Question for the electronics wizards please

24 VRT

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The mains transformer in my old 12v halogen bulb desk lamp has failed - I've changed bulbs, mains plug and fuse, all of which did not bring it back from the dead. It was sat there one day quietly illuminating my paperwork when it just died - no pop, no fizzle, no nothing - just on one minute and off the next. Normally I'd bin it but I just can't find a suitable replacement that is neither too small nor too big to sit on the corner of the desk, so I'm wondering whether it will be possible to replace the transformer? It would need to be a like for like as it sits inside a moulded cradle in the base of the light with another arch cradle over the top that's screwed down to hold the transformer in place. As such the dimensions are just as vital as the rating etc. If it is feasible to get like for like which isn't prohibitively expensive, then I can swap the transformer over and get to keep by much loved desk lamp!
Photos of the transformer are attached - dimensions are 47x29x40mm - any thoughts/suggestions will be gratefully received.
I have thought about using a mains wall plug transformer and wiring the 12v output from that through to the on off switch in the light, but I don't know if such a transformer will have enough oomph to power a 20W G4 halogen bulb and also if the on off switch will still be ok as it will be going from mains 240v to 12v?

IMG_20220316_130105 b.jpg IMG_20220316_122433.jpg IMG_20220316_122439.jpg IMG_20220316_122500.jpg
 

Benzowner

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A 20w bulb at 12v isn't too power draining, you could try someone like RS components for a replacement transformer, there may also be a rectifier in that as well to stabilise the output voltage.
 

m80

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This sort of thing could supply the light fitting,
then short out primary to secondary connections where the transformer used to be in the base.
As it's halogen there is no need to be concerned about polarity.

If you decide to upgrade the lamp to LED then polarity can be important, some lamps are bridge diode rectifier fitted.
 

Diesel Benz

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This sort of thing could supply the light fitting,
then short out primary to secondary connections where the transformer used to be in the base.
As it's halogen there is no need to be concerned about polarity.

If you decide to upgrade the lamp to LED then polarity can be important, some lamps are bridge diode rectifier fitted.

This one has DC output, any modern power supply would have a switching supply while the original one appears to be a "dummy" transformer, that is AC output. With a halogen bulb either one would work though.

The mains switch should remain on the mains side if the original switch was used. The amp rating is unlikely sufficient for switching the 12V feed.

The original transformer seems to have a high temperature fuse. Probably a one time fuse if there is no button to reset it (or it does not recover after being cooled).
 
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24 VRT

24 VRT

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Thanks for the info - the more I think about it the more inclined I am to use an external transformer and run the 12v in through the switch and then direct to the bulb feeds (I'll leave the old transformer in place as its weight is needed for stability). I hadn't twigged that I can run the halogen bulb on DC too - I had been hunting for a wall socket transformer with 12VAC output and could only find one in RS Components, but no store near me and its expensive when adding in delivery. So cost-wise it looks like a 12v DC plug in jobbie, which will be cheaper and easier to source.
I don't intend to change to LED bulbs going forward as I have a pile of spare halogens to use up which should keep me going for years.
Thanks again for the input.
 
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24 VRT

24 VRT

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Sorry Diesel Benz I didn't see your reply before I responded just now, and in particular your comments re the on off rocker switch. I guess I can see if it will work on 12v DC rather than the 240VAC but if necessary can change that out as it seems to be a standard panel mount size.
 

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This will do the job for under £5

20w at 12v is less than 2a, so the switch should be fine, but I would suggest switching off at the socket to be on the safe side, as the transformer would still be energised.
 

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I am fairly sure I have exactly the same lamp but in black that you can have for the postage cost. let me check to see if i can find it and I will PM you if I do.
 
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24 VRT

24 VRT

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This will do the job for under £5
I think it would be too large to fit inside the base - probably just squeeze its length in on the bottom plate but as the base unit is sort of conical, the transformers height would probably put paid to the idea. I've put it all back together again now, but I'll measure for size later on and see if it would work. Thanks for the suggestion.
 
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24 VRT

24 VRT

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I am fairly sure I have exactly the same lamp but in black that you can have for the postage cost. let me check to see if i can find it and I will PM you if I do.
It was made by Ring Lighting - model 50838
 

m80

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Some of these PSU's are load sensing, so drop to no output when there is no load.
Transformer input is a product of the load anyway, so the current draw when nothing is connected would be negligible.

If you pm your address I've one here you can have gratis. I'm just testing it to see if it is load sensing.
 
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24 VRT

24 VRT

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Some of these PSU's are load sensing, so drop to no output when there is no load.
Transformer input is a product of the load anyway, so the current draw when nothing is connected would be negligible.

If you pm your address I've one here you can have gratis. I'm just testing it to see if it is load sensing.
Thanks for the kind offer - I've taken flying haggis up on his black one so I don't need to mess around with mine now.
 
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