LED lighting transformer issue

HughH · 29 Apr 2024

Hi all, I hope somebody can help me on non-functioning domestic LED lighting issues.

We had a full house rewire about 18months ago as part of a renovation. We installed LED's downlights at the same time, each using its own individual 12V transformer. The transformers connect to each LED unit via a short cable with a keyed connector. The transformers sit in the ceiling space next to the LED's . All lighting circuits were working. A few months back I removed some switch plates and LED downlights for access to patch/fill/paint the ceiling and wall plasterwork. This involved disconnecting wiring from the plates, and unplugging DL’s from the 12 transformers. The transformer input wiring was not disconnected. Now, the switch plates have been reconnected and LEDs put back, but two DL’s are not working. The two units in question are on separate circuits;
DL1 - is on two-way switches
DL2 - is three-way switches
I can only surmise an error in re-connecting the switch plate wiring, despite noting where each wire was originally connected. I have used a voltage tester pen to confirm the DL1 & DL2 transformer brown input wires are made ‘live’ when using their respective switches. I have swapped the DL’s around with known working units but this has no effect.

Any ideas or suggestion on what further checks I could make are most welcomed.

ericmark · 29 Apr 2024

It is unusual to use 12 volt LED down lighters unless in a bathroom today, when we stopped using quartz halogen the advantages vanished, however many old systems have been converter to LED and the main problem is the rating of the power supply, in the old days we would see some thing like 20 - 105 VA marked on them, as they needed at least a 20 watt load, the new breed can work from zero, but does not matter if output is AC or DC the power supplies do not like being powered up with no load.

We tend to call the AC units electronic transformers, and the DC units drivers, not technically the right names, but it tends to be used, the driver should be variable voltage and fixed current, but the reverse is also often called a driver, one has to look at the description, if a single voltage marked it is a fixed voltage and with single current fixed current often in mA range.

However the problem is often the power supplies will not have an output unless there is a load, so testing with a volt meter can give you incorrect info. However step one would be to take a photo of the power supply, then we know what we are talking about, as so easy to jump to conclusions and get 2 + 2 = 22. The answers depends on what you have.

The same goes as to converting into 230 volt, easy to talk about it, but to convert within regulations not so easy, as often no earths with 12 volt lights, technically 230 volt need an earth taking to the lamp, even if the lamp does not need one, I personally would not be too worried about that, but to instruct how to change to 230 volt, we must tell you the rules.

Voltage tester pens only work with AC, and may not work with 12 volt. Likely the best test is substitution. In the main 12 volt LED down lights are AC/DC it does not matter, however that is not true for all, there are some which are DC only, since the G5.3 pins can go in either way around they normally have a built in rectifier so not polarity conscious, but can't guarantee all are like that, again pictures are good.

Murdochcat · 29 Apr 2024

Sadly a lot of these units are not too reliable and they might just be past their best. Have you tried plugging them into a transformer that does work?

HughH · 29 Apr 2024

ericmark said:
It is unusual to use 12 volt LED down lighters unless in a bathroom today, when we stopped using quartz halogen the advantages vanished, however many old systems have been converter to LED and the main problem is the rating of the power supply, in the old days we would see some thing like 20 - 105 VA marked on them, as they needed at least a 20 watt load, the new breed can work from zero, but does not matter if output is AC or DC the power supplies do not like being powered up with no load.

We tend to call the AC units electronic transformers, and the DC units drivers, not technically the right names, but it tends to be used, the driver should be variable voltage and fixed current, but the reverse is also often called a driver, one has to look at the description, if a single voltage marked it is a fixed voltage and with single current fixed current often in mA range.

However the problem is often the power supplies will not have an output unless there is a load, so testing with a volt meter can give you incorrect info. However step one would be to take a photo of the power supply, then we know what we are talking about, as so easy to jump to conclusions and get 2 + 2 = 22. The answers depends on what you have.

The same goes as to converting into 230 volt, easy to talk about it, but to convert within regulations not so easy, as often no earths with 12 volt lights, technically 230 volt need an earth taking to the lamp, even if the lamp does not need one, I personally would not be too worried about that, but to instruct how to change to 230 volt, we must tell you the rules.

Voltage tester pens only work with AC, and may not work with 12 volt. Likely the best test is substitution. In the main 12 volt LED down lights are AC/DC it does not matter, however that is not true for all, there are some which are DC only, since the G5.3 pins can go in either way around they normally have a built in rectifier so not polarity conscious, but can't guarantee all are like that, again pictures are good.

Ericmark,
Thanks for your comments. I've attached a pic of the driver (not transformer as you correctly point out). The same driver is used throughout the house (~30 units) and so far, so good, none have failed in 18-months.
I will substitute test as suggested, and post the result this evening.

HughH · 29 Apr 2024

Murdochcat said:
Sadly a lot of these units are not too reliable and they might just be past their best. Have you tried plugging them into a transformer that does work?

I have only swapped over the DL's themselves by unplugging from the Drivers. I will swap the Drivers now too and come back with the results.
Thanks.

Echo the husky · 30 Apr 2024

Those aren't 12V transformers, they are constant current LED drivers, If you plugged the LEDS in with the power on to the drivers you will have blown the LEDs due to over voltage.

ericmark · 30 Apr 2024

Echo the husky said:
Those aren't 12V transformers, they are constant current LED drivers, If you plugged the LEDS in with the power on to the drivers you will have blown the LEDs due to over voltage.

If down lighters are over 4.2 watt then even if a 12 volt lamp plugged into the driver shown it will likely be OK.

HughH said:
each using its own individual 12V transformer.

It says 35 to 48 volt, that is a long way from 12 volt.

HughH said:
DL1 - is on two-way switches
DL2 - is three-way switches

Not sure what you mean, two way OK on one way off the other, three way would be off, wait, enter lights on an office for example, the switch normally rotary with three positions. We can use multi switches for one light, with 2 x two way and then as many as you want intermediate switches, but these would be on the supply to the driver, not supply from the driver.

It is likely a driver can be damaged if left on with no lamp connected for an extended time.

HughH · 1 May 2024

ericmark said:
It says 35 to 48 volt, that is a long way from 12 volt.

I dont know what I was thinking when I typed the original post - sorry for the misinformation which is very unhelpful.

ericmark said:
Not sure what you mean, two way OK on one way off the other, three way would be off, wait, enter lights on an office for example, the switch normally rotary with three positions. We can use multi switches for one light, with 2 x two way and then as many as you want intermediate switches, but these would be on the supply to the driver, not supply from the driver.

I stand corrected; Three-way; my way (layman's) of explaining 2 x two way and x1 intermediate switch.

So, I substituted each driver with a new/unused unit and both DL's are working.

ericmark said:
It is likely a driver can be damaged if left on with no lamp connected for an extended time.

The lamps were disconnected for several weeks - to months, and it is very possible the drivers were 'on' in this period. If you don't mind explaining; how does a driver become damaged in this scenario?

ericmark · 1 May 2024

The unit should shut down with open or short circuit, but repeatedly testing to see if corrected, I have know over some time this to damage a switch mode power supply.

HughH · 2 May 2024

ericmark said:
The unit should shut down with open or short circuit, but repeatedly testing to see if corrected, I have know over some time this to damage a switch mode power supply.

Thankyou.

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LED lighting transformer issue

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