wiring pid controller circuit

[dve256]

You must not have the extra element outside the furnace as it will get very hot and you will need to put it in an earthed box with a fan to keep it cool.
It worries me that you appear to have one end of your element outside the furnace. This looks very dodgy to me.

Thats not what I meant by heat resistant wire on the outside.. I mean use wire able to resist heat say 200C rated. not, a resistance element wire. So even now I have the kiln working without fault (ok, just for 30mins) do I need to add to the circuit as you suggest?

Not sure what part you are looking at but its a pretty standard way of doing it the element is attached on the inside to bolts which come through the back of the kiln and connected with heat resistant wire. This is then housed to prevent touching the live stuff.
The thing hanging down is the thermocouple

There is a interlock which kills the power of the element when the door is open which resquline kindly helped me with the wiring, thank you.

You said that stretching the element fixed the problem, so it's possible what happened is that you had some of the element shorted out, reducing the resistance of the load and thus drawing too much current.

Yes it is working after stretching it out more. How would a 'short' occur in this curcuit? (or 'a' circuit)

Pretty pleased with the fact that is working really, however if its potentially a fire risk because of to much amps? then clearly I would need to think about modifying it.
But if the draw is too high won't it cut the power rather than cause a fire? I know if your wiring cannot handle the current then it can cause a fire but I have used thick enough wires only the plug is possibly under spec.

to find the current W/E=I ... so 3220(W)/240(V) = 13.416666(Amps)
to find the resistance E/I=R ... so 240(V)/13.416666(Amps) = 17.888199(Ohms)
find current W/R=I 240(V)/17.888199(ohms) = 13.416666(Amps)
multimeter says 15.1Ohms.

Sorry for the long post just trying to answer others questions and ask a few of my own.

 

[duke37]

Your latest picture shows a curly wire top right, I thought this was part of the element, apparently not.
Your equations are right but you have started at the wrong end, you have relied on the supplier giving you wire to the exact specification, wire can differ a bit in diameter and resistance from nominal.
So I=V/R = 240/15 = 16 A
P=V*V/R = 240*240/15 = 3840 W

Heat resistant insulation on the wire connecting to the furnace is a must and should be rated at say 30A to keep the wire heating low.
Its well past my bedtime now, so will leave it with you.

 

[daddles]

Yes it is working after stretching it out more. How would a 'short' occur in this curcuit? (or 'a' circuit)

Pretty pleased with the fact that is working really, however if its potentially a fire risk because of to much amps? then clearly I would need to think about modifying it.
But if the draw is too high won't it cut the power rather than cause a fire? I know if your wiring cannot handle the current then it can cause a fire but I have used thick enough wires only the plug is possibly under spec.

Imagine one turn of the helix. Now imagine the two ends of this one turn touching each other. That's one type of a short and that length of the helix would be shorted out. You probably would have noticed a bunch of them shorted together (would have looked like an extension spring with the coils touching). Still, having some shorted coils is the only hypothesis I can think of that explains the working after stretching.

There is no fire risk if you sized the wires properly and your home is wired correctly (i.e., the circuit breaker doesn't allow more current than the wires of that branch circuit can handle. If I were you, I would make damned sure that everything is done properly with respect to your local laws and codes. In the US, if you wire something up and it's not done per the code requirements and causes a fire, your insurance company will refuse to reimburse you. And rightly so, since the fire was your fault due to negligence or ignorance. Thus, if your plug isn't the proper one, get the proper one. Many of the rules and regulations are in place because someone died because that rule wasn't previously in place.

Overall, it looks like you did a nice job on the furnace. That's one I'd love to have in my own shop, as I occasionally heat treat tooling I make that's larger than I can do with a couple of torches. I'd also use it for case hardening -- about an hour ago I made a drill bushing; if I had a furnace, I'd make a bunch of them and case harden them all in one go.

 

[duke37]

I have had a look at the mains specification, it can go up to 253V.
253/15 = 16.9A
253*16.9 = 4267W
The garage is likely to be a on a fused spur and will be not happy with an overload.

I suggest that you need to install a dedicated circuit and the regulations state the it must be installed by a registered person.

 

[Resqueline]

There is a interlock which kills the power of the element when the door is open which resquline kindly helped me with the wiring, thank you.

Just be aware that there's still a potential for electric schock since the interlock doesn't break both phases. At least make sure that the SSR is breaking the Live wire.

