PDA

View Full Version : Elements, Relays, and Controllers


Stephen Bishop
02-12-2012, 08:57 PM
So I have been melting glass for around seven years in a modified Aim kiln. Basically just using the electrical components. So over the last several months I have experienced more problems with bad relays, element life, and now controller seems to have fried.

my questions:

First, I heard someone on craft web talk about French elements? Does anyone know if these are better?

How do I calculate the Watts needed to heat a certain volume? For instance Peter's 80 lb Crucible.

SSR however? when they fail don't they fail closed? adding over temp switch?

And Controllers? Fuji again? SOLO? Watlow? what are peoples thoughts?

Really would love to see different wiring diagrams for wire melters. I am tired of pissing in the wind! And know that there are some amazing wire melters out there for a weekend warrior/ middle school art teacher.

Grace upon Grace

Rick Wilton
02-12-2012, 09:20 PM
On my kilns, I ran two SSR's in series, if one fails the second will stop it. It's not ideal nor fool proof, but has given me a bit of peace of mind. I don't think they typically fail either open nor closed as there is no arcing in them to lock up. On a second kiln I have three SSR's one for each element, if any one fails it won't get to dangerously high temps.

Pete VanderLaan
02-13-2012, 04:25 PM
watts is AMPS x volts. You need 2000 watts per cubic foot to get good and hot.

Mark Jesson at Duralite makes elements for AIM Kilns Dudley Gibberson makes nice elements as well but they may be a bit too fine a gauge for you. No one I know is making elements with the french wire. I do want to get a roll with Charlie and Dudley and see what it does.

Go to Mark Lauckners site for Maybe Island Glass for a good notion of a well designed wire melter.

SSR's always have a live leg of power in 240V mode. Watch it. An SCR would be better but costs a lot more.

Dave Hilty
02-14-2012, 08:39 AM
I don't think they typically fail either open nor closed as there is no arcing in them to lock up. On a second kiln I have three SSR's one for each element, if any one fails it won't get to dangerously high temps.

From my own experience and any reports on Craftweb, the only SSR failure is closed, hence the concern for safety as the box overheats. It's been mentioned before but never install an SSR without the appropriate heat sink and smearing heat sink compound on the mating surfaces of the SSR & heat sink.

Pete VanderLaan
02-14-2012, 08:46 AM
SCR's always fail closed as well. It's a smear campaign for sure!

Dennis Hetland
02-14-2012, 09:42 AM
So I have been melting glass for around seven years in a modified Aim kiln. Basically just using the electrical components. So over the last several months I have experienced more problems with bad relays, element life, and now controller seems to have fried.

my questions:

First, I heard someone on craft web talk about French elements? Does anyone know if these are better?

How do I calculate the Watts needed to heat a certain volume? For instance Peter's 80 lb Crucible.

SSR however? when they fail don't they fail closed? adding over temp switch?

And Controllers? Fuji again? SOLO? Watlow? what are peoples thoughts?

Really would love to see different wiring diagrams for wire melters. I am tired of pissing in the wind! And know that there are some amazing wire melters out there for a weekend warrior/ middle school art teacher.

Grace upon Grace

A control unit should have two digital controllers in it. One that runs the furnace all the time with an SSR and another that controls a mechanical rely that is always closed unless the furnace reaches an undesired temp. In which case it opens and prevents an over temp situation.

Dennis Hetland
02-14-2012, 10:38 AM
You should build my design. I like it better than Mark Lauckner's. I take 26g ifb and rip them down the center. Then I take a 1" router and cut a groove centered 1 1/4" from the back side so I have a 1' channel with 3/4" on one side and 1/2" on the inside. Then I cut a 1/2" slice off the inside which gives me a 1/2" opening on the inside of the furnace wall. Then I cut the ends at 45 degrees so when assembled they make an octagon that supports it's self like a Roman arch. The inside diameter is 17"
The very bottom of my furnace is what's left of a Duncan kiln. I have plastic rammable on the bottom so the glass doesn't eat it up too bad. Six of the top seven layers hold elements. The top layer is a half layer that doesn't hold elements. on top of that I have fiber board, kasto lite 30 and plastic rammable all with a hole for the 80lb crucible. Hovering over that is an 8 sided slab of Kast o lite 30 that swings out of the way like a gate. The angle iron it's cast in has an inside diameter that is wider than the outside diameter of the ifb. The iron does not sit directly over hot elements.
To make the elements I use 5 1/2lbs of #11 Kanthol A1. I measure 36" for the first pig tail and attach it in the arbor, then I measure 43 1/2 feet and mark it with colored tape. I set the wire up to roll off the spool from a ladder with a rod. Then while my friend turns the crank I guide the wire onto my 5/8th" diameter arbor. When I have all 43 1/2 feet on the arbor I measure 4" and attach it with vise grips and twist up another 43 1/2 feet. I do this three times for one element then measure out another 36" for the other pigtail. Then I twist the pigtails with a vise and pliers. Then I use the arbor to stretch the elements. The inside diameter of my channel is 64" and where the holes are cut gives me an element length of 62, 60, 62 62, 60, 62. So I measure 62 " on the arbor and make the first section stretch to 62" (I also twist the 4" section and fit the piece that is straight exactly to the brick it passes through.)
Once the elements are made I install them as I assemble each layer of bricks. The furnace has already been wrapped with frax and stainless sheet metal that tightens like a hose clamp and applies pressure to the ifb keeping them in place. I designed the furnace to be easily rebuilt. The bottom of each layer provides the top of the layer below it. Keeping the elements from jumping out of the grooves.
When tied in parallel these elements will draw 34 amps at 240 volts

