Retrofit house with LEDs

[flippineck]

Moved house, and found that a few rooms have a bunch of 12v incandescent halogen reflector bulbs fitted in the ceilings.

Two rooms have six 35W lamps, another has five 35W lamps, another has 5 in it's ceiling.

Have been going round replacing all these halogens with LED equivalents & so far they all work fine.

I got to thinking though, with all the lamps coming out being fairly discoloured & the house being 30-odd years old, these lamps are all probably powered up by a few fairly rudimentary, 90's vintage wirewound AC lighting transformers, hidden up in the ceiling space?

From an economy point of view is it worthwhile my replacing the old transformers with more modern, purpose-designed LED driver units? Some googling seemed to reveal that trying to run LED bulbs on older 12VAC transformers designed primarily for feeding halogen lamps, can result in overall economy not being as good as one might hope from changing to LED lamps.

 

[Bluejets]

Economy would be in a matter of cents per year, more important would be that "some" or rather "most" mr16 led bulbs require the appropriate driver for correct operation and advertised lifespan.
Most electricians will know this and supply the correct matching equipment. Hardware stores in comparison, have no such comittment.
As for position of the driver, be it old install or new, should be within a meter or less of the fitting.
Also be aware that in many civilised countries, there are strict installation requirements on both the old halogen and the new led type drivers.
Incorrect installation could result in loss of any insurance cover in event of a fire.

 

[flippineck]

Used to be up to speed as an installation sparkie but that was a long time ago, it was 16th edition in the UK when I was doing it, think they're up to 18th edition now.. I left the electrical installation trade to become a comms engineer around the time LEDs were just beginning to make the earliest appearances. So I'd most likely call in someone with current regs to do the work. I was wondering if I was largely wasting my time changing all these lamps though, without attending to what's powering them!

 

[Bluejets]

As I said above, it would be in your best interest as far as lamp life and possibly any warranty, to ensure the correct driver is used with the LEDs.

I have seen even late model LEDs fitted to electronic LED driver units that are highly incompatible.

As you have not supplied any info there, then impossible to say.
All I can quote is that "some" early led bulbs ( usually array type) would run all day no worries on the w/w transformers.

 

[dave9]

There are MR16 bulbs with their own regulation circuit inside. They typically specify they are capable of a wide input voltage range, and are never those corn-row looking bulbs with a zillion LEDs on PCBs soldered together.

You are correct that you lose some efficiency continuing to use the lossy transformers, but only you know how much loss you will incur over time, based on hours per day use.

It's not a waste of time to change only the bulbs to LED. Your (MR16?) 35W bulbs are probably around 500 lumens and an LED replacement would be around 5W. Your transformers might be inefficient but at much lower load, there is lower loss too. Rough guesstimation is you'll end up using 1/7th as much power by changing the bulbs alone to LED, assuming you get "35W equivalent", 5W LED bulbs.

Getting a pro in to redo your lighting could end up more expensive. Since you already have the bulbs, see what their input voltage range is specified for. You don't necessarily need a proper LED driver if your bulbs are self regulating and just need the correct voltage. Practically all of them can run off DC because they're converting the AC to DC anyway, so you could just have a low voltage DC switchmode PSU (voltage regulating) for however many there are on each circuit. You can find these by simply searching for MR16 PSU and adding up how many amps your lights will consume, and adding some margin for a cooler running PSU.

Such a driver doesn't typically have a short distance limit since the regulation is at the bulb. You just need wiring capable of handling the load without too much drop which you should already have because it was handling 35W bulbs already.

 

[(*steve*)]

I've characterized a number of 12V LED bulbs for my own nefarious purposes and I have found that they may have inbuilt buck or boost regulators.

Those with boost regulators have an unfortunate failure mode when the input voltage rises too high.

Depending on what that voltage is, if they have a boost regulator, you need to be VERY sure that your input voltage doesn't rise above the output voltage. Typically it's higher than 18V, but I've had one as low as 21V (from memory). Those may have a short life if they are used with a 12V transformer designed for higher current draw. Once you swap to LEDs the output voltage may float higher by a couple of volts.

I simply connect a bulb to my variable power supply and set it for ~12V DC. Check the current, then drop the voltage to see what happens at lower voltages. After you've done that -- wind the voltage up slowly. For most "12V" bulbs, the current will drop as the input voltage rises (they should exhibit nearly constant power consumption). However if you find that it begins to rise again -- you most likely have a boost regulator and you've found the "never exceed" voltage. Naturally yo can damage these bulbs with excessive voltage, but reducing the voltage can be really hard on them too.

