Kiln control.

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Kiln control.

This topic has 35 replies, 15 voices, and was last updated 16 November 2017 at 17:48 by Neil Wyatt.

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14 November 2017 at 15:32 #34366
mark gallimore
Participant
@markgallimore42326
Burst fire vs phase angle
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14 November 2017 at 15:32 #327139
mark gallimore
Participant
@markgallimore42326
I am building (designing at the moment) a small kiln (approx 2kw). I already have the resistance wire and my calcs suggest 110vac is the most appropriate voltage.

To get the 110v I will use a step down transformer. To vary the power i have 3 control options – simple on / off, burst fire or phase angle. The latter two would regulate the 240 v feeding into the step down transformer.

I would appreciate opinions regarding the effect, if any, of feeding the altered waveform into the stepdown transformer – my concern is could it cause the transformer to overheat through inefficiency.

Thanks for reading,

Mark Galimore
14 November 2017 at 15:37 #327141
Brian Sweeting 2
Participant
@briansweeting2
A friend of mine built his own kiln using 240v and a simple temperature controller that used a solid state relay (ssr).

So far no problems melting aluminium or brass.

[Edit] Something like this…

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F311998479037

Edited By Brian Sweeting on 14/11/2017 15:41:36
14 November 2017 at 15:51 #327143
Anonymous
I can't see the point in running on 110Vac. Assuming you're in the UK wind the heating coil for 240Vac. That way you eliminate a large, and expensive, transformer. I agree with Brian, use a simple P(ID) controller and SSR. I bought a single channel temperature controller, thermocouple and SSR on Ebay a while back for about £18. At that price it's a no brainer.

Andrew
14 November 2017 at 15:58 #327146
Douglas Johnston
Participant
@douglasjohnston98463
Why do you need the transformer? I am also in the middle of making a kiln and am using 240V mains in conjunction with a solid state relay (SSR). The SSR is fed with a pulse width modulated signal derived from a 555 timer chip. This setup works perfectly to alter the power input to the kiln element.

I will also use a PID temperature controller with its output used to control the 555 timer through pin 4 of the 555 chip. This gives variable control of the kiln temperature without the need for a transformer.

Doug

Too slow in typing! Andrew has beaten me to it.

Edited By Douglas Johnston on 14/11/2017 15:59:49
14 November 2017 at 16:13 #327149
SillyOldDuffer
Moderator
@sillyoldduffer
In addition to Andrew and Brian's points a transformer isn't a resistive load. They're not really suited to either having either burst fire or triac regulators on the input. However, if you're stuck with a 110v element and already have a transformer, a phase-angle/burst-fire or SSR on the transformer's 110VAC output would be OK.

If I were building a kiln Brian and Andrew's method would be my first choice.

Dave
14 November 2017 at 16:25 #327153
Anonymous
Posted by Douglas Johnston on 14/11/2017 15:58:19:

I will also use a PID temperature controller with its output used to control the 555 timer through pin 4 of the 555 chip. This gives variable control of the kiln temperature without the need for a transformer.

The simple controller I have drives the SSR directly. It's either on or off. The response time of a kiln is pretty slow so on/off control, with varying mark:space, over minutes is easily as good as "proper" PWM.

Andrew
14 November 2017 at 16:57 #327159
Douglas Johnston
Participant
@douglasjohnston98463
Posted by Andrew Johnston on 14/11/2017 16:25:42:

Posted by Douglas Johnston on 14/11/2017 15:58:19:

I will also use a PID temperature controller with its output used to control the 555 timer through pin 4 of the 555 chip. This gives variable control of the kiln temperature without the need for a transformer.

The simple controller I have drives the SSR directly. It's either on or off. The response time of a kiln is pretty slow so on/off control, with varying mark:space, over minutes is easily as good as "proper" PWM.

Andrew

That's fine Andrew if the element is happy with 240V across it. I don't think my element will stand that which is why I introduced the 555 timer into the setup to reduce the power a bit. Once it is finished I will see if it was really necessary to include the 555 chip.

Doug
14 November 2017 at 16:59 #327160
duncan webster 1
Participant
@duncanwebster1
I hope at least one of you kiln builders is going to write it up for MEW! It's a very long time since anything was described
14 November 2017 at 19:45 #327194
Douglas Johnston
Participant
@douglasjohnston98463
Please don't ask me to do that, I promised Neil that I would write an article on another matter and that was a year ago and I have not done that yet. I do hope Neil is not reading this since I don't want to be excommunicated from MEW

Doug
14 November 2017 at 19:57 #327197
Neil Wyatt
Moderator
@neilwyatt
Posted by Douglas Johnston on 14/11/2017 19:45:52:

Please don't ask me to do that, I promised Neil that I would write an article on another matter and that was a year ago and I have not done that yet. I do hope Neil is not reading this since I don't want to be excommunicated from MEW

Doug

GET THEE HENCE TO A PLACE OF CONTEMPLATION!
14 November 2017 at 20:00 #327198
Neil Wyatt
Moderator
@neilwyatt
As long as the time constant for the controlled thing (furnace temperature) is significantly longer than the time constant of the controller all will be fine.

Furnaces take along time to heat up and cool down so almost any control method will work.
14 November 2017 at 20:20 #327201
John Olsen
Participant
@johnolsen79199
I would not advise using a triac controller ahead of a transformer. It can be done…Hewlett Packard did it years back as a preregulator on a fancy power supply….but you must use a controller that ensures that the phase angle on both halves of the waveform is the same. If you don't, you get DC in the transformer primary. The ordinary sort of triac controller does not maintain symmetry very well. I did try it once to see how it would work out for controlling a battery charger, but the transformer was not very happy about it. so I desisted.

