Blew another damn transformer on my Trane XB80

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:

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

Does that not seem wrong to you?

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

I read them. I understood them. I was just replying to the notion that he had connected the transformer wrong, based on wire colours.

NEVER ASSume anything - check the instructions, follow the instructions, and verify the results. Particularly with today's supply chain issues you NEVER ASSume something is what it says it is. Quality control is not anything close to what it was in, say, the seventies, and evenTHEN, it was not unheard of to have wrong documentation, or improperly assembled product (but not nearly as common)

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

On 4/10/2011 7:30 PM snipped-for-privacy@snyder.on.ca spake thus:

True that.

One thing nobody's yet explained about this whole puzzle is why there's an extra set of leads from the transformer (as shown in the O.P.'s pictures) that aren't being used. What's that all about?

Such a cap dissipates no energy at all.

What planet do you come from ??

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

What planet do you come from ??

.... Phil

"Tony Miklos"

.... Phil

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

... 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

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"

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.

Yawnnnnnnn....

(snip absurd drivel)

You ridiculous wanker.

.... Phil

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

Jeff

windings connected either in series or parallel to operate. Others have a center tapped winding - 110 on one half, 220 across the full winding - and still others have 2 separate windings that operate independently.

Real easy to find out - even in this case with the 110v primary open.

Connect 110 across the 220 (or 120 across the 240 - let's not get nit-picky over voltage ratings) or "high voltage" primary and check the secondary voltage. If he only gets 12 volts it is a totally separate and independent high voltage primary. If on the other hand he gets 24 volts, you hit the jackpot and HE screwed up..

This type of "dual primary" circuit is very "polarity" sensitive and the right colour wires need to be connected together, both in series and in parallel, or the "magic smoke" comes out very quickly.

Again , like I posted before - READ the instructions. FOLLOW the instructions, and VERIFY the result.

Part of verifying the result, or erifying an undocummented transformer, is to check the voltage on ALL winding, used or not, to fully understand their intended function.

If 110 across the black and white produces 110 across another pair, that other pair is is a "complimentary" primary and should, in all likelihood, be connected, phase for phase, across the black/white primary pair.

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

Big bad.

Zero out of ten.

.... Phil

Got a propane nozzle for next winter's icy steps from HF that came with instructions for assembling a pick axe hammer. Got an inspection camera, too, that was short the mini-plug to RCA plug cable to allow the video to be sent to a large TV or a recorder. Seeing that it was a video only tool, I assumed it would take a two conductor cable. Tried a video only cable, no joy. Tried a video/1 channel audio cable, still no joy. Tried a video and

As for quality control, I believe it was Micro$oft who began the outrageous procedure of charging people 30 bucks to get a preview (aka doing the final bug hunt in the real world) of Win98 when it first arrived. IIRC, you didn't even get a discount on the release version for being a beta tester. That's when it seems that QC finally fell off the face of the earth.

-- Bobby G.

Only one almost obvious flaw with that arguement - the ignition is NOT used when the system is running the "cool" cycle - which is what the OP says was running when the second transformer popped.

Also, the secondary resistance will be low enough, and the impedence of the ignitor (assuming it is spark ignited, and not hot surface) high enough, that the voltage across the primary would most likely be clamped to a reasonable level - and if not the electronics on the control board would be damaged, long before the voltage induced in the primary would get high enough to damage the windings or the insulation on them.

If, on the other hand, it is a hot surface ignitor, they run on line voltage (on any I've seen anyway) and a short as you envision would ALMOST DEFINITELY fry the control board.

I'm sure I am as baffled by that as you are. AC in not "polarity sensitive" and as long as neither side of the primary or secondary is grounded the control should not know which way the primary (or secondary) is connected..

I would SUSPECT, but do not know for sure, that all the relays etc are DC coils and all the circuitry on the control board is running on DC provided by a full wave rectifier bridge on the circuit board., and all the sensors also run on DC (and quite possibly - even likely - on

It would not surprise me there is a problem with the board. Trane has "upgraded" the board from a white-rogers unit with their part number CNT0377 to a new replacement kit, part number cnt05122 - which might lead one to ask the question "WHY".

This can be pretty well determined by installing the fuse I (and others) have recommended several times in the past.. If it blows the

The orange and red leads are to be used when you have 208 or 240vac. On the Honeywell transformers the black is the common and black to white=120vac, black to red=208vac and black to orange=240vac supply. The transformer was manufactured to be used on single or three phase systems and you are more likely to wind up with 208vac on a three phase system. The 32volt difference between 208 and 240 could adversely affect your secondary control voltage if you use the wrong tap. Oh yea, I for got to mention that on an electric furnace your supply voltage could be 240vac instead of the 120vac for a gas furnace.

TDD

Measuring amperage without breaking into the circuit requires either a current transformer or an "amp clamp" - which is either a current transformer or a hall effect device (generally) depending on whether it is AC or DC..

With DC there are also "magnetic" poximity amp meters that just sit against or over the conductor. - and of course there is always the "shunt" - which is technically part of the "ammeter" in series with the load and the "meter" is a voltmeter reading the voltage drop across the "shunt" which is just a very low resistance.

As noted before, correct.