Halogen to LED retrofit. Proper transformer?

Subject: Low voltage retrofit electronic transformer for MR16 halogen home potlight system, moving to LED

I’m a homeowner, small retail sort of sale. Canada, Ontario, between Toronto and Barrie.

I have a need to replace magnetic 12vac transformer service for 30 or more potlights. Installed halogen, gone to LED, in 2, 3, and 4 bulb sets per switch.

Not a big sale, and I’m having real problem finding source for proper no-load electronic transformers. Had the maker of the old magnetic ones, in Montreal, recommend Hatch, but they don’t respond to queries.

Thinking of putting up to 60 watt unit, dimming not required but desirable, in line to set of up to 4 bulbs, 7 watt each, MR16. Line is Romex 16 or 14 gauge. Up to 20 foot run from new transformer to bulbs. Assuming line loss perhaps .07 volt per foot. Yes?

Considering Hatch RS-12-60M, or LTF 60 watt no load at the moment. Or should I find something that puts out 14 volts, say, and have 12 volts at the bulbs?

Do you sell/ship to Canada? Do you deal with small retail guys like myself?

Does this approach make sense? Do you have product that would accomplish what I need? How expensive?

Hello RetroLED39.

If you’re looking for something comparable to Hatch RS-12-60M, take a look at 1866-1559-ND.

Of course, your voltage/amperage requirements will change depending on how many LEDs you are stringing together and what the requirements of those LEDs are. If you know the current requirements of the LEDs we can look at a constant current current driver that may give you a bit more flexibility.

We do ship to Canada (the part link I provided should be to our Canadian site) and pricing should be listed there. And we are happy to provide products and support to all customer!


Presumably, these replacement lamps are of a type designed for backwards compatibility with existing installations. Assuming this is the case and that the existing unit has not failed, the need for replacement is not immediately apparent. If the existing unit works, I’d suggest leaving it in place.

More like 0.02V/foot, assuming 16AWG copper and the 28W load mentioned. Doesn’t really matter as much in context of LED loads however, as LED retrofit lamps are internally regulated by necessity.

Again, the rationale for replacement is not apparent, though without documentation for the existing unit it’s difficult to offer a fully informed opinion. The Hatch unit mentioned appears to be an AC-output device, catering toward supply of incandescent lamps and in fact rather a very different animal relative to the 1866-1559-ND Jerry suggested. (It would appear that understandings of the context of the application may differ.)

As mentioned, small orders and shipping to Canada are both routine matters for us here at DK. Absent further information indicating otherwise though, I’d suggest that using your existing equipment is perhaps the best option at this time.

Thanks for getting back. Ceiling pot light arrays. Sets of 2, 3, and 4. Going to MR16 7 watt LED from halogen.

Run of romex 14 about 20 feet to each.

Hope to avoid replacing each and every magnetic 12 volt transformer in each pot. Will catch line after switch. Currently, no dimmers, but good if it can accommodate.

Line loss voltage issues? I hear .07 volt per foot. ?


Thanks, Rick. Existing units have failed in two sets, during local power out and surge. Montreal mfgr of magnetic transformer says not appropriate for LED, specially 7 watt. Rest likely to fail. Inefficient and shorten bulb life. Recommended Hatch as supplier.

Copy of response to Jerry Sturre:

Thanks for getting back. Ceiling pot light arrays. Sets of 2, 3, and 4. Going to MR16 7 watt LED from halogen.

Run of romex 14 about 20 feet to each.

Hope to avoid replacing each and every magnetic 12 volt transformer in each pot. Will catch line after switch. Currently, no dimmers, but good if it can accommodate.

Line loss voltage issues? I hear .07 volt per foot. ?


I’d gently lift an eyebrow toward characterizations of magnetic transformers as “inefficient” but could easily understand how they might permit ugliness on the power grid to pass through and cause harm to the relatively fragile electronics in a drop-in LED replacement lamp.

If I’m interpreting correctly (not always the case) you’re speaking here of deleting the voltage conversion at the fixture level, performing the 120->12 conversion between the AC line and your existing switches, and repurposing the existing 120V wiring between switch and fixture as low-voltage wiring.

Could such a scheme work? Likely so. Would you run afoul of local regulations and electrical codes in so doing? Probably. Could you do it anyway without gross risk to persons and property? Maybe. The devil’s in the details.

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Hi Jerry. Appreciate your feedback.

Tried the link to part number, per your suggestion, but neither my phone nor computer could make the connection from your note.

