LED Dummy needs help!

Simple, the LED's have an operating voltage, and with the parallel single LED's are starving the strip of the needed operating voltage.  Put a resistor in series with the two discrete LED's and it'll work.  Also, put the two discrete LED's in series, and I'd start with about a 470 ohm or larger resistor in series with them.

@gunrunnerjohn, thank you.

I have a good variety of resistors so this problem is likely solved.  In biblical terms, I have a fish to eat. thanks to you.

But, how can I learn to be a fisherman so I can solve such problems on my own?

Sorry, I don't give fishing lessons.

I suggest an EE degree.

Well, it takes some understanding. The problem is LEDs are special. Compared to an incandescent bulb, the LED has what we call a negative resistance. Once it starts conducting, it really starts conducting. That's why you have to have a current limiting resistor in series. An incandescent bulb starts out cold at a low resistance, then heats up and increases resistance until it self regulates.

So knowing that special thing about LEDS, when you put them in parallel with a special current limiting supply, whatever LED began conducting first stole all the current from the other LEDs so they did not light. Again, you have a current limited source from the regulator board. In terms of water, think of this as a tap where you just barely turned it on and it's limiting the flow. Now you send water down the pipe. If the first tap down the pipe opens up and begins flowing, the water never reaches the next taps.

What you did is when you add resistors to the one that lit up first (the discrete LEDs) you now resisted them to a fixed amount of current. They no longer "stole" all the current from the other LEDs when they began conducting.

This is a known thing when putting multiple LEDs in parallel. If they are not perfectly matched or if you are using a strip of LEDs and then single LEDs in combination, then everything needs individual current limiting resistors to ensure each device consumes only it's fair share.

Here is a video that might be a good explanation https://www.youtube.com/watch?v=Bhv-Tk7l1zI

@gunrunnerjohn posted:

Sorry, I don't give fishing lessons.

I suggest an EE degree.

Shucks!!!

And "Thank You" @Vernon Barry for the explanation.

Also note that the LED strip is actually groups of 3 LEDs in series with one resistor, and all the LED/resistor groups are wired in parallel. Your bare LEDs also in parallel with the LED strip had no resistor and stole the voltage as discussed above.
Bob

@Pingman posted:

But, how can I learn to be a fisherman so I can solve such problems on my own?

There's a bunch of us on the forum that are trying to learn to be fishermen, Carl.  Thanks for asking.  

Hang in there Carl. Nothing blew up so consider yourself lucky.

After almost 40 years in the electrical trade, electronics confuse the h#$@ out of me. But put me in front of a 480 volt motor controller and I can troubleshoot it with my eyes closed (well maybe not a good idea)

Bob

For us non EE's, a resistor substitution box is a nice tool ( this one you have to solder and assemble )

https://www.amazon.com/Elenco-...RS-400/dp/B00R6SOXLG

Start with the highest resistance ( 1000 x 1000 or 1 meg ohm ) and decrease it step by step till you get the brightness you want.

I used one for this project.

https://ogrforum.ogaugerr.com/...l-marker-replacement

Can't help but remember each time I use an LED that it was invented by one of my instructors at the U. of Illinois. Keeps me on my toes.

I actually have a substitution box from a long time ago, I haven't used it an many years.  This one is an R/C box that allows parallel / series connections with the caps or just resistors or caps.

It's so old that I don't remember what I added the black jack for, but it must be for some internal connection, perhaps between the resistor and cap in the series configuration?

@RSJB18 posted:

But put me in front of a 480 volt motor controller and I can troubleshoot it with my eyes closed (well maybe not a good idea)

Definitely not a good idea!  I was present when some poor soul got tangled up with the 480 power bus while in the Navy on the USS Shangri La.  There's no way you ever get the memory of that or the smell out of your mind!   That has to be a really terrible way to go!

S U C C E S S !!!

Tried 1K and 330 resistors and both lit.

Trouble is I did not have a good viewing angle and I don't know the formula involved in determining brightness.

Does a lower resistance value lead to more or less brightness?

@Pingman posted:

Does a lower resistance value lead to more or less brightness?

