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Old 09-12-2015, 09:59 AM
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Mark Rosenbaum Mark Rosenbaum is offline
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Furnace problems again....

I was called in this morning with my furnace in alarm. My regular electrician is out hunting ducks (of course, it's the start of teal season today...) Anyway, I have another electrician over here and he is not sure about the whole system because there is no schematic beside the simple drawing in the manual. We think that the problem is the logic control. It is dark. We think that is coming from the logic controller...The SCR is in alarm....I don't want to go in there and start reprogramming. it is above my pay grade. Has anyone had this piece punk out on them before? Any suggestions?
Thanks.
Update...we tested both coils---hi and lo, there is power going to each, but there is also power coming out of each. The transformer tests OK but does not turn on. Is that logic control unit controlling that?

Last edited by Mark Rosenbaum; 09-12-2015 at 10:48 AM.
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Old 09-12-2015, 11:07 AM
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The SCR alarm is line loss alarm.....
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Old 09-12-2015, 11:33 AM
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OK, we are back online....it was the fuse in the SCR. This is the second fuse that blew in a year or so....you have to check the simple things before you start to panic...thanks for listening....now back to work...
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Old 09-13-2015, 01:38 AM
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Glad you are back up and running! Mark you doing the show over here in P-cola this year?
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Old 09-13-2015, 02:55 AM
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No Scott, we are not going to P-cola this year. We decided to cut out our street shows this year and concentrate on getting people to come to the studio with our events. We will miss seeing the friends that we have made over the 30 years we have been on the road, but physically and financially this seems like the right thing to do right now. ...give my best to Molli
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Old 09-13-2015, 08:49 AM
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Mark: Have you ever had occasion to ask the people at the Watlow help line what factors can cause the fuse to blow? I am confused by the frequent infrequency of the failures and am wondering if there is something occurring within the studio usage that causes the failure.

Not only is the failure expensive, so is the fuse in question.
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Old 09-13-2015, 09:03 AM
Victor Chiarizia Victor Chiarizia is offline
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watlow tech support is great. always helped me with any problems. v
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Old 09-13-2015, 09:00 PM
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Quote:
Originally Posted by Pete VanderLaan View Post
Mark: Have you ever had occasion to ask the people at the Watlow help line what factors can cause the fuse to blow? I am confused by the frequent infrequency of the failures and am wondering if there is something occurring within the studio usage that causes the failure.

Not only is the failure expensive, so is the fuse in question.
Pete: The last time I had a problem with the smaller controller, I called Watlow and I was surprised by their lack of help. What he basically told me was that the person who installed the unit was the one to call....needless to say, I don't put much faith in their help line.
Honestly, I have much better luck on this board or contacting someone from the board. There is an amazing wealth of information at our fingertips that can relate to our very specific problems.
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Old 09-14-2015, 08:11 AM
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I would think this to be right up watlows alley and my experience with their help line has always been spot on.

My concern is why it hits the SCR and what can trigger that. I would think they would have a laundry list of common causes. It's a very expensive fuse and I keep hearing of people blowing them. Something they do usually have in common is the shop that built the furnace. I have never blown one but I certainly have a spare.
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Old 09-14-2015, 08:37 AM
John Riepma John Riepma is offline
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If it's a semiconductor-type fuse I think that it may be a loose connection doing it. I have a semiconductor fuse on a Din-A-Mite C SCR running an annealer, and when one of the connections at the element lead burned out it blew the fuse - twice. The folks at the electrical supply house where I got the replacements told me that the semiconductor fuses are extremely sensitive to such issues. I'd start by checking all connections, which is a good practice anyway.
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Old 09-14-2015, 01:20 PM
Brian Wong Shui Brian Wong Shui is offline
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I'm curious to find out if all the fuses that have been blown have been on furnaces with the power factor correction in the system.

Like Pete, I haven't had any problems with the semiconductor fuse blowing but I don't have a PLC switching the output of my Watlow Power Series.
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Old 09-14-2015, 05:29 PM
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I used to have the same thing in my Partlows.. was due to a Power Spike.. solution was the factory put a 'fliter' in all my Partlows.. never had an issue after that ...
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Old 09-15-2015, 11:34 AM
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Quote:
Originally Posted by Cynthia Daiboch View Post
I used to have the same thing in my Partlows.. was due to a Power Spike.. solution was the factory put a 'fliter' in all my Partlows.. never had an issue after that ...
M.Tart
Is that an aftermarket thing that I can add on at this end?
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Old 09-15-2015, 02:21 PM
Brian Wong Shui Brian Wong Shui is offline
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Hi Mark,

I not sure a power filter will help in your case. That might help with spikes on the power line and if you are getting those, the power company or your electrician should be able to use a line analyzer to see if there is a problem with the quality of the power.

