Blew another damn transformer on my Trane XB80

Page 9 of 12  
On 4/11/2011 7:26 PM, Don Klipstein wrote:

I completely agree. 400V was the minimum and most popular choice for transient protection, of course a cap that size for "back emf" protection has got it's work cut out for it.
I'm unfamiliar with those large caps you sent the link (and I'm not going to search these threads for it) to before. What are they used for? Crossovers?
I was a little surprised at this back emf theory and Phil's fix. I can't see where a low Q resonant circuit is going to be helpful, if anything depending where it resonates at, and how it is turned off (say at the breaker) it could add some dandy new problems. YMMV.
I'll leave you with this:
I learned long ago, never to wrestle with a pig. You get dirty, and besides, the pig likes it.
George Bernard Shaw
Jeff

I can't see that causing that much load.

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I would think that if it were a surge that was initiating the failures, it would have to be a large one to breakdown the insulation on the transformer primary. In my experience, I haven't seen a transformer fail from what could likely be attibuted to a surge. For example, after a lightning storm, I've had electronic gear that was dead and likely attributed to the storm. But all the transformers in the house, from the doorbell one to the plug-in wall wart type, to even the transformer in the failed electronics were all fine. I've never had a transformer fail where I've had suspicion it could be from a surge. IF it is a surge, it would almost surely have to be coming from either the blower motor or the compressor.
An interesting experiment might be to rig up a small air gap across the AC coming into the transformer. The size could be determined so that it would take say 1000V to bridge it. I'm sure there must be a chart or calculator online that would give you the size. If he rigged that up together with a fuse he could cycle the HVAC and see if any spark results. Also, if the surge is the failure mechanism, then the suggestions of adding fuses may not protect the transformer, at least not for long. The surges will still arc across the insulation and eventually break it down so that even normal voltage will start to short across.
As an alternate surge detector, he could use a MOV surge protector connected across the transformer with a low value, fast-blow fuse. If a big surge is there, good chance the fuse will blow. Could get those parts at Radio Shack for a few bucks. With either of those methods, if there is a surge, then he could replace the MOV fuse and then proceed to try to isolate where its coming from. IE, just cycle the blower via the fan switch to check that. Then leave the fan on constantly and cycle the AC compressor, etc.
On another note, the quality of these replacement parts in some cases is very poor. I recently had experience with a Sears dehumdifier that was about 4 years old where the blowr motor died. So, I bought a new motor from Sears. That lasted less than a year. Bought a second one and that one failed in a couple minutes. And I had verified that everything was correct. Fairly simple, it was just two speeds, AC, with relays choosing which winding to apply 120V to.
I then went online and looked at the feedback section at Sears for NEW ones that were identical. Overwhelming feedback that they were crap, with this fan motor failure being the main culprit. People posting the same experiences, with replacement motos failing in short order. And mind you, this is 4 years after the one I had. Obviously serious quality issues and no one is paying any attention.
Another factor is that in the drive to save energy, meet govt guidelines, etc, manufacturers today, in many cases, are using lower power devices that are closer to the margin of failure than they were 20 years ago.
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On 4/16/2011 8:18 AM, snipped-for-privacy@optonline.net wrote:

In a little transformer like this, the primary is very small gauge wire, a surge could easily do it.
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On 4/16/2011 12:20 PM, Tony Miklos wrote:

I've never seen it. In fact in my past life as a tech I rarely rarely replaced line driven transformers. Rewound quite a few switching transformers though.
Jeff
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On 4/16/2011 8:18 AM, snipped-for-privacy@optonline.net wrote:

I agree completely. Transformers are not fragile. Usually the transformers I've seen fail were caused by long term thermal issues. Undersized and overworked.
IF it is a surge, it would almost surely have to be

In which case it is a wiring issue because the line should absorb this. That 1mF cap is only 2,000 ohms at 60Hz. I still can't buy into Phils theory.

That has been suggested, or something very similar.

Yeah, but this transformer number 3, and near as we can tell they were all different. The OP needs to take a knife and see what damage if any lies in the wiring.

Always a good plan to see if you can track whether the problem is common. I did a quick search for him and came up empty. Apparently not a common problem.

