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Need Some Help From Somebody Who Knows About Kiln Electrics.


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#1 High Bridge Pottery

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Posted 10 November 2013 - 07:55 AM

Hello, I really need the help of somebody who knows what goes on with kiln electrics, I am very quickly trying to learn so this is my first port of call.

 

Bought an electric kiln about 8 months ago, told it was 6kw single phase kiln (UK Power) Got a single phase 32A 240V isolator switch and wired it into the plug. Were a little confused as there were 5 wires coming out of the kiln but two were held together so wired them into the plug together. It has a brown and blue going to live, two blacks going to neutral and a yellow/green going to earth.

 

So yesterday I went in the studio to check on the firing and the program had finished but the kiln was not loosing any heat and there was a funny smell in the room. When I unplugged the kiln from the socket it started to drop. Whenever the kiln was turned on at the wall it would start to heat up again even without the programmer plugged in.

 

Once it had cooled I took off the outside to have a look and found one very burnt/charred relay. I spent a few hours researching and looking and this seems like it could be a common problem that the relays break. Scary that it breaks into the on position.

 

My problem is that I do not know if it was a fault in the relay or if the kiln is just wired completely wrong. I had drawn a basic circuit diagram of what happens when the power comes into the kiln but I still haven't working out if it is right. This kiln has been fired many times up to top temperature, what confused me was that the kiln has no transformer to change the power so it has 240V coming into the relays and the relay was rated at 20A 220V - ac so this just seems wrong but I don't know why. I dont know what happens when the power is split like it is so if somebody could make me any the wiser it would be much appreciated.

 

I don't want to go any further until I know what is happening with the electricity as this was quite a scare.

 

Attached my circuit diagram, sorry if it is incorrectly drawn but I have tried my best to just understand how the power flows round the kiln.

 

I have just noticed that in my drawing the top relay has the power flowing the other way and I just got my arrows the wrong way round. Ignore that.

 

 

Thank you.

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#2 Marcia Selsor

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Posted 10 November 2013 - 09:35 AM

Maybe private message to Neil or Arnold. They are both experts on electric kilns. It is Sunday so a response could be slow.I think you're lucky that all you got was a charred relay.

Marcia

#3 Wyndham

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Posted 10 November 2013 - 04:21 PM

I'm not sure but it looks like you have a 20 amp 220 relay and circuit and a 15 amp 330 rely and circuit, which i don't understand. It would be better to lookup the make and model and the manual with schematics and parts to see what you have and what you need.

 

Generally a digital controller uses a low voltage 12 v to trigger the main 220(110 on each leg) of the relay but I don't see this in your diagram. I see something but doesn't look like what I'm familiar with.

Hold off till you have a clean schematic from the mfg. and someone that knows how the wiring goes. High voltages can kill.

 

Wyndham



#4 High Bridge Pottery

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Posted 11 November 2013 - 06:41 AM

The biggest problem I have is that it was custom made for somebody else that I do not know. I got this kiln 3rd hand. The circuit diagram will not be how it should be as I have just drawn it as I see it.

 

The relay has three pins on the top and bottom and two pins in the middle which is where the programer attaches to the relay. This looks like how it triggers the relay from the two middle pins.

 

The problem is I have no idea how old this relay is, I thought the 20A and 15A was just the difference between single and three phase power but that was just a guess. When the power comes into the kiln it splits to the different relays so there is actually 240V 15A going to each relay. I am looking to get somebody in who knows what they are doing but just trying to get as much help as possible :)



#5 Frederik-W

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Posted 11 November 2013 - 07:11 AM

Your diagram indicates that there are two sections of heating wire, these two sections are switched on in parallel.

i.e. There are two relays and each switches their heating section on at the same time with the 240V supply.

The wiring is correct for single phase where you have 2 supply wires - common to both relay contacts are the black, and then blue& brown together.

The wires that come from the programmer and run through the middle of the relays are what switches the relays on.

 

The relay switch rating is 20A at 220V (max) or 15A at 330V (max).

In your case you use 240V so your relay switch rating is slightly less than 20A.

 

Note that although your power is "split" into two sections, these sections do not necessarily draw the same current. How much each section draws depends on how long each section is and what type of wire. This depends on the design.

 

You have blown (fused together) one relay switch-contact in the "on" position so you need to replace it with a similar relay that can handle the current.

And the total current of both sections together must not exceed your 32A supply rating or it would trip.



#6 High Bridge Pottery

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Posted 11 November 2013 - 10:35 AM

Yes there are 6 top elements and 4 bottom elements linked up to the two relays, it was the top relay that went with the 6 elements. It looks like the elements are wired in parallel pairs.

 

From learning my basic physics again there should be more current going through the top relay as there is less resistance overall. I don't know if this helped the relay come to the end of its life or not.

 

Each relay should be around 15A but I haven't worked out what the difference between the two are. No idea what resistance each element has. I don't know if it works this way but the 110V difference divided by the 5A makes just over 20V an amp so then 240V it would take 19A which I would assume I am not over.

 

What happens if you do overload a relay?