I think that the problem may be coming from the switching of the outputs of the wallow power series.

This is a different case from switching the inputs because the watlow has a 10 second soft start if it detect the the loss of power. This is the mechanism that is used by the door switch and the high limit controller to cut the power to the elements

In the case of switching the outputs, the PLC is switching between the primary windings of the transformer. It is essentially taking the output from the watlow and making a decision about which primary winding to use based on how far the process temperature is sitting from the setpoint. If it is close to setpoint use the winding that gives a lower voltage. If it is far, use the winding that give the higher voltage.

So we have power that is being switched somewhat instantaneously into a transformer which is an inductive load. When the primary is switched, the voltage in the primary coil isn't zero and doesn't instantly drop to 0 before connecting the other winding. This can cause a current spike which can blow the semiconductor fuse (which are intentionally fast blow and sensitive to protect the switching diodes). This is just a theory since my furnace is not quite yours.

A quench arc device might help but I'm not sure if they are made big enough for this application. I'll poke around a little to see

Next time you shut down, you should inspect the contacts in the contactors to check if they are in good nick. Worn contacts can also play hell with clean switching. Kind of like points on a car.
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Old 09-15-2015, 02:44 PM
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Thanks Brian
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Old 09-15-2015, 04:14 PM
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I'm always trying to mentally collate the issues that come up with the fuse. It seems to me that the people who have had issues are either 3 phase or Hi Lo transformer clients. Is that the case?

My inclination, beyond tightening the wires in the power series unit, of which there are not a lot of wires to tighten ( but there's plenty in the relays!) that the 3 phase stuff has caused more than it's share of problems and a lot can indeed be attributed to "dirty " power. Sadly, your electric company is happy if the lights are on and they'll want little to do with your issues after that. I have mentally registered a fair amount of that stuff in the rust belt. I don't recall NO having the same issues but I'm always interested.
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Old 09-15-2015, 10:47 PM
Brian Wong Shui Brian Wong Shui is offline
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I don't have problems with my three phase system but I don't have PLC switching installed. My power feed is 240 closed delta and not 208 wye. wye vs delta should not be an issue since the load is balanced and the neutral isn't used.

So maybe the hi-lo switching stuff is causing the fuse to blow.

I think the three phase problems can stem from the power company using 2 transformers on the pole and supplying open delta instead of closed delta. I think that the watlow power series likes the phase currents to be close. If they drift too far apart a phase imbalance alarm is thrown. I'm not sure of the tolerance but I'm sure it is buried in the fine print.

The watlow will also throw the phase imbalance alarm if an element blows.
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Old 09-16-2015, 04:04 AM
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Mark,

That is a shame. Hate that I missed you last year.

Please keep me updated on anything you might have at the shop I am always looking for a reason to head your way.


Scott.
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Old 09-16-2015, 12:33 PM
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Quote:
Originally Posted by Pete VanderLaan View Post
I'm always trying to mentally collate the issues that come up with the fuse. It seems to me that the people who have had issues are either 3 phase or Hi Lo transformer clients. Is that the case?

My inclination, beyond tightening the wires in the power series unit, of which there are not a lot of wires to tighten ( but there's plenty in the relays!) that the 3 phase stuff has caused more than it's share of problems and a lot can indeed be attributed to "dirty " power. Sadly, your electric company is happy if the lights are on and they'll want little to do with your issues after that. I have mentally registered a fair amount of that stuff in the rust belt. I don't recall NO having the same issues but I'm always interested.
I am not on 3 phase...110 and 220 here. I do have problems with burning out the oven elements that are in one of my lehrs. Someone once mentioned that the power may be 230 instead of 220 at times. Does that make sense? Would that cause the fuse in the SCR to blow?
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Old 09-16-2015, 12:53 PM
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Most power is 230Volt these days and it won't affecct the life of the annealer elements. Not having tight connections will affect it as will gettin oil from your hands on the elements when they get installed. Clean them with acetone and wear gloves.

I think Brian gave a good explanation of SCR issues. I'm leaning more towards the logic unit as the gremlin. I do have one and it has never blown a fuse in six years. I've never blown an element either which is another potential source. I have almost melted my transformer from a short.
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