I did reply with load info a day or so ago, as well as to your colleague Rick_1976, applications engineer, at digikey@discoursemail.com.

The info I have currently dredged up suggests I may need a no-load electronic 12 volt AC output device, but I believe it’s not bright to ask for expert advice and then not take it.

The MR16 two-pin 12 volt bulbs would of course have their own driver device built in. I just supply as close to 12 volt AC as my line allows.

No more than 28 watts, 4 bulbs, on any one line.

Is the Hatch not correct, or are there just alternatives?

Regards and thanks.

Paul Nisbet

I think I’m confused as to what you’re needing. If they’re LED bulbs, they should be driven off DC unless there’s a converter as part of the package in which case they should take straight 120VAC . However, if they’re filament bulbs that require 12VAC (halogens can run off AC or DC - with some caveats) then you’d be looking at a transformer and as Rick mentioned there’s potential issues using your existing line as low-voltage wiring.

Can you clarify exactly what type of lighting your using with a link or more information?

Looping @rick_1976 back into this, as he is much more knowledgeable than I, and I think I’m missing something in the bigger picture here.

Jerry. Thanks. Much aggravation for small deal. Sorry.

Lamps are standard, off-the-shelf, MR16, 2-pin, replacements for old, hot, dangerous, halogens, in ceiling pots.

Yes, they contain, in the lamp body, the driver. They need 12 volt AC.

Indeed, if they were just the little two post quantum device that is the light emitting diode, pure magic, they would need DC, but they do their own rectifying.

Yes, I may have a line-loss issue, but am interested to see if this works.

Thinking that I need to provide overkill wattage and hope the lamps light.

Bulbs are rated at 7 watts each, putting out, they say, 500 lumens.

If this works, I can avoid replacing up to 30 individual transformers, one in each pot.

Pain in the ass. Expensive, in relative terms.

So, no-load or constant voltage? I think the internal driver makes the voltage constant. Literature suggests I provide no-load from an electronic, 12 volt, AC transformer.

Make any more sense?

Again, 2-pin, MR16 spotlight bulbs - off the shelf. AC.

Really, much appreciated.


I think I see what you’re looking for now. Click here to view the transformers we have in stock that are 115V in, 12V out, 40VA to 50VA power ratings which should cover your load.

Again, we can’t recommend doing it this way but I believe the link will have the products you’re looking for if you do decide to go ahead.

Much obliged. Yes, this is a bit of an experiment, and I plan on watching components like a hawk.

Ordering overly robust va capacity is one little insurance policy.

Fact is, I have seen outdoor multi-bulb system transformers offer a 14 volt option to cover line loss issues on large runs.

Any chance you have something that would put out 14 volts?

I’ll check these over and make a choice. Any recommendations on good brands to trust?

Thanks again. I appreciate the advice, and respect the caution. I’ll start with the runs where the old transformers are already blown by a town power surge - one at a time.

Be safe. Be well. These are odd times.


We’re a bit more limited for 14V transformers, but click here to view. These are 24VA and 84VA, so it depends on how much you want to go over your expected load.

As far as brands, I don’t really have an opinion as I’m not super experienced with transformers. But as they’re basically a coil of wire around a core I wouldn’t think brand would matter much. They’re pretty simple devices.

Super. Thanks. Would Rick know? I didn’t copy him on latest notes.

Seems these are magnetics. Sorry. Gotta be electronic, so the LED folk say.

The most “proper” approach here is probably to replace each transformer with a device designed for that specific purpose, such as the RS12-60M mentioned. We don’t carry those, or devices of a similar type. Reasons to go this route include it being blessed under likely regulatory constructs, backward-compatibility with traditional halogen lamps, and relative ease of adding dimming capability, particularly when halogen lamps are used.

Reasons not to go this route, particularly in conjunction with LED retrofit lamps, is that since they’re designed for use with incandescent lamps, sticking LEDs on the output is something of a hack which may yield undesirable behaviors in terms of flicker, delayed turn-on, etc. Attempting to add dimming via typical means with LEDs is likely to amplify such an outcome significantly.

A different approach, presuming future use of LED-based lamps exclusively, would be to replace the existing magnetic transformers with a small AC-DC converter, such as one among these. Most LED retrofit lamps will run very happily on DC, insofar as turning an AC input into DC is pretty much the first thing they all do internally. This approach may potentially be lower cost, but insofar as the suggested appliances are not purpose-designed for the task, some inspector-type person may look sideways at it if they were to take notice. Dimming would not be possible, and there may be a brief delay between turning the switch off and the lights going out, due to stored energy in the converter. Incandescent lamps installed in the future would likely experience shortened lifespans.

