CraftWEB Hot Glass Talk  

Go Back   CraftWEB Hot Glass Talk > Hot Glass > General Hot Glass Discussion

Reply
 
Thread Tools Display Modes
  #1  
Old 08-26-2019, 06:49 PM
Brian Graham's Avatar
Brian Graham Brian Graham is offline
Registered Abuser
 
Join Date: Mar 2004
Location: Akron - Ohio
Posts: 515
Brian Graham is on a distinguished road
Strange furnace behaviour - scr issue.

Situation - small wire melter with Watlow Din-a-mite and a watlow 96 series controller - type S TC. Temp will not go above 2000 during the day - drops to 1970'ish - will run back up to 2030 at night time. I thought that maybe the scr was not able to dissipate enough heat so I opened the box and directed a fan on it full time. Problem still occurs - both legs of my elements are drawing the same amount of amps - about 8. My old shop space was large and was not very hot compared to new space.
__________________
The revolution will not be televised.
Reply With Quote
  #2  
Old 08-27-2019, 07:39 AM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 21,245
Pete VanderLaan is on a distinguished road
It seems to me that if the elements are pullling what they've always pulled, "watts is watts". and that suggests to me that you are losing heat somewhere. What do you see when you shoot a laser thermometer at it? That includes the bottom.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #3  
Old 08-27-2019, 01:03 PM
Sky Campbell's Avatar
Sky Campbell Sky Campbell is offline
Registered User
 
Join Date: May 2002
Location: Gainesville FL
Posts: 956
Sky Campbell is on a distinguished road
Glass build up can really be a power sucking situation after it drives through the insulation. Iíd be interested to see what you find. I would also check your connections. A bad element connection can cause resistance and loss of efficiency. Bad thermocouple connections can cause errant temp readings.
Reply With Quote
  #4  
Old 08-27-2019, 02:09 PM
Eben Horton Eben Horton is online now
Registered User
 
Join Date: Apr 2002
Location: Wakefield, RI
Posts: 4,537
Eben Horton is on a distinguished road
Do you have this problem during the day if you are not blowing glass?
__________________
<eben epoiese>
Reply With Quote
  #5  
Old 08-28-2019, 08:13 AM
Brian Wong Shui Brian Wong Shui is online now
Registered User
 
Join Date: Oct 2002
Location: Atlanta, GA
Posts: 171
Brian Wong Shui is on a distinguished road
Is 8amps the usual current draw for your furnace at idle?

What type of furnace do you have? 3phase or single phase? Moly or wire? Assuming single phase, 1920W at idle seems low but it will depend on furnace construction.

Is the the process controller calling for 100% output when process variable is at 1970 while the setpoint is at 2030? If it is, then something is in the heater circuit that is preventing full power (loose connections) or there is a leak in the insulation (gas erosion around elements) or a big chunk of glass is sitting somewhere in the bottom (leak).

Is there a doorswitch contactor? Iíve seen the contacts in the contactor get pitted and increase the resistance in the circuit.
Reply With Quote
  #6  
Old 08-28-2019, 09:55 AM
Brian Graham's Avatar
Brian Graham Brian Graham is offline
Registered Abuser
 
Join Date: Mar 2004
Location: Akron - Ohio
Posts: 515
Brian Graham is on a distinguished road
Single phase - wire elements. I have run this type of furnace for years. I do not believe that I have a leak. I will check all of my connections when I get home. My door switch is a prox that operates a mechanical contactor. Amps in is same as amps to load on both legs of the 240vc. (through quick blow fuses, scr, contactor, etc. It is strange to me that the even idling - the temp will drop everyday and will go up every evening. The heat differential is not that great now that I have a fan blowing directly on the scr 24/7. The controller box has an exhaust fan that already pulled air up through the scr and out the top.
__________________
The revolution will not be televised.
Reply With Quote
  #7  
Old 08-28-2019, 10:31 AM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 21,245
Pete VanderLaan is on a distinguished road
wire elements do deteriorate but should correspondingly give a different amp draw as it occurs. How old are the elements? If your amperage has not changed in the draw to the furnace anytime recently, then logically one would look to something else causing it to lose heat with the amp draw constant. That still takes me to heat loss elsewhere. Either that, or the loss in draw is not in fact constant but is occuring when you're not looking.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #8  
Old 08-28-2019, 06:08 PM
Brian Graham's Avatar
Brian Graham Brian Graham is offline
Registered Abuser
 
