A Few Kiln building questions

chknifemaker

chknifemaker

Joined
Jun 30, 2013
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207
I'm building a 120VAC kiln to run off a 20 amps circuit(I'm using the120VAC Kanthanal Elements from Budgetcastingsupply.com) for annealing knives and have a few questions:

-when wiring the PID to the SSR and the thermocouple do you need to use the High temp wire in there?(I know you need it from the elements)

-I am using k-23 9" x 4 1/2" x 2 1/2" should I put a layer of k-wool(or what ever brand) in between the bricks and the shell?

-I was wondering if putting a heat sink on the SSR was necessary or not or maybe adding a fan?

Thanks that's it for now but mite come back with more
 
Wiring From the pid to the ssr no, From the ssr to the elements yes, from the pid to the thermocouple you should have been supplied with the proper harness

A heat sink for the ssr is necessary, without it you will shorten the life of the ssr, Adding a fan to keep the electronics cool is always a good idea

Adding kaowool on the outside won't hurt, But probably isn't necessary, However added insulation might save a couple bucks on your electric bill over the course of a year
 
With thermocouples you need to use wire that is specific to that variety of thermocouple. And this includes keeping the polarity straight as it depends on using very specific alloys. See a thermocouple works by creating a voltage that has to do with the difference in temperature between the ends, so one end is in the PID and one is in the kiln. Changing the wire in the middle could destroy any accuracy.

Consieveably you could use normal wires from the SSR until it got close enough to the machine to worry about getting hot then connect them to the high temp wire a reasonable distance from the actual hot zone. The only real reason I can see in doing this is if your SSR is a distance from the oven, and you didn't want to make the whole run in high temp wire or some such. That strikes me as a bad design but not fundamentally unsafe.

All SSR's I have seen might be rated for 30 amps with a heat sink but only 5 amps with out one. So you will want a heat sink, and don't forget the thermal grease to get a good thermal bond between the SSR and the heat sink. SSR's tend to fail on instead of off, and that is a fire risk so I wouldn't want to cut corners on them, as heat sinks are not expensive.
 
I was wondering about the fan I was thinking of using a computer fan but I think I would need a transformer for that is that true?
What other kind of fan could I use?
Thanks
 
chknifemaker said:
I was wondering about the fan I was thinking of using a computer fan but I think I would need a transformer for that is that true?
What other kind of fan could I use?
Thanks
Click to expand...

There are small box cooling fans in both 110 and 220. They are readily available so there is no need for a transformer. For example auber instruments has an SSR cooling kit with a 110 fan and temp sensor to only turn the fan on when the box is hot for about $15. Grainger and mcmaster carr have them too. No need to mess with a 5 volt or 12 volt system just for the fan.
 
This is how I handled my control box, when I build something the first word I think of is "free" and then "better", I ran my fan off from a 12 volt power supply/adapter, I'm sure everyone has a box full of those laying around ;0) The second thing I did was to use rigid wire for the element connections, I'm so afraid of wires rubbing against stuff and causing a short, and the third thing I did was to move the element connectors around to the side so there is nothing sticking out the back that will give you a shock, and no wires that can get caught on something when you move it around, more photos here http://www.bladeforums.com/forums/s...-bit-about-your-work!?p=12725618#post12725618

IMG_1943_zps52620cfb.jpg

IMG_1947_zps1ca8a344.jpg
 
I used longer stainless allthread through the walls for the element connections on my first 2 or 3 HT ovens. The idea being that the extra length allows the use of normal cable because the cold end is reasonably cold. It seems to work.



SSRs definitely need heatsinks. A lot of the Ebay heatsinks are only rated for 15A. They work fine for me, but domestic power points here are 13A, 230V. On a 20A circuit, you'll need something bigger.

Bear in mind that a 60A SSR on a 15A-rated heatsink is effectively just a 15A SSR.

+1 on the correct thermocouple cable. I buy Mineral Insulated thermocouples with transition joints to the cable, mainly to prevent me (or anyone else) lousing up the wiring. I have wasted too much time on thermocouple wiring problems in my day job to want to do it in my playtime. Something like:

http://www.omega.com/pptst/TJ36CAXL_NNXL.html

Extra Kaowool won't hurt and may do some good. I have never bothered because I want the IFBs held firmly in the frame and Kaowool inside the frame would have too much "give". Kaowool outside the frame is just too much work for too little gain IMO.

In fact, I don't even clad the outside in sheetmetal. Partly it's because I'm lazy, but I also think it's probably safer unclad. The highest outside surface temperature I've measured is 121 degC (250 degF) after 3 hours at 1177 degC (2150 degF) chamber temperature. The IFB is a lousy thermal conductor and touching it briefly at that temperature just feels hot enough to make you take your hand off. I'm pretty sure sheetmetal at the same temperature would cause damage. I built the first one intending to clad it, but wanted to know how hot it would get so I could pick the cheapest cladding that would live with the temperature. It didn't really seem to need it, though if I was going to use Argon in it, I'd clad the outside to minimize leakage.
 
Thanks for the pictures guys.
John:I like the idea of having the elements come out right in the control box I had already been thinking that but know that I know someone has done I think I will for sure. but why use bolts why not just stick the lose ends of the element right through?

