12v Lighting Problem

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sir1963

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Reply # 922711 27-Oct-2013 21:10

minimoke:
sir1963:
minimoke: Thanks everyone. I'm digesting all this information.

What I'm also not understanding is why does the transformer or my circuit board not trip. If a tail is failing and gets hot enough to melt the insulation I would have thought the fuse at the circuit board would have gone - isn't this what they are supposed to do? And how is it a transformer lets the wire get so hot. I'd have thought it would trip and then cool down and restart rather than just totally blowing.

I've got a dozen or so of these things sitting in my roof possibly cooking away!

Good thought, but wrong....sort of.

If you have a 5A fuse you would need to draw over 3000W for hours before the fuse blew
If you have a 10A fuse you would need to draw over 6000W for hours before the fuse blew.

So, if one of your light fittings shorted out here is a high chance that the resistance of the copper winding in the transformer would limit
the power drawn to less than this, however this is more than enough to cause a fire.

This is one of the reasons I hate low voltage lighting.

Personally I believe if you are going to use low voltage lighting its worth having a decent SMPS and running ALL the lights off it

Ahh - that makes sense at the circuit breaker end.

But the transformer has all these flash supposed settings so I wonder why these don't work.

On the transformer it says the LED glows:
- "ON" for normal operation.
- OFF - its out of order check mains power (nothing about checking tails / bulbs or that it is rooted!!)
- Slow flashing: Short circuit condition (but two melted wires touching doesn't trip it!)
- Rapid flashing: Transformer overload (its in the roof - who sees this before it blows!)

a 100w bulb handing from a wire in the middle of the ceiling seems a whole lot simpler!

Go and buy an LED lamp then.
1. It will save you power
2. Its low wattage will also men your wiring will not cook its self
3. The life expectancy of the lamp is a damn sight longer

1eStar

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Reply # 922726 27-Oct-2013 21:26

I've always installed 1 transformer per light. Unfortunately it's difficult to find led replacements for MR-16 with wide angle (60°) like your halogens. Your simplest remedy would be to source some 35w 60° IRC halogens which should drop your transformer load and they in theory have the same light output. I last found the afore mentioned bulbs at rexel. Good luck

Cloudconnext

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Reply # 923345 29-Oct-2013 07:24

One person supports this post

Take a different angle, dump the transformer, dump the halogen lamps. Filament lamps are end-life Tech IMHO.

Install 9 watt LED 230v down-lights, similar light output in lumens, but much lower ongoing power consumption.

Positives:

- no significant heat issues with lamp holder, i.e. higher MTBF
- no switch-mode power supply "transformer" to fail
- significantly longer lamp life (i.e. fewer lamp changes)
- much lower running costs (estimated ~80% less power than a 50 watt filament lamp)
- probably a lower fire risk than halogen lamps
- lower long term maintenance costs (lamps, transformer replacements)
- less roof space crawling

Negatives

- LEDs don't have the "sparkle" affect of a dichroic downlight
- claimed running time of up to 45000 hours for LED may be marketing hype, time will tell

....

mclean

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Reply # 923461 29-Oct-2013 11:10

Just some observations: The fitting in the photo in the OP looks like it has overheated. Also it looks corroded. Overheating is usually caused by poor connections. If your other fittings look like that you should get an electrician to replace them.

If the transformer has built in short-circuit protection then a fault on the 12V side is unlikely to trip the upstream fuse/MCB.

McLean

gregmcc

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Reply # 923478 29-Oct-2013 11:27

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First and formost the orginal posted has stated that they have changed the transformer, as they are working on fixed wiring it is illegal for them to liven it until it has been inspected by a registered electricain.

Second, obviously no idea on how to calculate loading of each transformer, it's a bit like running your car engine at full revs all the time, there is a reason why people don't do it as the engine won't last very long.

Third, get an qualified electrician in, obviously over heating problems and very close to a fire, should you be relying on advise of unqualified people?

