Djsfantasi: #*%# So, that sounds like I go with Yaakov's idea or stick with my regulator boards, which have current protection and don't need any resistors? And if I do that, then maybe just upping to larger size batteries, like 6 c cells for 9v will work?

Yaakov’s idea requires resistors also. I thought he mentioned using the power packs with the board (too late tonight for me to read back as to what exactly he said) but your experiments with 6V seem to indicate that won’t work. I suspect that it won’t work either as these power packs are only 5V. The advantage of Yaakov’s solution is instead of many batteries, a single rechargeable power pack will work and take up the smallest space. With two such power packs, one could be in the diorama while the other charges from any USB port or charger.

So, IMHO, the best solution is a 5V cell phone power pack, and a 1kΩ resistor in series with each LED. It’s not clear why you don’t like the idea of using a resistor.

Or putting six C (or D) cells into a battery holder for 9V (for a while, until they drop to 8V, at which time they will appear to be dead). This would be in about a month. But these won’t fit into a 3/4” depth. They are 1.04” in diameter plus the thickness of the battery holder. D cells are thicker.

Or use the wall wart with the board.

 

Attached to 6v as before using a 1k resister it is still very bright and is fine.

For the other thread participants, may I remind everyone of my comment regarding the importance of “plug and play” for modelers and artists. As we have rules of thumb for electronics, modelers have their own rules of thumb.

One such “rule” is whenever using LEDs add a 1kΩ resistor in series. Don’t worry about the current. Don’t worry about the voltage. Just stick in a 1kΩ resistor and everything will work. I know, this will blow your minds, but in practice it works well enough for our models.

 

Ah, so it was as I originally thought. Those are raw LEDs with no resistors. So the description saying they could run up to 12V with no resistors was utter nonsense, as the TS found out. Good thing I told him to try it only if he could spare one.

And the distribution board simply is a voltage regulator with optional pass through of the input. It does nothing useful for driving those LEDs, despite the insistence of two very knowledgeable members. Sure it gives you a convenient way to connect them all, but that is it. The 3.3V regulator is useless in this application.

It is simply wrong that they can be run from a constant voltage supply. They need a higher supply and a resistor each, as I have been saying from the start.

@Ya’akov’s idea of a power bank is sound, and gives you recharge capability. Replaceable batteries are also fine. The cheapest solution is a 3AA battery holder and 14 resistors. 4AA would be better because they would not be as affected by battery rundown. The resistors need to be chosen to give the desired brightness. If indeed the lights should be dim as @djsfantasi says, then the current will be maybe 2 or 3mA. For 14 lights at 3mA AA batteries would last 48 hours.

For constant brightness, a buck/boost converter would be the best bet. These are used in the better LED flashlights.

 

It is simply wrong that they can be run from a constant voltage supply. They need a higher supply and a resistor each, as I have been saying from the start.

Yes, you and I know it is simply wrong BUT in the modelling realm it is done all the time. And works. And Bob, with raw LEDs and not with specialized model lighting.

- from another episode of dj’s Believe It Or Not

 

Just stick in a 1kΩ resistor and everything will work. I know, this will blow your minds, but in practice it works well enough for our models.

With a 3.3V supply you will get well under 1mA that way. The lowest Vf white LEDs I could find were 2.7V @5mA.

And we know from the TS they are too dim at 3.3V with no resistor. Are you saying the resistor will make them brighter? (I know you are not.)

 

pretty good, but you absolutely need a 1kΩ resistor for each light in parallel. The math shows that for each additional LED, the LEDs will get dimmer and dimmer. With so many LEDs, they may not light at all.

I had explained several times earlier that I am powering 14 SMD LED lights and Bob, up above, had said using a resistor for each LED with 4.5v supply would solve the current problems, but now you are saying that would make the lights really dim. This is why I’m getting confused about a solution, maybe I’m not understanding your comments.

 

Yaakov’s idea requires resistors also. I thought he mentioned using the power packs with the board (too late tonight for me to read back as to what exactly he said) but your experiments with 6V seem to indicate that won’t work. I suspect that it won’t work either as these power packs are only 5V. The advantage of Yaakov’s solution is instead of many batteries, a single rechargeable power pack will work and take up the smallest space. With two such power packs, one could be in the diorama while the other charges from any USB port or charger.

