How do I check a 12V AC Transformer?

[Tony]

I have an overhead, ceiling-mounted,.tracklighting system which
consists of six 35W Halogen lights on a 9-foot track with a canopy
type, in-line transformer which is marked: I/P: AC120V-60Hz 1.5A, O/P:
AC 12V 50-230W. Been working fine for 2 years but suddenly died. After
making sure all connections were tight and of course checking the AC
input side (which was OK) I removed the transformer which contains 2
wires (black/white) going in and 2 wires (Red, larger gauge) coming
out. I just don't know how to check the output of the transformer to
see if I'm getting 12VAC out? Do I just put my test probes across the
two red wires? Or one at a time to a ground? Can anyone help me on
this. Thank you very much. (As you can see, I know very little about
electronics!)

 

[Meat Plow]

I have an overhead, ceiling-mounted,.tracklighting system which
consists of six 35W Halogen lights on a 9-foot track with a canopy
type, in-line transformer which is marked: I/P: AC120V-60Hz 1.5A, O/P:
AC 12V 50-230W. Been working fine for 2 years but suddenly died. After
making sure all connections were tight and of course checking the AC
input side (which was OK) I removed the transformer which contains 2
wires (black/white) going in and 2 wires (Red, larger gauge) coming
out. I just don't know how to check the output of the transformer to
see if I'm getting 12VAC out? Do I just put my test probes across the
two red wires? Or one at a time to a ground? Can anyone help me on
this. Thank you very much. (As you can see, I know very little about
electronics!)

Across the two red leads.

 

[Colin]

I have an overhead, ceiling-mounted,.tracklighting system which
consists of six 35W Halogen lights on a 9-foot track with a canopy
type, in-line transformer which is marked: I/P: AC120V-60Hz 1.5A, O/P:
AC 12V 50-230W. Been working fine for 2 years but suddenly died. After
making sure all connections were tight and of course checking the AC
input side (which was OK) I removed the transformer which contains 2
wires (black/white) going in and 2 wires (Red, larger gauge) coming
out. I just don't know how to check the output of the transformer to
see if I'm getting 12VAC out? Do I just put my test probes across the
two red wires? Or one at a time to a ground? Can anyone help me on
this. Thank you very much. (As you can see, I know very little about
electronics!)

Just put your meter across the two red output wires. Don't be surprised if
this shows as more than 12V AC. That would be normal.
I am guessing that if you disconnect the transformer completely and check
the wires using your meter on resistance range, the output would seem fine
but you would get no reading from the input.

 

[Tony]

Thank you very much for your quick reply! I just did exactly that and I
got a reading of
00.43 v

What the heck does that mean? thanks much

 

[Meat Plow]

Thank you very much for your quick reply! I just did exactly that and I
got a reading of
00.43 v

What the heck does that mean? thanks much

Well if the black and white wires are hooked up to 120 volts it means the
transformer is bad. But make sure your meter was on AC volts not DC.

 

[James Sweet]

I have an overhead, ceiling-mounted,.tracklighting system which
consists of six 35W Halogen lights on a 9-foot track with a canopy
type, in-line transformer which is marked: I/P: AC120V-60Hz 1.5A, O/P:
AC 12V 50-230W. Been working fine for 2 years but suddenly died. After
making sure all connections were tight and of course checking the AC
input side (which was OK) I removed the transformer which contains 2
wires (black/white) going in and 2 wires (Red, larger gauge) coming
out. I just don't know how to check the output of the transformer to
see if I'm getting 12VAC out? Do I just put my test probes across the
two red wires? Or one at a time to a ground? Can anyone help me on
this. Thank you very much. (As you can see, I know very little about
electronics!)

It's probably a switchmode power supply rather than a transformer, they
do tend to fail suddenly when they go.

If you have 120V in, the bulbs show continuity, and they don't light,
the transformer is bad.

 

[Meat Plow]

It's probably a switchmode power supply rather than a transformer, they
do tend to fail suddenly when they go.

Why would it need to be an SMPS and why would it fail more suddenly when
it goes compared to just a plain old transformer? I would ASSume that
since it needs to deliver 210 watts just a plain old tranformer would be
cheaper than an SMPS hence more profit for the manufacturer

 

[James Sweet]

Why would it need to be an SMPS and why would it fail more suddenly when
it goes compared to just a plain old transformer? I would ASSume that
since it needs to deliver 210 watts just a plain old tranformer would be
cheaper than an SMPS hence more profit for the manufacturer

210W at 12V is a *big* transformer, that's close to 20A. A transformer
of that capacity would be very bulky and expensive, most equipment these
days uses switchmode supplies because they're in fact much cheaper, they
use a lot less copper and iron. The SMPS that halogen fixtures use are
very cheap, they're more like light dimmers and put out a nasty waveform
that looks like 12V to an incandescent load.

Magnetic transformers will often smell bad for a while as the winding
insulation breaks down and turns short. SMPS fail suddenly when a
component shorts.