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Pieter Mostert

Under-Powered Relays And A Defective Controller

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My DTC 800 C controller died recently, and I'm trying to figure out the case of death. The error message I get indicates a problem with the circuit board, but suspect it may have been caused by receiving insufficient power. In the four firings I did before the controller packed up, the relays would buzz quite loudly when they were switched on, but they'd gradually become quieter as the temperature increased. The person I bought the kiln from assured me that the buzzing was normal, but after having read the trouble-shooting guide, I see that buzzing is a sign of the relays not receiving enough voltage.

In addition to the buzzing, at low temperatures the kiln would cut out, and this problem got worse with each firing. The cutting out was usually preceded by the relays being on for much longer than usual at that temperature. The odd thing is that I'd be able to restart the kiln using the pre-programmed 'cone-fire' setting, but not using any 'ramp-hold' firing schedules I set myself, except on two occasions. I was able to use the ramp-hold setting above 400 degrees C (752 F) though.

Any ideas why the relays would be under-powered at low temperatures, but not at higher ones, and why I couldn't restart (most of the time) using the ramp-hold setting?

Another (minor) problem I had, and which doesn't seem to be directly connected with insufficient voltage, is that when I wanted to reuse a ramp-hold firing schedule I'd programmed in before, the rate of temperature rise displayed would be one degree less than what I'd originally programmed. Has anyone come across something like this before?

I have a friend who will try to see if the rectifier on the circuit board is not producing enough voltage, and who will also check the transformer, but I'm not sure that fixing either of these problems - if they are problems - will be enough. I know I could get a replacement Bartlett RTC 1000 controller for about $250, although shipping and import duties would be quite a bit extra, since I'm in South Africa. As a cheaper alternative, I'm considering using a generic PID ramp-soak controller or an Arduino type micro-processor, but that will probably be the subject of another post.

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The buzzing noise you are describing may be the sound of the heating elements. The normal buzzing of elements lessens and then disappears as the elements get hot.

 

What error message appeared on the controller?

 

The DTC 800C was made by Bartlett Instruments for Paragon Industries.

 

Sincerely,

 

Arnold Howard

Paragon Industries, L.P., Mesquite, Texas USA

ahoward@paragonweb.com / www.paragonweb.com

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I thought relays used a couple of voltages. One to switch the relay and one that was powering the kiln. If the power running through the kiln was lower would that make any difference to the relay? I wouldn't think so. Maybe if the switching voltage was funky then that could effect the relay. I am only speculating.

 

Could be good to fire the kiln again and set up something so you can watch the voltage across a relay and see if it is doing anything. That would be the first place I would start.

 

I looking in to making a controller very briefly but it looks rather complex. Much easer to spend the cash on a new one.

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Arnold and Neil, it's good to know that the buzzing is probably just the elements, and that this is normal. The error message I get now is ErrE (defective controller), which appears after turning the isolator switch on and pressing Enter (when you turn the isolator switch on, ErrP appears first, but that's normal). I did get an Err- message once or twice (power loss during processing), and also Errt a number of times, but with the bottom part of the t missing. I first got these messages the day after my last firing, when I wanted to see how far the kiln had cooled down. I was able to get the temperature to display after pressing various buttons and turning the safety switch on and off. Now, when I try to do that, all I get besides ErrE is the last temperature I fired to and the time it took to reach that temp.

 

If it's just the controller that's defective, what would explain the power to the elements cutting out at low temperatures, but not at high ones?

High Bridge, I thought the switching voltage was too low, but it seems it probably isn't. Besides, I can't fire the kiln again until I've got the controller sorted out. Building your own controller is more complicated and more time consuming than buying one, but the money I would save is worth more than the time spent (for me, at the moment. I'm sure there are others for which it wouldn't be)

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As Neil said you probably have a defective controller.  You can use a regular PID ramp soak controller but bear in mind that you will have to write a program and it will not have the same features as a Bartlett controller.  I use an Industrial ramp/soak PID controller with excellent results. 

David

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It is a Eurotherm/Chessel Model 2416/P4/VH/LH/XX/XX/XX/ENG it controls a Eurotherm solid state Relay 24amp.  This is an industrial controller and maybe expensive.  Other PID controllers could be used but you must make sure they have a guaranteed soak or hold back  This means if you ramp to a temperature it has to stop and wait for the process to get there otherwise it could go though the whole program and think the kiln was following the program setpoint and the kiln might not be anywhere near the temperature.

David

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If it's just the controller that's defective, what would explain the power to the elements cutting out at low temperatures, but not at high ones?

 

 

When controllers go bad all sorts of goofy things happen. No rhyme or reason. I once saw a controller where 3 numbers on the keypad wouldn't work, but only in cone fire mode. Worked fine in ramp/hold. Goofy. Buy a new controller, pop it in and start firing pots again.

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Buzzing and erratic operation could be from degraded filter capacitors in the DC power supply to the electronics. Capacitors, especially cheap electrolytics, are usually the first components to fail.

 

... and often visual inspection of the capacitor (and the board near it) will strongly suggest that it has been fried. In which case replacement is a fairly low-cost gamble.

 

[Worked with my VCR!]

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Thanks for the reference, David. It looks like it may be over-kill for my needs though. I should be fine with a controller that doesn't have a guaranteed hold back, since I've kept records of the temperature rise during the four previous firings, so I can program a ramp rate that the kiln can keep up with.

The capacitors on the circuit board seem fine, so I think it's just a problem with the chip.

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