John
14 November 2017 at 20:30 #327202
Mike Poole
Participant
@mikepoole82104
eBay would seem to have ready made packages for kiln control at very attractive prices. I would definitely have a rethink about using a transformer and look at a resistance wire configuration for 240v. Unless you have one, a 2kVA transformer is a lot of money and I am sure resistance wire would be much cheaper.

Mike
15 November 2017 at 09:25 #327266
Douglas Johnston
Participant
@douglasjohnston98463
Posted by Neil Wyatt on 14/11/2017 19:57:41:

Posted by Douglas Johnston on 14/11/2017 19:45:52:

Please don't ask me to do that, I promised Neil that I would write an article on another matter and that was a year ago and I have not done that yet. I do hope Neil is not reading this since I don't want to be excommunicated from MEW

Doug

GET THEE HENCE TO A PLACE OF CONTEMPLATION!

That's told me-I'd better get off to the loo then.

On a serious note the PID controllers I have seen on ebay seem to be advertised as having a range of 0-400 degrees Celsius which would not be suitable for a kiln working at higher temperatures. Also some PID's have an output to directly drive an SSR while others have a relay output, so one would have to take care to get a suitable one.

Doug
15 November 2017 at 21:53 #327392
Roderick Jenkins
Participant
@roderickjenkins93242
Doug,

Have a careful look at the specs for the ebay PID controllers. Most of them will accept a type K thermocouple input which is good to about 1300C. However, they are often supplied with a TC whose insulation will only take a much lower temperature so they are advertised to reflect this.

HTY,

Rod
16 November 2017 at 00:02 #327401
Mike Poole
Participant
@mikepoole82104
I must I must admit that I only had a cursory look at eBay but is does seem that the choice of thermocouple is the limiting factor to the range. Heating elements seem very cheap on the face of it, longevity is unknown though. It certainly seems the basic components of a small muffle furnace would not cost too much. Is it time for an MEW muffle furnace to be built?

Mike

Edited By Mike Poole on 16/11/2017 00:02:32
16 November 2017 at 10:00 #327426
Douglas Johnston
Participant
@douglasjohnston98463
Posted by Roderick Jenkins on 15/11/2017 21:53:46:

Doug,

Have a careful look at the specs for the ebay PID controllers. Most of them will accept a type K thermocouple input which is good to about 1300C. However, they are often supplied with a TC whose insulation will only take a much lower temperature so they are advertised to reflect this.

HTY,

Rod

I did wonder about that Rod and I looked up a data sheet on these PID's. That indicated they were available with different input temperature ranges and each range had its own part number. I can't understand why they would do that if they were suitable for different ranges. Can anybody who has one marked for 400 degree C tell us if they are happy to work perfectly well above this value?

Doug
16 November 2017 at 10:19 #327427
not done it yet
Participant
@notdoneityet
Can anyone tell me why I cannot see the posts by Douglas Johnston, please? They are totally invisible, only known to exist from quotes and the 'lastest forum posts' list!
16 November 2017 at 10:25 #327428
Michael Gilligan
Participant
@michaelgilligan61133
Posted by not done it yet on 16/11/2017 10:19:30:

Can anyone tell me why I cannot see the posts by Douglas Johnston, please? They are totally invisible, only known to exist from quotes and the 'lastest forum posts' list!

.

At a guess … You have inadvertently activated 'Ignore member'

MichaelG.
16 November 2017 at 11:07 #327440
not done it yet
Participant
@notdoneityet
Surely if one clicks accidentally on the ignore button there is a confirmation request before that poster is ignored?

I see no way of unblocking, if that were the case. I've never blocked anyone, to my knowledge. And usually if a post were to be blocked, the missing posts would be indicated (for continuity), even if the post were missing? Forum has some peculiar quirks, it seems.
16 November 2017 at 11:31 #327449
Michael Gilligan
Participant
@michaelgilligan61133
Posted by not done it yet on 16/11/2017 11:07:00:

Surely if one clicks accidentally on the ignore button there is a confirmation request before that poster is ignored?

.

Indeed there is:

.

But it was the only explanation I could suggest.

MichaelG.

.

I think you can administrate blocked members via the 'Settings' menu

… but I'm on the 'bus at the moment, and one demo is enough.
16 November 2017 at 12:40 #327458
Micky T
Participant
@mickyt
Doug

you will need to replace the supplied thermocouple with a type K thermocouple that are available on ebay which would reach the required heat range

**LINK**

Mick

Edited By Micky T on 16/11/2017 12:40:50
16 November 2017 at 12:46 #327461
Douglas Johnston
Participant
@douglasjohnston98463
Posted by not done it yet on 16/11/2017 10:19:30:

Can anyone tell me why I cannot see the posts by Douglas Johnston, please? They are totally invisible, only known to exist from quotes and the 'lastest forum posts' list!

I blame the Russians, they seem to be hacking everybody at the moment. Hold on let me just check that I really do exist……….. yes it seems that I do!

Doug
16 November 2017 at 12:49 #327462
Roderick Jenkins
Participant
@roderickjenkins93242
Posted by Douglas Johnston on 16/11/2017 10:00:36:

I did wonder about that Rod and I looked up a data sheet on these PID's. That indicated they were available with different input temperature ranges and each range had its own part number. I can't understand why they would do that if they were suitable for different ranges. Can anybody who has one marked for 400 degree C tell us if they are happy to work perfectly well above this value?

Doug

I bought a MYPIN TA4 SSR a few years ago and hooked it up to my homebrew muffle furnace. Worked fine with a Type K thermocouple – I didn't take mine up to more than 900C to protect the nichrome windings. It looks like that model has been superceded by the TA4 SNR **LINK**

Rod
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