A third, more radical approach alluded to previously, would be to modify the existing electrical architecture (top, below) by placing the conversion mechanism between AC line and existing AC switches, repurposing said switches and downstream wiring as a low-voltage system, as in the bottom figure. This also should “work” but would most likely be frowned upon by official types for various reasons, especially if the installation of the converter were done in a janky or haphazard manner.

Much of the weeping and gnashing of teeth surrounding topics such as this stems from efforts to cram LED technology into legacy installations to which it is fundamentally ill-adapted. Running a 12V MR16 LED retrofit lamp using an electronic ballast (“transformer” is a term best reserved for magnetic devices) as proposed involves (roughly and typically) the following chain of conversion processes: 120VAC–>170VDC–>17VDC–>12VAC–>17VDC–>(some mA DC, controlled current). Several of these happen internally to the devices involved and are thus not apparent, but happen they do, with losses at each stage.

Further, fixtures designed for incandescent lighting agents are designed to limit heat transfer to the surrounding environment, which is precisely the opposite of what’s required to gain maximum benefit from an LED source. Modern LEDs have rated lifetimes on the order of 80K hours, or about 9 years running 24/7/365. Stick them in something that looks like a traditional “bulb” however, and one ends up buying replacements at a rate not that much different from the old incandescents, due to the fact of poor thermal management when packaged into such form factors.

As for dimming, the traditional way to achieve this was through the use of devices known as thyristors to chop off parts of the AC waveform, lowering the average voltage applied to an incandescent lamp which for practical purposes looks like a resistor, providing a consistent and continuous path for current flow. The AC-DC conversion that happens internally to an LED retrofit lamp does nothing of the sort. Because thyristors depend on current flow to remain in an “on” state and the cessation of current flow to turn “off”, and because the driver circuit in an LED lamp generally doesn’t care what the average voltage applied is so long as it’s somewhere in the broad span between “enough” and “too much,” trying to dim LED retrofit lamps using legacy dimmer technology is a dog’s breakfast of competing technological requirements, often resulting in an outcome that is less than appealing.

Honestly, were I in your situation I’d consider sticking the halogen lamps back in until you decide to replace your fixtures. Incandescent lamps are 100% efficient when operated in a space that is being actively heated, which is more of the year than not this far north, and during our two weeks of summer we get 12-14 hours of daylight, reducing the need for artificial lighting significantly compared to the dark/cold season. But hey, it’s your place, your call.

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Rick. Hi again. I’m sure I’ve become a total pain in the ass. Sorry.

I’ve been taking notes. LONG time since my undergrad physics and chemistry days. They had barely invented the transistor back then. Pluto was still a planet. A buck was still worth a buck.

So, are you saying that I can feed my light bulbs direct current notwithstanding that they, presumably, have, internally in the housing, a rectifier to do that, along with all the other “stuff” required by the various real LED units in the “bulb”?

Now, to be clear. The pot lights I’m dealing with were never incandescent fixtures. Halogen. MR16, 2-pin spotlights. Little hot bastards. Now banned in Europe, and soon to be gone here I assume.

What I’m working on now are two separate sets of pots, one switch each, where the old magnetic transformers have “blown”, kaput, dead. I connected with their manufacturer in Montreal who said they were not suitable for LED. He’s gotta know. But, I want to “fix” these first, so am experimenting with this scheme to avoid, if possible, replacing each and every old magnetic transformer with an electronic ballast, one by one.

I plan to put the device, a new electronic ballast, AFTER the switch and in the line to the set of three bulbs. I have abandoned the concept of dimming.

Now, DC transmission is more efficient over long distances than AC, so I may avoid some line loss, yes? But, if the MR16 bulbs have a rectifier already, I don’t want to confuse them.

I see several units in your product list that put out 12, 13.5, and 15 volts DC and wonder if they might work, downstream of the switch, and with enough extra juice to light the bulbs with suitable power.

RSP-320-13.5 for example. I assume it’s electronic. The literature doesn’t say, but it doesn’t LOOK magnetic.

Otherwise I just find an electronic ballast, output 12 or 13.5 volt AC and let the bulbs do what they need to do. Like the Hatch, which you don’t carry.

And you’re right. This is a patch, a hack, an experiment. Thinking it can’t set the house on fire, and if it works, so much the better.