Dennis Hetland
02-14-2012, 10:46 AM
I tried to post photos, but was unable. Here's a link to the pics on my FB page http://www.facebook.com/media/set/?set=a.133964496675853.27570.129039483835021&type=3

Tom Clifton
02-14-2012, 04:51 PM
I tried to post photos, but was unable. Here's a link to the pics on my FB page http://www.facebook.com/media/set/?set=a.133964496675853.27570.129039483835021&type=3

I just got an error message


This content is currently unavailable
The page you requested cannot be displayed right now. It may be temporarily unavailable, the link you clicked on may have expired, or you may not have permission to view this page.

Rick Wilton
02-14-2012, 04:56 PM
works fine for me though.

Paul Bevilacqua
02-14-2012, 07:07 PM
Stephen, I lost elements frequently until I went to Duralite elements and Spectrum Premium Nuggets on my AIM melter.

Dave Bross
02-15-2012, 05:32 AM
Here's something I'm still doing and it works surprisingly well:

http://talk.craftweb.com/showthread.php?t=7256&highlight=variac

http://talk.craftweb.com/showpost.php?p=97677&postcount=30

I use mechanical relays and a warning light for the door switch cut off. I took a hit of 240v once and don't care to repeat

SSRs always failed "on" for me. Heavy lightning hits here allowed me to have multiple experiences.

Dennis Hetland
02-15-2012, 08:24 AM
Stephen, I lost elements frequently until I went to Duralite elements and Spectrum Premium Nuggets on my AIM melter.

You're right! It is easier to pay other people to do it for you.
(BTW Aim wire melters suck)

Dennis Hetland
02-15-2012, 08:28 AM
Here's something I'm still doing and it works surprisingly well:

http://talk.craftweb.com/showthread.php?t=7256&highlight=variac

http://talk.craftweb.com/showpost.php?p=97677&postcount=30

I use mechanical relays and a warning light for the door switch cut off. I took a hit of 240v once and don't care to repeat

SSRs always failed "on" for me. Heavy lightning hits here allowed me to have multiple experiences.

A Variac brand auto transformer sounds like a pretty cool thing to put on your furnace except they cost more than an SCR. Someone could do the same thing with a welder for a lot less.
What model number are you using?

Dave Bross
02-15-2012, 01:41 PM
Welders don't have the duty cycle to do it. They're rated for being used a certain percentage of time them cooling off. Glass furnace duty will melt them down.

The variacs I use I find used on Ebay. Whatever voltage/amp capacity I need and not Chinese. I prefer ones that will run higher over voltage (over line voltage). They're quite inexpensive in 120v versions. You could run a bigger furnace by using multiple variacs putting how ever many elements on each variac to stay within the rating. Sometimes you see them on ebay manufactured as a stack of multiple variacs.

The increase in element life is phenomenal.

As far as cost...it replaces the digital controller and the SSRs and they're quite rugged in regards to things like lightning and other voltage surprises. Not so the digital stuff. I really don't miss having to decode the instructions for programing the digitals either.

Tom Clifton
02-15-2012, 02:23 PM
A Variac brand auto transformer...except they cost more than an SCR.
Don't get an SCR as a discrete device confused with the term "SCR" referencing an entire controller.

Variacs are typically a manually operated device (turn the knob). An SCR controller used in a "current limiting" manner should yeild virtually the same results as a variac, but you can typically program them for annealing etc. Automated control. If you just need to hold at a specific temperature for long periods of time the variac would do well once you get the right setting and leave it alone.

A solid state relay would operate much the same as a manual "infinite control" on kilns. It periodically turns the elements full on to full off with the assiciated heat/cool cycle that is rough on wire elements. Here is where the variac shines. You only want half the heat - lower the voltage and let the wire maintain a constant (and lower) temperature all the time instead of cycling it between full on and full off which causes thermal expansion and contraction of the elements as well as more errosion during the times when the element runs at higher heat.

