Yes, I would be more than willing to do that, but my electricity training is not quite up to the 101 level that trader4 seems to think I should have; can you suggest a specific fuse rating that I should use? Thanks!
OK, so now I'm a jerk for suggesting that you should have taken some basic measurements, starting with the transformer output current, instead of just continuing to replace transformers and watch them blow. A component that supplies power fails by burning up. You've replaced it several times now. You think just MAYBE it's a good idea to see how much power it's be asked to supply instead of just buyng new transformers? If a fuse blew out, would you just keep putting in new fuses or would you measure the current and see what it is? I'd have measured the voltages and currents on both sides of the transformer after the first one failed.
I find it hard to believe that Trane uses transformers in it's furnaces that are so under-rated that they burn out in a day. I also question the soundness of anyone telling you to start installing transformers capable of delivering more power without even taking some basic measurements and finding out what's drawing current and if it's excessive for some reason. If you had a light circuit that was blowing fuses, would your approach be to put in a bigger fuse or would it be to find out what's really going on? If you have a short somewhere and you put in a large enough transformer, you think you might eventually heat something up enough to start a fire, like maybe in the thermostat wiring in your walls?
So, you had the time to obtain a new transformer, put it in, but didn't have the
1 minute it would take to use a VOM to measure the current and voltage on the secondary? If it were me and I saw transformers burning up, I wouldn't leave it on until I had some confidence as to what was going on.=A0>But of course, I'm repeating myself
Yes, by putting in each new transformer and watching it fail.
What were the specs of the original transformer?
Yes, it's called an open neutral. Can be quite dangerous.
It doesn't take any 220 (240) circuits to cause that.
It would seem to me that you are going to have to get yet another transformer. Put a fuse on the primary, 1/2 A I would think. Slow blow, perhaps less.
Then I'd check a couple things.
Note where it says that the integrated controller is polarity sensitive. Check to make sure it is correct.
Then I would look to see if anything looks overheated on the integrated controller.
I doubt it is any of the motors as those probably all run on line voltage.
Jeff
I said no such thing. Your advice is perfectly sound, but your suggestions were just some of many, and you seem to think I didn't follow *yours* (not true), and yes you were kind of a jerk in the way you voiced it. It wasn't really necessary, was it? You apparently don't have the patience to read everything I wrote, otherwise you wouldn't claim that I'm just "replacing transformers and watching them blow".
More evidence that you've chosen not to read everything that was written.
I'm not an idiot. Not completely, anyway.
I know how to measure voltages (and I did; I mentioned that already) and resistance to test for open circuits (continuity - See? I know some of the terms. I even know the difference between A/C and D/C). But measuring and understanding the ramifications of current (amperage) is where I get a little fuzzy. Would you help me out? That's why I came here.
I agree completely. I had my reservations about following such advice (and I only went a *little* higher on the replacements; far less than what some suggested), but I'm not an expert and many people were singing the same song:
"Discount the first failure, things simply get old and fail" "The second failure could likely just be an inferior replacement part."
Clearly the third failure proves those two theories false. Live and learn.
I already explained what happened. I'm sorry you feel the ongoing need to point out the stupidity of my approach. It is what it is.
By golly, I think I'll do that again, it was such great fun.
I advised you the last time to measure the 24 volt circuit amperage draw and convert that to the specs (volt-amps) of the transformer. If the draw is out of bounds of the specs then the 24 volt circuit is the problem. You can't put a band-aid on a bullet wound.
Steve,
If you are not comfortable with taking current measurements, or do not have an ammeter, or do not wish to sit there waiting for some unusual condition which is drawing too much current, you could temporarily install an in-line fuse holder and automotive cartridge fuse rated at or above the secondary side amperage which the transformer is rated. With this fuse installed on the secondary side, in series with the load, you could then determine if the load is indeed drawing too much current from the secondary and burning out the transformer, versus primary side excess voltage being the problem.
A rough guess would be that the contactor coil should maybe be drawing about a quarter to a half an amp of current at 24V. The transformer secondary should not need to source a lot more than that amount of current to provide adequate power to the coil of the contactor.
Fuses are a lot cheaper than transformers......
There may be an intermittent short in the wiring to the coil, a short in the coil itself, a breakdown of the coil insulation allowing a short to ground when the coil heats up or cools or vibrates, etc.
Smarty
Yes, you did, and thanks for the suggestion. I've never used my meter to measure amperage before, and I don't know how to do that conversion, but I will study up on it.
I think someone already mentioned the possibility of a bad neutral connection allowing the supply voltage to shoot up.
TDD
Yes Smarty, I would very much like to try this approach because I don't want to zap any more transformers. Lots of people have suggested it, but there appear to be more types of fuses than there are insects, and I have no idea what
*exact* type to look for. That's why I asked earlier in this thread if this particular transformer:The specs on the original transformer were: Class 2, 115V primary (60hz), 24V (35VA) secondary. Any chance you could point me to some _exact_ fuse solutions for this application? There's a virtual six-pack of beer in it for you. :-)
On 4/9/2011 2:04 PM Steve Turner spake thus:
It's not a "conversion".
