I have a 120 vac solenoid that continually destroys my digital circuit that is operated within the same cable. Is there a capacitor or diode arrangement that I can install across the solenoid to prevent this from happening ??? Thanks John

 

> I have a 120 vac solenoid that continually destroys my digital circuit that is operated within the same cable. Is there a capacitor or diode arrangement that I can install across the solenoid to prevent this from happening ??? < Peculiar to run digital circuit with 120VAC in same cable. Better solution is to run separate isolated, shielded cable for 5VDC digital signals. But, could try GE V150LA20B varistor across solenoid leads. Will it work? Try it and see. Regards, Al Boake P.E. Nordberg/Metso Minerals 414-769-4668 [email protected]

 

As previous comment you should really run digital signal in seperate cable.... The varistor is a good idea, however it may be also worth looking at limiting the induced signal in the digital wiring. Maybe a zener diode or capacitor would help here? but it depends so much on the digital signal, and devices driving - receiving signal.

 

hello - If you think a snubber circuit will work to suppress any arc then use a disk capacitor / resistor snubber placed in parallel with the device on the board. Select a 0.1 mfd. 400 v cap. and a 50 to 100 ohm 1/4 watt resistor soldered in series with the cap. Place both pieces in parallel with the device. Or a Varistor V130LA10A should work. Bob Hogg www.almegcontrols.com

 

Hi John! If you MUST have them in the same cable, try this: 1. Place an RC snubber (0.1 mfd cap in series with 100 ohm resistor) across the solenoid. This will help absorb the spike generated when the solenoid is turned "off". Be sure the cap is rated for at least 200 volts and I'd recommend using at least a 1 watt resistor. 2. Add clamp diodes from the digital input to "ground" and positive supply. These "short" any spikes that do get coupled into the input to the appropriate power rail instead of damaging the input. For best results, Shotkey type diodes should be used. I'd seriously consider separate cables and/or shielding if possible. Harvey

 

> I was working on a startup of a clean in place system in Canada when the snubber network across a steam valve solenoid failed. (400v .1 uf capacitor and 1/4 watt resistor) the capacitor shorted and smoked the resistor and subsequently spikes propagated back through ground to a TTL level controller. The controller went nuts and consequently went into a pre mature fresh water rinse and caved in a tank due to thermal shock.

Afterwards in doing forensic studies of the situation I found that spikes can exceed 1000 volts. I believe something a little more substantial than 400v caps and 1/4 watt resistors are in order for 110v snubber networks.

regards,

frank