I can't find my MicroLumina Lighting Tips that talks about how to use MicroLumina current limiters. Does anyone have a quick tutorial on those? I do remember that each LED takes 3v and the current limiter takes something like 2v, so you can light three 3v LED in a circuit with a current limiter and 12v input. But I don't quite remember how those are wired, the 3 LEDs in series with the current limiter? Or is the current limiter in parallel? And if you have to align the current limiter a certain way, which pin gets + vs -?
Thanks in advance!
dave
Any LEDs used with a current limiter must be wired in series with the current limiter. If you need to know the polarity of everything, ask: I have both MicroLumina instructions and those that came with some I got from Digi-Key.
So that's simple: CL and 3 LEDs in series on a single 12v circuit... ;D
dave
With incandescent bulbs, there's a valid argument against putting lamps in series: requires trial & error to identify the one that burned out. But much less important with long-lived LEDs.
A question on current limiting resistors: If I have 4 LEDs in series, does each need its own limiting resistor? Or, if I have 3 that come pre-wired with resistors and add a 4th one that doesn't have a resistor, will that work?
dave
If LEDs are in series (anode on 1st connected to cathode on 2nd etc.) then only one resistor is needed. But it won't be the same value as a resistor for a single LED. Each LED drops between ~2 (red, green & most colored LEDs) and ~3 volts (white and blue LEDs). The resistor only needs to limit current for the voltage left over after the LED voltage drops are added up.
This is one reason I bought the lab power supply: It lets me adjust both current and voltage accurately, so I can figure out things like this without worrying about letting the magic smoke out. Mine is likely to be idle into mid-September if you want to borrow it.
Quote from: jbvb on August 10, 2025, 02:53:11 PMIf LEDs are in series (anode on 1st connected to cathode on 2nd etc.) then only one resistor is needed. But it won't be the same value as a resistor for a single LED. Each LED drops between ~2 (red, green & most colored LEDs) and ~3 volts (white and blue LEDs). The resistor only needs to limit current for the voltage left over after the LED voltage drops are added up.
This is one reason I bought the lab power supply: It lets me adjust both current and voltage accurately, so I can figure out things like this without worrying about letting the magic smoke out. Mine is likely to be idle into mid-September if you want to borrow it.
I have a lab power supply, I just don't know all the ways to use it, or more importantly how to calculate the resistor value to prevent the magic smoke from escaping. What I'm thinking right now for the machine shop is 3 pre-resistored larger LEDs over the shop area and a single smaller size LED without a resistor for the office. Those 4 LEDs should work with my 12v aux power bus, as long as I wire them correctly. I'll probably do a similar set-up for the 2nd floor space, too.
dave
(https://modelersforum.com/gallery/24-100825160515-558152283.jpeg)
Is this what you were looking for?
Tom
Quote from: ACL1504 on August 10, 2025, 04:06:52 PM(https://modelersforum.com/gallery/24-100825160515-558152283.jpeg)
Is this what you were looking for?
Tom
Yeah, that works for current limiters, and a CL "eats" about 3 volts, apparently. But if I put 3 LEDs on that 9V battery, with no current limiter but with the correct sized resistor, I should be able to drive all 3 LEDs that way.
dave
Here's how to figure out what resistor you need.
QuoteOhm's Law
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage. This is true for many materials, over a wide range of voltages and currents, and the resistance and conductance of electronic components made from these materials remain constant. Ohm's Law is true for circuits that contain only resistive elements (no capacitors or inductors), regardless of whether the driving voltage or current is constant (DC) or time-varying (AC). It can be expressed using a number of equations, usually all three together, as shown below.
V = I × R
R =V/I
I =V/R
Where:
V is voltage in Volts
R is resistance in Ohms
I is current in Amperes
So if your LED draws .05 amps you dive the voltage (12volts) by how much current the LED draws and you come up with (240 ohms) the correct resistor to use. Always use the next size up. If you come up with an odd number like 975 ohms, use a 1K ohm resistor.
Now let's see how many LED's you can blow up.
Bernd
Quote from: Bernd on August 10, 2025, 07:09:40 PMHere's how to figure out what resistor you need.