No doubt.
At least transformer based wall warts are going away. That is not bad.
I don't think this is a surge problem, it will probably be a wiring problem, but it could also be something in the controller board. That would surface by going through all cycles.
Jeff
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On 4/9/2011 10:22 PM, Phil Allison wrote:

Oh my gawd, someone agrees with me. Looking at the picture says a lot. Burnt on the primary side, looks like new on the secondary. And this is the third transformer with an open primary!
I don't know about a the 1uF cap, seems way too high so I'll delete what was below and pretend I didn't see it.
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"Tony Miklos don't know much"

** Why ?????
It ( likely ) needs to absorb a transient back emf generated by a powerful blower fan.
Non puny size cap will ever do that and using 1uF cases no harm whatsoever.

** Nothing like doing the old Ostrich trick when the brain gets overloaded.
Wot a jerk off.
.... Phil
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Put 3A automotive fuse on secondary. Use light bulb trick to find shorts. Two 12 V light bulbs in series that draw no more than 40 VA.
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"Stormin Mormon"

** You need to ask Agent 86 that one....
... Phil
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wrote:

A capacitor across an AC supply??????????????? As a surge protector???? Have not heard of that before.
A capacitor across the AC line would appear as a load - and could form a resonant l/ci tank circuit, which would also appear as a low resistance -causing high current to flow
There are 2 other POSSIBLE issues here though - - -.
Both are perhaps long shots - but mabee worth investigating.
The transformer primary APPEARS to be saturating. Primary current on an unloaded transformer CAN, in some cases, excede full load current. Possibly the transformer requires MORE load on the secondary than it is getting.
An example is a microwave oven transformer. With no load on either the high voltage or low voltage secondary, the primary will generally saturate and overheat. If you remove the high voltage secondary and add your own windings to make a "custom" transformer, it is not uncommon for the primary to saturate at no/low loads - overheating the transformer.
Like I said - a long shot, but possibly worth investigating. adding a small 24 volt pilot light across the secondary MAY solve that kind of a problem.
The other POSSIBILITY is a DC bias on the primary, which WILL cause saturation on 1/2 cycle of the AC. Need a scope to check that effectively - or something like a 10uf nonpolarized capacitor and a 100K ohm 1/2 watt resistor in series across the primary, with a DC voltmeter connected across the cap. Make all connections BEFORE turning on the mains power. You should expect to see readings of +/- approx 25-35mv across the cap in a normal residential situation.
Lets say you read 275mv DC on the line, and the transformer primary resistance is 2 ohms.. That will put a DC current of 137.5ma through the primary - which when added to the normal AC current on the one half cycle will greatly excede the saturation current of the primary.
A half wave rectified load on the same circuit could put a DC component across the line.
An AC (nonpolarized) capacitor IN SERIES with the primary would remove the DC component from the primary winding, but finding a capacitor that would ballast the primary properly (allow full rated primary current) while not causing a series resonance (which would appear as a short circuit across the mains) is not something I would try to calculate.

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"Phil Allison"

** Then your ignorance is showing.
The stated reason for the capacitor was in relation to the "blower fan" inside the same unit as the small tranny.
The event the cap has to deal with is a back emf surge generated by that fan when the AC supply is suddenly disconnected - for whatever reason.

** Draws 45mA continuously.
Yawnnnnnnn....

** Yawnnnnnn....
(snip absurd drivel)

** The primary appears to be EXPLODING !!
You ridiculous wanker.
.... Phil
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wrote:

Phil - your mamma should wash your mouth out with soap. I SAID the other two scenarios were long shots - but so is everything else that has been suggested. The windings of the trasnformer do not APPEAR to be overheated - looks like just blackened at the connections between the winding and the connecting wires.
It is definitely a strange failure - and I don't think it has been properly analyzed to determine exactly what/where the problem is. As Arthur Conan Doyle said, "after you have eliminated all the possibilities, whatever remains, however improbable, must be the truth"
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** You need to get your hands off of it.

** And I said they were ridiculous drivel.

** Your opinion is based on your ignorance only.

** See the vaporised metal coating deposited on the plastic cover next to the tranny?
That is a damn EXPLOSION !!
It happened very suddenly and made a loud bang too.
I said:
" High voltage spikes on the primary could also cause insulation failure leading to the damage seen in the pics - lightning does this sort of thing. So also could back emfs from the blower fan if the is a bad connection in the AC supply feed."
If the insulation on the enamel wire of the primary is punctured by a HIGH VOLTAGE SPIKE, effectively shorting out most of the primary - then the 120 AC supply ( no fuse exists remember ) will easily turn the two exposed wire ends into metal vapour !!!
Cos they just became the fuses.
It just so happens that many small transformers made in China, India & Sri Lanka etc are very prone to this sort of failure - due to bad manufacturing practices.
.... Phil
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wrote:

So you are agreeing with what I said before - most likely problem is cheap crap component.
We can be relatively sure it wasn't lightning 3 times. If the back emf from the motor is causing the problem, the bad connection to the motor should have made itself VERY evident by now. Not saying it is NOT part of the problem - like you, I wasn't there watching it fail - and neither you nor I heard the noise you speak of.
And IF the problem is what you say it is (and I'm not saying it is not), then probing the old primary and getting to the winding beyond where the solder joint "exploded" you should be able to measure a significantly lower than normal primary resistance.
That measurement has not, as far as I know, been made and reported.
If it was mine, or if I had the transformer at hand, I'd have it apart and analysed in no time. If the primary is shorted, I'd know, within an hour or two of the failure.. And with that second primary, it would not be hard to determine if the 110 volt primary is shorted without even dissassembling the transformer..
At this point no-one has actually posted FOR SURE what the primary configuration is. Is it a mult-tapped primary, set for 115, 208, and 230 volts, or is it 2 independent primaries, or is it 2 primaries that need to be connected either in series or parallel depending on the voltage (115 or 230)
I don't know this, and you don't know either unless you are clairvoyant, because it has not, to this point, been established and reported.
So we are all guilty of the same thing - making ASSumptions.

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< snipped-for-privacy@snyder.on.ca

** Not true at all.

** What is clear is that the primary has suddenly drawn a very large current and that means there are SHORTED turns inside the primary.
Go away wanker.
..... Phil
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This one is a grasp at a straw. Was a magnet stuck on the transformer at the time that it blew?
I realize that not too many people run transformers with magnets stuck to them. But doing that does make their cores more prone to saturation.
--
- Don Klipstein ( snipped-for-privacy@misty.com)

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Steve Turner wrote:

In addition to all the other observations and suggestions found in this thread, there is one additional possibility to consider: Your Trane machine simply hates you.
I've seen malevolent machines. I've been victimized by our metal overlords.
Tell the truth, have you never been tempted to shotgun a lawnmower?
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<SNIP to malevolance of machines, not just furnaces>

http://www.ssiworld.com/watch/lawn-mower.htm
Linked from http://www.watchitshred.com
That place even shows shredding of some engine blocks. They make shredding of bowling balls look easy!
Is a computer or some other electronic device ticking you off? http://www.ssiworld.com/watch/e-scrap.htm
They even shred shredders: http://www.ssiworld.com/watch/shredder.htm
--
- Don Klipstein ( snipped-for-privacy@misty.com)

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On 4/12/2011 11:12 PM, Don Klipstein wrote:

Having an extremely warped mind, I thought some Hollywood special effects guys should get together with a shredder company and make a very special YouTube video of an Islamic terrorist being tied up in a big burlap sack with a hog. The whole squirming mass would be dropped into a monster shredder and all the sound effects, blood and guts would be awesome. At the end, a disclaimer would read.... "No actual pigs were harmed during the production of this video" Of course the reaction would be the same as the nut-jobs who were upset about their Koran being burned and went around killing everyone they could find who they believed to be a Christian.
TDD
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The Daring Dufas wrote:

Your idea tracks with one described by an acquaintance of mine.
He envisioned a web site, "stopthedesecration.com."
On the web site, a (masked) host is seen standing in a warehouse chock full of Wahabi-sanctioned Korans. The site promises that for every outrage committed in the name of Islam, some book (or a portion) will be desecrated! There is also a "catalog" of outrages and consequences (if I remember correctly).
* Every anti-American or anti-western sign shown on TV = One page ripped out and stomped. * For every non-Muslim injured in the name of Islam = One entire Koran shredded. * For every non-Muslim killed in the name of Islam = One entire Koran shredded, mixed with pig blood and feces and flushed down a toilet.
Appropriate videos will be cataloged, each showing the offense AND the sanction in graphic detail. A continuous scroll appears on the screen: "Only YOU can stop the desecration! Do not permit your friends and family to harm others!"
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