# Need Help Identifying Part

#### quickcurrent

Joined Mar 30, 2016
6
Hi all,

I have a halogen light transformer 110-130V to 12V, 105W that stopped functioning (not passing any current at all.

I have taken a pair of photos of the circuit board after I took it out of the case, and found a burnt fuse. That fuse is labeled 1.5A on the board.

The fuse is the small cylindrical part at the end of the red wire soldered to the corner of the board.

Since the transformer goes from 115V to 12 V, I wonder if that fuse would be 110V or 12V since it's not labelled for voltage, only for amperage. Can anyone determine that from looking at the photos, or have any other comments that may help me determine what to get to repair this transformer?

I am doing this only for educational and hobby purposes, as these things are quite inexpensive from Ali Express, and I'll probably have to spend as much to get a package of fuses as to get a new transformer.

Thanks,

quickcurrent

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#### mcasale

Joined Jul 18, 2011
210
What do the red wires and white wires go to?

My experience with fuses is that they are usually rated for high voltages, unless it's an automotive type, in which case it would be something above 12VDC.

#### Marcus2012

Joined Feb 22, 2015
383
Hi
As the wattage for the unit is 105W we can work out maximum current that will be on either side of the transformer (if it were 100% efficient of course) So 105W/115V=0.913A on the primary coil and 105W/12V=8.75A on the secondary. As the fuse is rated at 1.5A it's fair to assume it's on the primary and is on the "live" connection to household outlet. What probably happened is a load was placed on the secondary coil of the transformer that drew more than it's rated current (14.3A ish to draw 1.5 A on the primary) and the fuse blew. If this happens on multiple units under rated current I would begin to look for a design flaw.

#### Lestraveled

Joined May 19, 2014
1,946
There is a reason that the fuse blew. It could be an overload or a component failure. You know the current for the fuse, 1.5 amps, and the fuse voltage can be anything above 12 volts. You could even use a 2 amp fuse. If there is a component failure on the board, replacing the fuse will tell you. If it blows a second fuse, throw it away.

#### quickcurrent

Joined Mar 30, 2016
6
OK, this transformer is used in a ceiling fixture to taken in the standard 110-115V and reduce the output to the five halogen bulbs down to 12V. I put it in about 2 years ago, and I understand these things last about 2 years from what I've read. All electronic components (coil, capacitors and resistors) appear OK except for this fuse (nothing burned out or discolored). A while back some of the halogen bulbs started burning out (I assume too much voltage getting to them), then they all stopped lighting, which prompted me to check the continuity across the transformer (normal power was coming in, but nothing going out) so I took out and put a new transformer in, and all is well. I just thought I'd play around with this transformer to see if I could bring it back to life!

Is it necessary for something to be wrong with the transformer for the fuse to burn out? Or could it have been a power spike that burned it out and replacing it would restore the unit to normal?

By the way, the two red wires take in the 110-115V power and the two white wires go to the 12V halogen bulbs.

#### Marcus2012

Joined Feb 22, 2015
383
It could have just been aged Halogens that drew more current or maybe one popped as that can sometimes cause a fuse to blow or breaker to trip. You could probably just bridge/replace the fuse and it would work fine I imagine.

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#### quickcurrent

Joined Mar 30, 2016
6

I'll look for a package of 110-115V 1.5A fuses and replace the burned out one and see what happens.

#### SLK001

Joined Nov 29, 2011
1,548
Looking at the transformer, you would have needed a LOT of current to burn it out. Is the black covered secondary wire flat?

#### Marcus2012

Joined Feb 22, 2015
383

I'll look for a package of 110-115V 1.5A fuses and replace the burned out one and see what happens.

If you removed the current fuse and bridged it with some wire temporarily it would be fine to test under a low load just to make sure it works before you buy some fuses. Just be wary or live currents etc. I just noticed you other question as well sorry, yes you are right the red is the AC and white is the DC

#### quickcurrent

Joined Mar 30, 2016
6
SLK001, there is no black wire anywhere on the transformer. There are only two red wires for incoming AC current and two white wires for outgoing DC current. All wires are braided white metal (assuming aluminum).

Thanks Marcus2012, I'll test first, these fuses aren't exactly easy to find!

#### SLK001

Joined Nov 29, 2011
1,548
SLK001, there is no black wire anywhere on the transformer. There are only two red wires for incoming AC current and two white wires for outgoing DC current.
Alright... look at the round toroidial thingy on your PCB. There is a dark (it looks black to me) secondary winding of ~12 turns. I was curious as to whether the wire was flat or not. And flat magnet wire DOES exist - I've used it before.

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Joined Apr 30, 2011
1,569

#### quickcurrent

Joined Mar 30, 2016
6
SLK001, that is flat plastic, not a wire, appears to be holding the coil in place or act as insulator.

Thanks, KJ6EAD. One fuse from Littlefuse $8.57 plus shipping (I assume); complete transformer$3.50 shipping included from Ali Express !!! :-(

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#### SLK001

Joined Nov 29, 2011
1,548
SLK001, that is flat plastic, not a wire, appears to be holding the coil in place or act as insulator.
Really? I thought that it was an attempt by the manufacturer to double insulate the transformer by wrapping the secondary in an insulator. If it is not this, then it is a very expensive holder.

#### quickcurrent

Joined Mar 30, 2016
6
These things are made in China, SLK001, they are made quite cheaply there.

#### Howard Evans

Joined Aug 17, 2015
2
SLK001, that is flat plastic, not a wire, appears to be holding the coil in place or act as insulator.

Thanks, KJ6EAD. One fuse from Littlefuse $8.57 plus shipping (I assume); complete transformer$3.50 shipping included from Ali Express !!! :-(
It is NOT flat plastic, it IS wire. This is NOT a simple transformer. It does NOT produce DC for the halogen lamps. It is a high-frequency AC-to-AC power converter that acts like a 110 VAC to 12 VAC step-down transformer. The white wires for the lamps are connected directly to the 12-turn flat-wire secondary. There is AC applied to the lamps but it is not 50 Hz or 60 Hz and bears no relation to the incoming power-line frequency on the red wires. The incoming power does not directly excite the primary of the toroid transformer. Incoming power is rectified to drive the power oscillator at the other end of the board. This power oscillator drives the primary of the toroid transformer. The change in frequency from power-line frequency to an ultrasonic frequency allows for more power density in the toroid transformer, which is why you can get >100 watts transferred from primary to secondary with such a tiny core.