QuoteOhm's Law
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage. This is true for many materials, over a wide range of voltages and currents, and the resistance and conductance of electronic components made from these materials remain constant. Ohm's Law is true for circuits that contain only resistive elements (no capacitors or inductors), regardless of whether the driving voltage or current is constant (DC) or time-varying (AC). It can be expressed using a number of equations, usually all three together, as shown below.
V = I × R
R =V/I
I =V/R
Where:
V is voltage in Volts
R is resistance in Ohms
I is current in Amperes
So if your LED draws .05 amps you dive the voltage (12volts) by how much current the LED draws and you come up with (240 ohms) the correct resistor to use. Always use the next size up. If you come up with an odd number like 975 ohms, use a 1K ohm resistor.
Now let's see how many LED's you can blow up.
Bernd
I guess the current draw for the LED should be on the LED package? For 2 of the LED models I have, the spec sheet https://www.mouser.com/datasheet/2/143/17-21-BHC-AP1Q2-3T_datasheet-51933.pdf says "forward current 25ma, peak forward current 100ma" For 4 LEDs, each at 25ma, that's 100ma or .1a. R= V/I, R = 12v/.1A or 120 ohms?
dave
Usually, you want the steady-state current. Peak inrush current is what won't *quite* let the magic smoke out.
If the LEDs are in parallel, the currents add up, but the voltage drop is that of a single LED.
If the LEDs are in series, the voltage required to light them all is the sum of the voltage drops of each LED. The current is that of a single LED.
Quote from: jbvb on August 10, 2025, 10:02:28 PMUsually, you want the steady-state current. Peak inrush current is what won't *quite* let the magic smoke out.
If the LEDs are in parallel, the currents add up, but the voltage drop is that of a single LED.
If the LEDs are in series, the voltage required to light them all is the sum of the voltage drops of each LED. The current is that of a single LED.
So if I have 4 pre-resistored LEDs in series, I can cut the resistor off of 3 of them and everything will work OK?
dave
Quote from: deemery on August 11, 2025, 08:18:56 AMQuote from: jbvb on August 10, 2025, 10:02:28 PMUsually, you want the steady-state current. Peak inrush current is what won't *quite* let the magic smoke out.
If the LEDs are in parallel, the currents add up, but the voltage drop is that of a single LED.
If the LEDs are in series, the voltage required to light them all is the sum of the voltage drops of each LED. The current is that of a single LED.
So if I have 4 pre-resistored LEDs in series, I can cut the resistor off of 3 of them and everything will work OK?
dave
What I'd expect is I'd need to remove all 4 resistors, then add a different resistor in series with the 4 LEDs. Resistance calculated to pass the proper current after the voltage drop of the 4 LEDs is subtracted from the supply voltage.
Quote from: jbvb on August 11, 2025, 08:24:55 AMQuote from: jbvb on August 10, 2025, 10:02:28 PMUsually, you want the steady-state current. Peak inrush current is what won't *quite* let the magic smoke out.
If the LEDs are in parallel, the currents add up, but the voltage drop is that of a single LED.
If the LEDs are in series, the voltage required to light them all is the sum of the voltage drops of each LED. The current is that of a single LED.
So if I have 4 pre-resistored LEDs in series, I can cut the resistor off of 3 of them and everything will work OK?
dave
What I'd expect is I'd need to remove all 4 resistors, then add a different resistor in series with the 4 LEDs. Resistance calculated to pass the proper current after the voltage drop of the 4 LEDs is subtracted from the supply voltage.
Now I'm back to being confused. I thought each LED eats 3v, so 4 of them would totally consume 12v, so no resistor needed? But how do I determine or measure the voltage drop for a single LED?
dave
QuoteNow I'm back to being confused. I thought each LED eats 3v, so 4 of them would totally consume 12v, so no resistor needed? But how do I determine or measure the voltage drop for a single LED?
dave
If they are wired in "series" they consume the 12v. Wired in "parallel" each will only take 3V.
Bernd
This lovely creature will explain how it's done.
Bernd
Quote from: Bernd on August 11, 2025, 09:16:45 AMThis lovely creature will explain how it's done.
Bernd
Thanks, that's a great video for dummies. The one remaining question I have is how to determine the voltage for the various LEDs I have. For some, I can find the spec sheet. After searching, I found the "forward voltage" range for the 0805 LEDs, it provides a range: " Forward Voltage VF 2.7 3.3 3.7 " (min, typical, max), so I presume I should use 'typical'? Is there a way to determine the voltage for an unknown LED (using a voltmeter and power supply where I can set both voltage and max current?)
