Help Needed: rigging up three 3v leds with a single 12v power supply

So I’m wanting to make a wonky lighting fixture using LED flame bulbs, but removing the edison connector and rigging them up to a single plug in power source. I did find a stack overflow with a similar question, but wanted to check with y’all to see if there’s other considerations I should make. Link to said stackoverflow here: automotive - I'm trying to use 3v LEDs in a 12V circuit, in my car - Electrical Engineering Stack Exchange

These are flexible boards with a grid of LEDs on them, and the only thing I’m cutting out is the 240v to 3v bit. I’ve seen a single “bulb” converted to run off batteries, but given that this is a bit different, I just wanted a little advice.

If your LED’s forward voltage is truly 3V at the desired current, you have 3 in series, and you’re using a constant 12V supply then you have 3V of overhead. Simplest way by far would be to put a resistor in series. Simple application of Ohm’s law (assuming 20mA current):

V = I * R
3V = 0.020A * R
3V / 0.020A = R
150 = R

Of course there are other ways to do it that are more efficient, but that comes at additional cost and complexity.

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Thank you for the explanation!
Yeah until the bulbs arrive I’m working off assumptions, so I’ll check them with a multi meter and then buy a power supply and all the other goodies I’ll need.
*edit: assuming it’s the same as an example project with the same kind of bulb of a similar size

Can you find a use for a fourth LED? Or wire a fourth one into the series and hide it somewhere…

You don’t say how many LEDs are on each grid but depending on how many there are, you might need to pay attention to how much power your series resistor is going to have to dissipate. It would be helpful to know more about these LED “grids”.

So I got back to this after the longest time, the bulbs I have are putting out 4.7ish volts DC, with a tiny nudge over into 4.8 once. I meant to check this sooner, but finding a non frustrating way of cracking them open made this take a backseat.


I recently found out you can get wall adapters on amazon that have variable DC output, so I’m thinking one of those may be my best bet. It’ll be one bulb per fixture, wires running up the chains to meet at the wire from the wall adapter
This wall adapter goes up to 12v, but some go higher.

Basically, I’ve got some brass censers that I’m gonna put these in, then hang them from a trellis frame that itself hangs from the ceiling.

Not sure what you mean by the bulbs “putting out” voltage. Do you mean that’s what it takes to make them light up?

It might be best to bring them up to the space (no need to crack them open) and we can do some testing with the bench power supplies.

I’m trying to rig up a trio of these led flame bulbs with a single power source. By checking the power coming into the leds from the 120v converter, I was able to see that they run off about 4.7v the reason I’m not just hooking them up a regular screw in fixture is I need to fit them in a smaller space.
Also upon looking back at my original post I left out a lot of detail, so I apologize for that

If you’re already running wires and already plugging into the wall, why not run them off the 120 they are designed for?

Edit: Never mind. I see the smaller space thing.

Like I suggested, your best bet is to bring them up to the space and test with a bench power supply. You might find that a 12V supply powers all three at a brightness that is acceptable. Or not. But you know.

I’d be happy to meet you up there and help out.

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