Join Date: Mar 2004
Location: Akron - Ohio
Posts: 515
Brian Graham is on a distinguished road
Elements are only about 2 months old. Every time I have checked the amp draw it reads consistently around 7.5 - 8 per leg - I believe unit is stated to pull no more than 17 so I seem to be good there. The only thing I have not looked at is the element connections - I will do that here shortly. As always...the temp is slowly climbing back up as I near evening time.
__________________
The revolution will not be televised.
Reply With Quote
  #9  
Old 08-28-2019, 06:41 PM
Eben Horton Eben Horton is online now
Registered User
 
Join Date: Apr 2002
Location: Wakefield, RI
Posts: 4,537
Eben Horton is on a distinguished road
I donít mean to sound like captain obvious but can the furnace keep up with the door opening and closing when you work? Thatís why I asked if it happens during the day if you are not blowing glass.
__________________
<eben epoiese>
Reply With Quote
  #10  
Old 08-28-2019, 08:06 PM
Brian Graham's Avatar
Brian Graham Brian Graham is offline
Registered Abuser
 
Join Date: Mar 2004
Location: Akron - Ohio
Posts: 515
Brian Graham is on a distinguished road
That is not a problem Eben.
__________________
The revolution will not be televised.
Reply With Quote
  #11  
Old 08-28-2019, 08:14 PM
Brian Wong Shui Brian Wong Shui is online now
Registered User
 
Join Date: Oct 2002
Location: Atlanta, GA
Posts: 171
Brian Wong Shui is on a distinguished road
Couple random thoughts

Are you reading the current with a true RMS clamp meter? If not, the reading could be off.

Have you checked the voltage going into the furnace? Maybe the line voltage is sagging during the heat of the day when everyone is running their ACís

If you have a spare din-a-mite, swap it and see if the problem goes away?

Dying watlow 96? People have been having trouble with their 981 dying. 96 is the same vintage. Swap a spare in if you have one.

Has the PID settings of the controller changed? Bad PID Numbers can make a controller do some strange things.

Has something changed with the thermocouple leads that could affect the reading?

As Eben asked, can the furnace recover when you are blowing glass opening and closing the door?
Reply With Quote
  #12  
Old 08-28-2019, 08:20 PM
Brian Graham's Avatar
Brian Graham Brian Graham is offline
Registered Abuser
 
Join Date: Mar 2004
Location: Akron - Ohio
Posts: 515
Brian Graham is on a distinguished road
Meter is RMS clamp - I did check the voltage today at mid afternoon when electric was at peak and was getting 120vac per leg. I checked the element connections a bit ago and found only one wire that was slightly oxidized at the split nut. I cut the end off/ stripped it fresh and reconnected it. All connections were super tight.
__________________
The revolution will not be televised.
Reply With Quote
  #13  
Old 08-29-2019, 07:43 AM
Eben Horton Eben Horton is online now
Registered User
 
Join Date: Apr 2002
Location: Wakefield, RI
Posts: 4,537
Eben Horton is on a distinguished road
So strange.
__________________
<eben epoiese>
Reply With Quote
  #14  
Old 08-29-2019, 09:48 AM
Rick Wilton Rick Wilton is offline
Registered User
 
Join Date: Oct 2005
Location: Calgary, Alberta Canada
Posts: 202
Rick Wilton is on a distinguished road
have you checked the line VOLTAGE? When I moved into a commercial space the voltage was only 208V not 220 like my last location and that was a MAJOR difference on my fusing kilns. I needed to add a whole new element as I couldn't get to temp fast enough.
Reply With Quote
  #15  
Old 08-29-2019, 12:46 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 21,245
Pete VanderLaan is on a distinguished road
well, he said he checked it at peak voltage. That's when he said it was at it's lowest ebb. I think Brian has an excellent set of fixes listed that are worth going through.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #16  
Old 08-29-2019, 02:52 PM
Rick Wilton Rick Wilton is offline
Registered User
 
Join Date: Oct 2005
Location: Calgary, Alberta Canada
Posts: 202
Rick Wilton is on a distinguished road
True BUT while you will get 120v on a single leg (as he said he has) with three phase power it's only 208v across any two lines. If the power is three phase he is definitely NOT getting 220-240 v across two legs.

