best method for converting 120vac to 5vdc

Thread Starter

wlbooth08

Joined Sep 2, 2020
1
I'm and hvac contractor. and i want to make a tester that i can plug directly in to circuit broads that have multiple 120vac signals. i want to make a tester to plug directly to the board to see if they are getting a voltage. i know i can just use a multi-meter just trying to make my job more efficient. I would like to be able to illuminate a few 5vdc leds. the circuit will share a neutral but multiple 120vac signals. Do they make a relay that will use a 5-12vdc relay that has a 120vac trigger?

Thanks in advance.
 

bobcroft

Joined Aug 22, 2011
5
I'm and hvac contractor. and i want to make a tester that i can plug directly in to circuit broads that have multiple 120vac signals. i want to make a tester to plug directly to the board to see if they are getting a voltage. i know i can just use a multi-meter just trying to make my job more efficient. I would like to be able to illuminate a few 5vdc leds. the circuit will share a neutral but multiple 120vac signals. Do they make a relay that will use a 5-12vdc relay that has a 120vac trigger?

Thanks in advance.
If you use a relay that has a 120 VAC coil you can put the 5 VDC on the contacts to drive the LED's via suitable current limiting resistors. Ths effectively isolates the 120 VAC from the 5VDC but you would need a relay for each LED. I am not sure if that is what you were asking though. You could also do it using a capacitive voltage reducing circuit but I'll leave that to others with the proper expertise to answer more fully.
 

RPLaJeunesse

Joined Jul 29, 2018
110
Point of information: LEDs don't run off voltage, they run via current. Proper small LED operating current is in the range of 1mA to 20mA. Choosing 10mA is a safe bet for most LEDs. Most single LEDs will have a forward voltage burden well below 5V, which is why a LED needs a resistor to operate from 5V. The resistor works with the difference between forward voltage (about 1.6V for red to 3.2V for blue/white) and 5V to establish the proper operating current for the LED.
 

lyleleverich

Joined Apr 2, 2019
28
You can simply use some old style neon indicators with a resistor in series if all you want is to verify 120VAC, similar to the small, 2 lead test lamps sold everywhere. Just tie one lead of each together to the neutral if you want multiple probes.
 
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