Poor man's auto-dimming of LED strings? - The Planted Tank Forum
 
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post #1 of 8 (permalink) Old 01-18-2012, 06:03 PM Thread Starter
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Poor man's auto-dimming of LED strings?

Now that my time-consuming DIY setup has been going for quite a while without any serious issues, I find myself needing to create some problems to solve. Here's my latest idea:

I'd really like to have some sort of automatic dimming circuit on my DIY LED fixture. The fixture uses two Meanwell 48Ds. For those not familiar with the lingo, these are voltage-controlled, not PWM-controlled--they put out 0-1.3A depending on a 0-10v control voltage that you supply.

Right now I generate the control voltage with a wall-wart-plus-variable potentiometer circuit. The wall wart puts out 10v, and I use the potentiometer to dial that voltage down as necessary. The system works well, but it's purely manual system--I haven't yet figured out how to automate it so as to get a nice sunrise or sunset effect.

I had a crude idea to skin this cat. My thought is to use two different wall warts, in series, each connected to a different timer. Let's say one is 3v and the other is 6v. If you set the timers right, could you wire up a system that would provide either 3v, 6v, or 9v depending on the time of day? Or can you not use wall warts in series like that?

sns26

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post #2 of 8 (permalink) Old 01-18-2012, 06:52 PM
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i dont think there is a electrical solenoid. :P

the moment u cut power to one, id assume the circuit would be cut and the entire circuit will shut down.

I dont see how you could apply resistance or variable resistance without crafting a new circuit.
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post #3 of 8 (permalink) Old 01-18-2012, 08:48 PM
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My first thought when starting to read your post was double wall-warts in parallel on different timers. Funny you had same idea, and the next paragraph explained it. I have never tried that, nor do I know if it is safe/electrically sound, so be sure to look into that. Maybe try the diy forum on head-fi.org, explain what you are trying to do, and likely get an answer. That forum was invaluable when I was building my current headphone amps, which are both powered by wall-warts.
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post #4 of 8 (permalink) Old 01-18-2012, 11:24 PM
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Wouldn't a capacitor be your friend here?

Put it in line with the control voltage supply...

Gradual ramping of the voltage as the capacitor charges and then as it disccharges will give you a simple, and REALLY cheap answer.

I think someone who actually understands electronics should cut in here and explain why this is either a good or bad idea!

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post #5 of 8 (permalink) Old 01-18-2012, 11:53 PM
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It may work your way but it can have electrical problems. First thing would be to add some N14148 diodes on the 3V and 6V source to not allow any power to creep back into the source voltage. Second, wall warts are rated for their voltage at MAX draw. So if it's a 12v, 1A rated wall wart, it may put out 17v with 0A, 15V with 0.5A, etc. They are not a consistent source of power. It may work, but I'd certainly try it out on my protoboard first and measure the voltage. Power can be dangerous though, so only take this on if you're confident. My first DC rectifier bridge didn't work out and send diodes firing in to the air. Blast cap's wide open too on my protoboard trying stuff.

The other way to do it without timers would be using something like a Arduino Nano board but they only provide a low ampege output, so I would use that to trigger relays to add the additional voltages. Your way may work, again I'd proto it and measure with a multimeter for whats coming out of it before potentially blowing my LED's or drivers and I'd certainly use some diodes to prevent backwards voltage, caps to clean the power a bit, etc.

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post #6 of 8 (permalink) Old 01-19-2012, 03:54 AM
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Quote:
Originally Posted by silvawispa View Post
Wouldn't a capacitor be your friend here?

Put it in line with the control voltage supply...

Gradual ramping of the voltage as the capacitor charges and then as it disccharges will give you a simple, and REALLY cheap answer.

I think someone who actually understands electronics should cut in here and explain why this is either a good or bad idea!


I looked into this a bit more, and apparently the two different voltage power sources is a terrible idea, because if they are both on at the same time, the higher voltage one will dump into the other and fry stuff/burn your house down.
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post #7 of 8 (permalink) Old 01-19-2012, 09:38 AM
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Quote:
Originally Posted by Secretninja View Post


I looked into this a bit more, and apparently the two different voltage power sources is a terrible idea, because if they are both on at the same time, the higher voltage one will dump into the other and fry stuff/burn your house down.
I wasn't talking about using multiple power sources.

Simply a diode to prevent washback and a large capacitor in series on his 10V supply should provide a slow build and fade to and from 10V as the timer turns it on and off.

Since this is on the control side, and not the power side there is much less risk or terminal disaster.

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post #8 of 8 (permalink) Old 01-02-2017, 08:23 PM
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cheap led sunrise /sunset

Use a TS420 around 18.00 from ebay
You can dim upto five mean well LDD drivers by taping into the gate leg of each of the contollers
5 channels mosfets to dimming pins of the ldd drivers
I built it and it does work well
though I did use one of the mosfet channels to pwm a couple of fans

check out link to web page below

Connecting high power LEDs to the TC420
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