#7 ayjay

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Posted 11 November 2013 - 11:33 AM

If you need to talk to someone on this side of the pond, I can recommend Alan from the website linked to below, I doubt there's anything he doesn't know about kiln electrics.

 

He fixed my controller when the relay in it got fried, (says he's seen lots go like that - too much power going through a tiny relay) he fitted two much larger relays in the kiln rather than in the controller, so that all the controller is doing is switching them on and off  and not passing the power (6.3Kw) through the controller - (something like that anyway).

 

They're at the wrong end of the country really for a visit but if you're fitting the stuff yourself he'll be able to point you in right direction, or possibly recommend someone closer.

 

http://www.processco...s.co.uk/E1.html



#8 High Bridge Pottery

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Posted 11 November 2013 - 12:27 PM

Ah great :D thank you for the link.



#9 Frederik-W

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Posted 12 November 2013 - 06:37 AM

Yes there are 6 top elements and 4 bottom elements linked up to the two relays, it was the top relay that went with the 6 elements. It looks like the elements are wired in parallel pairs.

 

From learning my basic physics again there should be more current going through the top relay as there is less resistance overall. I don't know if this helped the relay come to the end of its life or not.

 

Each relay should be around 15A but I haven't worked out what the difference between the two are. No idea what resistance each element has. I don't know if it works this way but the 110V difference divided by the 5A makes just over 20V an amp so then 240V it would take 19A which I would assume I am not over.

 

What happens if you do overload a relay?

 

The top element (with 6 elements) will carry less current because it it is longer and therefore has more resistance.

( I = V/R where I is the current, V the voltage and R is the resistance).

However this is not always the case. If the top element uses e.g. thicker wire with less resistance than the bottom one, you cannot compare simply based on length.

A kiln might e.g. use one type of wire in the door and another type in the walls of the kiln.

Different sections are then connected in series and/or parallel to load a 3-phase system equally.

 

You can measure the resistance with an ohm-meter (multimeter) to get some idea what the relative resistances are, but the resistance changes when the elements get hot.

If you overload a relay the contacts spark and get pitted and can then stick together when it switches. This can happen over time.

There is no harm in using a slightly bigger relay  e.g. 20, 25, 30 Amp- just to be safe. As long as the controller can switch the relay coil.



#10 neilestrick

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Posted 12 November 2013 - 09:56 AM

Relays fail. Assuming you haven't changed anything else on the wiring, just replace the relay. Usually when they fail that hard, they fail off, but it is definitely possible for them to fail on. This is why, even with a digital controller, you should always make sure the kiln has shut off at the end of a firing. In a kiln with only two relays, one being stuck on means half the kiln is powered up, and that can mean overfiring if you are doing low fire work. In a 3 section kiln it usually just means it only cools to a certain point, however it is still possible for that portion of the kiln to overfire a bit.


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#11 High Bridge Pottery

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Posted 12 November 2013 - 10:45 AM

Nice to know that I can go over the amps with no harm. I will have a test of the resistances etc. when I buy myself a multimeter today.

I haven't changed anything else, hopefully a new relay will be on its way very soon as I have been in contact with Alan.

 

The kiln just sat at 1100 till I realised and turned it off, about 160 lower than top temp. The glaze came out quite satin compared to what it usually looks like. It was actually very nice.



#12 Chris Throws Pots

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Posted 16 November 2013 - 05:25 PM

Relays fail. Assuming you haven't changed anything else on the wiring, just replace the relay. Usually when they fail that hard, they fail off, but it is definitely possible for them to fail on.

 

Hi High Bridge,

 

This past spring I had a kiln scare in which even when the controller was showing idle, the elements were heating up. I have very little knowledge of wiring/electronics, so I am unable to weigh in on your diagram and any other thoughts shared so far on the thread. That said, my relay failed on. Basically it soldered its own connection point in the on position, so unless the kiln was turned off at the power source (in my case the breaker), the elements were receiving power.

 

I would start with replacing the relay as Neil suggested. If the same issue happens again there is likely something wrong in the wiring. And that potential issue in the wiring could be making your relays fail on.

 

Good luck!

 

C


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#13 yedrow

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Posted 17 November 2013 - 02:19 AM

I had a problem with my kiln's relays so I put bigger relays on it. I've had several successful firings now. It's an old kiln and I think it loses heat too fast so the current passing through the relays is greater than that which would pass through a relay on a new kiln. Also, the relays that came with the controller looked pretty cheesy, not that looks matter lol.

 

Joel.



#14 High Bridge Pottery

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Posted 17 November 2013 - 09:31 AM

Hi Chris, sound like exactly what happened to me.

 

Got some new relays on their way thanks to ayjay :) and they are 30A so a little over-spec for what I need which is nice. I have looked at the wiring and brushed up on my electronics. I have decided there is no problem with it. Maybe I am wrong but the whole electronic side of it is quite simple. It just looked very complicated to start with!

 

I had many a successful firing with the old relay before it broke but I am now replacing both of them. Mine is also an old kiln that looses heat fast but I never thought about it causing more damage to the elements, good point.

 

Maybe it is time to order that ceramic fiber to fill in some gaps  :lol:






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