But if I'm right and 4 LEDs each consume 3v, I don't need any resistor?
dave
Here's a page that talks about how to figure out voltage for an unknown LED: https://electronics.stackexchange.com/questions/173468/easy-way-to-figure-out-a-leds-vf-in-order-to-pick-an-appropriate-resistor The simple answer is for me to get a cheapo voltmeter that includes an LED measure :)
dave
My lab power supply lets me set voltage and current independently. The gauges claim a precision of 0.001 but there's no expensive sticker on it confirming that precision. Most frequently, I set the "typical" voltage and slowly turn up the current, stopping when I get to the brightness I want. Then I choose resistors based on the sweet spot voltage & current.
You could make up your 4 LED series string temporarily with clip leads and see what voltage it actually drops, and what current gives you the brightness you want.
From the Department of Things I Don't Understand: Turns out my old voltmeter has an LED setting. I tried the new and old voltmeters on a set of 5mm LEDs (nice and big, easy to apply the leads.) I tested the LEDs, they light up with the MicroLumina LED tester. But when I apply the meter leads, no matter which way I apply them, I get "0L". What I expected to happen was the LED would glow a bit, and I'd see something around 3 volts.
dave
Quote from: deemery on August 12, 2025, 01:19:48 PMFrom the Department of Things I Don't Understand: Turns out my old voltmeter has an LED setting. I tried the new and old voltmeters on a set of 5mm LEDs (nice and big, easy to apply the leads.) I tested the LEDs, they light up with the MicroLumina LED tester. But when I apply the meter leads, no matter which way I apply them, I get "0L". What I expected to happen was the LED would glow a bit, and I'd see something around 3 volts.
dave
From the Department of Electrical Devices Research play with this calculator.
https://ledcalculator.net/ (https://ledcalculator.net/)
Bernd
Quote from: Bernd on August 12, 2025, 04:40:45 PMQuote from: deemery on August 12, 2025, 01:19:48 PMFrom the Department of Things I Don't Understand: Turns out my old voltmeter has an LED setting. I tried the new and old voltmeters on a set of 5mm LEDs (nice and big, easy to apply the leads.) I tested the LEDs, they light up with the MicroLumina LED tester. But when I apply the meter leads, no matter which way I apply them, I get "0L". What I expected to happen was the LED would glow a bit, and I'd see something around 3 volts.
dave
From the Department of Electrical Devices Research play with this calculator.
https://ledcalculator.net/ (https://ledcalculator.net/)
Bernd
The second thing it asks for is "LED Voltage Drop". That's what I was expecting to get from the multimeter. And this presumes a string of identical LEDs, but I'm hoping to do 3 of one type and 1 of a smaller type. Tomorrow, I'll solder together the string of (4) LEDs and try James' "successive approximation" approach. Today I practiced soldering very thin wires, for me soldering is a perishable skill!
dave
Several VOMs (Voltmeter/Ohmmeter/Milliampmeter) I've owned have had a little diode picture at one dial position. What that does on mine is tell me if the diode was blown (didn't conduct either way) or functional. The test current is enough to make all the LEDs I've tried glow, but I'd have to read the instructions to say what the display shows while doing this. Do you still have the instructions for your VOM?
Clip leads are inexpensive and more convenient than soldering while you're still testing things.
Quote from: jbvb on August 12, 2025, 10:03:43 PMSeveral VOMs (Voltmeter/Ohmmeter/Milliampmeter) I've owned have had a little diode picture at one dial position. What that does on mine is tell me if the diode was blown (didn't conduct either way) or functional. The test current is enough to make all the LEDs I've tried glow, but I'd have to read the instructions to say what the display shows while doing this. Do you still have the instructions for your VOM?
Clip leads are inexpensive and more convenient than soldering while you're still testing things.
I have the instructions for the new VOM, and followed them. An on-line discussion said 'connect the black lead first', but the order in which I applied the probes didn't make any difference with either meter.
dave
Quote from: deemery on August 13, 2025, 08:36:12 AMI have the instructions for the new VOM, and followed them. An on-line discussion said 'connect the black lead first', but the order in which I applied the probes didn't make any difference with either meter.
dave
A simple question to Google asking for forward voltages of LED's gave a cheaper answer than buying a VOM. Probably asking ChatGPT would have helped too.
https://www.circuitbread.com/ee-faq/the-forward-voltages-of-different-leds (https://www.circuitbread.com/ee-faq/the-forward-voltages-of-different-leds)
Bernd
Connecting black before red is correct with the grounded side of a live circuit, but not applicable to this case.
