Correct SSR for 240 furnace?

okay... so I may be fighting the thermal mass of my kiln to then. Ughh... I'm guess I will need to get that third element running then.

I'm running it right now and it won't get over 200 C (which is the same temp that I ran my auto tune at)... so I'm checking my PID settings to see if that is the issue.
 
If your output is 100 % (output light on constantly) and the temperature is not moving at all, you've hit the point where the heat loss equals the heat input and it's at the higherst temperature it can reach with the input power available. You will want to know the oven temperature, ambient temperature and power input at this stage, to work out the power needed to reach any given higher temperature.

If the output is 100% and the temperature is rising, but slowly, you are up against the thermal mass. It's worth timing how long it takes to heat up by a given amount (say 10 degreesC) at various temperatures; maybe 100-110 degC, 150-160 degC, 200-210 degC, and so on, as it lets you get a feel for how it's working. If you are good with the maths, you can actually model things pretty accurately.

I'm not, so I just plot it out on graph paper and take an educated (?) guess at what will happen with, for example, twice the power.

How big is your oven and how heavy is it?
 
The outside dimensions of the kiln are 50"x16"x13". The inside is 10"x10". No idea of the weight!

Well.... I've since fired up my forge warming up this part of my shop considerably... and then re-fired the kiln after changing some of the PID settings. It is now rising very, very slowly. It got up to 230 C pretty fast.. but it's taken almost 1/2 hour to get to 240.

The output is 100%

So any ideas as to the best course to increase the power? Different elements? Different SSRs rated at higher amp so I can run the two elements in parallel instead of serial? ..which would bring the amps up to 50. Or additional SSRs so that I can run the third element?

This is frustrating because the kiln that I dismantled to make this was a 240V, 30 watt kiln with 4 elements and it got up to austentizing temps just fine with it's old relays, kiln sitter and infinity switches. And all I've done is re-arrange the firebricks into a different shape I so wish I would have taken a picture of the original wiring to see how the elements were wired. All I know is that they were wired to two different relays and two different infinity switches.

Ugghh... I may have to abandon this right now and start re-building my gas HT forge.. This blade needs to be heat treated so I can finish it to put it on the market.
 
Well it finally seemed to stabilize at 300 F. I then took a look inside and the elements were definitely not up to full power. Sort of a dull red-orange. So I added kaowool insulation to the entire kiln and re-wired to run a single element in order to get higher amps on at least one element and that immediately got the kiln up to 500 F... but now it is starting to stabilize again. So... not enough power I guess.

My plan is to start shopping for some thicker gauge high temp wire to make a set up of appropriate elements. And I will also decrease the volume of the inside of my kiln by decreasing the width from 10" to 5".

Also.. I would great appreciate it if anybody could suggest of a good source for thicker gauge (14?) high temp wire. I plan to wind it myself... so I just need a spool.
 
well.. the issues I've had since switching to one element were due to the thermocouple. I switched and now it's coming up to temp just fine.

So... now I just need to order elements, higher amperage SSR to eliminate the extra one in the box, new thermocouple, and then shrink the internal volume of the kiln and I should be fine. But it looks like this sword will be quenched today....
 
It never bloody ends. My PID is measuring almost 200 degrees higher than actual.. and there is at least a 100 degrees difference between the door of the kiln and the back. That might be an issue with a leaky door as well as the ports for the elements. At least I'm hoping. I have a new thermocouple on the way.... but are there any PID settings that could lead to this??
 
If your controller (it's not technically a PID) is set for a diffetent thermocouple type (K vs J etc) you could see this. Additionally, most controllers have the capacity to enter an offset. It can be either the reading + a fixed 'x', or 'x' can be a percentage of the reading. Look in your manual for info concerning 'offset' or 'calibration'.
Best,
Steve
 
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