Fourth, lots of people offering advice, how many of those are actually qualified as an electrician and hold a current practising license? If you can't answer yes to both you are more than likely offering advise on a subject you don't have there relevent exepeience in.

minimoke

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Reply # 923494 29-Oct-2013 12:22

gregmcc: First and formost the orginal posted has stated that they have changed the transformer, as they are working on fixed wiring it is illegal for them to liven it until it has been inspected by a registered electricain.

Second, obviously no idea on how to calculate loading of each transformer, it's a bit like running your car engine at full revs all the time, there is a reason why people don't do it as the engine won't last very long.

Third, get an qualified electrician in, obviously over heating problems and very close to a fire, should you be relying on advise of unqualified people?

Fourth, lots of people offering advice, how many of those are actually qualified as an electrician and hold a current practising license? If you can't answer yes to both you are more than likely offering advise on a subject you don't have there relevent exepeience in.

Thanks GregMC Firstly I have had an electrician in to check the overall lighting problem and he could not find a problem. He did suggest all the earthquakes may have loosened things but he couldn’t actually find this as an issue. Secondly the light fittings / transformers etc were installed by an electrician and signed off by the electrician around 6 years ago.

I have just checked again on the consumer build website and it says I can
"Replacing switches, socket outlets, lamp holders, ceiling roses, water heater switches, thermostats and elements.
Repairing light fittings.
Moving, repairing or replacing flexible cords connected to permanently connected outlets or ceiling roses."

Clearly it doesn’t specifically mention "transformers" but is a Transformer not close to a "Thermostat - yes I know they are different. Is removing the halogen tail any different from replacing a "lamp holder"?

When the electrician came around to check things all I could say was the light bulbs keep blowing. Next time I hope I can say a bit more!

Edit. As an aside this particular light fitting wasn't blowing bulbs when the electrician came around - it was a our standard 100w downlights that kept blowing.

minimoke

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Reply # 923499 29-Oct-2013 12:29

mclean: Just some observations: The fitting in the photo in the OP looks like it has overheated. Also it looks corroded. Overheating is usually caused by poor connections. If your other fittings look like that you should get an electrician to replace them.

If the transformer has built in short-circuit protection then a fault on the 12V side is unlikely to trip the upstream fuse/MCB.

It has dfintly overheated - its melted the plastic right off teh wire - so teh two wires are nw touching.

The light fitting is above the kitchen sink - perhaps there is a bit more moisture up there than I thought.

gregmcc

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Reply # 923503 29-Oct-2013 12:41

The 12v side of the transformer would be ok for a non-electrician to work on, but as you said the transformer has been changed, this would mean that work on the 240v was done. BTW transformer is nothing like a thermostat other than they both start with a 'T', and been perfectly honest if you don't know the difference this is a very good reason to not be doing electrical work

As an electrician (yes registered and a current practising lisence) working in the industrial area, it seems to me that the transformer is severaly overloaded, it may be a 150VA transformer but running it with 150W of lights is it's maximum load, general rule, 1 transformer for each light, the next problem may be the type of transformer you are using, you did say it is on a dimmer?, what kind of a dimmer -trailing edge? leading edge?, now what kind of transformer, wire wound, electronic - if electronic is it a dimmable one? if dimmable, is it the right one for the dimmer you have? Again some are universal, some require a leading edge dimmer or a trailing edge dimmer.

There are lots of things to factor in here that the average person or even the average domestic electrician doesn't know about.

The best starting point is the one light - one transformer rule, make sure the transformer is bigger than the actual load, 50w bulb, 75VA transformer, make sure it's the right transformer for the dimmer.

LED lights may be the way to go, although initally expensive, they require a special driver transformer to be dimmable, but they use way less power and several can be used off one transformer depending on exactly what you get.

Don't rely on the consumer build website for advise, www.ewrb.govt.nz, has a home owners PDF you can download which tells you what you are allowed to do.

You did say that one of the problems is the 100w downlights keep on blowing, #1 reason too hot, a 100w bulb for a down light is too big, 75w, #2 reason, don't buy the cheap bulbs, they are useless, spend a extra, buy a quality one, put a CFL or LED bulb in instead.

minimoke

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Reply # 923517 29-Oct-2013 12:56

Cloudconnext: Take a different angle, dump the transformer, dump the halogen lamps. Filament lamps are end-life Tech IMHO.