So, IMHO, the best solution is a 5V cell phone power pack, and a 1kΩ resistor in series with each LED. It’s not clear why you don’t like the idea of using a resistor.

Or putting six C (or D) cells into a battery holder for 9V (for a while, until they drop to 8V, at which time they will appear to be dead). This would be in about a month. But these won’t fit into a 3/4” depth. They are 1.04” in diameter plus the thickness of the battery holder. D cells are thicker.

Or use the wall wart with the board.

I suggested a PD trigger board producing 9V, and a PD power bank. Not a 5V input.

 

Bob, up above, had said using a resistor for each LED with 4.5v supply would solve the current problems, but now you are saying that would make the lights

Who said that? They can be run at full brightness from a 4.5V battery.

The can be fairly bright from a fresh new 3V battery, but they will fade quickly.

@djsfantasi said they SHOULD be run dim for this application, but I saw no one who said they MUST be dim with a 4.5V battery.

My recommendation for the simplest long lasting solution is a 6V battery and resistors. Use the distribution board if you want, but in pass through mode.

 

I suggested a PD trigger board producing 9V, and a PD power bank. Not a 5V input.

My mistake. That certainly would be viable.

@djsfantasi said they SHOULD be run dim for this application, but I saw no one who said they MUST be dim with a 4.5V battery

Exactly

My recommendation for the simplest long lasting solution is a 6V battery and resistors. Use the distribution board if you want, but in pass through mode.

I agree with the first half. Not sure about the second statement.

but now you are saying that would make the lights really dim.

Let me clarify. If you used one resistor for all of the LEDs, thst would be problematic. One resistor for each LED is desired.[/QUOTE]

 

@Doane2u
Do you dislike using resistors? Why?

 

Ok, thanks for clarifying. I was not clear about the space under the board, sorry, stupid of me.. there is 3/4” depth which is the 1x2 flat frame with plywood and foam scenery above it and below the frame are 4 3/4” feet in the corners so I actually have 1-1/2” clearance. That’s how I have been able to fit the 2x c cell battery packs under there that have sliding covers. The are thicker than the 3/4” 1x2 frame but you can’t see them unless you get down at surface level. Sorry I didn’t clarify that earlier.

 

Last night I replaced the current 14 light diorama 2x 9v // supply with an 8 cell AA flat pack battery case I have putting out 12v to drive the regulator current limiting board. If the AA cells are 2500 mAh each that should last quite awhile, a LOT better than the 2x 9v batteries I was disappointed in. The board is current limited for the SMD lights so I see no need to use resistors with it? I have another diorama using this board with about 8 SMD lights powered by a 12v wall dc unit and no resistors and have had no problems, but I would rather have it self contained. And another one has 5 of the SMD lights with a 2x c cell 3v pack directly and no resistors and has been working fine for about a year of brief on periods to show customers.
I agree that your other rechargeable options are a better solution, I don’t like the battery waste either. I would like to figure out how to do the recharge option Yaakov mentioned, but will probably need some specifics about how to do it. From the very start I should have asked, how do I light 15 of these 3v SMD lights with a self contained powered source!

 

Last night I replaced the current 14 light diorama 2x 9v // supply with an 8 cell AA battery case putting out 12v to drive the regulator current limiting board.

And did it work?

 

And did it work?

Yes it works fine, the board will handle AC or DC in and I mentioned I have been running that other diorama with a 12v dc wall drive with no problems.

 

Yes it works fine, the board will handle AC or DC in and I mentioned I have been running that other diorama with a 12v dc wall drive with no problems.

Now this is what does not make sense. If the output is coming from a 3.3V regulator, it makes absolutely no difference whether you give it 6V or 12V (except that the 12V will waste more power and produce more heat.). The lights should operate exactly the same.

Please measure the input and output voltages on both boards with the LEDs connected (no resistors) while feeding them 6V and 12V. And tell us how the lights look for each case.

The only way it makes sense to me is that the LEDs used with the two boards have different Vf, making one set brighter than the other. This is why you cannot drive LEDs with a voltage. One batch may behave quite differently than another. The resistors make up the difference.

