Blew another damn transformer on my Trane XB80

_04012009.pdf

Just a thought,

When you put the new transformer in does the "Diagnostic Light" LED turn on ? Does the LED blink or flash in one of the patterns indicated in the "diagnostic codes" section that you posted a link to ?

The "diagnostic codes" imply that the control board can detect several of the problems mentioned by others. Maybe a good starting point as there is not enough time to test with test equipment.

robb

"robb"

** From the damage to the tranny visible in the photos - the primary has developed an internal short ( due to insulation failure) and since there is no fuse link in series, the resulting current was high enough to make an exposed wire leading to the terminals explode.

An internal short could develop due to heat alone because of an overload on the tranny - but this requires a fault to exist on the secondary side which seems not to be the case.

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.

I suggest you provide the next replacement for that vulnerable tranny with some "protection" - firstly an in-line fuse of say 1/4 amp AND a capacitor wired across the primary of say 1uF rated for continuous use across the AC supply.

If there is an overload on the tranny, the fuse will blow.

The 1uF capacitor should suppress spike voltages enough to save the tranny from harm.

..... Phil

1 uF sounds a little high.

I would think .01 uF at 400V would be a better bet. Or an MOV (metal oxide varistor) or three (across the line and then from each side to ground).

I don't think this is a voltage spike problem though. Voltage spikes take out other components first.

Jeff

** No it ain't.

** Think again.

** Bad idea.

** Not on the AC supply they don't.

..... Phil

I thought you had simply misspoke and that this was an honest error.

The reactance of a 1uF cap at 60Hz is: 2652 ohms (1/(2*pi*F*C) Online calculator:

V^2/R = W

Assuming primary, as why would you put it on the secondary:

120^2 / 2652 = 5.43 W

Does that not seem wrong to you?

If not then go buy a 200V non polarized 1uF cap. It is no easy chore.

Jeff

I have some big ass mylars, I think they are 4uF @ 200v.

** Completely.

Such a cap dissipates no energy at all.

What planet do you come from ??

** 1uF caps for use across the AC supply are cheap and plentiful.

Typical examples are metallised polypropylene " class X2 " types and sell for $1 or $2 each.

What planet do you come from ??

.... Phil

"Tony Miklos"

** They won't last long if connected across the AC supply.

.... Phil

I know, I was just about to reply to my post saying that the voltage rating is VDC.

** Film caps rated at 600VDC will generally last a fair while wired across a 120 volt AC supply ( but not with a 240VAC supply ) - but is it far better to use a purpose designed and agency approved "class X1" or "classX2" capacitor.

... Phil

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.

"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

What a jerk you are. You do realize that is 45mA running through that.

Jeff

** What sort of know nothing JERK thinks that capacitors dissipate energy ??

Then proceeds to calculate the reactive impedance and treat it the same as resistance ??

Big bad.

Zero out of ten.

.... Phil

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"

** 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

It doesn't have to dissipate energy to explode. That is a lot of joules.

So I left out the PF, so what?

My first encounter with you, but no doubt others have had the same reaction. Telling an inexperienced OP to put in a 1mF cap without any specifics, and that for the dubious goal of "suppressing" the back EMF of a motor running off the line has a disconnect from reality. Transformers are generally much hardier devices than the solid state components they feed.

Say what you want. You've already made your mark and I really don't care what you add. I've taken away what I need to know about yourself, and the OP is off somewhere else.

Happy now?

Jeff

"Jeff Thies" Phil Allison

** Jeff - you are much worse than merely a know nothing idiot.

You are one colossally narcissistic fool and a public menace.

God knows what it is you DO know something about - but certainly electricity and electronics are not among them.

Piss off and stop TROLLING .

.... Phil

"Smitty Shitty Two"

**As if you have the metal capacity for any such thing. ** Blatant lies.

I only call fuckwits fuckwits.

Shame is, the whole of usenet has been taken over by them.

.... Phil