The initial center breaker (whatever that is) tripping may be due to several things.
1: Pure overload. The kiln draws a lot (as has been pointed out), and together with other (varying) loads in the house it could be too much for even the main breaker.
2: Moisture content in the bricks could trip a ground fault breaker (if that's what it is). After several attempts the resulting heat has driven out the moisture.

 

[dve256]

I have had a look at the mains specification, it can go up to 253V.
253/15 = 16.9A
253*16.9 = 4267W
The garage is likely to be a on a fused spur and will be not happy with an overload.

I suggest that you need to install a dedicated circuit and the regulations state the it must be installed by a registered person.

Is there no other way to fix the problem? What if more wire is added to the circuit as you previously suggested?
I do have a 200A tig welder which I am only able to use up to about 2/3 power before the fuse goes in the plug of the welder. Maybe I could kill 2 birds with 1 stone? Could I change to an industrial plug on the kiln? do those industrial outlets work with 240V as we have duduced thats what the kiln system needs.

 

[dve256]

Just be aware that there's still a potential for electric schock since the interlock doesn't break both phases. At least make sure that the SSR is breaking the Live wire.

The initial center breaker (whatever that is) tripping may be due to several things.
1: Pure overload. The kiln draws a lot (as has been pointed out), and together with other (varying) loads in the house it could be too much for even the main breaker.
2: Moisture content in the bricks could trip a ground fault breaker (if that's what it is). After several attempts the resulting heat has driven out the moisture.

Please clarify are you saying the door interlock is not going to kill the power and I can still get a shock off the element when the door is open, I don't understand.

 

[duke37]

You have not clarified whether the trip was due to overcurrent or earth leakage, this must be done. If your welder blows a fuse before the trip goes off, then you are likely to have an earth leakage problem with the furnace.

To get under the 13A limit, you will need another 5 ohm of wire but 10 ohm would give a bit of leeway. This will reduce the rate of temperature rise of the furnace.

You will need a registered installer to upgrade your supply.

 

[dve256]

I am not sure why the first 2 times it tripped but maybe it was as daddles explained the coils touching around the corners shorting out some curcuit. Or possibly an earth leakage because of moisture would make sense.
Similarly to when I use the welder the light dims a little for the kiln also.
Can you tell me where I add the wire in on the circuit just so I am sure, thanks. the wiring diagram is on page1.

 

[Resqueline]

Identifying the breaker that tripped will tell you & us what happened. How many Amps is it, or is it rather a ground fault interrupter?
Some shorted turns in a few corners might have increased the Amp draw a little but imho can't explain the big change you've got in run time.
Interlock:
I've added colors to the wires. Blue is Neutral and is always safe to touch, red is Live and is always unsafe. Purple is the wire that needs to be unpowered with kiln open.
If you can positively identify & connect Live & Neutral exactly as shown the kiln should be safe enough. If not then you'll need to add a contactor.
The extra piece of heater wire is added inside the kiln, neccessitating an extra coupling point (orange) to splice the wires.

 

[(*steve*)]

Blue is Neutral and is always safe to touch

Eeek! Unless you have an active/neutral fault somewhere that has reversed them.

Always treat both as live!

 

[Resqueline]

Hehe, yes, it was a daring statement and of course you're right, one really shouldn't bet one's life that someone haven't made a (house) wiring error somewhere..

 

[dve256]

Its the middle one that went off on the pic, earth protective device. says 80A

If you can positively identify & connect Live & Neutral exactly as shown the kiln should be safe enough

I dont understand your point, I have connect everything up as per diagram?

 

[duke37]

Is that the one with the red button which probably says test? There should be a label saying the fault current for trip, probobly 0.03A. If this is the one which has tripped, then you have earth leakage on your furnace. You could try blowing into the furnace with a fan heater to dry the bricks.

With regard to the live and neutral, you must not assume that everything is wired and working correctly. As it stands, you are breaking the line only (if nothing fails) and the neutral is still connected. This should be safe but I have known the neutral to rise to 80V due to a fault in the supply transformer, You should include a motor contactor with a start button and stop button so that you need to start the furnace when it is loaded. The door switch would be connected as a remote stop. A light across the furnace supply should be added to show that power is on.

 

[duke37]

I have had another look at your picture, as far as I can tell it says 80A which is the current carrying capacity and 30mA which is the earth leakage trip level RCCB means residual current circuit breaker.