Author Topic: Yet another relay switching question...  (Read 1186 times)

Entrant_21

Yet another relay switching question...
« on: June 02, 2009, 08:19:07 PM »
Hi, I'm using a relay as a method of remote bypass in a pedal and theres a loud pop when its de-energised

I have read all I can on GEOFEX on relays and have tried using a capacitor and diode across the voltage pins, this reduced the pop somewhat, but not a lot.

Are there any other solutions to this?

I have read about a voltage ramp circuit, which makes sence to me but have not seen a schematic for it.

thanks to anyone who can help :)

BAARON

Re: Yet another relay switching question...
« Reply #1 on: June 02, 2009, 09:17:05 PM »
The pop might be from the sudden draw/lack of draw of current from the relay, much like the LED pop you sometimes run into.

Perhaps try the method mentioned here for eliminating LED pop?

http://www.muzique.com/lab/led.htm

Just make sure you're still feeding enough power to your relays once you've got some little current limiting resistors in front of them.

Also, if you have more than one relay, make sure they each have their own current limiting resistor.  Don't just share one between them all.
B. Aaron Ennis
If somebody makes a mistake, help them understand what went wrong.  Show them how to do it right.  Be helpful.  Don't just say "you're wrong, moron."

brett

Re: Yet another relay switching question...
« Reply #2 on: June 03, 2009, 02:48:03 AM »
Hi
the induced voltage when you switch off a relay can be hundreds of volts (due to the inductive effect of the electromagnet).  It is important to prevent this peaking too high, and it is also important not to let this voltage collapse too quickly.  The diodes that you see across relays are for dumping this voltage, but they are highly conductive and generate high peak currents (potentially spraying RFI). 

If the relay has 100uH inductance, I *think* a resistor of 1k to 10k should be about right (LR = 0.01 to 0.1 s)
cheer
Brett Robinson
Let a hundred flowers bloom, let a hundred schools of thought contend. (Mao Zedong)