Blew another damn transformer on my Trane XB80

Page 8 of 12  
On 4/10/2011 11:29 PM, Phil Allison wrote:

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

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On Mon, 11 Apr 2011 15:28:09 -0400, Jeff Thies wrote:

The sad part is Phil usually is right with things involving pro-audio gear. I would take his word hands down on guitar and power amps. But you cannot know everything about any kind of electronic device like he would like others to believe he does. And why he traps people with one decent reply then comes back scathing is beyond me.
--
Live Fast Die Young, Leave A Pretty Corpse

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"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
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"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
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"Jeff Thies is a Moron "
** Piss off - you fuckwit WANKER !!!

** FFS IMBECILE -
I suggested a capacitor of " 1uF rated for continuous use across the AC supply"
Standard practice with inductive loads for decades.

** Only thing a fool like YOU is expert on is puling your tiny cock in public.
FUCK OFF - DAMN TROLL !!
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PF of a capacitor suitable to connect across an AC line is usually less than .01.

<Make that longish story shorter>
Phil Allison is well known in sci.electronics.design to be quick to get brash, even calling people names and sometimes a little worse. If only he would avoid that, a lot more people would think a lot more highly of him than they do now, since he does fairly well know what he is talking about when it's electrical.
--
- Don Klipstein ( snipped-for-privacy@misty.com)

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I think Rod Speed is much worse. Meanwhile, it appears to me in my experience in s.e.d. that P.A. is, like R.S., an Aussie.
--
- Don Klipstein ( snipped-for-privacy@misty.com)

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On Tue, 12 Apr 2011 00:12:48 +0000 (UTC), snipped-for-privacy@manx.misty.com (Don Klipstein) wrote:

That would go a long ways to explaining his potty mouth.
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On 4/11/2011 10:01 PM, snipped-for-privacy@snyder.on.ca wrote:

Perhaps that goes all the way. Hey, I learned something about Oz today. Funny the guys from NZ I know seem quite nice. I suppose it was a surly lot they are descended from... or is it the climate? No matter.
Jeff
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On Mon, 11 Apr 2011 23:07:50 -0400, Jeff Thies wrote:

A friend traveled to NZ then to OZ in 2004. He said when he got off the plane in NZ he thought the pilot had landed in China because 99% of the people around were Asian. I have relatives living near Sidney and they said this isn't the case there.
--
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With AC, volts times amps is not necessarily watts.
If determination of volts and amps are both "true RMS", (non-"true RMS" meters are usually OK for line voltage and for current through a cap across an AC line),
then volts times amps is "volt-amps". Ratio of power consumption (in watts) to VA is power factor. Capacitors have very low, ideally zero, power factor.

Digi-Key has 3 easy enough to find 1uF ones with X1 or X2 rating, all $3-plus plus shipping with minimum order requirement to avoid a surcharge.
Among those 3, my favorite is FC233820105, which is by Vishay/BC Components. Its datasheet refers to 2 UL standards and 2 CSA ones, and has a link to an application note making a claim that the referenced UL ones are sufficient for achieving the "UL Recognized" ("backwards UR") mark.

That one needed me to delve into its datasheet to see that it claims to meet the two relevant UL standards and that it has X2 rating. Its AC voltage rating is 275 volts. 91 cents each plus shipping, with a minimum order requirement to avoid a surcharge.
Any of the 4 capacitors above (2 mentioned specifically) look good, in the unlikely event what is needed is a capacitor across the line.

--
- Don Klipstein ( snipped-for-privacy@misty.com)

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<SNIP to getting a nonpolarized 1uF cap suitable for 120 VAC>

200V DC rating is not enough, despite 120 VAC having a peak voltage of only 169 volts.
AC does make things worse, by rapidly repeated severe voltage swings combined with some development of heat.
The capacitor needs to have an actual AC rating, and one that includes your AC voltage with a comfortable safety margin. If it has a DC rating, chances are that will be around 400 volts DC. And not every cap rated 400 VDC is dsafe for use with 120 VAC, even if non-polarized.
Preferably, it should be "UL recognized" or the like, for some assurance that it is reasonably reliable against failure, or at least an unsafe failure.
Back in the early 1980's, in an experimental sodium lamp ballast, I have blown an 800VDC cap and two 600 VDC ones with 240-260 VAC 60 Hz with less than 10 operating hours of this combined among the three of them. One of those capacitor blowups was a spectacular one that left a major oil stain on the ceiling above. I learned the hard way that actual AC ratings are required here.
================================== One more thing: If there is a switch upstream of a capacitor across a power line, then the switch may be in for severe contact pitting.
Then again, I doubt a voltage spike lasting long enough to burn out a transformer will be absorbed by a 1 uF cap across a 120V AC line.
I would lean to looking for intermittent overload by the transformer's load, the transformer's load intermittently drawing a large amount of DC (such as by failing-open one diode in a bridge rectifier).
Or, the transformer being connected incorrectly.
(Such as a 120V/240V one with 2 primary winding sections needing both primary sections to be connected in parallel with each other for full power handling at 120V, but only 1 of them is being used.)
--
- Don Klipstein ( snipped-for-privacy@misty.com)

