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Old 26th Jan 2019, 8:10 pm   #1
Lancs Lad
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Default A Quick Question about Halogen to LED conversion

I have a halogen downlighter over my back door. It contains a 50 watt dichroic bulb, powered by a 12 volt transformer.

I want to buy a replacement LED bulb that will fit straight in, but Google is so confusing!

It's just a dichroic reflector bulb with the two pins coming out of the base.

I've been trawling Amazon all afternoon, getting more and more confused.

Someone! Please tell me just what exactly I need to order!
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Old 26th Jan 2019, 8:39 pm   #2
G4YVM David
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Default Re: A Quick Question.

https://www.ebay.co.uk/itm/4x-Philip...gAAOSws0pcRLdY
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Old 26th Jan 2019, 9:10 pm   #3
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Default Re: A Quick Question.

Hi Peter,
The 12V transformers used to drive 50W halogen lamps usually have a rating of 20W to 60W. They generally don't like running loads less that 20W, so with the LED at only 8.2W, the transformer will just shut down.

Therefore you will also need to change the transformer as well to a proper LED type.

Hope that helps
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Old 26th Jan 2019, 9:12 pm   #4
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Default Re: A Quick Question.

Thankyou, David, for your reply. I really appreciate it.

I know I'm probably being over-cautious (and, yes I know, annoying) but are they 12 volt ones?

What should I actually type into Google that will connect me to the right LED bulb? MR...what?

Sorry if I'm being a bit thick - it's been a long day!

Many thanks.
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Old 26th Jan 2019, 9:14 pm   #5
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Default Re: A Quick Question.

Thanks, Nick! Really good to hear from you.

But that's what I was hoping NOT to hear!

Surely I can replace the bulb without having to replace the transformer aswell!

Can I? Surely it's not impossible!
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Last edited by Lancs Lad; 26th Jan 2019 at 9:23 pm. Reason: Despair!
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Old 26th Jan 2019, 9:27 pm   #6
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Default Re: A Quick Question about Halogen to LED conversion

Changed my kitchen halogens for LEDs, would they work? No!
Ended up changing the power supply as well.
Gives a good light, now!

Alan
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Old 26th Jan 2019, 9:42 pm   #7
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Default Re: A Quick Question.

Quote:
Originally Posted by Lancs Lad View Post
What should I actually type into Google that will connect me to the right LED bulb? MR...what?
The 12v ones I’ve been using are known as MR16, and can be had in various forms of LED.

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Old 26th Jan 2019, 9:52 pm   #8
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Default Re: A Quick Question about Halogen to LED conversion

Interesting to see my thread title has been amended!

Just wondering if it makes any difference that the transformer is a really heavy 'brick' type, and not one of those lightweight electronic ones? It weighs about as much as a brick aswell! Are they more tolerant?

I just want to change the bulb - not the whole installation!
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Old 26th Jan 2019, 9:55 pm   #9
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Default Re: A Quick Question.

Quote:
Originally Posted by Lancs Lad View Post
Surely I can replace the bulb without having to replace the transformer aswell!
Can I? Surely it's not impossible!
Sadly not! At the time halogens were popular, 20W ones were the lowest power and 50W ones sort of became the standard. Hideously inefficient things that generated far too much heat.
It became the norm to run one lamp from one electronic transformer poked up into the ceiling void, so a separate transformer for each light fitting.
These were designed to supply a constant 12V, unrectified AC at high frequency.

The LED replacements will give the same light output but at a fraction of the power, so a 50W equivalent only consumes 8.2W! Consequently, an electronic transformer with a minimum rating of 20W, won't drive an 8.2W LED.

Different transformers behave differently. Some won't start at all, some will just pulse on and off, others will work for a short time and then shut down.

So, assuming it's an electronic transformer, replacement is the only option!

Cheers
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Old 26th Jan 2019, 10:02 pm   #10
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Default Re: A Quick Question about Halogen to LED conversion

If it is a heavy 'brick', it is probably a conventional transformer and pretty old!
The LED's I've come across have inbuilt switch mode power supplies so will probably work ok with this sort of transformer.

You will just have to try one and see. A conventional transformer won't have a minimum load requirement so shouldn't mind the much lower load of the LED.

No guarantees though - LED's are designed to be driven from the correct power supply!!

Cheers
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Old 26th Jan 2019, 10:17 pm   #11
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Default Re: A Quick Question about Halogen to LED conversion

Our kitchen has multiple 12V 20W halogen spots fed from conventional wound transformers. I've had no problem changing them to LED equivalents.

Our family bathroom has multiple 12V 50W halogen spots, each one fed from one of those common yellow electronic transformers. These too I'm progressively changing to the LED equivalents as they expire. Again, despite using electronic transformers, the changeover has been totally trouble free.

That's just my personal experience - I guess that some electronic 'transformers' may behave differently.

