Shower fan/light transformer failure Ask questions and find answers to many subjects relating to electrics and electrical work

[mick.n]

Just found this website in my search for advice.

In December 2007 i bought this from wickes

http://www.wickes.co.uk/Fans/Fan-with-L ... nvt/713002

Fan is 240volt, light is ran from 12volt transformer

Last month the transformer for the light failed, as it was still under warranty wickes replaced the transformer. This week the transformer failed again.

Here is the transformer

[IMG]http://i162.photobucket.com/albums/t249/mick_n/DSC00043.jpg[/IMG]

I am wondering if it is the way i connected it that is causing the transformer to fail. The wiring diagram supplied with the instructions is this

[IMG]http://i162.photobucket.com/albums/t249/mick_n/scan0001.jpg[/IMG]

I did'nt want to utilise the overrun timer so i bridged the connections marked in the diagram as "L" and "SW", so that when i switch on by the pull cord in the bathroom the fan and the light come on & the fan stops immediately when switched off.

Any help appreciated!

[ericmark]

I see nothing wrong with what you have. The instructions don't seem to match the transformer as instructions say max 20 watt but transformer says rated at 50 watt and also I can see no reason why the light should not be used independent from fan. Yet the instructions warn against it so I wonder if the transformer would be cooled by fan or light fitting cooled by fan if former would the removal of over run could cause a problem. I would not have thought so but wonder if I have missed something?

[mick.n]

Thank you ericmark for taking the time to reply.

The bulb used is rated at 20W, so this is well within what the transformers max rating. I took apart the failed transformers just as a matter of interest, and in each case, a resistor had burnt out.

There is no provision to cool the transformer and no such mention of cooling is stated in the instructions (Apart from a minimum distance of mounting the transformer about an inch or 2 away from the light source for obvious reasons). I even mounted the transformer on "standoffs" so air could more easilly circulate around/underneath it.

Now in each case, the failure occured at switch on......you could hear a "phutt" sort of sound as the light went off.

The more i think about this i am inclined to believe that there is some sort of "back EMF" from the fan motor at power up...... and maybe by wiring the fan unit up to utilise the overrun timer (By running a permanent live to the terminal marked L and just the switched live to the SW terminal as per wiring diagram) this may solve the transformer blowing problem.

The reason i didnt connect it this way initially was that i was not prepared to have a permanent live to the fan unit unless it was coming from an isolation switch ( I have read on this site about a house catching fire because of this!)


I edited the original post to show a link to the fan i have.

Any further suggestions/comments appreciated!

[ericmark]

I did make up a quick instruction for isolation on my site for someone else with same problem. See "Wiring a Bathroom Light and Fan independantly" and to fit isolation is not so easy requiring at least two poles. The back EMF could cause a problem but in real terms I think any normal inverter should have been able to cope with this and to me it seems faulty.
Eric

[mick.n]

Many thanks once again ericmark. The diagram you mention would be the correct way to go & when time permits i will do it as such.

For the meantime i will just leave the transformer disconnected (Got another replacement one from wickes yesterday).

Must admit that the transformer supplied with these fan packs does seem a little cheap & nasty, but there you go!

Best regards & thanks again.

[ChrisCyp]

I have just installed the same unit and guess what! After the second switch activation the MCB flipped and inspection shows that the txfmr has failed. Unfortunately I cut the 12 volt cable to extend it so I doubt if Wickes will refund - but I will try. Could the fact that these units are around £8 from Wickes when a similar looking one from B&Q was nearer £36 be anything to do with it I wonder?

[mick.n]

[quote="ChrisCyp"]I have just installed the same unit and guess what! After the second switch activation the MCB flipped and inspection shows that the txfmr has failed. Unfortunately I cut the 12 volt cable to extend it so I doubt if Wickes will refund - but I will try. Could the fact that these units are around £8 from Wickes when a similar looking one from B&Q was nearer £36 be anything to do with it I wonder?[/quote]

Hi chriscyp, i just revisited this post as i have just had another transformer blow for the 3rd time! I would take it back for a refund\replacement assuming you havent allready.

When i first bought mine in dec 2007 the price was £39.99. When i went back to the store i noticed they were selling them for £8.99 so i bought another as a spare.

As it is a struggle to get into my loft to replace this transformer every couple of months i wonder if anyone could recommend an alternative transformer that would do the job?