As you said watts are watts BUT if your line voltage isn't what you expect the actual watts produced is significantly less.
Reply With Quote
  #17  
Old 08-29-2019, 05:30 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 21,245
Pete VanderLaan is on a distinguished road
I wouldd tangentially agree that a real problem in the rust belt is variance of the power supply. Brian is right in it and the power company stance is that "the lights are on". As I recall, the shop was in the process of being moved.

So I would still think that Brian' s thoughts about methodical replacement of components is a really wise layout. Watlow has not been the company we had all thought it was in the past.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #18  
Old 08-29-2019, 07:21 PM
Brian Graham's Avatar
Brian Graham Brian Graham is offline
Registered Abuser
 
Join Date: Mar 2004
Location: Akron - Ohio
Posts: 515
Brian Graham is on a distinguished road
Boom! Solved.

Collective hive mind - I love this place. My problem ended up being an intermittent scr output issue. I kept measuring amps, resistance, and voltage. Viola! I finally found that one leg of the scr was only allowing 53 volts through. Luckily I always buy 3 phase din-a-mites - I switched to the last unused leg and was now getting the appropriate 120vac on both legs.

I actually have a very steady power service. I have taken so many readings the past week at every conceivable time. Rock solid readings of 120 per phase to my sub panel every time.

So...intermittent problem it was. Persistence pays off I suppose. Once I made the switch and powered it back up, it started running up fast like it always had. Thank you again for everyone that chimed in. Did I mention that I love this place?!?
__________________
The revolution will not be televised.
Reply With Quote
  #19  
Old 08-31-2019, 09:54 AM
Brian Wong Shui Brian Wong Shui is online now
Registered User
 
Join Date: Oct 2002
Location: Atlanta, GA
Posts: 171
Brian Wong Shui is on a distinguished road
Great. Problem solved.

So Iím curious. Whatís the clamp meter reading now since youíve corrected the problem?
Reply With Quote
  #20  
Old 08-31-2019, 12:26 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 21,245
Pete VanderLaan is on a distinguished road
I am curious as well but about something a bit different. On the units I've built using both a Watlow and another SCR, essentially one leg of the power was actually being passed through the SCR without being modulated. The other leg was indeed being messed with changing the sine wave etc . So, on a number of these units, I've seen the three phase SCR's as well as relays being used and one leg of the unit seems to get fried more than I might expect. I recognize that the cold creep is an issue for all of them and am simply not sure if cold creep maintenance is part of the problem or if something else is also going on.

On this unit, I presume that one leg maintained 120V and it was likely the leg that was not being monitored although we may all think both are being monitored, so the other leg dropped to 59 volts, apparently at very regular intervals. So is this something in the SCR that's failing , or what?

I mean it's great to have this extra leg one can use if one leg fries but that doesn't make me feel a lot better about what I just stated.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #21  
Old 09-01-2019, 08:32 AM
Brian Graham's Avatar
Brian Graham Brian Graham is offline
Registered Abuser
 
Join Date: Mar 2004
Location: Akron - Ohio
Posts: 515
Brian Graham is on a distinguished road
The model of scr I was using could control three legs and did not have a pass through for a non modulated leg. So the leg that went bad was one being modulated by the controller. Only this leg went bad -the other two are still fine. I did just restart the furnace a moth ago after routine maintenance. I guess the bad leg would come and go. I know it read 120 when I read it before. The Watlow SCR's can be found for under $30 and I scoop them up when I find them even cheaper on ebay.

On my controllers, I always protect all power legs with quick blow semiconductor fuses in order to protect all electrical components. I had an scr fried before by a surge hitting the non modulated leg.
__________________
The revolution will not be televised.

Last edited by Brian Graham; 09-01-2019 at 09:05 AM.
Reply With Quote
  #22  
Old 09-01-2019, 09:36 AM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 21,245
Pete VanderLaan is on a distinguished road
so then, the question for me becomes "Did the modulated leg go bad because of the other controller and the information it received from that controller, or did it go bad just because of use?"

