On 07/20/2020 07:43 PM, Gene Heskett wrote:
Interesting. I wonder if he accidently fixed an unwanted ground, or made
a bad one good doing it? Murphy is alive and well despite our reward
funds.
Yes, he had unwanted grounds (loops) all over the place.
Actually, he has NO ground, only a neutral, which is
connected to some 120 V loads. Clearly not NEC compliant.
Also, he had the grounds for the servo amps looped all over
the place, had the signals and grounds to the servo amps
following wildly different paths, all sorts of stuff. I had
him rewire so the signal and ground
for the servo amp inputs were bundled together, and logic
power and enable follow the shortest path.
He had to rewire the thing at least a dozen times, but it
eventually cleared up the issues.
I just instinctively know how to wire signals in a
high-noise environment, so I didn't know how touchy
things actually were.
One of the shortcuts I took in my servo amps was to not
isolate the power stage from the logic, and to
only have one ground, common for both the power stage and
the logic. I SHOULD have also opto-isolated the enable pin
on the servo amp. So, if you have long wires on that common
ground, a star connection from the distant motor power
supply, large voltages will appear on the ground for the
logic as well.
That was the basic problem. I had to have him put a
terminal block as close to the servo amps as
possible, so the path from one amp's ground to the other was
as short as possible. Then, bundling the PWM, direction and
ground to the servo amps finished the fix.
I've sold 124 of these PWM servo controllers, and NEVER run
into a problem like this. I've had a few people run into
minor noise issues, but this one really had me going in circles.
Jon
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