To measure current (which, properly speaking, is what you're measuring, not "amperage"), you have to break the circuit and put the ammeter in series with the circuit, so that all the current goes through the meter. (As opposed to measuring voltage, where you put the meter *across*, or in parallel with, the thing whose voltage you want to know.)
In your case, since you want to see how much current is being drawn from the transformer, you'd put the ammeter between one of the transformer secondary leads (doesn't matter which one) and whatever wire from your unit that's supposed to connect to that lead.
Since you're measuring AC current, you'll need an AC ammeter, which rules out most digital multimeters, which only are designed to measure DC current. Not sure where you'd (quickly, easily) get an AC meter. Maybe others can suggest? But that's how you do it.
An amp meter goes in series with the secondary (or primary) of the transformer. You can convert amps to volt-amps by multiplying volts times amps. 24 volts times 1 amp = 24 volt-amps. I don't remember if transformers are rated differently for the primary or secondary or which one is usually used. It might be in the technical data usually packed with the transformer or stamped on the transformer somewhere.
If the spec is for the primary then it would be 117 x amps. Of course the measurements should be taken while the unit is in heat mode.
The blower motor is NOT running on the 24 volt transformer, so will have NO effect on the transformer.
You NEED to fuse the secondary - then IF it is an overload problem you will just pop the fuse, and not the transformer. 24 volt, 35 VA = 1,5 amp FAST BLOW fuse.
If the fuse does not blow and the transformer does, it PROVES, almost beyond a doubt, that you have bad luck getting a good transformer.
The other option is to closely monitor the primary current and see what you have.
On 4/9/2011 2:21 PM Steve Turner spake thus:
Well, it's not exactly rocket science. And you can't hurt anything, unless you get a fuse that's too big (i.e., rated at too many amps).
First thing you gotta figure out is how much current your transformer is rated at. Since your wiring diagrams don't say, we have to take an educated guess.
The only thing connected to the transformer is a thingamajig called the "integrated furnace control" (IFC). Even without seeing this thing, I can guess with confidence that it's an electronic circuit board which controls the operation of the furnace. Since it undoubtedly does so through relays (either mechanical or electronic), it's safe to assume that it doesn't draw much current.
Let's say 1 amp to start. We could be wrong, but that's a good starting point. So what we need is a fuse rated at *at least* 24 volts (could be much more, up to 120 or 240 volts), and *exactly* 1 amp. To be on the safe side, let's get a "fast blow" fuse. Hey, fuses are cheaper than transformers, right?
So install such a fuse, run the unit and see what happens.
If the fuse blows right away, it's probably too small, so use the next bigger fuse; let's say 1.5 A.
Now you want to stop at some point, let's say 2-3 amps, because now you're getting up to where you may be exposing whatever fault there is with the unit and risking blowing the transformer again. If this happens, you're going to have to bite the bullet and find out what's wrong with the damn thing. But at least your 3rd transformer will still be intact.
MWBC is not legal for a furnace and never has been (at least in Canada) and a main panel neutral problem should have manifested iteself with light bulbs flaring/dimming or other indications of "wonky" voltage elsewhere in the house.
On 4/9/2011 2:30 PM A. Baum spake thus:
Using the primary side would be more conservative (= a bit safer), since it will include any losses between primary and secondary sides. But it really doesn't matter. And I'd much prefer to measure current on the secondary side, rather than deal with 120-volt juice.
He still has the problem of finding an AC ammeter, since a DMM won't handle AC current.
On 4/9/2011 2:42 PM snipped-for-privacy@snyder.on.ca spake thus:
I agree. Suggesting that the OP's problem is due to a buggy Edison circuit (and why don't they just call them that, since that's what everyone else calls 'em?) is just grasping at straws. Possible, sure, but highly unlikely.
Most control boards have a place to plug in a low voltage blade fuse just like the ones introduced to automobiles by GM years ago. The value will vary from 3 to 5 amps. A one amp fuse should be sufficient for the primary/120volt side. The primary fuse should be installed in series with the black/hot wire of the transformer and the low voltage fuse should be installed in series with the red/R wire OOPS! I just noticed something from the pictures of the burned transformer! The wire colors in the control system of air handler/furnace wiring can vary a little from manufacturer to manufacturer and I just saw something that may be a problem causing confusion. The transformer in the picture has a YELLOW wire in place of the RED low voltage output. The black/hot and white/neutral are for the 120vac connection and the yellow/R and blue/C are on the other side of the transformer. The red and orange wires should be taped up because they are for 208-240 volt connections. If the red wire on that transformer were hooked to the red wire connections shown in the wiring diagram, it will burn up. Yellow is usually the low voltage wire color used for safety switches, pressure switches and interlocks. The blue wire is the common 24vac and is often grounded to the metal cabinet of the furnace. A seasoned HVAC tech would have seen the anomaly immediately and it wouldn't have posed a problem.
TDD
TDD
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