I had hoped to find a device that was cheaper, but sometimes when you go “cheap”, you get “CHEAP”.

If you could set me straight on the DC or AC thing, that would save me some confusion.

I’ll leave you alone after this. I KNOW you have better, and more profitable, things to do.

Much appreciated.

Let’s meet up at the curmudgeon’s club and share stories sometime. Prune juice is on me… :wink:


“Incandescent” is a blanket term for lamps operating on the glowy-wire principle, halogens being a subset thereof that include some stuff from the right-ish side of the periodic table to help the glowy wire last longer.

I’d presumed that the existing units had a transformer per fixture, rather than per lamp. If the latter is the case in your installation, the rationale for adjustment of things would appear rather stronger. The mechanics of where exactly things might fit is something rather difficult to gauge from this side of the screen.

That’s a notion more germane in the context of utility transmission lines, and subject to a lot of footnotes. In this case, I think it a relative non-issue.

There’s a possibility that lamps with some arcane mechanism for accommodating dimming might experience some confusion, but the example device pictured above doesn’t seem to mind in the least. If anything, I’d imagine LED-based lamps to last longer on a DC feed, due to a typical failure mechanism becoming irrelevant when a DC source is provided.

Many of those have a facility for adjusting output voltage +/- 10% or so, though again I wouldn’t expect line loss to be a substantive issue. You’re feeding rabbits through a trough sized for horses here. A 12V output device would probably be quite sufficient, on further contemplation.

Its electronic nature is more implied by the nature of the specifications on the datasheet, rather than being explicitly stated. That device is rated for 321W though, and was mentioned given the possibility that you were thinking of using a single converter for the whole works, pre-switch. Something like the IRM-30-12ST might have a chance at fitting into a single-width junction box at the fixture level, and be capable of supplying up to (4) 7W lamps. Again, your intentions regarding architecture and physical location of components is not altogether clear, but to the extent that replacements can be made with a lesser disturbance to that which exists, so much the better.

So long as you understand that and it’s potential repercussions, we’re OK.

The devil’s in the details, and the obsolescence notice for commonsense-ND came out quite a while ago. Item will become unavailable when existing stocks are depleted…

And one MORE thing.

If I feed them DC, will I have to get the wires attached to the correct leads?

How would that work?

I know that by convention LED emitters have one long lead, one short. Polarity matters. Get it wrong, no photons.

Will the internal circuitry in the bulb built-in driver deal with that?


Rick. Thanks again. You have been, as the English put it, a brick about this. I hope there’s been some entertainment value in it for you.

I do like the concept of feeding the little buggers DC.

Yes, on sober reflection, halogens are clearly incandescent. Kinda like my wife when I fail to pull off one of my hare-brained schemes - like this one.

One query more. Literature on LEDs indicates I should overpower my source by at least 20%. Four bulbs at 7 watts makes 30 watt output a tad skimpy. Got one just a little bigger? I only have one run of 4 bulbs. Rest are 2 and 3.

Pics attached. Of course I can’t expect someone in Thief River Falls to know what’s in my house, let alone in my head.

You’re WAY farther North than we are. I have a God-daughter studying nursing in Thunder Bay. The Great White North.

Actually, you’re close enough to Canada to be honourary Canadian. Patient and helpful enough to qualify as well.

My wife recently retired from a large company here that has a major accounting and technical hub in Egan. Has friends there.

It is soooo sad, the ongoing events and troubles in Minneapolis. And elsewhere. The world could be so much better a place, but that takes a lot of work that people don’t seem to want to invest.

And Canadians are often wrongly smug about what goody-two-shoes we are. We do the same evil things to our indigenous people. No good reason.

Oops. Soap box alert. Rant warning. I do belong in the Geezer-Coot Section of the Curmudgeon Club. BTW, I like prunes.

Of course I just assumed you were in Thief River Falls. These days, could be anywhere. India.

I plan on installing this magic box in accessible lines in the basement that then run up in the wall to the ceiling of the main floor to the sets of pots. AFTER the switches. Each switch covers one set of 2, 3, or 4 bulbs. Romex, 16 or 14 gauge.

Currently (pun?), no dimmers in switches. Would dimmer likely work?

Sounds as if Thief River might be a Swedish or Norwegian agricultural settlement of a century or more ago. I just looked it up.

I’ll order a few of whatever these boxes are and get out of your hair. This has, for me, been an enlightening (ha ha ha) experience.

I hope.


Paul Nisbet

Couple more pics.