Building a kiln controller

if you have a 30 amp kiln, then the sum of the element usages is 30 amps, not 30 amps each.

Now we're getting somewhere. I doubt each element is 25 amps. Most likely, the whole kiln with all switches on high draws 25 amps. Does it plug into a 30 amp circuit? If so that is the 25 is probably the max it will draw. Are you running single phase power? If so your kiln (not each element)is listed at 22 amps.

So, let's say it does plug into a 30 amp outlet. Then you will build a control box that your kiln plugs into. All kiln switches will remain on high, the controller will do the rest.

Here's how I have done it:

Purchase a CAL9500P controller with SSR output List $225 a 40 amp SSR with heat sink, maybe $50 a metal box, $15 a plug to plug the box into the wall $15 an outlet to plug the kiln into $8 a simple on/off switch and fuse $5

Wire it all together and plug it in. My first kiln has a kiln sitter so I use an 1800F cone to protect against runaway.

My second kiln has 2 controllers in the box. One just monitors for high temp runaway.

Jack

If you're controlling a US 220-volt circuit, you really should have a relay in each hot leg.

OK, I tried the price thing with K and it didn't work.

I have 17 programs in my CAL9500P right now and have only used 51% of the memory.

Jack

You will be at least $350 into a controller if you build it but it's worth every penny.

Jack

Why?

Jack

So that when the power is off, the power actually is off. Say, for the sake of argument, that you have a microswitch attached to the lid, in series with the controller output, to turn off the power when you open the kiln.

Say you're raking with a long metal tool.

Now say you only turned off one of the legs of the circuit. Guess what, that element still has a potential of 110 volts relative to neutral (which in most places is tied to earth) and is capable of putting up to 30 amps through the shortest path between the tool in your hand and your foot on the ground (or, if you have a wood floor, your hand on the shell of the kiln, which is quite possibly also tied to neutral.)

I solve that problem by using a 2 pole definite purpose contactor with all safety and overtemp devices wired in the coil circuit. It cuts both legs before the control relay. On my small kiln I turn the manual switches off before reaching in.

Jack

It does plug into a 240 30 amp 30 amp plug

Jack that's exactly what I needed. Thank you I will take your advice and set it up that way I will tell you how it goes. Thank you again

Complicated in the sense of ordering something that needs to be modified (5vdc) output when he could just order a simple relay drive and power it with 120V or order an SSR drive.

Jack

This may not adequately address many people's financial situations, but if you're going to put $350 plus labor into building one, what is the advantage over spending the extra $150 and buying one?

My line of thought usually follows the question, "What am I good at?" and usually when I answer the question, I find that I end up ahead if I put the time into what I'm good at, then sell my work to earn money to pay someone else to do what I'm not good at, in this case build a controller. Especially since, for me, it is an endeavor I would engage in too seldom to ever really *become* good/fast at it.

nJb wrote:

Learning how to do something new and what do you do when your controller fails?

If you know how its built, it is much easier to repair it when it breaks. That's not an "if" it breaks, its a "when". and some of us just can't resist the "how do you do that" thing. It's what got me into glass in the first place. and $150 buys alot of fusible glass, right?

I can see your point re; the curiosity, but...

From a purely financial viewpoint, I think I would have to take a good hard look at that $150 and ask myself whether I would be shortselling my time by building it myself vs. making salable product. In other words, it might COST me more (that I could have spent on glass) to save the $150 vs. making salable product in the same time frame. There are a LOT of variables involved, but it's something that self-employed people (or people who supplement their main income with their art sales) often fail to take into consideration in the "make it or buy it?" equation.

For example, a fellow not l>

What Javahut said. AND, your comparing a $500 controller to one you build for $350. The $350 controller has $300 in whistles and bells. Whistles and bells that are worth something.

Jack

well, except for the fact that if you can build a small one, you can build a big one (the concept scales). the cost to build a big one may be 2k-3k, to buy a big one might be 15k-20k, making your savings be a lot more.

That's a good point, if I was in the market for a large kiln or expected that I would be. However, I was just using my particular situation with the kiln class to illustrate the fact that sometimes, when you take your time for labor into consideration, it's less expensive to buy something than it is to make it.

That's what I was w>