Prolonging The Life Of Relay Switches

[Mossyrock]

It has been suggested to me to run a small fan, aimed to blow across the computer controller, during firings to prolong the life of the relay switches. Does anyone else do this and can you tell if it has helped? I had a couple of relay switches to go out after only about 50 firings (low-fire).

[bciskepottery]

I've heard of folks using a fan to keep the electronic controls/circuit board cool during hot weather -- if the controls/circuit board get over a certain temperature, it automatically shuts down the kiln. Similarly, in cold weather, I've heard of folks using a heater to warm up the controls/circuit board -- usually when the temperature is below freezing. Not aware of using a fan to prolong relay life.

 

 

[kilndoc]

First off, let me say that I am a full-time, professional Kiln repair technician, and have been working in the field for 16 years.

Mechanical relay switches are moving parts and will wear out through use. They are the source of the 'clicking' noise that you hear during a firing. The addition of a fan blowing across the control box is an attempt to keep the control box cooler and thereby increase the life of the components. I would say that anything you can do to keep the control box cooler will be of benefit overall, but this may not be a solution to the problem you are having. It is addressing the symptom (my relays have gone out after only 50 firings) without identifying what the causal issue may be; or if an issue actually exists.

 

If, for example, you do ^10 crystalline firings, with prolonged holds and complicated ramps, the relays will need to cycle MORE often during a single firing than a standard ^04 glaze firing. This will, naturally, cause them to go out in a much shorter 'number of firings' than one would expect.

 

Other factors can cause this as well such as old wiring in the control box, small gauge wires in the box where a larger gauge would work better, loose female disconnects (a common cause of overheating), and the list can continue.

 

I would suggest contacting your local kiln repair technician, or the kiln's manufacturer, and give them the full details of what is going on. They can give you more specific information and suggestions based on the details of your phone call.

 

 

 

 

[Mossyrock]

Thanks kilndoc.....to date, all of my firings have been low-fire and my kiln is only 2 years old. I replaced the relays and when talking to two other potters about it, they said it was suggested to them by the mfg kiln tech for their kiln (L&L and Skutt, respectively) to use the fan to help prolong the life of relay switches. I guess it would probably prolong the life of all components if it helped keep the heat away. My kiln has the 3" bricks so it doesn't get too hot on the outside....again, I'm only doing low-fire. I am going to experiment with mid-range firings soon so it seems the fan would even be more important.

[jupdyke]

I believe the issue is actually that there are two kinds of relays. Mechanical and solid-state. I'm and engineer by trade so I don't know a whole lot about kilns specifically, however the components used to control them are what my masters degree was in. Basically, a mechanical relay has a little electro-magnet that pulls a metal tab into contact with a second tab. I have never seen a single one of these that was not inside a plastic cube (these are nicknamed 'icecube relays'). The since it is moving back and forth you hear the click when it connects. The more they click the sooner they wear out. But they are really cheap and easy to replace, just plugs into a socket. They shouldn't get hot and cooling them will not help their life. It is possible that they get hot if too much power is being run through them, but that would be because the relay was not rated for the load. But again they are inside a plastic box so a fan wouldn't help them.

 

On the other hand a solid state relay is a fancy transistor and will get hot. All integrated circuits get warm and have a temperature that they will fail at. So you want to keep them cool. This is usually done with a heat sink / heat spreader and fan. Basically its a block of aluminum with fins on it to help transfer the heat away. Not all chips need these, but many must have them. Basically its the same as your computer. If you look inside you can see heat spreaders and fans to keep parts cool. I would bet that the person who designed the kiln did the calculations to see if they needed these head spreaders and / or fans. That being said if your kiln is in a hot location like a garage in the middle of summer in Texas, that might not be the conditions the designer intended. So running a fan over them would help.

 

The control circuits are not really a 'relay', it drives the relays but I could see how many people would call the whole electronics section the 'relays'. These electronics can also get hot and fail and a fan would help to cool them off too, which could increase the life of the electronics. But again is the air flow actually going over the area that is hot? I would bet it is in a box and the air is not really helping.

 

So that is a bunch of mumbo jumbo that doesn't really help you. LOL. Here is what I would do:

 

Listen for clicking when the kiln is running. If there is a regular clicking sound then you have a mechanical relay and a fan will not help them at all. but they are cheap and easy to replace, many just plug in.

 

Check the electronic box to see if it is getting really hot. You can put your hand on it and feel. If you can keep your hand on it, then the electronics are plenty cool enough. The parts inside might be getting hot, and I don' t advocate opening it while it is running unless you know what you are doing. But you could also epoxy some heat spreaders onto any ICs that were hot. You can buy them online and just glue them on. Make sure to use thermal epoxy so it can conduct heat.

 

AGAIN DO NOT OPEN THE ELECTRONIC BOX UNLESS YOU KNOW WHAT YOU ARE DOING! I believe many of these are 220v. But you could run the kiln and then unplug it open the electronics box and put your fingers on the tops of the black chips. If there is room to epoxy a heat spreader then that might help. But if your electronics are working fine I seriously doubt that you need it.

 

most electronics run better the cooler they are, I don't know why you would warm them up in the winter unless you were worried about water condensing on them. But instead of warming them up I would just make sure it was water tight.

 

Those are my thoughts. Those of you who are more knowledgeable about kilns can put me in my place now.

 

josh