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"Don Klipstein"

** You missed the point entirely.
A voltage spike ( or a series of them) can easily cause insulation failure in the enamel winding wire of the primary - then the energy to explode the lead in and lead out wires comes from the 120 volt AC supply.
.... Phil
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Is the O.P. having other things in his house blowing from voltage spikes severe enough to blow transformer primary winding insulation?
I have seen lots of things blow from line voltage surges, but no transformers indoors blowing when line voltage spikes blow other things.
My experience is that usual 120V-primary step-down transformers can produce pulses of 2 kilovolts when used on pulses in reverse. In fact, I have done that with about 8 different transformers dozens of times each, and none of them lost their ability to do that. (I am aware of line voltage spikes being noted to get even higher.)
There is also the issue of line voltage surges not easily being loaded down by capacitors for whatever reason. I have experience with them blowing things that had capacitors, including a CFL that had probably a 22 or 47 uF capacitor across the output of its internal bridge rectifier as they usually do. No transformer failures in the same house from the same event, though there were electronics failures.
The usual solutions to absorb line voltage spikes are MOVs and other devices that absorb voltage surges by becoming conductive in response to excessive voltage.
--
- Don Klipstein ( snipped-for-privacy@misty.com)

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"Don Klipstein" Phil Allison wrote:

** Totally irrelevant.
The furnace unit and the transformer in question are all we are discussing.
You have clearly not bothered to read my first or my other posts in this thread.
Eg:
" 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."
Whenever AC power to that furnace is disconnected, the blower fan will deliver a back emf spike - meanwhile that poor, little tranny is wired in parallel with it. Other devices in the house are NOT involved.
Most AC supply transformers can tolerate repeated 2kV spikes on the primary till the cows come home - but a badly wound one cannot. This is a specific and fairly recent problem with small transformers made in China and elsewhere in Asia where the makers are not fully aware of the issue of insulation failure in the enamel windings.
Once there is a layer to layer insulation failure ( between adjacent wires) in the primary of that tranny - the AC current draw will jump up to many amps and may cause the feed in and out wires to explode - as seen in the pics.
If the spike voltage is suppressed, the tranny will likely survive.
A 1uF cap provides a low impedance path for such a back emf spike, virtually shorting it out.
OTOH a varistor provides no conduction path until its breakdown voltage is exceeded, but is also a means of suppressing the spike voltage to a safe value.
.... Phil
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Why would that be, in your words, "totally irrelevant" to whether or not the O.P. had any electrical/electronic failures elsewhere in his home attributable to voltage surges?
As opposed to 3 transformers blowing in the same appliance with nothing else anywhere in the home running into trouble from voltage surges?
While I have experienced roughly 8 transformers surviving repeated abusive pulse-in-reverse-direction developing about 2 KV across the primary without any degradation against ability to do so?

Why would the solution be deploying a capacitor, rather than repairing the poor connection or deploying a voltage-dependent spike-absorbing device such as an MOV?

So, why should we hear about problems about that from only one customer blowing 3 of them?

Why should 1 uF protect the trannies in question while 22-47 uF fails to protect a compact fluorescent lamp from a line voltage surge that blows even other electronics in 2 houses but did not blow any in-home trannies?

Certainly protects against applying for even a microsecond more than roughly 250-300 volts across transformer primaries, where it appears to me that we agree that transformer primaries usually survive 2,000 volts pulse voltage?
I seem to think that the trannies are probably blowing from either improper wiring (connecting only 1 of the 2 primary winding sections possibly noted for 120V usage), or from secondary load malfunction including bridge rectifier failure in manner of a diode "failing open".
Or, extreme-oddball trouble such as sticking a magnet to the tranny. But that's grasping-at-straws, like line voltage irregularities that blow 3 trannies in 1 piece of equipment but draw no other complaints such as blowing of electronics downstream of the tranny in question, or elsewhere in the house where one appliance blew 3 trannies.
--
- Don ( snipped-for-privacy@misty.com)

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On Mon, 11 Apr 2011 23:26:45 +0000 (UTC), snipped-for-privacy@manx.misty.com (Don Klipstein) wrote:

I have to agree with Don. DC power component on secondary OR primary, or not connected right are the 2 most likely problems after "cheap crap component"
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** You are both wrong.

** Which is no help to the OP.
.... Phil
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Please add helpfulness, as opposed to adding nothing but saying who is wrong.
I chimed in explaining stuff every time. At this point that I respond to, you are doing nothing but claiming who is wrong.
It appears to me, posting nothing but who is wrong is even lower than my grasping-at-straws bit of any magnets on the transformer in question.
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- Don Klipstein ( snipped-for-privacy@misty.com)

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On 4/11/2011 7:26 PM, Don Klipstein wrote:

Yes, many moons ago I was playing with adding a mylar cap in series with the primary of a neon sign transformer. It worked great for making the neon dimmer which was my attempt, but I recall measuring a much higher voltage across the cap due to the reactence and impedence of them in series. I'm guessing but I think it was up in the 400vac or so range maybe higher. Not good for the transformer winding either. I didn't blow them but stopped using them after reading the voltages.
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