A COB LED is just multiple small LED dies in a single package. Example: the square ‘10W’ LEDs have nine 1W dies, arranged 3 strings in parallel, each string with 3 in series. The big square 100W has 100 1W dies, 10 series/10 parallel. Some vendors may be calling it a ‘COB’ when it’s not, multiple individual LEDs on a circuit board is not really COB.
To make the dimming work, you’ll need a DC converter with adjustable output voltage, and then a potentiometer of some sort to control it. The dimming is done by giving the bulb less than 12V. A converter with fixed 12V output will work with a dimmable bulb, it’ll just run at full output all the time.
Eh, I are these MR16’s not like other ‘dimmable LED bulbs’ which do not dim with voltage? The “110v” bulbs (60w bulbs and similar) are intended to run on a wide range of voltages without dimming. Instead they look at the waveform to see if it’s been “chopped” (like shown here) and adjust the output accordingly. Those bulbs are also unable to achieve a full 0% - 100% dimming range.
I have no experience with the MR16 replacement bulbs - maybe they are a whole different ballgame.
Just to restate, a dimmable bulb doesn’t have any dimming hardware inside, it’s dimmed by varying the voltage supplied to the bulb. You’ll need a setup like: 12-14V wall wart, adjustable DC-DC converter, and a dimmable bulb.
Another variation would be a 110VAC to DC converter, with output voltage externally adjustable from 0 to 12V. Probably not going to find such a thing though.
Check posts #65 & 66 here: Driver for car dome/trunk lighting - #64 by comfychair
There’s two different adjustable DC-DC converters there, either one will work powered by a 12V wall wart. The larger one is still damn small, and the onboard adjustment pot can be removed, 3 wires soldered to the pads, and connected to a larger external pot (5K works fine) for dimming. If you use a 12V wall wart, turning the pot wide open more or less sends the full input voltage straight through to your bulb. Turn it down and the bulb gets less than 12V, all the way down to zero volts and zero light output. A separate switch, or a pot with a built-in switch wired to disconnect the wall wart from the DC converter’s input can be used to turn it fully off.
Thanks for clarifying, I thought it meant a bulb with a built in driver. (I edited my post) So the question should have said “can I use a LED driver switching power supply to run the bulbs that already have a built-in driver?”
Thanks I may look into that type of converter, I could mount the Pot right in the base, if I go non-dimmable I’d have to replace the momentary rocker switch in the bulb housing, (a direct replacement rocker switch from Digi-Key is $5.13 shipped)
Actually, if I go non-dimming I guess I could mount any size switch in the base as well, but having the switch in the bulb housing may be more convenient if I have the base placed out of the way, or have stuff in front of it. The flexible “snake” tube on this light is about 30” long.
You may be right, I haven’t used any MR16 stuff either. If this were my project, I would gut the cheapest MR16 bulb I could find and just use it as a housing.
This one uses a fixed 85-265VAC 600mA “3-4x 3W” driver.
The on/off switch needs to cut power to the input of the 12V supply, not the output between the supply and bulb. Mounting the switch in the head gets less convenient if you have to run another set of wires through the gooseneck.
Ah, I see, so if I put the switch on the output (12v) side then the transformer would always be “powered up” with current flowing through the windings, even though the bulb is off. Would that be an issue?
I guess that’s why I’ve heard leaving “wall wart” transformers plugged in all the time uses electricity, running up your electric bill?
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The original switch is in the head, so there already are 2 pairs of wires running up to the head, (one pair to the socket and the other pair to the switch) the wires are marked “300volts” but they are thin, (about 22ga) I’m kind of sketchy about having 115VAC running up through those wires, but maybe that’s how it was with the original halogen set up? (all of the wires ran to a circuit board, none were directly connected to the AC input cord)
Higher voltage is ok with very small wiring. Compare apples to apples and it makes sense.
To get 9 watts from 120 volts takes only 75mA. The same 9 watts from 12 volts is 750mA. Wire gauge size is determined solely by the current. The wire insulation is what has to be up to spec with high voltage.
I understand wire gauge is determined by current, (and the length of the wire run) I do remember I used to know how to figure out what wire gauge was needed using the length of the run with Ohm’s law I believe.
I wasn’t sure about what the amperage was, so thanks for figuring that out for me. So the current pulling on the AC side (through the switch) would only be 75mA? I guess it would be ok to push 75mA through aprox 5 feet of 22ga. The insulation is thin on these wires but the wire is rated for 300v.
So to wire this up I would run one side of the 115VAC power cord (from wall outlet) up to one leg of the switch, and the other side of the power cord to the transformer input. Then run the remaining leg of the switch to the remaining lug of the transformer input. Correct?
Does polarity matter, for either the AC input or the DC output?
On the AC side, switch should be in the ‘hot’ line. It’s some safety thing, I guess. If the light has an older unpolarized plug it really doesn’t make any difference since which one is hot and which is neutral will change depending on which way the plug is oriented in the socket.
The DC side may not matter either, if the bulb you end up with is able to run from either AC or DC 12V. Bulbs with rectifier diodes inside will run the same from either polarity DC.
For the power supply, I found this little gem in the basement tonight:
It’s from a lighted (LED) sign, and it’s rated 12v dc, 2000mA on the output.
I guess this should provide ample power, about double what is needed according to comfy’s earlier post.
I was thinking about just running a “footswitch” extension cord right into the base of the light and just plug it in, or I could mount a rocker or toggle switch right through the lamp base and solder some leads to the lugs of the transformer plug.
As an manufacturer of led lightings, I can tell you yes, the 12V MR16 led bulb has its own driver inside the base, you needn’t any other transformer.
For more technical details, you can view our website: http://www.greelux.com
Question about a transformer for this bulb, I have 2 different transformers…
This one (output: 2000mA) which is very lightweight.
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And this one (output: 1000mA) which is much heavier:
Why is the one with less output current so much heavier? (thought it would be the other way around) Different metal in the coil/windings?
The heavier one shows “Class 2”
The clue is one calls itself a transformer and the other doesn’t. The heavy one has an Olde Timey transformer with two sets of windings inside, the light one is a switching power supply.
