I have a motor that has a 24 Vdc (15 ohm) brake attached that tends to weld / burn up the contacts in the ice cube relay that controls it after a year or so. I was wanting to put some protection on it. Would it be better to put a flyback diode across the brake or an RC snubber across the relay contact?
4
-
3\$\begingroup\$ Possible duplicate of Correct use of Flyback or Snubber diode across Motor or Transistor? \$\endgroup\$– Keith MNov 11, 2015 at 20:57
-
\$\begingroup\$ I was wanting to know which snubbing device would work best for my application. A flyback diode OR an RC snubber. \$\endgroup\$– David E.Nov 11, 2015 at 20:59
-
\$\begingroup\$ A bit more information is required because right now there isn't any information to imply you need any \$\endgroup\$– user16222Nov 11, 2015 at 21:13
-
\$\begingroup\$ More info: The relay contact arcs when the brake is turned off. I have observed some pitting and discoloration around the contact itself. The current draw is well within the relay's rating of 10 amps so I assume it is back EMF that is the issue. The last time the relay failed was 2 days ago and the moving common contact was stuck in the on , relay off, position. \$\endgroup\$– David E.Nov 11, 2015 at 21:42
Add a comment
|
2 Answers
\$\begingroup\$
\$\endgroup\$
You have to decide whether it is current thru the contacts that cause the problem or open circuit voltage spikes that cause problems. What do the symptoms tell you?
What does a welded contact mean - think about this - does it mean it has just gone open-circuit and an arc has caused it to splutter some contact material up into some form of plasma that has welded the contacts shut OR, does it mean that the contacts have welded upon making initial contact due to long-term surface erosion of the contact giving higher-than-normal contact resistance.
I'm using your words here and extracting symptoms that make sense to the words you have chosen to put in your question.
answered Nov 11, 2015 at 21:13
\$\begingroup\$
\$\endgroup\$
voltage creates the arc circuit, current through the circuit burns away the metal, both energy factors are present when erosion occurs. a typical sized RC will possibly absorb much less energy than a sizable diode can allow on a hispeed discharge. capacitor absorbs energy and resistor dissipates it. diode channels the energy elsewhere so that the system natural and other impedance discharges it and other occupants on that circuit may then need to deal with it also. if the discharge energy is small then R/C may work but calibration of the size is critical. a diode is possibly more cost-effective if you can live with the reverse voltage on the brake. this design was not a good application for an unprotected ice cube. sounds like a specmaster catalog-data selection and not an applications qualification.
