Transformer replacement in a downlighter

[NickB_99]

Hi,

Now getting round to sorting out a faulty downlight I found when I moved in to my house.

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• NickB_99
• 30 May 2015
• 1

I had disconnected at the junction box as soon as I found it! Just getting round to fixing.

The burnt out half of the connector block had a loose wire, which I assume was the cause.
I've checked the grey supply cable from the small junction box back to a larger junction box and it is all fine. Measured the voltages under operation and they seem ok too. Damage seems to be to the transformer and at the connector.

The downlight is a 50w halogen bulb and the 4 bulbs in total operate from a dimmer switch.
Each bulb has its own transformer and I tested with one of the other transformers and it works fine.

Close up of existing transformer

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• NickB_99
• 30 May 2015
• 1

Was after advice for a suitable replacement and looked at screw fix to see if anything was suitable.
E.g. Get a pre-wired transformer? (as existing cables from bulb to 12v terminals are not in good shape so replace)
For a single 50w/12v bulb is a 20-60VA transformer ok, or do I need more headroom ideally? E.g. 35-105VA

 

[Taylortwocities]

For a halogen lamp 50Watts is the same as 50VA, so the 20-60VA tranny will be just fine.
But the existing one should still be OK. Cut back the burnt wires to bright copper and install a new terminal block.

 

[PrenticeBoyofDerry]

Was after advice for a suitable replacement and looked at screw fix to see if anything was suitable.
E.g. Get a pre-wired transformer? (as existing cables from bulb to 12v terminals are not in good shape so replace)
For a single 50w/12v bulb is a 20-60VA transformer ok, or do I need more headroom ideally? E.g. 35-105VA

Either will be suitable for 50w load, but you do need a dimmable trany, if you have a dimmer switch.

If the 12V terminals are burnt out on the lampholder, you may need to replace the lampholder also, or clean the damaged ends off.

Were these transformers and connection beneath thermal insulation?

 

[NickB_99]

For a halogen lamp 50Watts is the same as 50VA, so the 20-60VA tranny will be just fine.
But the existing one should still be OK. Cut back the burnt wires to bright copper and install a new terminal block.

Will give this a go before buying a new one.

Either will be suitable for 50w load, but you do need a dimmable trany, if you have a dimmer switch.

If the 12V terminals are burnt out on the lampholder, you may need to replace the lampholder also, or clean the damaged ends off.

Were these transformers and connection beneath thermal insulation?

The lamp holder looked fine, no sign of damage there, so will try cutting back damaged cable to fresh copper.

Not sure what you mean on last Q - under thermal insulation as in beneath loft glass-wool/thermal insulation?

 

[PrenticeBoyofDerry]

Not sure what you mean on last Q - under thermal insulation as in beneath loft glass-wool/thermal insulation?

Yes beneath or covered in loft insulation, as they should not be, the lamps and tranys need ventilation.
Which then normally compromises, the thermal/heat loss properties of the room below. On these occasion, loft braces are advised.

 

[NickB_99]

Not sure what you mean on last Q - under thermal insulation as in beneath loft glass-wool/thermal insulation?

Yes beneath or covered in loft insulation, as they should not be, the lamps and tranys need ventilation.
Which then normally compromises, the thermal/heat loss properties of the room below. On these occasion, loft braces are advised.

Some gaps had been made in the loft insulation, they weren't covered.

Will look at tidying up installation regardless.

Thanks.

 

[PrenticeBoyofDerry]

https://www.tlc-direct.co.uk/Products/JC94020.html

 

[ban-all-sheds]

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• NickB_99
• 30 May 2015
• 1

TBH I can't see why either of those junction boxes was needed.

 

[PrenticeBoyofDerry]

The tranny will be prewired, so reason one for JB. And the lampholder will have come with pre-fitted connector box, so reason two.
I personally would like to position the tranny, a sensible distance from the heat of the lamp. So that junction/joint, I would be happy with, even though the picture shows the tranny closer than my liking.

 

[ban-all-sheds]

The tranny will be prewired,

 

[Taylortwocities]

Yes. But under the cover you will find that the PRI & SEC wires are soldered on to the transformer's PCB.

Like this

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• Taylortwocities
• 1 Jun 2015
• 1

I don't know about you but I'm not keen on soldering 1mm T&E onto a PCB. I find a junction box so much easier to use!

 

[ban-all-sheds]

OK.

Foolishly I assumed that if the maker had gone to the trouble and expense of providing a removable cover that there would be something worth accessing under it.

 

[333rocky333]

Doesnt the square symbol and 2.5mm mean that beneath the cover there are screw in or push in terminals that accept 2.5mm cable.
though do agree J/B is less hassle.

 

[Taylortwocities]

Doesnt the square symbol and 2.5mm mean that beneath the cover there are screw in or push in terminals that accept 2.5mm cable.
though do agree J/B is less hassle.

Good question. And if so, does that apply to the PRI or SEC connection?
Would like to see beneath that particular cover!

 

[EFLImpudence]

Doesn't it say 0.75 ?