The Watlows do seem to have a finite life span which is notable. The curiosity is that I have not really seen this in the single phase tooling and that's true across the board. The three phase Stadelmann units have generally been substantially more trouble than the single phase ones at just about every level of operation.

It strikes me that in general, three phase power is less consistent than single phase. I have to wonder if variance in the power supply contributes to the issue. When I was selling components for these things, it was always the three phase tooling that had the substantial and occasionally consequential failures. Things like fires...
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #23  
Old 09-01-2019, 10:29 AM
Brian Graham's Avatar
Brian Graham Brian Graham is offline
Registered Abuser
 
Join Date: Mar 2004
Location: Akron - Ohio
Posts: 515
Brian Graham is on a distinguished road
I believe they just go bad from use. I use the switched DC signal type as I think this is better than having a 120vac signal pumping into them. Maybe I am wrong on this idea. As stated prior, I always isolate my components with the semiconductor fuses. I have only had two ever go bad on me over 20+ years.

Speaking of 3-phase components - the Eaton contactor on my single phase Stadelman was a 3-phase model. It did blow a leg and I did the same thing by simply switching to the unused leg. I expect wear on a mechanical contactor more so than an SCR....

I really believe that an SCR gives longer element life on a wire unit....maybe this is a flawed observation...I dunno...lol
__________________
The revolution will not be televised.
Reply With Quote
  #24  
Old 09-01-2019, 01:35 PM
John Riepma John Riepma is offline
Registered User
 
Join Date: Apr 2003
Location: Grand Haven, MI
Posts: 497
John Riepma is on a distinguished road
OK, I've started to post this several times now and chickened out because I don't need the abuse that I think it may generate. But here goes:

I had a problem after we moved our studio that I could not get the furnace to come up to temp. The initial problem was a switch from 240v to 208 3 phase service. A boost transformer was needed to get the voltage up to 240v. That was the simple part. The furnace would still not get up to temp, and when I measured voltage and amperage into the SCR everything appeared fine. The problem became apparent when I measured 21KVA into the SCR and 17KVA out. Could not figure out how I could be losing that much current in the SCR, and I did a lot of research and came up with nothing. I finally found a site (can't find it right now) that mentioned that in a perfect world (I assume that this is one not supplied by Consumers Energy) the sine waves of the current cross at a median and do not overlap. I think that I remember this being called apparent power vs actual power, and I apologize but I can't find the link to the article right now

Thinking about this for a while, I surmised that the SCR on the controlled leg (not the through leg) was being "chopped" by the SCR at its leading edge and by the trailing edge intersecting the following wave. Maybe some people on this board can state that more intelligently than me.

Soooo....knowing that volts times amps equals watts, and assuming that if approximately 4000 watts were disappearing into the SCR, and assuming that this would be pretty obvious from a heat standpoint if not a visible light, and not knowing what else to try I switched the leads into the SCR and immediately started getting 21KVA out. It's been working this way now for 8 years, same SCR which is a 3-phase Watlow and I'm using two legs as others have mentioned.

Maybe this does not solve the problem that Brian has mentioned but its a really easy thing to try.
Reply With Quote
  #25  
Old 09-01-2019, 03:33 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 21,245
Pete VanderLaan is on a distinguished road
I have heard of three failures on the eaton relay at this point and had one myself which at the time was attributed to cold creep. Now I doubt that. that's an expensive relay, running about 700 bucks retail.

Push come to shove, I'm always suspicious of three phase stuff. It may be irrational but I made a point of studying failures in studios of all kinds and three phase just kept coming up.

John your experience is not the only one I've heard of like that. I'm much happier with gas equipment again. I like some heat with my explosions. Electric ones make such irritating noises like giant bugs being zapped. They never smell good either.
__________________
Where are we going and why am I in this basket?
Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Forum Jump


All times are GMT -5. The time now is 02:13 PM.


All published comments within these message boards are the opinions of its contributor and does not represent
the opinion(s) of the owner(s) of this website. Please see the Terms of Use file for more details.

Books to Help Artists Avoid Online Scams: Top 10 Email Scams | Social Media Scams

Powered by vBulletin® Version 3.7.2
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
© CraftWEB.com. Opportunity Network. 2008. All Rights Reserved.