maximum amount of LED drivers on one circuit?

15 Aug 2013
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United Kingdom

I've just changed over to LED bulbs on my Kitchen downlights and have a few questions.

There was a 4-gang switch which I have now changed over to a 4-gang trailing edge dimmer switch.

On that 4 gang switch:

1 knob operates 7 x MR11 bulbs and 6 x MR16 bulbs (13 transformers)
1 knob operates 5 x MR16 bulbs. (5 transformers)
1 knob operates 2 x MR16 bulbs - which I'm keeping as halogen as they're rarely used.
1 knob operates an unknown source (there's a blanking plate by the back door so I assume it goes to that).

Firstly, after swapping the bulbs to LED, all of the MR16's light up, but there's some flicker + buzz + varying brightness. Secondly, none of the MR11 bulbs lit up so I've changed over their halogen transformers to Varilight LT YT50's. The MR11's are now all working.

I assume I need to change all of the halogen transformers that remain on the MR16 bulbs to LED drivers to get them functioning correctly?

My other question is, is there a limit to the amount of drivers I can have running on each circuit? Currently each bulb runs off it's own transformer and whilst it'll cost more in drivers, this is probably the way I'll keep it as everything's hidden up in the ceiling.

Should I just get another 11 Varilight LT YT50's and changed the remaining halogen transformers?

Thank you!
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Number one you need to use the word electronic if the units are electronic, I know some thing which transforms 230 volt to 12 volt English wise is a transformer, but electrically a transformer is just the wire wound bit, and even when it does not transform but only isolates we call it a transformer, and when it has other electronic components as well we call it an electronic transformer, or a switch mode power supply, and there is a world of difference.

So MR16 refers to multifaceted 16/8th of an inch, so it does not matter if 12 volt or 230 volt with a GU10 connection, G5.3 or even E14 screw they are still MR16, and technically very few LED lights are MR16 as they don't have a reflector, OK we know what most people mean when they say MR16 but it is so easy to make errors.

So most G5.3 lamps to replace the quartz MR16 I have seen are for use on an AC supply, and often have 50 Hz marked on them, so need a toroidal lighting transformer rather than an electronic lighting transformer. The problem with all transformers is in-rush but toroidal lighting transformer seem to be worse than electronic transformers, so around 300 VA (or watts) is about the limit for a single switch, the switch could likely take more, most are rated at 20 amp, but the in-rush can trip some breakers, so by separating this reduces the in-rush.

In the main the LED replacement for the 12 volt MR16 lamp works A1 with a toroidal lighting transformer, only problem is with electronic transformers or switch mode power supplies where there is a minimum as well as maximum output. Also because the switch mode device works in the kHz range it can with a diode become a little radio transmitter, but if the unit says 0 - 100 VA then likely it will work OK, but if it says 20 - 100 VA then the LED lamps are likely not going to exceed 20 VA so will fail.

With quartz lamps you could not use dimmers, it would cause the tungsten to deposit on the quartz and make them go black and fail early, LED can be dimmed but needs to again be a dimmer designed to work with LED lamps, and really needs to be type that uses a neutral, and with the UK often no neutral at the switch, so it is a lottery as to if they will work with any electronic switch which does not use a neutral, even if not a dimmer switch.

Driver like transformer seems to have changed meanings, all LED lights need a driver, as an LED will burn its self out on thermal run away without one, they are current sensitive devices and DC, but with most spot light packages the driver is built into the lamp, as is the rectifier so it can work on AC or DC can be either way around, so most the units called drivers are in fact a simple 12 volt DC power supply, but there are some real drivers as well, so you have to read the label so if it says 320 mA 6 - 50 volt it is a true driver and all LED's are connected in series, but if it says 12 volt 0 - 5 amp it is a power supply designed to power lamps with built in drivers.

The G5.3 package is also used in boats and caravans, and the lamp is often DC only with a voltage 10 - 30 volt, they fit the same holders and look the same as the 50 Hz lamps but are normally more expensive as they have a true switch mode driver built in.

By this point I expect your eyes are starting to glaze over, so the cure is easy as @EFLImpudence says, use 230 volt, in the main 12 volt was used as the filament was thicker so lamps lasted longer, once you move to LED except may be in a bath room you don't need extra low voltage (under 50 volt AC) low voltage (under 1000 volt AC) works just as well, so if you really want little spot lights everywhere making the room look like a planetarium, then use 230 volt.

But if you look on this page you will see most modern transformers even the electronic type do go down to 0 output of the 9 shown on that page, only one starts at 20 VA. So you need to read what it says on the existing units, and actually say what you have.

My MR16 12 volt G5.3 lights run off a unit like this
and it was just a simple case of swapping quartz to LED did not have to change anything.
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Ok, thanks for all the input, appreciate the info ericmark. Looks like the consensus would be go to 240V GU10's.

So my next question is:

Rather than replace the whole fire rated downlight (, is it OK to swap out the MR16 Lamp holder and replace with a GU10 lamp holder. Or are there any other implications involved?

Thanks again!
The problem is that the fittings were designed to be safe when there was only 12V present. You are now introducing 230V and become responsible for the design. I suggest you replace them with units guaranteed to be safe.
I was going to say that it depends on the lamp holder as they're both 50mm diameter, but not necessarily the same size overall. It's not the sort of thing I would normally do as the 230v fitting will have a built in connector and cable strain relief for T&E.

If replacing the whole downlight it's worth double checking the hole diameter as they can vary.

Also, do you really need dimmers? I only ask as they cause more problems with flickering lights than they're worth.
So my next question is it OK to swap out the MR16 lamp holder and replace with a GU10 lamp holder.

Meaningless question. MR16 is the size of the lamp in eighths of an inch. MR16 lamps come with GU10, GU5.3, SES, SBC bases among others.
I just classed it as a DIY question. Nothing wrong in general. It's just a will it fit question. The issue really is whether it is safe to do so...
I have some MR16 pods which have a bayonet corrector into the bit in the ceiling and I would not be happy with over 24 volt on that system, the same applies to the two catenary wires strung across the room, the M5.3 holder can take 230 volt bulbs with no charge, but since in this country we tend to use 12 volt, there is a very real risk some one will fit a 12 volt bulb into a 230 volt fitting, I thought my stock of 110 volt bulbs was hidden and my wife would never find them, same with the Son bulb, but she did, and with the Son bulb there was a big bang.

So yes you may be able to change the holder, but is it worth it?

The other thing I have found, is not only does lumens matter but also area, use a 2D lamp at 1000 lumen and it lights the room far better than a MR16 lamp at 1000 lumen. I know you can get gx53 lamps, but in the main with LED it seems you have to get lamps where you can't change the bulb, these
are larger diameter to the MR16 replacements there are many more, and tend in general to light the area better, size does matter.
there is a very real risk some one will fit a 12 volt bulb into a 230 volt fitting

It's funny you should say that. Only a few weeks ago I had a guy with a house full of 12v downlights who decided he wanted to replace them all with GU10's. He called me in after having replaced the ones in his bedroom to find that they didn't work. Turned out that he had ran them from the 12v drivers. I just said to him that it was a good job it wasn't the other way around :D


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