Light Transformer Wiring Problem

[winston1]

The normal definition for a transformer is a wound device. It does not have to reduce or increase the voltage as it can be a 1:1 isolation transformer so your definition is incorrect.

Switch mode power supplies in 12 volt lighting circuits change not only the voltage but also the frequency and waveform. Transformers don't do this.

A (perhaps) better method of describing them would be "electronic transformer replacement circuit". But here is no such thing as an electronic transformer.

 

[JohnW2]

Oh, not that arguement again. OK, here goes. ... transformer ... noun ... 1. an apparatus for reducing or increasing the voltage of an alternating current.

As I need not tell you, that definition would not encompass some quite common components which we would all agree are transformers!

By definition, that box is a transformer. Voltage can be transformed (increased or reduced) in a number of ways. One of the ways is having a number of wire windings on a common core. Another way is to use electronics, such as a switched mode power supply.

That is all true but, as I say every time this issue gets discussed, I do think that it makes sense if, assuming one has a reason for not using a more specific/correct term (i.e. switched mode power supply), one used the term (as on the component pictured in this thread) 'electronic transformer' when that's what one is talking about. At least for those in my generation, 'transformer' (without qualification) implies a wire-wound component, and there is still a lot of merit in distinguishing between them and electronic devices with similar functionality.

To call an SMPS a 'transformer' (without qualification) is, to my mind, a bit like calling an MCB a 'fuse'.

Kind Regards, John

 

[EFLImpudence]

(Is it possible that the manufacturer has decided to use the metalwork of the fitting for the return connection?!? ... I suppose that is considered acceptable practice for SELV?)

It must be but, even though there is a cover, as the Live could come out and contact the metal ceiling fixture which is connected to the light fitting it does not seem ideal.

I'm a bit confused. If the transformer pictured is part of the light fitting, can the fitting as a whole really be regarded as SELV - given that there is an LV cable entering it and just terminated by screw terminals in a connector block (and not even any apparent cable clamp). As you say, one of the LV conductors could theoretically come adrift and touch anything - including any metalwork of the fitting. Does that really qualify as SELV?

That's why I expressed some reservation.

The ones I have seen, as said, have a marked Class II "transformer" which as in the picture has a metal ceiling bracket to which attaches a metal cowl (if that's the right word) this in turn has a threaded metal tube fixed to it with a nut.
The bottom of the tube attaches to the lamp housing.

It had G4 capsules which were supplied by ONE wire each. All connected to the transformer.
The second conductor was the metal of the fitting itself connected by a wire fixed by the tube nut and to the transformer.

 

[EFLImpudence]

The normal definition for a transformer is a wound device. It does not have to reduce or increase the voltage as it can be a 1:1 isolation transformer so your definition is incorrect.

Switch mode power supplies in 12 volt lighting circuits change not only the voltage but also the frequency and waveform. Transformers don't do this.

A (perhaps) better method of describing them would be "electronic transformer replacement circuit". But here is no such thing as an electronic transformer.

All too technical in my opinion.

I think you will have to get used to calling them 'wire wound transformers' and/or 'electronic transformers' because that is what the manufacturer calls them.

Your definition dates from when that is all there was.


You may just as well say the internal combustion engine is not an engine because an engine is something powered by steam.

 

[JohnW2]

That's why I expressed some reservation. ... The ones I have seen, as said, have a marked Class II "transformer" which as in the picture has a metal ceiling bracket to which attaches a metal cowl (if that's the right word) this in turn has a threaded metal tube fixed to it with a nut. ... The bottom of the tube attaches to the lamp housing. ... It had G4 capsules which were supplied by ONE wire each. All connected to the transformer. ... The second conductor was the metal of the fitting itself connected by a wire fixed by the tube nut and to the transformer.

As I said, that sounds all wrong to me. It might be Class II within the 'transformer' but there is an unclamped LV cable with the conductors terminated by screw connections, presumably in the vicinity of the metal ceiling bracket which, in turn, is in continuity with the metal 'cowl', tube, and lamp housing. That surely makes the fitting as a whole Class I?

I suppose one could, as required for a Class I fitting, earth all that metalwork and also connect the metalwork to one side of the output of the SMPS (facilitate using the metalwork as an ELV return path), but I don't think it would then be SELV!

Kind Regards, John

 

[JohnW2]

You may just as well say the internal combustion engine is not an engine because an engine is something powered by steam.

I think you'll find that Mr Archimedes (and maybe even those of much earlier civilisations) were inventing and constructing 'engines' (particularly for military purposes) an awfully long time before anyone had even dreamed of steam power

Kind Regards, John

 

[EFLImpudence]

To be fair there is a cover which acts as a cable clamp.

Also, is a single plastic cover over a connector block double insulated?
Are choc-blocks considered to be double insulated?

 

[EFLImpudence]

I think you'll find that Mr Archimedes (and maybe even those of much earlier civilisations) were inventing and constructing 'engines' (particularly for military purposes) an awfully long time before anyone had even dreamed of steam power

Yes, I believe the ancient Egyptians had a steam engine.

 

[JohnW2]

To be fair there is a cover which acts as a cable clamp. Also, is a single plastic cover over a connector block double insulated? Are choc-blocks considered to be double insulated?

I'm not certain of the answers to those questions (I suspect the answers may be 'it depends'!) but it just doesn't feel right to me!

Kind Regards, John

 

[ericmark]

A transformer but clearly not electric. As to a 1:1 isolation transformer does it really transform anything! Yes we refer to isolation and auto transformers but again a switch mode power supply does not have to contain a transformer. 30 volt input can be regulated to a 12 volt output without any transformer. In the main the unit shown does the following.
1) It transforms AC to DC and charges a capacitor.
2) It transforms DC to AC at high frequency.
3) It transforms the voltage to a lower value and isolates.
4) It regulates output to 12 volt.
So in the main it transforms so can't really see a problem in calling it an "Electronic Transformer".

 

[winston1]

From Wikipedia:

A transformer is an electrical device that transfers energy between two circuits through electromagnetic induction. A transformer may be used as a safe and efficient voltage converter to change the AC voltage at its input to a higher or lower voltage at its output. Other uses include current conversion, isolation with or without changing voltage and impedance conversion.
A transformer most commonly consists of two windings of wire that are wound around a common core to provide tight electromagnetic coupling between the windings. The core material is often a laminated iron core. The coil that receives the electrical input energy is referred to as the primary winding, while the output coil is called the secondary winding.
An alternating electric current flowing through the primary winding (coil) of a transformer generates a varying electromagnetic field in its surroundings which causes a varying magnetic flux in the core of the transformer. The varying electromagnetic field in the vicinity of the secondary winding induces an electromotive force in the secondary winding, which appears a voltage across the output terminals. If a load impedance is connected across the secondary winding, a current flows through the secondary winding drawing power from the primary winding and its power source.

That first sentence seems pretty clear to me and definitely rules out SMPS being transformers.