MR16 Bulbs - use 12V AC or DC?

I'm preparing for putting together a cable lighting system, where a bunch of MR16 fixtures hang from two bare wires suspended overhead. Traditionally, these systems use 12V AC with halogen bulbs, and there is a transformer that converts the 120V AC to 12 V AC.

Naturally, I'm planning on using LED bulbs instead of halogen. However, because LEDs draw much less current, many of the halogen 120V->12V transformers don't work properly. You need a different type of transformer, which is less common. However, 120V AC -> 12 V DC transformers are quite common.

As I look at different LED bulbs I've noticed that many say they work on both 12 V AC and 12 V DC. This leads me to wonder, since I am going to use exclusively LEDs, not halogens, does it even make sense to run 12 V AC? Would it make more sense to just do 12 V DC and then I would be able to use a common DC transformer to power it?

Does anyone know if the bulbs that operate on both 12 V AC and DC perform similarly to either? Is one better than the other for some reason? I know that internally it is being converted to DC anyway, so that's why I'm thinking that maybe DC makes sense, but I don't want to just assume that.

Also, if a bulb does not say either AC or DC, could I assume that they just aren't saying that, and it does in fact run fine on DC, or would there be some bulbs that could only run on AC?

I would like to make this somewhat future-proof if possible.

I can only speak for the Samsung MR16 bulb I reviewed in this forum a week or two ago. It has a regulated driver and it doesn't matter if the voltage is 8 or 16 volts DC, it puts out the same amount of light. It falls out of regulation under 8 volts (~7.75v). On a 12 volt AC transformer it performs the same. When waving a pencil in front of it, I see no strobing. It is one of the better LED bulbs available.

JohnR66 said:

I can only speak for the Samsung MR16 bulb I reviewed in this forum a week or two ago. It has a regulated driver and it doesn't matter if the voltage is 8 or 16 volts DC, it puts out the same amount of light. It falls out of regulation under 8 volts (~7.75v). On a 12 volt AC transformer it performs the same. When waving a pencil in front of it, I see no strobing. It is one of the better LED bulbs available.

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Thanks...I read your review and it seems like it has potential; unfortunately, you said it doesn't support dimming and in my case I think that would be a deal breaker.

Two other LED bulbs I've tried, the Home Depot EcoSmart and the Philips AmbientLED, will also work on 12 volts DC. I have a rather large sealed lead acid battery in my room that is charged with a solar panel which I use to run two lights, a radio, and my laptop computer.

The issue with LED MR-16 replacements is with "electronic" halogen "transformers" that use a switch-mode type supply. Some of them may need a minimum amount of load to start up and would not operate properly when faced with the lower current draw of an LED MR-16. A regular old, heavy "magnetic" transformer should work.

yuandrew said:

The issue with LED MR-16 replacements is with "electronic" halogen "transformers" that use a switch-mode type supply. Some of them may need a minimum amount of load to start up and would not operate properly when faced with the lower current draw of an LED MR-16. A regular old, heavy "magnetic" transformer should work.

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Yes, I've read that to be the case. I was having a hard time finding a transformer that would operate on a low enough load with AC, which is why I was investigating DC options. Now I found http://lightechinc.com/let-60w-ac-120v-117v-class-2-l/ though which, as far as I can see, looks to output 12 V AC and work down to a 2.9W minimum load, is dimmable, and also looks to be really cheap at $13.

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DarkNova said:

Yes, I've read that to be the case. I was having a hard time finding a transformer that would operate on a low enough load with AC, which is why I was investigating DC options. Now I found http://lightechinc.com/let-60w-ac-120v-117v-class-2-l/ though which, as far as I can see, looks to output 12 V AC and work down to a 2.9W minimum load, is dimmable, and also looks to be really cheap at $13.

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There may be a problem with that transformer. When I look at page 2 of the PDF for the Lightechinc 60 watt unit, they show a maximum of 2 meters from the transformer to the LED. I'm in the same boat as you or even more so with an already existing Halogen cable system we'd love to upgrade to LED but are waiting for a bit of a price drop in MR16s as well as locating an appropriate transformer.

Hugh

SciGuy said:

There may be a problem with that transformer. When I look at page 2 of the PDF for the Lightechinc 60 watt unit, they show a maximum of 2 meters from the transformer to the LED. I'm in the same boat as you or even more so with an already existing Halogen cable system we'd love to upgrade to LED but are waiting for a bit of a price drop in MR16s as well as locating an appropriate transformer.

Hugh

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Hmm, that's strange. Do you think that they mean by the "2M" that's just the length of the blue wires connected to the box? I would of course join those wires to some beefy cables to bring the 12VAC to the cable lighting. Or would there be another reason for the distance limit?

It might depend on the specific LED bulb you are looking at.

For instance, the Array lighting MR16 bulbs do actually come in separate 12VAC and 12VDC versions
It's possible that on AC the LEDs are actually only glowing for part of the time, whereas on DC they would be on all the time (and possibly therefore dissipating too much power)