Testing Transformers

[RmBo_0]

Hi,

Could anyone give me some advice on methods of testing 12v transformers if at all possible? Why I ask is because been to a customers because one of the under cabinet 12v lights wasn't working. First I tried changing the lamp which didn't work but worked in another fitting. Then just assumed it was the transformer. So swapped it like for like but still didn't work. Then I tested continuity of the cables and IR and they where fine. Checked all connections and they are ok as well tested voltage after the transformer between earth in the JB and the 2 cables which showed as 80v ish? same for the other transformers.

My plan of action is to swap the transformer but I've got the feeling this isn't going to solve the issue.

 

[telectrix]

have you checked the lamp holder for signs of damage? quite often this is the problem.

 

[stef]

Check for input voltage, if present check the secondary, if no 12v present then either one or both windings have open circuit. If you can easily remove the tranny, use an ohm meter. Primary winding should read some hundred ohms whilst secondary should read just a few ohms. Hope this helps.

 

[stef]

Also bear in mind, if you measure the secondary to earth you will measure a floating voltage, thus might explain the 80 volts.

 

[RmBo_0]

have you checked the lamp holder for signs of damage? quite often this is the problem.

Yeah swapped it with one of the other working ones and still didn't come on.

 

[RmBo_0]

Check for input voltage, if present check the secondary, if no 12v present then either one or both windings have open circuit. If you can easily remove the tranny, use an ohm meter. Primary winding should read some hundred ohms whilst secondary should read just a few ohms. Hope this helps.

I'll try that when I'm there next cheers.

 

[ackbarthestar]

Some electronic constant voltage transformers (smps) need to be loaded on the secondary outputs.

Using a digital voltmeter often has too higher input resistance to provide the necessary loading and hence the output appears to be 0V.

You could stick a 50W halogen lamp across the output terminals to see it it lights up, which appears to be what you have done, albeit in the fitting.

So the other possibility is, as Telextric has stated, make sure you have a good contact in the fitting - sounds like good old MR16s

 

[i=p/u]

Squeeze them together again with screwdriver, had it last week..,

 

[RmBo_0]

The lamp holder is ok. I put it in another fitting and it lit up. It's got to be a problem with the transformer but didn't know how to test it. The fact that I swapped it for a new tranny like for like and still not working is what's thrown me. MR16's are a pain in the backside

Thanks for the advice though chaps.