If using a relay or contactor with LV electronics, use a R/C snubber across the coil.

 

Given that the input is 110 volts AC, it is not a low voltage circuit. Except by some standards.

 

The reference was to any L.V. electronics that May also be included in the device or installation!

 

Here's the schematic.





It's a 110 V DC relay driven by a 110 V AC supply that is half-wave rectified by the 1N4005 and filtered by the 10 μF capacitor.

Without the capacitor, the relay armature would vibrate since the applied voltage would alternate between zero and 155.54 V peak (110 * 1.414 = 155.54 V) in consecutive half-cycles.

The 4.7 kΩ voltage-dropping resistor is used to ensure that the average DC voltage does not exceed 110 V.

Nandu.

 

Here's the schematic.

View attachment 268575

View attachment 268577

It's a 110 V DC relay driven by a 110 V AC supply that is half-wave rectified by the 1N4005 and filtered by the 10 μF capacitor.

Without the capacitor, the relay armature would vibrate since the applied voltage would alternate between zero and 155.54 V peak (110 * 1.414 = 155.54 V) in consecutive half-cycles.

The 4.7 kΩ voltage-dropping resistor is used to ensure that the average DC voltage does not exceed 110 V.

Nandu.

There is an AC operated version of that relay available, and unless the relay is soldered into the system, unplugging the relay and plugging in an AC operated version will be very simple.
Of course, this is based on only the information presented, which is obviously only a very small part of the system. And that link was to a collection of information about crystal radios, which it is not clear how that relates at all.

 

You're right, MisterBill2. A 110 V AC relay would reduce the part count to one!

That link is not related to this thread. It's the link to my blog (auto signature).

Nandu.

 

In addition, a simpler fix that will reduce the part count and improve efficiency will be to install a second diode in parallel with the DC relay coil, exactly the same as is done to reduce the spike with a DC circuit and a switch. As the supply polarity reverses the diode conducts and the current continues to flow, so the relay does not vibrate. Doing this will eliminate the need for the capacitor and both resistors. I suggested this in an earlier post but it seems nobody noticed. And the 4700 ohm resistor will not
be needed because the average voltage on the relay will be reduced.
It really does work, folks.