I'm sorry I have not followed this thread so I may be talking out of turn here. But what is the picking voltage of the relay? Can you try tacking a zener across the coil of the relay? Or a zener and a fast switching free wheeling diode? If the transient is very fast, the zener will not work but if it is slow enough it might work. The reversed diodes with the zener in parallel might work. Varistors can sometimes shunt motor noise, but they must be carefully selected. Is it a DC motor? Is it a servo or stepper? If it is a DC motor I am not sure that a varistor is a good choice. I have only used them on AC motors. But someone else on the list would know. I have had good success with diodes to shunt transients and back emf. I would be interested to know how you solve the problem. ----- Original Message ----- From: "Cedric Chang" To: "Microcontroller discussion list - Public." Sent: Monday, March 24, 2008 11:42 PM Subject: Re: [EE] question on a motor noise problem 2: motor > > >> On Mar 24, 2008, at 5:56 PM, gardenyu wrote: >> >> Thanks a lot for your kind reply. >> >> I would look at D2 tomorrow, if this is really an issue, do you >> have any suggestion on cutting this surge off? RV2 is supposed to >> be a surge protector, maybe it's not strong enough. >> >> It's some new version that I have, for some reason the designer >> didn't like the snubber, >> >> the relay is certainly a problem, I noticed before that when it's >> turned off and not yet turned on, the voltage can rise quite high >> that causes the relay to click back and forth for times. Do you >> have any suggestion on related problem? Thank you so much. >> >> >>> From: cc@nope9.com> Subject: Re: [EE] question on a motor noise >>> problem 2: motor> Date: Mon, 24 Mar 2008 15:49:53 -0600> To: >>> piclist@mit.edu> > I would resume that circuitry not shown ( some >>> form of logic ) gets > a surge of voltage applied to it and that >>> it enters some unexpected > state. My recommendation is to measure >>> the voltage at pin 2 of D2. > If you are getting drive voltage at >>> pin 2 after the "stop" is pushed, > then your logic is getting >>> hammered by a voltage spike.> > Are Q4 and Q? ( the Q below Q4 ) >>> acting as an active motor brake ? > The circuitry shown does not >>> seem to offer any snubbing of the > voltage spike you would get >>> from the motor. The relay is going to > allow the motor to be >>> disconnected for several milliseconds, > certainly long enough to >>> allow voltage spiking to occur. I am > assuming the relay is a >>> "break before make" variety, otherwise I > don't see how the relay >>> contacts would survive.> > This design seems a bit strange to me. >>> I await the commen >> ts of other > PLs. The fact that R25 is missing renders C20 as >> useless.> > cc> -- > http://www.piclist.com PIC/SX FAQ & list >> archive> View/change your membership options at> http:// >> mailman.mit.edu/mailman/listinfo/piclist >> > > Without seeing the rest of your circuit, i cannot suggest a "best > solution". I can suggest that you put a voltage snubber on the DRIVE > + line. The maximum voltage you apply to the DRIVE+ line dictates > the voltage rating of the parts you use for the voltage snubber. Try > first putting an MOV ( metal oxide varistor ) across DRIVE+ to > ground. Multiply the maximum voltage for DRIVE+ by 1.1 and select an > MOV that has that voltage rating. Without knowing how much current > your motor draws and it's inductance, I would say start with an MOV > that absorbs about 5 Joules. I also don't know where you buy parts, > so I cannot suggest a source for the MOV. > > cc > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist