What is it?

Hello everyone. First, I want to say that I am not an "electronics guy", as will become evident as you read further. I am trying to solve a problem with a setup on our shooting range that traverses the target. It appears to be mechanically (the cables, pulleys, etc.) fine, but the motor runs at a very slow speed, or quits running all together. The mechanics are quite simple, with a trolley that runs back and forth on a track via a cable. The switch is a simple toggle switch.
I replaced the motor with another one, and the test motor also ran at a very slow speed (with no load), and then quit.
Now I am working on exchanging the transformer. The system plugs in to 110v and the transformer steps it down to 24v (I am assuming DC). I have found and ordered the replacement transformer, but I have a question about another component inside the transformer "box". I have included pictures. I think that this may be a capacitor, but I cannot find it via my crude attempts on Google. I would like to know what it is (capacitor? resistor? what?), as well as what currently available part that I should replace it with, if necessary.
**broken link removed**

I know that newbies shouldn't play with electricity, but the original manufacturer of this equipment wants $500 for a replacement "box". This is not rocket science...I just need to know what to call the part soldered onto the wire (red/hot lead from the transformer) so that I can replace it if necessary.

Thanks in advance!


Brad

Its called a Metal Oxide Varister or MOV for short... It's for the removal of transient spikes.... They come in differing voltages...
https://en.wikipedia.org/wiki/Varistor

Should I replace it? Do they go "bad"?

I don't think it is an MOV.

The photo is clear enough to show that the mains comes in from the connector at the bottom left, and goes from there to the transformer via the black wires. The transformer output, 24 V ac, goes via yellow wires to the bridge rectifier, the square component bolted down in the bottom left of the box.

Bridge rectifiers like that have ac input on opposite corners, and the dc output on the other diagonal. The ac inputs on yours seem to be top left and bottom right of the bridge rectifier, and the dc outputs are top right and bottom left.

The mystery component appears to be connected between one of the dc outputs and the connectors on the box, and it seems to be in series with the load. I think that makes the mystery component either a PTC or and NTC thermistor.

A PTC thermistor is used as a self resetting fuse. PTC stands for positive temperature coefficient, and the resistance will increase as they heat up. If too much current is taken, the thermistor gets hot, its resistance increases and the current is reduced.

An NTC thermistor is used as an inrush limiting device, maybe used as a soft-start. The idea is that there is some resistance in series, to limit the current at start-up, but after that the NTC heats up and its resistance drops allowing full power through.

I am not sure which is used. I would think that the PTC is more likely. Either way, the voltage across the mystery component should be less than about 1 V when running.

https://www.farnell.com/datasheets/1902602.pdf shows some. I have no idea what the rating is.

If you want to fault-find, take lots of photos to make sure you can put it back. Then disconnect the transformer from the bridge rectifier. If you connect the mains, the output of the transformer should be around 30 V ac. To test the bridge rectifier, find the ac connections, labelled "~" and the dc connections, labelled + and - . If you connect a voltmeter, set to dc to the dc connections, and connect a 9 V battery to the ac connections. The voltmeter should read about 1 V less than the battery voltage. Now reverse the battery, and the voltmeter should read the same.

If those are OK, put it back together and turn on. Measure the voltage on the output. It should be around 30 V dc. Now connect the motor. If it doesn't run, and the voltage across the mystery object is more than 20 V, try connecting an ammeter in parallel with the mystery object. If that makes the motor run, it looks like the mystery object need replacing.

PTC resettable fuse
72v @ 2.5A ?
https://www.digikey.ca/product-detail/en/RXEF250-1/RXEF250-1-ND/1114066

I was having a look with a magnifying glass at the "thing". It has a symbol, (see picture) then 72. Under that, it says "X250"

Thanks for all the input! I really appreciate it!

From the digi-key link I posted earlier there is a data sheet link available there that has the device markings listed there along with the logo your mystery part has..

**broken link removed**

Thanks a bunch to all of you who offered help....and to this website. I have received my new transformer, and installed it, and everything is working fine. I did not (at least at this point) have any trouble with this other component. You guys have all been a great help though, as I was totally in the dark about what to do about replacing this part if my new transformer didn't work.

Cheers!

Transformers usually exhibit symptoms on failure, smell of burning, getting hot etc, if they suddenly fail, it can be if a embedded thermal fuse is fitted, the problem is these are a one-time device and are very difficult to find and replace, one sign is if you can see two small conductors exiting the winding and one end connected to an input conductor or winding.
They are more of a nuisance than anything and they can often be jumpered in conjunction with the proper external fusing.
Max.

THis box is simply a transformer, PolySwitch (PTC) and full wave bridge diode.
Since full wave bridges tend to have low duty cycle (10%) current surges pumping the external load Caps and Polyswitch. It is sometimes useful to add an ICL or inrush current limiter if the device is power cycled frequently (>1/hr) to avoid the peak surges that stress to the load caps. They look like Polyfuses but ate NTC instead of PTC and are cheap and come in a wide range like fuses.

Since you have already failed one transformer ( rapidly aged by heat ) evaluate your load does not exceed 50% of the transformer VA rating because pulse mode operation reduces the efficiency of the transformer, raises conduction losses , causes premature transformer failure etc.

i.e. get a bigger transformer or a proper supply such as a SMPS or PC PSU.

ALso test the external switch used to switch the external Caps or regulator ...on or off (my assumption) THe contacts may have developed a large resistance (>1Ohm) instead of 10 mOhm