I tried the diode test function of my fancy VOM with a purple LED. It didn't report continuity with either polarity, but it did light the LED with the correct polarity,.
Bernd, I'd trust the manufacturer's spec unless something blew up when I followed it. But there are a lot of oddball parts out there; I'd always verify any general result from web search. And AI can be completely sure about a totally bogus result, so I treat it like that type of person.
Since I can't seem to use my meters to measure the forward voltage through LEDs, I think what I can do is use the information I do have (including Bernd's link), and assume (a) the LEDs will all take 3v (b) if the smaller LED takes less, the larger LEDs will be able to 'eat' the extra voltage. So then, it's just a case of determining the resistor for 4xLED in series.
Screenshot 2025-08-13 at 10.26.18.jpg
Now if I assume the big LEDs are 3v and the little one is 2v, then the average is 2.75, and here's the result:
Screenshot 2025-08-13 at 10.32.09.jpg
But once I get things assembled, I'll first test with the lab power supply, setting it to 12v and then slowly increasing current until I'm happy with the result. Assuming the magic smoke stays in place, then I'll figure out the actual resistor value from the current on the power supply.
dave
From my Velleman E12 Series resistor assortment (610 pieces), your choices would be 47, 56 or 68 Ohms. I'd chose higher over lower. 68 will be easier to find than 56 because 68 is in the E6 series. I plan to go to Seashore Thursday, could drop one off on my way home.
Quote from: jbvb on August 13, 2025, 11:08:47 AMFrom my Velleman E12 Series resistor assortment (610 pieces), your choices would be 47, 56 or 68 Ohms. I'd chose higher over lower. 68 will be easier to find than 56 because 68 is in the E6 series. I plan to go to Seashore Thursday, could drop one off on my way home.
I have some resistor sets, no need to stop by. But at some point, we'll have to do a huddle using your meter and my meter on LEDs to see if we can figure out why I wasn't getting my expected results.
dave
Quote from: jbvb on August 13, 2025, 09:56:12 AMBernd, I'd trust the manufacturer's spec unless something blew up when I followed it. But there are a lot of oddball parts out there; I'd always verify any general result from web search. And AI can be completely sure about a totally bogus result, so I treat it like that type of person.
I don't know what's so hard about figuring this out.
QuoteWhat you should find is that red, green, or yellow LEDs have relatively low forward voltage ranging from 1.6-2.2V. However, blue and white LEDs can begin conducting from 2.5-4V.
This gives you a range of voltages used by the various colored LED's. That chart I linked to gets you down to a closer voltage for the color you are using. Besides an LED is current controlled and not voltage controlled. Filament bulbs are voltage controlled and not amperage controlled. You can take a 12 volt bulb and hook it to a 12 volt car battery capable to 200amps or more cranking the engine over yet the bulb doesn't blow. You can also hook an LED (.025 Ma)to that same car battery with a (12v/.025Ma = 480 ohms)or higher (510 ohm) resistor with out blowing it up.
I'd go with the higher voltage with what ever color LED you are using and the higher Ma suggested for that color and then work my way down till I get the brightness I want. Problem solved. Nothing magical about it. Just like figuring out how to set your CV parameters on DCC.
Bernd
I spent some time looking at a -bunch- of tech data sheets for the 3 common sizes of Surface Mount (SMD) White LEDs.
0603. Footprint: 1.60 x 0.80 x 0.40mm.
0805. Footprint: 2.00 x 1.25 x 0.80mm.
1206. Footprint: 3.20 x 1.60 x 1.10mm.
This is not a scientific sample, but the average forward voltage for 0603 and 0805 was pretty common around 3v. But for 1206, here was more variation. It's perhaps unfortunate the first one I looked at showed Vmin 1.8, Vmax 2.4. https://www.farnell.com/datasheets/3497852.pdf Others showed (min/max) 2.8 - 3.8, 2.8 - 3.7, and 2.8 - 3.4. So as long as I don't happen to hit a device from that first 1206 vendor, I should be OK assuming a 1206 LED should accept 3.0v. ;)
Bernd, this is why I was making this "harder than it should be". And why that article you sent earlier that asserted a single common value for Vforward wasn't matching what I was reading before I did a bit more research.
dave
Dave,
I believe you want to wire your lights in series, correct?