That is why a lightbulb rated at 1720 hours lasts a lot longer if just left on than if it is turned on and off every 2 minutes. If you want it to run even longer, use a dimmer which is essentially a digital analog to a variac (but not exactly).

And, yes you could probably use an industrial strenght 2kw light dimmer on a >>small<< wire melter. Somebody want to try and post the results...

Pete VanderLaan
02-15-2012, 03:10 PM
Welders don't have the duty cycle to do it. They're rated for being used a certain percentage of time them cooling off. Glass furnace duty will melt them down.

As far as cost...it replaces the digital controller and the SSRs and they're quite rugged in regards to things like lightning and other voltage surprises. Not so the digital stuff. I really don't miss having to decode the instructions for programing the digitals either.

************************
I agree, welders have been tried and the duty cycle was too severe.
I am using a much simpler SCR on the furnaces I'm building with Charlie and they are very nice and are about half the cost of a Watlow. There is almost no programming beyond setting the amps.

Dennis Hetland
02-15-2012, 03:46 PM
Don't get an SCR as a discrete device confused with the term "SCR" referencing an entire controller.

Variacs are typically a manually operated device (turn the knob). An SCR controller used in a "current limiting" manner should yeild virtually the same results as a variac, but you can typically program them for annealing etc. Automated control. If you just need to hold at a specific temperature for long periods of time the variac would do well once you get the right setting and leave it alone.

A solid state relay would operate much the same as a manual "infinite control" on kilns. It periodically turns the elements full on to full off with the assiciated heat/cool cycle that is rough on wire elements. Here is where the variac shines. You only want half the heat - lower the voltage and let the wire maintain a constant (and lower) temperature all the time instead of cycling it between full on and full off which causes thermal expansion and contraction of the elements as well as more errosion during the times when the element runs at higher heat.

That is why a lightbulb rated at 1720 hours lasts a lot longer if just left on than if it is turned on and off every 2 minutes. If you want it to run even longer, use a dimmer which is essentially a digital analog to a variac (but not exactly).

And, yes you could probably use an industrial strenght 2kw light dimmer on a >>small<< wire melter. Somebody want to try and post the results...

I understand all that. My reference was to the price. Why spend an enormous amount of money extending the life of something that can be replaced so cheaply?
SCR s are dimmer switches.

Tom Clifton
02-15-2012, 03:59 PM
Why spend an enormous amount of money extending the life of something that can be replaced so cheaply?

Is there ever a convenient time to replace elements? IMHO I can spend $100 on a 20 amp (used) variac once then elements every x months or $100 on new elements twice as often. Beyond that, I completely agree with you.

Tom Fuhrman
02-15-2012, 05:25 PM
back in the stone age I used to use a range control connected to a sign timer control with a wire attached to turn down the annealer. We also used to used some very big dimmers for the same purpose. Back then there were no digital controls, SSR's, or SCR's. and they worked.
I also worked at GE my senior year in high school 2nd shift building variable transformers. They were the latest technology back then. We built a lot of custom stacked units and always had a hard time getting the center shaft that they attached to, to line up and give ease of turning them all at one time. We got them to align by using a big hammer. We used to make some that were stacked 6 to 8 high and each about a foot in diameter. I also saw a lot of them fail as it was still in days that they were trying to figure out the best way to wind them. I never really knew where they were all going, but was told many were going to new commercial buildings and some of the big ones were running elevators.
Anyone who was into stage lighting back in the 50's remembers when we used big units coupled together to run the lighting dimmers. There may still be a few of those available in some lighting boneyards. Trying to dim one bank of lights while bringing up several other banks at the same time meant you had to almost be an acrobat and use both arms and your legs.

Stephen Bishop
02-15-2012, 06:56 PM
I GOT TO SAY I LOVE THIS SITE! It is so amazing the knowledge!

Stephen Bishop
02-15-2012, 06:59 PM
Not sure how to respond to all the help! But Peter when the FRENCH CONNECTION happens let us know! I am so TIRED OF FIXING CRAP! Seems like every two months I am chasing down parts and have to believe that there has to be a better way!

Thanks for everyones help...MOre questions to come

Pete VanderLaan
02-16-2012, 04:19 AM
Use an SCR with soft start on the elements and most of your problems will go away. Don't handle elements without gloves on. Clean them with acetone if you do touch them.

Tom, Thank you. A stroll down memory lane.

Dave Bross
02-16-2012, 05:28 AM
Yeah! Go Tom F.!

Love those "History Channel" posts.

I'm a sucker for a good story.

Dennis Hetland
02-16-2012, 07:51 AM
Is there ever a convenient time to replace elements? IMHO I can spend $100 on a 20 amp (used) variac once then elements every x months or $100 on new elements twice as often. Beyond that, I completely agree with you.

Why not use a rheostat like on old school kilns?