 

[flippineck]

Best info I can find for the spot bulbs I'm using. Taken from several sources, accurate detailed info seems to be hard to find.

ASDA energy saver LED MR16 5.2W GU5.3
Supermarket code 5 054781 983262

Made in China for ASDA stores ltd

YKMR16B3-5.2W
Voltage DC/AC 12V
Current 850mA
Power 5.2W
PF >0.5
2700K
GU5.3
Ra ≥80
345lm
36° Beam angle
Operating Frequency: 50/60Hz
Lumen Maintenance Factor ≥0.7
Non dimmable

One manufacturer states "Designed specifically for replacement of inefficient quartz
halogen lamps with an environmentally safe, efficient low voltage lamp"

 

[dave9]

I would do as Steve suggested, measure their current with a variable voltage PSU, or (at a risk to the bulbs) pull all the 35W bulbs and measure current at the existing bulb socket using a makeshift pin header with leads to one of the LED bulbs. With all the old bulbs pulled you should have max voltage coming from the transformer.

Work quickly measuring current in case it's quite high, then if it is not crazy high, I'd install the rest of the LED bulbs in that circuit and measure again.

As far as using a buck or boost regulator, if you can get the bulb lens off to see the circuit board trace routing, or make an educated guess based on the # of LEDs, you might be able to figure out if it's using a buck or boost regulation circuit.

For example if it has only 3 LEDs, it's got to be buck because their highest possible sum forward voltage is lower than the spec'd input voltage. If it has an odd # of LEDs above 3 it's probably boost. If an even # of LEDs above 3 it could be either but as Steve mentioned a boost will lower current as input voltage rises.

 

[(*steve*)]

as Steve mentioned a boost will lower current as input voltage rises

Either buck or boost will do that.

A linear constant current source will exhibit a constant current.

 

[dave9]

^ I agree in an ideal circuit, but some buck circuits are pretty crude and their output power goes down with input voltage, so you may not see near the same level of current reduction. IMO many manufacturers are already hitting a price floor on how cheaply they can make their bulbs.

 

[flippineck]

One popped (whilst being driven by one of the original incandescent driver transformers) so I decided to open it up. Sorry about the quality, struggling with a very old phone cam here. Apologies for the bottle of clove oil, I've toothache :-(

Hoping that you guys might be able to tell enough from what's visible, what I should buy at the electrical wholesalers tomorrow. They sell 12v constant voltage LED driver modules, 240VAC in, nominally 12VDC out.. I'm hoping these might suffice given that the bulbs advertise a specific requirement for that voltage.. the little PCB inside would seem at a cursory glance to be complex enough to perhaps perform a built-in current controlling function to the actual 6 LEDs themselves?

 

[flippineck]

8-pin DIL chip seems to be marked
02521EG or 0Z5Z1EG ( possibly EGM)
CJ2J7F.20

what looks like 4 fat diodes are 5554B

inductor on one side marked 680

 

[dave9]

Yes it looks like a current regulating circuit in the bulb so a 220VAC to 12VDC supply with ample current margin should work.

 

[flippineck]

Thanks. I'll try just one 12VDC supply to start with & maybe get the multimeter on it to see what voltages and currents are where.

It's actually looking like a lot of the existing ceiling transformers are well due for replacement anyway - found more than a couple of the seemingly blown incandescents in the house are actually fine, with the transformers behind them being discoloured & crispy with healthy mains in, 0V out. A fair proportion of the 'good' supplies have a very aged appearance.too.

Out of interest.. What would be likely to happen if someone fitted a constant voltage LED driver supply rated for say 6W, then someone else at a later date tried to replace the 5.2W LED bulb with a 35W halogen? I guess it depends on the individual design of the driver unit but do these things tend to have a graceful overcurrent shutdown mode?

 

[dave9]

I would not assume they have a graceful overcurrent shutdown. You could ask the manufacturer if you can get a hold of them, or size the supply to handle 35W/bulb, or put fuses on each run to the sockets, or put a sticker in the socket that reads max 6W (or whatever the max per bulb might be based on PSU capacity minus a margin, divided by # of bulbs), or a combination of those latter 3. LED bulbs run cooler but a sticker might still degrade from heat and fall out at a later date. Maybe it could be etched or engraved or ?? instead of a sticker.