Install 9 watt LED 230v down-lights, similar light output in lumens, but much lower ongoing power consumption.

....

Id quite like to replace (I have a couple of LEDS elsewhere and they have run with no problems) but I have two 3 gimbal fittings in the kitchen, The cost of fittings and gib repairs / painting are prohibitive at the moment. May look at it again when EQC comes around.

minimoke

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Reply # 923543 29-Oct-2013 13:53

gregmcc:

The 12v side of the transformer would be ok for a non-electrician to work on, but as you said the transformer has been changed, this would mean that work on the 240v was done. BTW transformer is nothing like a thermostat other than they both start with a 'T', and been perfectly honest if you don't know the difference this is a very good reason to not be doing electrical work

As an electrician (yes registered and a current practising lisence) working in the industrial area, it seems to me that the transformer is severaly overloaded, it may be a 150VA transformer but running it with 150W of lights is it's maximum load, general rule, 1 transformer for each light, the next problem may be the type of transformer you are using, you did say it is on a dimmer?, what kind of a dimmer -trailing edge? leading edge?, now what kind of transformer, wire wound, electronic - if electronic is it a dimmable one? if dimmable, is it the right one for the dimmer you have? Again some are universal, some require a leading edge dimmer or a trailing edge dimmer.

There are lots of things to factor in here that the average person or even the average domestic electrician doesn't know about.

The best starting point is the one light - one transformer rule, make sure the transformer is bigger than the actual load, 50w bulb, 75VA transformer, make sure it's the right transformer for the dimmer.

LED lights may be the way to go, although initally expensive, they require a special driver transformer to be dimmable, but they use way less power and several can be used off one transformer depending on exactly what you get.

Don't rely on the consumer build website for advise, www.ewrb.govt.nz, has a home owners PDF you can download which tells you what you are allowed to do.

You did say that one of the problems is the 100w downlights keep on blowing, #1 reason too hot, a 100w bulb for a down light is too big, 75w, #2 reason, don't buy the cheap bulbs, they are useless, spend a extra, buy a quality one, put a CFL or LED bulb in instead.

I couldn't find the homeowner guide on that website but a link pointed me to the MED wbsite which has a guide that mentions recessed downlights and Auxiliary equipment which does specifically include transformers. It says “You must install and maintain recessed light fittings and their auxiliary equipment in such a way that they are electrically safe, and to prevent:
(a) The risk of fire;
(b) Damage to your home; or
(c) Excessive heat transferred being to the building elements.

Given I know the difference between a transformer and a thermostat I reckon I can swap transformers over. Excepting of course where there is a problem.

So heres a frustration as a consumer. Lighting shops sell these three gimball fittings and single transformers that will apparentyl take the 3 x 50w halogens. And they sell downlights rated to 100w. No mention of heat as a potential issue - itehr than make sure there are no batts over teh fiting and keeping it clear.

But heat sounds like something to think about with my other lights. I think I am using standard 240V 100w bulbs. Can you suggest what brands I should be looking out for. The 200w halogens I've been using in other fittings are Marexim.

I did start looking at the LED thread but was able to work out easily what to replace a standard 100w downlight with. Given my lights are only a few years old and I would need to replace 16 for starters the cost was looking prohibitive so I didn't delve further. Perhasp I should go back to that thread.

mclean

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Reply # 923547 29-Oct-2013 14:08

The light fitting is above the kitchen sink - perhaps there is a bit more moisture up there than I thought.

Probably explains the corrosion. Lights over the sink (or anywhere in the kitchen) should be "closed" type, that is they should have a CA or CS rating, so air can't go through. Otherwise they work as a moisture extraction system, which is not good for them. It's a code requirement, so your sparky will know.

McLean

minimoke

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Reply # 923569 29-Oct-2013 14:42

mclean:
The light fitting is above the kitchen sink - perhaps there is a bit more moisture up there than I thought.

