Dynomotion

Group: DynoMotion Message: 878 From: ca_gray751 Date: 1/26/2011
Subject: DC Ground
I was having some trouble where anytime I activated a solenoid, I would get a step pulse on one of my axis. While troubleshooting I noticed that I had continuity between the kanalog ground and earth ground. I traced it down and it was coming through the USB connection to the kflop. I removed the USB shield and this severed the continuity as well as solving my problem of getting a step pulse when using the solenoid.

Is there a better way to severe the this connection without having to hack up a usb cable?

Thanks,
Allen
Group: DynoMotion Message: 879 From: Tom Kerekes Date: 1/26/2011
Subject: Re: DC Ground
Hi Allen,
 
Yes the USB Shield is connected to DC gound at KFLOP.  We have found this gives the best USB reliability but does potentially make ground loops.  Usually the DC ground is connected to the earth ground at the PC anyways.
 
Did you try a reverse diode across your solenoid?  Otherwise when you break the circuit a huge voltage spike might be generated (ie 40,000V spark).
There are now low cost USB isolator devices that will isolate both the DC ground as well as the shield from the PC.  I've been meaning to try one to see if they help or cause any problems.
 
Regards
TK
 

Group: DynoMotion Message: 881 From: ca_gray751 Date: 1/26/2011
Subject: Re: DC Ground
It definitely created a problem on this machine. Funny thing is I currently have two machines built and the other machine, which is almost identical, has not had this problem.

I have a USB isolator that you mentioned. I tried it on another system that was using a different type of USB controller. I cant say it solved the problem that I was having because it created whole new ones. I disconnected it and put it on the self.



--- In DynoMotion@yahoogroups.com, Tom Kerekes <tk@...> wrote:
>
> Hi Allen,
>
> Yes the USB Shield is connected to DC gound at KFLOP.  We have found this gives
> the best USB reliability but does potentially make ground loops.  Usually the DC
> ground is connected to the earth ground at the PC anyways.
>
> Did you try a reverse diode across your solenoid?  Otherwise when you break the
> circuit a huge voltage spike might be generated (ie 40,000V spark).
>
> There are now low cost USB isolator devices that will isolate both the DC ground
> as well as the shield from the PC.  I've been meaning to try one to see if they
> help or cause any problems.
>
> Regards
> TK
>
>
>
>
> ________________________________
> From: ca_gray751 <agray@...>
> To: DynoMotion@yahoogroups.com
> Sent: Wed, January 26, 2011 9:12:21 AM
> Subject: [DynoMotion] DC Ground
>
>  
> I was having some trouble where anytime I activated a solenoid, I would get a
> step pulse on one of my axis. While troubleshooting I noticed that I had
> continuity between the kanalog ground and earth ground. I traced it down and it
> was coming through the USB connection to the kflop. I removed the USB shield and
> this severed the continuity as well as solving my problem of getting a step
> pulse when using the solenoid.
>
> Is there a better way to severe the this connection without having to hack up a
> usb cable?
>
> Thanks,
> Allen
>