12v downlight: transformer delay 15s

[gav123]

The old coil transformer for my kitchen ceiling downlights finally went kaput.
It was rated 200w, and supplied 4 x 50 W 12v downlights.

I took it out, and swapped in a halolite 200w electronic transformer from screwfix.

This works fine when 'warmed up'. But from cold it's been taking 15s for the lights to actually come on. I'm guessing this is more than 'soft start'.

I've exchanged for another one, with same results. (I'm not ruling out 2 faults transformers -- the one I got in exchange was clearly a return)

Any thoughts?

 

[bernardgreen]

A 50 watt lamp takes 50 watts only when it is at normal running temperature ( white hot ) as their resistance is much lower when cold than when hot. Therefor before it gets hot it takes a lot more power and this will be overloading the electronic transformer. Many electronic transformers will shut down to a very low voltage to protect themeslves in this situation.

The lamp filaments will slowly warm up on this reduced voltage until at some point the transformer is no longer overloaded and it will then give full output and the lamps will light fully.

 

[JohnW2]

A 50 watt lamp takes 50 watts only when it is at normal running temperature ( white hot ) as their resistance is much lower when cold than when hot. Therefor before it gets hot it takes a lot more power and this will be overloading the electronic transformer. Many electronic transformers will shut down to a very low voltage to protect themeslves in this situation.

Indeed - and the same would not have happened with the OP's old 'coil transformer'.

Do I take it that what you're implying is that to a 200W rated 'electronic transformer' is not really big enough for a total (when hot) incandescent lamp load of 200W (the OP's 4 x 50W)?

Kind Regards, John

 

[ericmark]

Easy to prove remove one lamp if that cures problem then get a larger power supply.

However I will point out the old transformer will have been rated 0 - 200W the new one likely something like 50 - 200W so will not power LED lamps.

There are some now rated 0 - 200W even of the switched mode type may be prudent to select one which will run LED's in the future.

 

[gav123]

thanks -- this seems to be the problem. Everything is fine with only 3 wired in.
So I'll go up to a higher power rating.

 

[winston1]

It is because it is NOT a transformer but a switch mode power supply. Get a real transformer, like you had before, and it won't happen.

 

[JohnW2]

It is because it is NOT a transformer but a switch mode power supply. Get a real transformer, like you had before, and it won't happen.

Indeed

Indeed - and the same would not have happened with the OP's old 'coil transformer'.

Kind Regards, John

 

[EFLImpudence]

but a switch mode power supply.

You mean one o' they there electronic transformers?

 

[JohnW2]

but a switch mode power supply.

You mean one o' they there electronic transformers?

I don't know about you, but I don't have any real problem when people call them 'electronic transformers', since that gives a reasonable insight into what they are talking about - it's when they are referred to just as 'transformers' that I get a bit upset!

Kind Regards, John

 

[winston1]

but a switch mode power supply.

You mean one o' they there electronic transformers?

NO, they are not transformers which is a wound device of coils on a magnetic core. The term electronic transformer is incorrect even though it is widely used by manufacturers. They are switch mode power supplies and they operate completely differently to transformers.

 

[JohnW2]

NO, they are not transformers which is a wound device of coils on a magnetic core. The term electronic transformer is incorrect even though it is widely used by manufacturers. They are switch mode power supplies and they operate completely differently to transformers.

All true. However, in the same way that no-one expects an 'electronic tape measure' to have a tape, an 'electronic cigarette' to contain tobacco, a 'electronic dice' to be something one throws etc. etc., no-one really ought to be confused or misled into thinking that an 'electronic transformer' is a wirewound component. Just as with the tape, cigarette and dice etc., they are electronic devices which replicate some of the functions of the traditional items.

It is, IMO, calling a SMPS just 'a transformer' which is wrong, misleading and potentially confusing.

Kind Regards, John