>
> 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  
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>

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
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