Display case for minis build

[whitebeard]

Hit a bit of a snag. The more lights I hook up the dimmer they all become as a whole.As you can see the middle column gets dimmer when I turn the others on. Have a light switch pack that takes D cells coming in the mail to fix the issue.

Can you post the circuit you are using (LED, batteries and resistors)?

You might also considr using any old phone charger as a DC power supply.

[phoenixcinder]

I was thinking of a plug in power supply but honestly it won't be on for long amounts of time plus it would add an ugly cord dangling from the unit I would prefer not to have. Currently the unit is running on one of those 3 aa battery packs you see fairy lights attached to all the time. I posted a wiring diagram in an earlier post

[phoenixcinder]

Are you going to remove or to paint the the Lego pieces later?

They are only temporary as they take up way to much realty. Just there to hold the slats up. I am waiting on a mini wood turning lathe to arrive in the mail so I can make proper pillars

[whitebeard]

Looked at the schematic.. LEDs typically require a resistor in series because it is unlikely that your battery exactly matches the designed voltage drop. You may increase your battery life, and more importantly, protect the LEDs by adding one. I'm not sure how an LED behaves when run over voltage... it could also be that this fixes the issue of needing more / larger bateries.

[Anderas]

I am sure how LED behave when they get too much volts.
Bigger batteries are a solution only if there is a small resistor in the circuit.

When they get too much, they give you less light for the same amperage, forever. If you continue to give too much, they turn off completely after few minutes or seconds, depending how much too much you give them.

On the other hand, when you give them less than they need, they work just fine and they even get more efficient. But of course they give you a little less light then.

Luckily LEDs are less prone to burning out than normal diodes, the light emitting feature itself works like a (small) resistor.

[whitebeard]

I am sure how LED behave when they get too much volts.
Bigger batteries are a solution only if there is a small resistor in the circuit.

When they get too much, they give you less light for the same amperage, forever. If you continue to give too much, they turn off completely after few minutes or seconds, depending how much too much you give them.

On the other hand, when you give them less than they need, they work just fine and they even get more efficient. But of course they give you a little less light then.

Luckily LEDs are less prone to burning out than normal diodes, the light emitting feature itself works like a (small) resistor.

I appreciate you are trying to simplify so I get the "like a (small) resistor" comment where in reality you cannot design the circuit treating an LED like a resistor. So we are AGREED on the above points.

However, we also have the known situation where he has more lights hooked-up and they are dim and when he hooks up fewer lights it looks good. He also has a lighted HQ board that is working fine with a similar circuit. If we assume the LEDs are not already permanently damaged (performance degraded), the question about LED behavior is:

Q: Is the light emitted purely a function of the current? Or if the voltage is wrong (too high), the efficiency for the same amount of current is compromised (temporarily)? I can imagine the possibility that the P-N junction leaks current and is rendered far less efficient by a large voltage and therefore a proper amount of amps actually results in less light (temporarily, not necessarily permanently).

If the above behavior is possible with 2-5x over-voltage conditions then adding a resistor will gain efficiency and result in the current battery powering more lights / the same lights for longer.

On the other hand, an LED output could be independent of voltage (and a function of current only) for 1-5x over-voltages and we can reasonably conclude from the dim LEDs that a resistor will not solve anything. So he can safely add a second battery in parallel to the first. In a final step, he can add resistance in the final configuration until the lights dim very slightly, then back off, to optimize battery life.

Like I said, I do not know much about LEDs.

It might be helpful if we could propose a simple non-destructive test with a second circuit using LEDS which have not been exposed to the raw voltage drop to show the proper efficiency which can be achieved? Like some number of LEDs in series where you remove one until they light up... Then you know the approximate proper voltage drop as battery voltage / number of LEDs.

Alternatively, providing the specs for the LEDs and battery would allow Anderas to quickly design the circuit.

[Anderas]

Alternatively, providing the specs for the LEDs and battery would allow Anderas to quickly design the circuit.

Just add 100 R and you're on the safe side would be what I state.

You're the one doing robotics daily, Whitebeard. I am the one who has a few 100 LEDs in the hobby room in a forgotten carton and who did experiment with them a bit, 10 years ago, sometimes with and sometimes without smoke.

Do you think a constant current source would help him?

[whitebeard]

Alternatively, providing the specs for the LEDs and battery would allow Anderas to quickly design the circuit.

Just add 100 R and you're on the safe side would be what I state.

You're the one doing robotics daily, Whitebeard. I am the one who has a few 100 LEDs in the hobby room in a forgotten carton and who did experiment with them a bit, 10 years ago, sometimes with and sometimes without smoke.

Do you think a constant current source would help him?

Thanks for the vote of confidence. I'm more of a mechanical systems and software guy. My area is dynamic systems (like robots and vehicles) and I like to write software to simulate behaviors. These days I work in the automotive sector taking sensor output (Radar, camera, etc.) to identify the driving environment. Unfortunately still lots of problems to solve there. My circuit capabilities are quite limited.

I think I finally figured out how to design a circuit with an LED in it. The LED's power consumption changes exponentially with the voltage drop, but the spec will indicate an approximate voltage drop and current value for the ideal operating point (manufacturing tolerances can be large). If you just take these as constraints, you can solve for the resistance that should go in front of it to drop the battery voltage to that level. Then you can play around in the neighborhood of that resistance to adjust brightness, etc.

In answer to your final question. Sure, if you had a constant current source set to the combined requirements of the LEDs (wired in parallel), then it would automatically setup the proper voltage. Not sure how to do this cheaply.

[phoenixcinder]

lol all of this is way over my head . Just hoping the beafier battery pack I have coming in will solve this

[whitebeard]

Just send me whatever info you have on where these LEDs came from. And what type of battery you are using (as well as the new one you plan to use). And I'll take a quick look.