly with 220 and it would do OK with 110 or
use 33ft of 16 gauge to get the 11 ohms which would work for 220 for a while and a very long time with 110
I went with 50 ft of 14 gauge and my 11 ohm element with survive a long time with 220 making 4400 watts.
all the elements would draw the same 20 amps at 220v, produce 4400 watts and 10 amps at 110 for 1100 watts.

Same reason you must use the correct sized wire for circuits in your house or shop, even though there you are trying to avoid heat. With Kanthol you must avoid completely burning it up.
14 gauge copper 15 amps max
12 gauge 20 amps
10 gauge 30 amps etc etc.
 
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Thanks a lot. I'm going to give myself a lesson in VOM meter today then.

But it sounds like if I just take one of my elements out of action altogether then I would be okay. I ended up adding the third element on a whim right at the end of the construction because I saw that I had room right along the bottom. This kiln should heat pretty evenly with just the two I believe. Does this sound right.... given that my elements are 110v?
 
I haven't read all the posts, so this may have been pointed out, but I looked at the schematic and am not sure about some things.
It looks like you are running the PID on 240VAC, and the LED indicator on the same. Make sure they are all rated for that or there will be smoke. It appears that you have a fuse on one leg only.
You also show no neutral or ground lead coming in.

I would normally run the PID ( and the indicator lamp) on 120VAC with one leg off the power switch, and the other the neutral. I would put a switch between the main power switch and the PID. In this setup, a single fuse in the hot line ( after the PID fuse) would be fine. I would run the fan off 120VAC, too.
 
That schematic is from this sticky: http://www.bladeforums.com/forums/s...eat-Treat-Oven-Wiring-Schematic-Future-Sticky I was just attaching it so folks knew what I was using.

I'm not actually running the LEDs or the door switch in that schematic. I AM running the toggle switch and no LEDs (for now).

Wait.... I wonder if you running into the same thing I was. When I open that PDF it opens in layers. In the left hand column you will see the layers and at the top is an option to flatten. Unless you do that the schematic will only be partially complete. i.e. when I open it you don't see one of the 240 legs. I hope that is what is happening otherwise I'm utterly confused!

I'm also confused because the manufacturer of the kiln said that all the elements in this kiln should be 240.. not 110. He said they were 240 running parallel.... So I don't know. This is frustrating.

My wife is bringing home my volt meter this afternoon.. so hopefully I will learn something.
 
Okay... the whole element thing is really dawning on me in terms of it's importance.

Here is the deal. I took a 240V top loading kiln that 4 sets of elements. Each of the 2 sets were controlled with their own infinity switch. I dismantled the firebricks and re-built a 40" long front-loading furnace that will enable me to heat treat swords. I wasn't able to fit in 4 sets of elements so I reduced to three. So... I ran three sets of elements off of one set of SSR's. That is probably the issue.
 
what kind of material were you all using to pass your element thru to isolate them coming out the case?
 
You can find some ceramic tube, use old thermocouple sheaths or make the holes fairly large say 3/4" and the pack kaowool around the element so it must say in the center of the hole where it passes through the metal box. A internet search for ceramic tube will show lots of options.
 
Exactly, without the ground and neutral wires being in the schematic, some of us are totally stumped! The way I read that schematic, it looks much more like 110v wiring, where there's 1 hot, a neutral, and maybe a ground. Any thoughts on this?
 
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