Transformer For Spotlights in Bathroom not Working


Postby nb99 » Tue Oct 04, 2016 5:03 pm

Hi All

I'm fairly DIY handy but don't know much about electrics but need advice on bathroom spotlights issue. We had a bathroom wired (by a pro) with 4 spots, each of which has its own transformer. The details on them says: Prim: 220-240V~50Hz 60VA Cos=0.99. SEC: 11.5V~rms MAX 4.9A 3-60W which means little to me but I guess enough to anyone who knows electrics. The 4 bulbs are halogen, 35W.

1 of the lights has basically never worked. I pointed this out to the electrician who said the transformer must have been broken, came back and replaced it. It worked briefly and then stopped again.

I know there's an equation to work out how many bulbs you can put on the circuit/which transformer is needed but I don't know if it applies when there is a transformer for each bulb. Could I get advice please on whether this is just a case of replacing the transformer of the non-functioning spot or if all 4 need to be replaced to accommodate all 4 lights on the same circuit. Either way I'd appreciate advice.

Thanks for any/all input.

NB
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Postby kbrownie » Tue Oct 04, 2016 8:11 pm

It normal for each lamp to have it's own transformer, but not unusual that a group of lamps are supported by just one.

So it can be either way, but it is much better to have each lamp on it's own.

Generally the info on the transformer relates to the primary supply (240v mains voltage) the secondary supply (stepped down from 240v-at 11.5V) and the range of watts per transformer (so between 3-60w).

So each transformer will be happy to feed a 35w halogen lamp. (the halogen lamps are very much out of favour and LEDs are preferred but they require drivers rather than transformers).

If one lamp is failing, there a few things to consider. Lamp failed, transformer failed, loose connections, faulty lampholder. or any combination of these. So not always lamp/transformer. It is very common for the lampholder to become faulty!
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Postby nb99 » Tue Oct 04, 2016 8:39 pm

Many thanks for your reply. Thanks for clarifying all that - was pretty much what I thought but wasn't 100% sure. It's not a loose connection or the lamp holder as I've swapped about the various parts (including the transformer) and the transformer is the weak link each time. What baffled me completely was how the second transformer failed within 24 hours. It led me to believe the circuit could perhaps have been "overloaded" but it seems that's not possible.

Sounds like I'll have to replace the transformer again and see if that works this time. Unless you/anyone else has any other ideas?

Thanks again.
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Postby nb99 » Tue Oct 04, 2016 8:42 pm

One other question. As I stated, the existing transformer has an output of 3-60W, which is obviously a range. I'm looking at one on the web which is 48W - does this mean it will work from 0 to 48W or just 48W exactly (seems unlikely?). Thanks.
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Postby kbrownie » Wed Oct 05, 2016 6:59 am

48W will be it's maximum output. So it will be fine on a 35W lamp.

Something to look at with lampholders, is the pinholes where the the lamp slots into, that can become enlarged/misshaped and not make good contact with the pins of the lamp. I have known lots people, even electricians that have failed to diagnose this fault and blame the transformer or other components!
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Postby nb99 » Wed Oct 05, 2016 7:08 am

I promise I'll double check/test the lampholder again before ordering the new transformer!

Thanks - your advice is much appreciated.
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