More.

@gunrunnerjohn posted:

Definitely not a good idea!  I was present when some poor soul got tangled up with the 480 power bus while in the Navy on the USS Shangri La.  There's no way you ever get the memory of that or the smell out of your mind!   That has to be a really terrible way to go!

That really sucks John. I've had some close calls but that's about it. I've seen enough training videos to be scared straight.

As I've always said here on the forum, electrical safety is paramount. If you are not sure, call a professional.

@Pingman posted:

S U C C E S S !!!

Tried 1K and 330 resistors and both lit.

Trouble is I did not have a good viewing angle and I don't know the formula involved in determining brightness.

Does a lower resistance value lead to more or less brightness?

You will want to pick the resistor to balance the brightness of the strip and the individual resistors.  I frequently tap off the strip to light markers and rear lights on observation cars, so I tweak the resistor to make the brightness of those work with the brightness of the main cabin strip lighting.  A higher resistor value will dim the separate LED's, and a lower value will make them brighter.

@Pingman posted:

S U C C E S S !!!

Tried 1K and 330 resistors and both lit.

Trouble is I did not have a good viewing angle and I don't know the formula involved in determining brightness.

Does a lower resistance value lead to more or less brightness?

Think about the water in the pipes mentioned earlier. The valve is the resistor- cracked open (high resistance) little water, full open (low resistance) lots of water.

It takes a village....

Also, without getting too far down the rabbit hole of an EE degree, understanding the difference between a current regulating supply and a voltage regulating supply.

Current = amount of flow

Voltage = pressure

So again, if you use a current regulating supply like the JWA unit, you set the current and it senses the current through the circuit and changes the voltage output to limit the current through whatever the load is. This is why again, when you had the single LED begin conducting, the voltage the regulator output lowered to limit the current through that LED that was conducting,. Your LED strip, being a strip might have series wired LEDs and thus require a higher voltage, not to mention it also probably has current limiting resistors. So again, with a current limiting power regulator, it varies the output voltage output so that the resulting resistance of the load maintains a limited current.

Conversely, since we are putting LED strips that already have a current limiting resistor, and then we add single LEDs in parallel and properly add each one with a current limiting resistor- now ideally we use a fixed voltage output regulator. That's because again we took the step to add the resistor for each LED and so we work from an assumed source voltage to achieve a certain limited current.

I personally tend to use a fixed voltage regulator for LED circuits and then use an appropriate current limiting resistor for each LED. But more typically, I'm just using a strip that already was designed for fixed voltage.

You can use a current regulating supply regulator and in some ways, there is some safety in that it will limit to a very small current in the event you make a mistake or miswire something. That said, again, where you go hooking up multiple LEDs or strips in parallel, there is a chance when using a current limiting configured regulator, one LED strip conducts first and "steals" the current from the others in parallel.

The fact is, either mode of regulation limits in some way the circuit. That's why you can use a current regulator and as long as the load is fixed, you set the current and it results in a voltage and current through the circuit. However, a fixed voltage regulator only sets the voltage. The current is based on the resistance of the load. That is why you must then use individual resistors on LEDs to limit the current through that device.

The LM317 regulator can be used in either mode- current or voltage regulation. It's all about how a board is designed and configured.

The reason I used a constant current design is simple, I find it allows much finer adjustment of the intensity, and it also allows me to have a maximum current limit from the power supply to avoid overheating.  The constant current also allows for any LED configuration as long as it's within the range of the input power to the module.  On 18 volts, you can have one or more LED's in series and the intensity is the same regardless without changing the intensity control.  You need balancing resistors for dissimilar loads with constant voltage as well, so adding the resistor really isn't just for the constant current configuration.

Carl,

If you want to learn electronics, the place to start is Ohm's law.

I= current

V= voltage

R= resistance

Ohm's law: I=V/R

Plain english version: The current is equal to the voltage divided by the resistance provided by the resistor and the LED. The LED and the resistor make up the load of the circuit, which is why you will see the resistor referred to as the load resistor. The greater the value of the resistor, the lower amount of current to the LED, results in dimmer light.