Martin
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Old 26th Jan 2019, 10:51 pm   #12
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Default Re: A Quick Question about Halogen to LED conversion

Hi Martin. I've got a Planetarium ceiling as well. I'm sympathetic to the lad from Blackburn's frustration and my research was confusing as well but different people reported different experiences. You'll have to just "suck it and see" L Lad. Our first mistake in the south was to buy replacement 50w 12v Halogens that blew two Transformers designed for 20w.

BTW I've just a couple of 20w Halogens operating in the kitchen but before I think about replacing the entire night sky I've re-cycled a trendy three light fitting [those 35w halogens with substantial pins] from my daughters bedroom minimum legal height ceilng. This was a pain as she leaves the light on and in the summer especially, we didn't need the heat generated either.

I spotted a simple dome light fitting in a skip down the road which she recovered. Two Meccano brackets and it looks great with a 28w = 90 low energy bulb. The kitchen, however, has a very high ceiling and we have lots of 35w bulbs left. The central ceiling lights [separately switched] have been blanked off and the bedroom light is operational there now. More light, useful heat and it's not on all the time so relatively economic domestic harmony. A win/win until I ultimately replace the lot or come up with something else!

Dave W

Last edited by dave walsh; 26th Jan 2019 at 10:57 pm.
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Old 26th Jan 2019, 10:57 pm   #13
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Default Re: A Quick Question about Halogen to LED conversion

In my experience it’s very hit and miss. I would say 25% of the time they will work . As an electrician I often get phone calls saying will you come and check my spot lights they stopped working. First thing I say have you changed the lamp ,yes they say then I ask is it a LED and yes .Straight away that’s the reason .
It’s not worth changing the transformer for a LED driver. Scrap the whole fitting and start again Andy
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Old 26th Jan 2019, 11:10 pm   #14
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Default Re: A Quick Question about Halogen to LED conversion

With a load of radio gear in the house, I vetoed 'electronic transformers' and used one iron transformer per lamp back in the halogen days. Funnily enough, it just works with LEDs and the HF receivers are OK.

David
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Old 26th Jan 2019, 11:22 pm   #15
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Default Re: A Quick Question about Halogen to LED conversion

I changed 3 MR16 halogen bulbs for LEDs but the electronic transformer didn't like it with the LEDs flickering. Changing one LED back to halogen cured the problem but I swapped the electronic transformer for a conventional iron one driving the 3 LEDs. Problem solved, no flickering.

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Old 26th Jan 2019, 11:33 pm   #16
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Default Re: A Quick Question about Halogen to LED conversion

Our ceiling three halogen spot fittings, quite elderly but I don't know what sort of transformers, made nasty noises when three LEDs were fitted. I left one halogen in each one and they have been fine. Fortunately there is a good colour and light output match so the one odd bulb doesn't show unless you look right at it.
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Old 26th Jan 2019, 11:44 pm   #17
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Default Re: A Quick Question about Halogen to LED conversion

Thanks for all your informed replies.

But, oh dear! I'm no wiser what to order!

It's a conundrum, isn't it?
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Old 27th Jan 2019, 12:11 am   #18
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Default Re: A Quick Question about Halogen to LED conversion

You said that the transformer is a heavy brick.
It is most likely to be an iron and copper transformer and will power up to enough LEDs to light several rooms.
It will also power a single LED too.
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Old 27th Jan 2019, 5:21 am   #19
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Default Re: A Quick Question about Halogen to LED conversion

If the transformer is a conventional copper/iron unit as sounds very likely than any standard retrofit LED lamp will be fine.
The LED will have a much lower wattage than the halogen lamp, but that is of no consequence.

If the transformer is an electronic type then it wont reliably work any standard LED lamp. Electronic transformers usually have a minimum load for correct operation, this is often 20 watts and they wont therefore work an LED lamp that uses only a handful of watts.
And even if the transformer DOES accept such a small load, the lamp may be killed by the very high frequency output.

As the existing transformer is reported to be large and heavy it is almost certainly a copper/iron type and therefore suitable for LED lamps.

Electronic transformers intended for halogen lamps need to be replaced with a DC power supply intended for LED lamps, these are cheap and are widely available.

A halogen lamp will operate from AC at line frequency, or from high frequency AC or from DC.

An LED retrofit lamp will operate from line frequency AC or from DC but wont work reliably or at all from high frequency AC.

The voltage must be correct, but virtually all such lamps are 12 volts. Other voltages do exist but are very rare and almost unknown domestically.
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Old 27th Jan 2019, 9:40 am   #20
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Default Re: A Quick Question about Halogen to LED conversion

Option 1. Change the bulbs for MR16 LED and see what happens. In the event that they flicker, you have two more options:

2. Rewire so that the transformer feeds all the LEDs instead of just the one.

3. Rip the lot out and change to GU10 holders and new LED bulbs. They look almost identical once installed, but need no transformer. This ended up being my solution and was quick and easy. Not too expensive either even though I have something like 30 of them here!

Recommend going for "cool white" rather than warm.
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