Submitted by irreligiosity t3_z27xi1 in DIY
I'm doing a Christmas lights show this year with addressable pixels and want to include some of my old RGB LED lights, but the inline PWM controller for them prevents me from rapidly switching them on and off because it takes a second to boot up. I figured as a solution I could just keep the controller powered and use a relay to switch the power to the LED strand, but this results in the LEDs being dimmer than normal.
I tried using both a BJT and Mosfet in conjunction with the solid state relay, but it didn't make any difference - the LEDs were still dimmer than they should be. How can I pass the PWM signal from the controller to the LEDs without adding a significant amount of resistance and dimming the lights?
The light strand is a 24v, 300mA rgb LED with a built in PWM controller.
The solid state relay is SSR-25DA 25A 250V
The Mosfet I tried was a 2N7000G
The BJT I tried was a MJE172
Thanks for the help.
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**Resolved - going to use SPDT relays. Thanks for the help.
ntyperteasy t1_ixf63yr wrote
This is a bit complicated for a DIY thread, but here, hold my beer...
I found one data sheet for that relay and it says it has a 1.6 V "voltage drop" which is an indication of the loss in the relay when on. This is a poor man's way of specifying the "on state resistance". This is why you are getting such a dim output. Since you are controlling the low level signal after the PWM controller, the voltage drop is too much. If you insist on doing it this way, then you need a way to increase the voltage again, but that seems a bit ridiculous...
If you buy the SSR from a place like Digikey that lets you sort by specifications and has detailed datasheets, you can sort them by the "on state resistance". They have models that range from 0.001 ohm to 10 ohms. I will guess you have one on the higher end of this range...