I'd wire them in parallel. Why? If one of the LEDs dies the others will also go out. Now you need to find which one gave up the ghost. Think of it like looking for the bulb that blew in the Christmas tree lights in a string of many. Just a suggestion to contemplate.
Bernd
My first LED installations are about 30 years old, they all still work except for a couple where my error put the wrong voltage to them after they were in service. AFAIK the greedheads haven't yet corrupted individual LEDs with "planned obsolescence" like the little nick in the filament of both incandescent bulbs and vacuum tubes. So I don't worry about diagnosing failed LEDs like I do with incandescents.
I did a bit of web research on LED failures. Seems they follow the relatively common "bathtub model" where there are initial failures due to manufacturing problems, etc, a long time with very few failures, and eventually an increase of failures as they start to reach end-of-life. See https://www.osram.com/Graphics/XPic6/00102625_0.pdf for a good discussion.
So that tells me it would be A Good Thing after I assemble my light string, to let it 'burn in' for a day or so before installing it, and once it's installed, to not worry. ;D
dave
Well, I got the 4 LEDs soldered up (with sufficient cursing). And that includes resoldering a wire back onto the LED when I accidentally pulled it off (while working on the heat shrink tubing...)
I set the power supply for 12v, and then started at about 0.008a. Here's the result at .012a
IMG_0978.jpeg
So if I've done the calculations correctly, R=12/.012 or 1k ohms. And that current is less than the 20ma/.02 for LEDs, right?
dave
That could have been done cheaper with a 12volt power supply and a couple of resistors plus some math.
https://www.amazon.com/Variable-ENGINDOT-Adjustable-Adjustment-Alligator/dp/B09KMS74PT (https://www.amazon.com/Variable-ENGINDOT-Adjustable-Adjustment-Alligator/dp/B09KMS74PT)
Bernd
Quote from: Bernd on August 15, 2025, 09:01:15 PMThat could have been done cheaper with a 12volt power supply and a couple of resistors plus some math.
https://www.amazon.com/Variable-ENGINDOT-Adjustable-Adjustment-Alligator/dp/B09KMS74PT (https://www.amazon.com/Variable-ENGINDOT-Adjustable-Adjustment-Alligator/dp/B09KMS74PT)
Bernd
I'm sure you've used an expensive tool that you had where there was a cheaper alternative, too! ;D But it worked, and I learned from the experience. Runs in my mind, though, that power supply was significantly cheaper when I bought it.
dave
QuoteI'm sure you've used an expensive tool that you had where there was a cheaper alternative, too! ;D
Yes I have. I'm sure the Carvera CNC machine comes to your mind. That's a multi material use device, as where that power supply is a single use device.
I had to research what that "MicroLumina" product was. Looks like it can be used if don't know what your power supply voltage is or varies while in use. I can't see using that if one knows how much voltage a power supply puts out.
B~
The "MicroLumina device" is just a current limiter for LEDs. But that consumes voltage (about 3v) when it's put in the circuit. So with a current limiter, I could power 3 LEDs on a 12v circuit. Without one, I get 4 LEDs on 12v.
I bought that power supply when I did my Arduino project animating a ball signal.
dave
QuoteThe "MicroLumina device" is just a current limiter for LEDs. But that consumes voltage (about 3v) when it's put in the circuit. So with a current limiter, I could power 3 LEDs on a 12v circuit. Without one, I get 4 LEDs on 12v.
B~
Quote from: deemery on August 16, 2025, 09:35:09 AMThe "MicroLumina device" is just a current limiter for LEDs. But that consumes voltage (about 3v) when it's put in the circuit. So with a current limiter, I could power 3 LEDs on a 12v circuit. Without one, I get 4 LEDs on 12v.
I bought that power supply when I did my Arduino project animating a ball signal.
dave
Dave,
The great thing about the ML Current Limiter is that it will handle from 9 - 90 volts, per Bill Satore when he gave a clinic at one of the Modeler's EXPO.
Tom