PC ATX supplies are usually not  good choice for several reasons:

#1 they are designed for high power not the several Watts used by KFLOP and Limit switch wiring.

#2 they often have an earth GND connection.

#3 the 12V and %V are not isolated

Grounding is very complex.  Ground loops (Ground circuits connected at more than one place) should be avoided.

 

I am using a standalone 4 pin molex 12/5v power supply to power the KFLOP/KANALOG wherein I use the 12v side to power limit switches using the kanalog opto inputs.

As its comes from the factory this power supply has a 3 prong cord that connects the 12 and 5 returns to earth ground.  If I leave this connected then the kflop return will be connected to earth ground.  The USB shell and USB return are connected in the small form factor computer that I am using.  It does not get earth ground from any other source, but will through the kflop via the USB shell.

The kflop/kanalog return is also connected to the VFD and drive units but neither of these connections is common to earth ground unless it gets to earth ground through the kflop.

So the question.  Should ground the kflop (and computer, drive and VFD electronics) to earth through the KFLOP power supply or should I isolate them by leaving the ground unconnected to earth.

Hi Colin,

I don't claim to be an expert but that sounds reasonable to me.

The only disadvantage I see is if there would be a lot of noise and big voltage spikes on earth ground it would then be coupled into KFLOP and such.

It might be interesting to connect the grounds together with something like a 1K resistor to see how much current is behind that 25-30V differential.

Regards

TK

 

Hi Tom,

The PS is actually a 1.5 amp standalone hard drive power supply. Not really a large computer PS.

Ok so, I have confirmed no ground loops, it has the 1 earth connection through the PS and that's it. I guess the question is should that stay or go?

At work we use AC grounds for all shielding and isolate everything, but we have no earth ground besides seawater.  I am inclined to think that with this situation having a single point earth connection for the kflop will add some protection. The kflop power ground is 25-30v from earth when the spindle is turning if the kflop is isolated.

Colin

 

On Tue, Jun 6, 2017 at 3:15 PM, Tom Kerekes tk@... [DynoMotion] <DynoMotion@yahoogroups.com> wrote:

 

PC ATX supplies are usually not  good choice for several reasons:

#1 they are designed for high power not the several Watts used by KFLOP and Limit switch wiring.

#2 they often have an earth GND connection.

#3 the 12V and %V are not isolated

Grounding is very complex.  Ground loops (Ground circuits connected at more than one place) should be avoided.

Regards
TK

On 6/6/2017 10:55 AM, Colin Fera colin.fera@... [DynoMotion] wrote:

 

I am using a standalone 4 pin molex 12/5v power supply to power the KFLOP/KANALOG wherein I use the 12v side to power limit switches using the kanalog opto inputs.

As its comes from the factory this power supply has a 3 prong cord that connects the 12 and 5 returns to earth ground.  If I leave this connected then the kflop return will be connected to earth ground.  The USB shell and USB return are connected in the small form factor computer that I am using.  It does not get earth ground from any other source, but will through the kflop via the USB shell.

The kflop/kanalog return is also connected to the VFD and drive units but neither of these connections is common to earth ground unless it gets to earth ground through the kflop.

So the question.  Should ground the kflop (and computer, drive and VFD electronics) to earth through the KFLOP power supply or should I isolate them by leaving the ground unconnected to earth.