I plan on getting my thermocouple from auberns and the wire comes with so I should be good there I hope to get it build this month(I'm tired of annealing in ashes) so maybe I'll skip the k-wool Idea I wasn't to sure of the necessity of it and I think I'll just forgo it and I'm going to add a fan and a a heat sink(I'm using the 40A ssr from auberns so I'm getting the 40A heat sink to go with) I'm really excited!
Thanks for all the help
Oh one more question was what do your guys use for the control box? (I want it to mount to the side of the kiln and I's like it to be metal is there and metal box or something I could convert to make it work?)
 
chknifemaker said:
but why use bolts why not just stick the lose ends of the element right through?
Click to expand...

If you stick the kanthal wires inside the box you will have flaming hot wires inside the control box, the stainless steel bolts have far less resistance then the wire and only get slightly warm

chknifemaker said:
Oh one more question was what do your guys use for the control box? (I want it to mount to the side of the kiln and I's like it to be metal is there and metal box or something I could convert to make it work?)
Click to expand...

I made my own box from a metal component board I took from the inside of an old non working organ that my dad refused to scrap when he was alive
 
Auber sells boxes with pre cut holes for the pid. They will also put an external heat sink on it so that the heat will radiate outside the box instead of inside. Looking and planing a build of my own that is what I thought.

Of course I am planning on building three paid controlled devices soonish. A smoker, a sous vide controller and a heat treat oven. Kind of funny that the oven is the one not used for food. Though I have hear stories of people reheating lunches at work in the heat treat ovens.
 
Why not build one control box and just plug in whichever device you want to use?

With most PIDs, you'll need to change the PID terms as well, but that's pretty quick. With the Omega CN7823, you might not even need to do that. It stores 4 sets of PID terms and uses the one closest to the setpoint. I don't know what temperature range is needed for smokers, but there's no overlap between HT and sous-vide, so just setting the temperature could select the appropriate terms.
 
timgunn1962 said:
Why not build one control box and just plug in whichever device you want to use?

With most PIDs, you'll need to change the PID terms as well, but that's pretty quick. With the Omega CN7823, you might not even need to do that. It stores 4 sets of PID terms and uses the one closest to the setpoint. I don't know what temperature range is needed for smokers, but there's no overlap between HT and sous-vide, so just setting the temperature could select the appropriate terms.
Click to expand...

I have thought about it, mostly it seems like bad practice to disconnect and reconnect the various temp sensors, K type thermocouples look good for the smoker and the heat treat oven but an RTD looks better for being emersed in water for the sous vide controler. I might be able to get something with the smoker and heat treat oven, but it would involve some kind of connector between them as I would need to move the different SSR's to a seperate box. It raises the cost a bit, but as a basic PID controler is under $50 I am not sure if the added issues and costs for a movable box saves money or not.

For example for the sous vide I want to be able to plug in any slow cooker to it, but I don't want to put the heating element of the smoker on a plug in case someone plugs it in to a non controled outlet.

It could be done sure, but I am not sure that the savings on not buying multiple PID's makes up for added costs and complexity.
 
timgunn1962 said:
I used longer stainless allthread through the walls for the element connections on my first 2 or 3 HT ovens. The idea being that the extra length allows the use of normal cable because the cold end is reasonably cold. It seems to work.



SSRs definitely need heatsinks. A lot of the Ebay heatsinks are only rated for 15A. They work fine for me, but domestic power points here are 13A, 230V. On a 20A circuit, you'll need something bigger.

Bear in mind that a 60A SSR on a 15A-rated heatsink is effectively just a 15A SSR.

+1 on the correct thermocouple cable. I buy Mineral Insulated thermocouples with transition joints to the cable, mainly to prevent me (or anyone else) lousing up the wiring. I have wasted too much time on thermocouple wiring problems in my day job to want to do it in my playtime. Something like:

http://www.omega.com/pptst/TJ36CAXL_NNXL.html

Extra Kaowool won't hurt and may do some good. I have never bothered because I want the IFBs held firmly in the frame and Kaowool inside the frame would have too much "give". Kaowool outside the frame is just too much work for too little gain IMO.

In fact, I don't even clad the outside in sheetmetal. Partly it's because I'm lazy, but I also think it's probably safer unclad. The highest outside surface temperature I've measured is 121 degC (250 degF) after 3 hours at 1177 degC (2150 degF) chamber temperature. The IFB is a lousy thermal conductor and touching it briefly at that temperature just feels hot enough to make you take your hand off. I'm pretty sure sheetmetal at the same temperature would cause damage. I built the first one intending to clad it, but wanted to know how hot it would get so I could pick the cheapest cladding that would live with the temperature. It didn't really seem to need it, though if I was going to use Argon in it, I'd clad the outside to minimize leakage.
Click to expand...

This wiring looks good at first. But if on notices, the TC wires are paced between two hot high voltage metal studs. It should be apparent that the TC wires should be routed another direction. From an electronics POV, pacing a DC millivolt line through a AC loop is also not good.
 
Good spot Stacy. It was the only photo I could find of the long studs.

It was very much a Work In Progress when the photo was taken.

The themocouple cable actually comes out of the top and the AC cable comes out of the bottom in the finished article. The power cable is now also glanded for strain relief.
 
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