Dimming an AC/DC Power Converter

[twalker1998]

For a show I'm working on at my high school, we're wanting to put LED strip lights on part of our set. The link below are the lights we bought.

https://www.amazon.com/Landscape-de...953686&sr=8-4&keywords=dimmable+led+strip+12v

We want them to be dimmable, and although the amazon page says they are dimmable, there is no sort of control mechanism to dim the lights. My question is, if I were to hook the 12V power supply to a dimmer on our dimmer rack, would that actually dim the LEDs? I'm worried that dimming a power supply like that would fry the power supply and not actually dim the LEDs, and I'd rather not test it to find out. We're obviously operating on a budget, and this was about all we could afford. Any advice would be appreciated.

 

[TupeloTechie]

I wouldn't try to dim the power supply, or even have it on a dim-able circuit. For this kind of LED Strip you will need a separate, DMX controlled, Pulse Width Modulation Dimmer, or decoder as they or commonly called. You then plug your power supply into the decoder. Luckily as long as you aren't looking for 16-bit resolution, they are pretty cheap. A quick search on Amazon found this for $25.99. It includes clear wiring diagrams and 3 channels, in case you would like to split up control over three parts of the set.

 

[JD]

Although the LEDs are dimmable, the power supply is not. Any power supply that contains a transformer, capacitors, or switch-mode drivers would react in a very negative way. If you can live with a stage hand dimming them from stage, you could resort to a 20 ohm 50 watt wire-wound variable resistor line this: http://www.walmart.com/ip/Ceramic-D...29710&wl11=online&wl12=45514755&wl13=&veh=sem
You would put the 12 volts across it and feed the LED strand from the tapper to negative. It will get very hot! (by nature) and it will add a bit more than 1/2 amp to the draw on the supply, but it will dim the strand.

 

[SS Minnow]

Although the LEDs are dimmable, the power supply is not. Any power supply that contains a transformer, capacitors, or switch-mode drivers would react in a very negative way. If you can live with a stage hand dimming them from stage, you could resort to a 20 ohm 50 watt wire-wound variable resistor line this: http://www.walmart.com/ip/Ceramic-D...29710&wl11=online&wl12=45514755&wl13=&veh=sem
You would put the 12 volts across it and feed the LED strand from the tapper to negative. It will get very hot! (by nature) and it will add a bit more than 1/2 amp to the draw on the supply, but it will dim the strand.

NOOOOOO! DO NOT plug the psu into a dimmer. It will not dim the LEDs and will likely smoke the power supply at the very least. Looking at the pic of the stuff in the package, I see an IR remote that one would use to control the color and dimming functions. The little white box appears to be the IR Receiver/Controller. Without a dmx interface that works with the LEDs you are likely limited to controlling them with the remote. Cheers...

 

[Josh Rawls]

NOOOOOO! DO NOT plug the psu into a dimmer. It will not dim the LEDs and will likely smoke the power supply at the very least. Looking at the pic of the stuff in the package, I see an IR remote that one would use to control the color and dimming functions. The little white box appears to be the IR Receiver/Controller. Without a dmx interface that works with the LEDs you are likely limited to controlling them with the remote. Cheers...

I think JD meant connect the output of the PSU to the variable resistor. That would work just fine.

 

[n1ist]

That particular LED strip is simply groups of three LEDs in series with a resistor, so putting the variable resistor in series between the positive output of the supply and the strip will work (and would be better than wiring it up as a voltage divider...) . For strips that have constant-current sources, then the only way to dim them is with PWM.