Xmas light string controller

I'm pretty sure your assumed pin layout is wrong given the SCR would blow itself up if you put the lighting load on the gate. More than likely you have SCRs that use an alternate pin configuration than whatever data sheet you looked at showed or you read one of them wrong.

 

That would make sense. I'll look for another pin configuration spec

 

You are right. The pin out spec for my XL1225 thyristor had to be wrong. It showed the light string connected to the gate. I assume that the gate is connected to the "black blob", the anode is connected to the light string, and the cathode to ground. So I rewired the new SCR (TN1610H-6T) the same way. Now I get no lights at all lit on the new SCR string when I just replace the old one with the new one. Your suggested new circuit should correct that. I will use R1 in place of the light resistance load. Correct? Same value as the lights? The rest is pretty straight forward. Thanks again for all your help. It's guys like you that make life much easier.

 

IT WORKS!!! I treated the left side of your circuit as the existing board and just added the resistors on the right along with the new SCR and lights. You're an electronic genius. Thanks for all of your help.

 

Your welcome.

 

Just wanted to let you know I tried 5 strings of lights in parallel with the circuit you recommended. The 150 ohm resistors burnt up in about 5 seconds. They were 2 watt resistors. Thought that was big enough but not by a long shot. I think I burnt out the circuit board too. I can replace the board with another one. Any more suggestions? Thanks.

 

If you had been able to measure the voltage across that resistor while it was burning out, you can figure how high a wattage you need in that resistor. I find it a bit odd though that the resistor burned out soon enough for you to know it was the resistor but then everything else died too, unless the resistor failed short which isn't usually the case.

Maybe get a few higher wattage resistor and put them in series and remove them one by one until the thing has a good balance between temperature and functionality.

 

Replaced the resistors with the same wattage and replaced the circuit board too. Still getting nothing even with one string. I got something else wrong. Still digging. Thanks for your help. I first started with a quarter watt 150 ohm resistor on one string of lights. It burnt out quick there too but not before I figured that with 5 strings it should need just under 1 watt. That's when I bought 2 watt resistors. Must have figured wrong.

 

Got it working again with one string. I'll take it slow from here.

 

Got 2 strings working in sync but when I went to 3 strings the controller started acting irregular. With 4 it got even worse. Maybe next Christmas. Thanks to dknguyen and tcmtech for your help.