Probably explains the corrosion. Lights over the sink (or anywhere in the kitchen) should be "closed" type, that is they should have a CA or CS rating, so air can't go through. Otherwise they work as a moisture extraction system, which is not good for them. It's a code requirement, so your sparky will know.

Thanks. Thats interesting. The sparky who put them in originally never mentioned it. And the guy that came round recently didn't mention it either.

I think from this thread I have now learnt:
Moisture from sink cause moisture in light fitting. Moisture in light fitting causes halogen bulb pins / socket to corrode and deteriorate. Pins/ Socket that deteriorate cause problem with power supply. Problem with power supply causes heating which in turn causes plastic to melt which causes wires to touch and the resulting short causes the transformer to blow.

A logical diagnostic path?

gregmcc

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Reply # 923576 29-Oct-2013 14:49

minimoke:
I couldn't find the homeowner guide on that website but a link pointed me to the MED wbsite which has a guide that mentions recessed downlights and Auxiliary equipment which does specifically include transformers. It says “You must install and maintain recessed light fittings and their auxiliary equipment in such a way that they are electrically safe, and to prevent:
(a) The risk of fire;
(b) Damage to your home; or
(c) Excessive heat transferred being to the building elements.

Given I know the difference between a transformer and a thermostat I reckon I can swap transformers over. Excepting of course where there is a problem.

So heres a frustration as a consumer. Lighting shops sell these three gimball fittings and single transformers that will apparentyl take the 3 x 50w halogens. And they sell downlights rated to 100w. No mention of heat as a potential issue - itehr than make sure there are no batts over teh fiting and keeping it clear.

But heat sounds like something to think about with my other lights. I think I am using standard 240V 100w bulbs. Can you suggest what brands I should be looking out for. The 200w halogens I've been using in other fittings are Marexim.

I did start looking at the LED thread but was able to work out easily what to replace a standard 100w downlight with. Given my lights are only a few years old and I would need to replace 16 for starters the cost was looking prohibitive so I didn't delve further. Perhasp I should go back to that thread.

The lighting shops will sell whatever they can get away with, although they are required to have each type of fitting tested to make sure they are compliant with NZ standards. I wouldn't rely on the shops giving sound advice about what size bulbs should go in them, they are sales droids and do not have any technical knowledge.

As far as bulbs, stay away from anything at the likes of Bunnings/mitre 10/supermarket, go to an electrical wholesaler, such as JA Russell/Stewarts/Ideal/Cory's and buy from there, make sure they are smaller than the rated wattage of the light fitting.

mclean

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Reply # 923648 29-Oct-2013 16:29

Moisture from sink cause moisture in light fitting. Moisture in light fitting causes halogen bulb pins / socket to corrode and deteriorate. Pins/ Socket that deteriorate cause problem with power supply. Problem with power supply causes heating which in turn causes plastic to melt which causes wires to touch and the resulting short causes the transformer to blow.

A logical diagnostic path?

Not the power supply - a poor contact is all you need to get overheating. I don't know why the transformers failed, but the short circuits will have given them a good test! With electricity it's sometimes better for things to fail.

McLean

minimoke

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Reply # 924394 30-Oct-2013 19:47

Having a closer look at the bulbs, on one the pins are decidedly brown looking rather than shiny. Another bulbs pins are in the middle of dull and shiny.

So I've been down to the local electrical supply shop (not the lighting one) and got me 3 new 50w halogens. The guy happily sold me a 150w transformer for the bulbs knowing what I was going to do with them. And while I was at it I got three new tails.

Wired the transformer in - little red light glowing nothing blew all good.

Replaced the 3 tails. Power back on red light on all good.

Replaced bulb one. The fit into the tail was much firmer than the bulb I had pulled out of the old tail. Powered up all good.

Replaced second bulb - same process all good

Replaced third bulb, still a very firm fit into tail. Powered up and all good.

So now I have a light fitting with three lights merrily glowing away and I'm a happy camper.

Thanks for all your help seems like problem solved.

Next job - check out LED's

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