 

Now this is what does not make sense. If the output is coming from a 3.3V regulator, it makes absolutely no difference whether you give it 6V or 12V (except that the 12V will waste more power and produce more heat.). The lights should operate exactly the same.

Please measure the input and output voltages on both boards with the LEDs connected (no resistors) while feeding them 6V and 12V. And tell us how the lights look for each case.

The only way it makes sense to me is that the LEDs used with the two boards have different Vf, making one set brighter than the other. This is why you cannot drive LEDs with a voltage. One batch may behave quite differently than another. The resistors make up the difference.

Ok, will do

 

From the very start I should have asked, how do I light 15 of these 3v SMD lights with a self contained powered source!

You can by first stopping trying everything under the sun. Mixing boards, 1kΩ resistors, various voltages, etc…

…And design or accept the design of a board or system that works for your specific case.

To design what you need, we need to know how many hours you’d like it to run??? I’ll just assume your power source is 2500mAh.

14 leds at 15mA requires almost 3A. With a 2500mAh source, the LEDs will run for less than an With 2 9V common batteries, it would run for ~30 minutes. If you were to parallel the AA batteries in two sets of 4, you’d still have 6.0 volts and 5,000mAh, which would run for ~1h20m.

The board was designed for a narrow circumstance. Certain LEDs. Certain power input. And you’re trying to muck around with those values and as you’ve seen, it doesn’t always work like you want. I’d put the board aside!

I’m assuming a power pack of 4 AA batteries which will provide 6.0V. Connect the - terminal to the negative lead of all the LED lights. Connect the positive terminal to one side of 14 220Ω resistors*. Connect the other side of each resistor to each of the LED lights. One resistor: one LED.

Re: my re: * note. I got 220 by using the formula I mentioned earlier. I had to adjust my choice because 186Ω is not a standard value. 220 is. I used 3.2 V for the LED because that’s what usually a white LED has as it’s forward voltage (Vf). And per the specs it runs on 0.015A.

R = (Vs-Vf)/(current)​

R = (6,0-3.2) / 0.015​

R = 2,8 / 0.015​

R = 186Ω = ~220Ω​

​

I know, that’s a lot of math. But it’s the foundation for what you’re trying to do. LEDs run at various levels of current. From 7mA to 20mA. That’s why different resistor values work (and where the “just use a 1kΩ resistor” came from)

You can temporarily wire up various resistor from 2.2 Ω to 3.0 kΩ. The SMD light will go from very bright white to a dimmer yellow light. That’s what I did for my model rr layout. I run at 12V. Interior apartments and hallways use a 2.2kΩ resistor. Exterior lights and signs plus storefronts just use the included resistor.

I don’t have your LED lights to test my calculation. So you’ll have to try various resistors. You could even customize each light of the diorama individually by doing this. If you want to go crazy, use a miniature 3kΩ potentiometer inline with a 230 Ω resistor to give you fine control of each light!

 

BobTPH:
OK, I retested everything. I used fresh batteries on the two different boards with the dimmer max on both and no resistors.
All lights are the 0402 SMD LED lights

The 12 connector board:
8AA in series for 12v with the 14 lights attached 3.6v out each connector
12v wall DC supply 3.6v ea light connector

The other 28 connector board:
2 c cells 3.4v in = XX nothing out
4 c cells 6.2v in = 3.5v out at light connectors with no lights attached 3.4v out with 1 light attached
12v DC wall supply = 3.5v out at connectors with 1 light attached

Looking back at post #11 I must have screwed up something, maybe the lighting in the room was making them look dim or the dimmer on the board was set wrong... sorry...

 

14 leds at 15mA requires almost 3A.

No, it requires 210 mA. About 10 hours operation from AA cells. And if you are right about wanting them dim, they probably need a lot less than that.

 

OK, I retested everything. I used fresh batteries on the two different boards with the dimmer max on both and no resistors.

So what you have proved is that it has a crappy voltage regulator. The 3V case is correct, the regulator needs 4.3V to operate. That is called the drop out voltage. The output voltage should be 3.3V for all inputs above that.

And once again, you said something about the board regulating current. It does not do that.