Blew another damn transformer on my Trane XB80

Page 6 of 12  
On Wed, 13 Apr 2011 19:22:37 -0400, "Stormin Mormon"

I don't remember the details, but I know quite a few DO work that way - and they also used 12 volt DC blower motors, without a transformer, by basically using the heater element as a rheostat..
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"Stormin Mormon"

** My 1600 watt "Black & Decker" hot air gun is made exactly like that.
.... Phil
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Phil Allison wrote:

Lots of ripple. If it were on audio circuit, lots of hum!!!!

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A unidirectional pulsing waveform has a DC component.
That analyzes to a sum of DC, fundamental frequency AC, and AC at harmonic frequencies. The average as averaged over a whole cycle is the DC component.
It is fairly well known that a transformer driving a halfwave rectified load can run into core saturation problems from the DC component in the unidirectionally pulsing current waveform.
--
- Don Klipstein ( snipped-for-privacy@misty.com)

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On Apr 12, 8:49 pm, snipped-for-privacy@manx.misty.com (Don Klipstein) wrote:

Interesting theory. One helpful piece of info which it's quite amazing we still don't have is what the currents are on both sides of the transformer. For saturation to occur I would think the transformer would have to be close to fully loaded. Which it could be, given the trends to lower cost, cheaper components, etc.
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On Wed, 13 Apr 2011 04:22:15 -0700 (PDT), " snipped-for-privacy@optonline.net"

As I posted in an earlier post (not sure what values I used, but I'll run a scenario anyway), assuming a 2 ohm winding, a 2 volt DC component will cause 1 AMP of current to flow in the winding. IF that coil happens to be the primary of a 40va transformer, The full load current on that transformer is about 350ma, so the probability that 1 amp of current in the primary, with no AC voltage applied, would have more than saturated the core is pretty good. Add the quiescent current of the primary, and you have a saturated core. And that's just a 2 volt DC component on a 115 volt primary.
If the primary is 4 ohms instead of 2, you have half an amp with 2 volts, or 1 amp with 4 volts.
Doesn't take much to put 2 volts DC across a 115 volt line.
See http://sound.westhost.com/articles/xfmr-dc.htm for more information from someone who may have a bit more credibility than you guys may give me.
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** A 40VA tranny designed for 120 volt 60 Hz operation has a primary resistance of 16 ohms.
Getting a 2 volt DC offset on a 120 volt AC supply takes some doing.

** Like hell.
For a 2 volt DC offset to exist, the peak voltage in one polarity must be 6.3 volts higher than the other.
With a typical impedance at the outlet of 0.25ohms, this equates to 25 amps peak load in one polarity and none in the other.

** I helped Rod write that article.
Toroidal trannys are very sensitive to DC offsets while regular E-core types are hardly bothered by them - the difference is that while the former has no air gaps in the core, the latter is full of them.
.... Phil
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Steve Turner wrote:

Steve,
Not to be rude or anything, but a LOT of talk has gone on about your problem and I have not seen any further posts from you on the matter. No comments about any suggestions at all.
I'm not going to spend any more time on this thread until we hear back from the original poster with more information otherwise we are simply blowing smoke (sorry - couldn't resist).
John :-#)#
--
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
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On 4/13/2011 10:51 PM, John Robertson wrote:

Just mentioned elsewhere that I have a new transformer on order and I can't really do anything until that arrives. Rest assured I appreciate all the input and I'm taking it all into consideration. Thanks.
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On Wed, 13 Apr 2011 23:32:56 -0500, Steve Turner

You bought the fuses, right? I DON'T want to hear about another blown transformer.
--Vic
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"Vic Smith" Steve Turner

** Be real smart for the OP to purchase some OTHER 120/24 volt tranny and use it.
The things are a dime a dozen.
And fit a "slo-blo" 1/4 amp fuse to the primary.
.... Phil
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Phil Allison wrote:

What is fuse gonna do? Instead of blowing x-former,, blow fuses? Then still it is not right. Let;s go back from begining. How old is the system? When this blowing tranny started? From day 1 or some time(month, years after the system is installed? If tranny is hot to touch when in use, that is rad flag.
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"Tony Hwang"

** Blow immediately if the tranny is overloaded.

** This is the usual purpose of fuses.

** Then you can find the cause of the overload - cos the tranny still functions.
Fuckwit.
.... Phil
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wrote:

A RAD flag - is that something like a "turkey timer" that pops up when the rad overheats?
The fuse would hopefully pop first, saving the transformer long enough to actually do some troubleshooting.
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Steve Turner wrote:

Hi Steve,
Have you tried asking Trane themselves if they have a suggestion as to the cause of the problem?
http://www.trane.com/Residential/Customer-Care/Feed-Back
Of course they may just send you to your local dealer, but it is worth a try...
John :-#)#
--
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
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** The fuse will actually help you diagnose the problem.
If the fuse opens soon as AC power is applied - the tranny is being overloaded.
If the fuse opens after some time because insulation in the primary side has failed, replacement fuses will open immediately despite the secondary being disconnected.
...Phil
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Phil Allison wrote:

This isunthinkab;e crazy idea but is the x-former being put in backward? Rgwew i a such thing as current limiting x-formers. One thig I'd try then I'd put in proper Wattage low value resister to lower the primary voltage.
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"Tony Hwang"

** You must be totally schizo.
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On Fri, 15 Apr 2011 14:04:11 +1000, Phil Allison wrote:

Ironic statement of the year candidate!
--
Live Fast Die Young, Leave A Pretty Corpse

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On 4/14/2011 11:18 PM, Tony Hwang wrote:

My word, you need sleep or something. Backwards would, oh never mind you just proved you have no electronics knowledge.
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