Dimmer and transformer

[svtiss]

Hi
I need to dim 12v lamps , can I put a dimmer in primary coil 120 AC transformer.
I allready tried it and it did work , But is that correct ?
Low voltage dimmers cost much more., Any ideas?
Thanks

 

[stevez]

That's a good question. As you point out - it does work to some extent. Typically the dimmer is made for the resistive loads that filaments present. The transformer is an inductor but if terminated in a resistive load - would the dimmer see only resistance - or at least nearly enough that the difference is minor? Again, good question.

 

[svtiss]

Thanks ,
still hope to get the answer ....

 

[Hero999]

It depends on the transformer. If it's a traditional heavy laminated/torroidal iron transformer then no. If it's a modern electronic transformer (essentially a switched mode power supply), then yes.

 

[svtiss]

well, it works and no heat , and the transformer is traditional style , but I just want to know why I cant use it ???
RF noise ?? or ...?

 

[Dean Huster]

There are no state laws against doing it, no religious sanctions (that I know of), and most of the radical groups don't really care. So, if the transformer remains cool at all settings of the dimmer and the FCC doesn't come knocking on your door complaining about excessive RF destroying the radio and TV reception on the block, then stay with the simple solution.

Dean

 

[Hero999]

The reason you can't do it is because the transformer is inductive and the dimmer is designed for a resistive load and might be destroyed when driving an inductive transformer.

 

[grim]

the dimmer almost certainly works by firing thyristors part way through the two halves of the sine wave. if the two are not ballanced exactly it will start to bias the core in one direction - think of it as +100 -99 +100 -99 +100 -99 eventually the core COULD saturate. a lot depends on how gappy the core is.

It also depends on the flux density the tranny is designed to operate at. if i was designing a transformer for this purpose i would definately reduce the flux fom the typical 1.5T to 1.2 or so.

 

[svtiss]

Thanks, everybody for your help.