Replaced old halogen transformer - lights noticeably dimmer

[Ben Lumley]

Hey,

I've replaced a 20year old (ish) 12volt transformer with an equivalently rated new one.

The lights work - but are noticeably dimmer/yellower. I'm pretty sure this is because the new transformer is 11.4 or 11.5 volts, rather than the 12v of the old one?

Does anyone actually make one at 12v these days? Is the old one even 12v? Or was labelling more relaxed in the 90s and this old one was also 11.something volts?

Thanks!

 

[securespark]

When you say "equivalently rated", how many lamps are connected to it and what value are these lamps in watts?

And what rating is the new transformer in VA?

 

[Ben Lumley]

2 * 35w halogens.

Old transformer had 100va written on it.

New one was rated 35 - 105.

 

[securespark]

And you have not changed the lamps for LED or lower wattage?

How about the wiring on the SELV side?

If the csa (wire thickness) is not sufficient, you can get voltage drop on a long run causing dimness.

How thick is the wire that feeds the two 35W lamps and how long?

 

[Ben Lumley]

Thanks for your replies

Not switched to LED/Low wattage no - parents' house. I suggested it, they didn't want to in case they didn't like the light...!

Honestly not sure how thick the SELV wire is - it looks the same as the regular 230v loop/mains wiring in the house. And not sure how long it is either... I pulled the wires out from the old transformer and put them in the new one assuming it would be a like-for-like swap and all would be well.

Worth investigating the wire lengths? Maybe shortening them as far as possible?

 

[securespark]

OK. How far apart are the two fittings?

And the transformer - is it remote from both fittings?

Are there two cables connected to the transformer, or is one light fitting looped from the other?

This can cause excessive volt drop in some cases.

 

[Ben Lumley]

Fittings are 1 - 1.5 metres apart. Transformer is remote yes - it's been sited for ease of access I guess; just inside the loft hatch and 50cm or so up, screwed to a joist.

Can't remember if the lights have their own cable run back to the transformer or not I'm afraid. Sounds like whatever it is I should move it to 1 run per light back to transformer and as short as possible - put the transformer mid way between the pair?

 

[JohnW2]

OK. How far apart are the two fittings? ... And the transformer - is it remote from both fittings? ... Are there two cables connected to the transformer, or is one light fitting looped from the other? ... This can cause excessive volt drop in some cases.

All perfectly true, but AIUI all the OP has done is changed the 'transformer', in the same location (and not changed any of the wiring), so presumably the reduction in brightness of lights must be related to the transformer?

Kind Regards, John

 

[Ben Lumley]

OK. How far apart are the two fittings? ... And the transformer - is it remote from both fittings? ... Are there two cables connected to the transformer, or is one light fitting looped from the other? ... This can cause excessive volt drop in some cases.

All perfectly true, but AIUI all the OP has done is changed the 'transformer', in the same location (and not changed any of the wiring), so presumably the reduction in brightness of lights must be related to the transformer?

Kind Regards, John

That was where I started, suspecting the 0.5v less to be the cause - but I'm all ears for whatever anyone has to say/suggest!

 

[endecotp]

How have you measured the voltage?
Can you measure what the old one was supplying?

 

[JohnW2]

That was where I started, suspecting the 0.5v less to be the cause - but I'm all ears for whatever anyone has to say/suggest!

Well, as I said, if the 'transformer' is the only thing that has changed, that has to be the explanation and, as you say, a lower voltage (if that's what you have) could explain it. A small reduction in voltage can have a surprisingly large effect on light output.

Kind Regards, John

 

[Ben Lumley]

How have you measured the voltage?
Can you measure what the old one was supplying?

No - the old transformer was totally dead, says 12v on it.

New one I've not measured, it says 11.5v on it. Everyone seems to sell 11.4-11.6v ones now; 12v seems hard to find!?

 

[Ben Lumley]

That was where I started, suspecting the 0.5v less to be the cause - but I'm all ears for whatever anyone has to say/suggest!

Well, as I said, if the 'transformer' is the only thing that has changed, that has to be the explanation and, as you say, a lower voltage (if that's what you have) could explain it. A small reduction in voltage can have a surprisingly large effect on light output.

Kind Regards, John

Know where I can get a 12v one? Even though advertised as 12, most places seem to sell ones that are stamped 11.4-11.6 on if you look in screenshots, including the replacement that's in at the moment.

Starting to think I should force an LED conversion...

 

[JohnW2]

Know where I can get a 12v one? Even though advertised as 12, most places seem to sell ones that are stamped 11.4-11.6 on if you look in screenshots, including the replacement that's in at the moment. ... Starting to think I should force an LED conversion...

What sort of base do your 35W halogen lamps/bulbs have? Have you considered changing them to 40W or even 50W ones if they are available in your type?

Kind Regards, John

 

[333rocky333]

The 12 volt one sounds like it may have been a "torroidal" transformer whereas the new ones are electronic ones, do you have a pic of the old one.

in the 90's the fashion was to use these and run each light back to it the lengths sometimes in excess of 3metres.

https://www.tlc-direct.co.uk/Products/TLT100slash2.html

it then became popular to use electronic and shove through the downlight hole, but there usually limited to 2metre sometimes less