Hi, 

Thanks for the reply and the advice.  There is in fact a dead short between USB and PC chassis, isolating the case will fully isolate kflop and the PC from earth ground. I will go ahead and do that.  

On Sun, Nov 15, 2015 at 2:55 PM, Hardy Family hardy.woodland.cypress@... [DynoMotion] <DynoMotion@yahoogroups.com> wrote:

 

Ideally, have all signal/power grounds return to a common point ("star ground").  Given that the USB ground is a necessary connection, that might not be practicable.  So the next best option is to ensure that there is only one signal/power ground connection to each component of the system - star ground where possible, otherwise daisy-chain.  If even that is impractical, then try to minimize the area formed by any ground loops, by bundling ground wires next to each other. 

So in your case, isolating the PC case would only be necessary if there is a dead short between the USB ground and the PC case.  In my experience, embedded PCs are designed to be either completely isolated or isolated at high frequency by a choke or bead.

Earth ground should be protective only.  You really don't want to use it (machine chassis, PC case etc.) for any normal power or signal reference.

Regards,

SJH

On Sun, Nov 15, 2015 at 1:46 PM, Colin Fera colin.fera@... [DynoMotion] <DynoMotion@yahoogroups.com> wrote:

 

Hi,

The question:  Should I put a plastic plate between my PC metal case and the aluminum plate its mounted on (mounted with my drives and kflop+kanalog) in order to prevent kflop+kanalog from getting earth ground at its DC ground through the USB plug?

background info:

I am using a small form factor vesa mount PC, with  a nice all metal case.  I have this mounted with my kanalog+kflop and 3 servo drives on a 2 foot square aluminum plate which I plan to turn into an enclosure once I have everything working.

The plate is earth grounded through the drive heat sinks as well as a noise filter and the mill chassis.  

So I have realized that the kflop ground is getting earth ground through the USB shield ground which is getting earth ground through the interface between the PC metal case to aluminum plate interface.

Thanks,

Colin

Woah - you should not have any connection to neutral on your equipment side.  The 10v you are seeing indicates a fairly high unbalanced load on your ac circuit, but should have no relevance for your equipment.  Any DC connection is a bad fault since neutral and active can sometimes be swapped, or neutral can disconnect at the panel leaving everything live.

If you are using the typical "brick" type supply, then you should be good to go because they will be isolated at DC.  Only your earth ground will run the through the supplies, if anything.

Regards,
Sjh

On Nov 15, 2015 5:31 PM, "Colin Fera colin.fera@... [DynoMotion]" <DynoMotion@yahoogroups.com> wrote:

 

Hi TK,

I was talking about isolating the PC case from earth, not the KFLOP.   So looking at your posted link should I leave the PC case grounded?  The PC power supply and the flop for that matter are small switch mode style supplies like what laptops have.  

Ok so I tried isolating the PC.  When I do this I get ~ 10v  between the machine chassis (earth ground) and neutral, through the flop power supply. Any thoughts on if this is ok?  

I am using a sub panel so neutral is NOT bonded to ground in the panel.  I don't think this matters but that sub panel is on a GCFI breaker.

Thanks.

On Sun, Nov 15, 2015 at 4:37 PM, TK tk@... [DynoMotion] <DynoMotion@yahoogroups.com> wrote:

 

Hi Colin,

You might read this wiki article:
http://dynomotion.com/wiki/index.php?title=Noise_-_Typical_Problems_and_Resolutions#Ground_Loops

The mounting holes on all our boards (except the ones labled "GND") are fully isolated.  So adding a plastic mounting plate shouldn't be required or make any difference.

HTH
Regards
TK

On 11/15/2015 3:40 PM, Colin Fera colin.fera@... [DynoMotion] wrote:

 

Hi, 

Thanks for the reply and the advice.  There is in fact a dead short between USB and PC chassis, isolating the case will fully isolate kflop and the PC from earth ground. I will go ahead and do that.  

On Sun, Nov 15, 2015 at 2:55 PM, Hardy Family hardy.woodland.cypress@... [DynoMotion] <DynoMotion@yahoogroups.com> wrote:

 

Ideally, have all signal/power grounds return to a common point ("star ground").  Given that the USB ground is a necessary connection, that might not be practicable.  So the next best option is to ensure that there is only one signal/power ground connection to each component of the system - star ground where possible, otherwise daisy-chain.  If even that is impractical, then try to minimize the area formed by any ground loops, by bundling ground wires next to each other. 

So in your case, isolating the PC case would only be necessary if there is a dead short between the USB ground and the PC case.  In my experience, embedded PCs are designed to be either completely isolated or isolated at high frequency by a choke or bead.

Earth ground should be protective only.  You really don't want to use it (machine chassis, PC case etc.) for any normal power or signal reference.

Regards,

SJH

On Sun, Nov 15, 2015 at 1:46 PM, Colin Fera colin.fera@... [DynoMotion] <DynoMotion@yahoogroups.com> wrote:

 

Hi,

The question:  Should I put a plastic plate between my PC metal case and the aluminum plate its mounted on (mounted with my drives and kflop+kanalog) in order to prevent kflop+kanalog from getting earth ground at its DC ground through the USB plug?

background info:

I am using a small form factor vesa mount PC, with  a nice all metal case.  I have this mounted with my kanalog+kflop and 3 servo drives on a 2 foot square aluminum plate which I plan to turn into an enclosure once I have everything working.

The plate is earth grounded through the drive heat sinks as well as a noise filter and the mill chassis.  

So I have realized that the kflop ground is getting earth ground through the USB shield ground which is getting earth ground through the interface between the PC metal case to aluminum plate interface.

Thanks,

Colin