Re: Treadmill motors and interference
Posted by
beer@s...
on 2000-08-28 08:59:32 UTC
On 27 Aug, CAD_CAM_EDM_DRO@egroups.com wrote:
DC motor controller, for all the fanciness, uses simple phase control -
it's a glorified light dimmer circuit and most of know how noisy they
are !
That being said, there's no reason not to use a cap on the motor.
There are a couple of caveats here, though.
1. Use the smallest cap that solves the problem, recognizing that as
the cap gets larger and larger, the controller is less able to regulate
the speed of the motor. Not too big a deal - much of the "regulation"
comes from flywheel effect - but worth a bit of thought.
2. Pick a cap rated for high ripple currents ! It may self-destruct
- gloriously - if you don't.
Also, you do seem plagued somewhat more than most by interference
problems. You may wish to do two more things.
1. Put some sort of AC line filter on the low power electronics,
especially one that touts protection against " common mode noise".
2. Build an optoisolator setup for your system and use a separate
power supply to power it.
This last point is VERY important, the separate power supply is
critical. Resist at all costs using power from your computer's power
supply. Use a little wall wart if you have to.
The purpose of optoisolators in this type of control is only partly for
protection of the electronics. It would take an outrageous,
catastrophic failure of the controller to actually cause damage to the
computer. ( I'm sure this has happened, but I;ve never run across
it )
Optos are really used to solve ground problems that arise through either
the long lines connecting the equipment OR more frequently, ground
problems caused by the 110v neutral bouncing around, which can and DOES
happen.
When I RE-WIRED my electronics shop, I did it right. I RE-WIRED it
with a single point ground from EACH outlet: a separate wire ran from
each duplex receptacle back to a point on cold water pipe. Previous
to that, I could induce erroneous ( and just plain weird ) readings
using sensitive test equipment and BIG power devices. Problem went
away after the rewire.
Since no one wires their shop this way, not even me ( even though
we all should if we have sensitive electronics and big motors on the
same chunk of wire ), extra care must be taken with grounds.
One more thing .. calculate your maximum step rate, consult your
controller manufacturer for minimum allowable pulse width, then look
HARD at the datasheets for the various optos, specifically, the Ton and
Toff times. Many optos will be too slow for "stepper" use.
Alan
--
Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta
>The large amount of interference is expected. The circuit used by the
> I guess the question is, should I accept the cap as being a realistic and
> reliable solution?
DC motor controller, for all the fanciness, uses simple phase control -
it's a glorified light dimmer circuit and most of know how noisy they
are !
That being said, there's no reason not to use a cap on the motor.
There are a couple of caveats here, though.
1. Use the smallest cap that solves the problem, recognizing that as
the cap gets larger and larger, the controller is less able to regulate
the speed of the motor. Not too big a deal - much of the "regulation"
comes from flywheel effect - but worth a bit of thought.
2. Pick a cap rated for high ripple currents ! It may self-destruct
- gloriously - if you don't.
Also, you do seem plagued somewhat more than most by interference
problems. You may wish to do two more things.
1. Put some sort of AC line filter on the low power electronics,
especially one that touts protection against " common mode noise".
2. Build an optoisolator setup for your system and use a separate
power supply to power it.
This last point is VERY important, the separate power supply is
critical. Resist at all costs using power from your computer's power
supply. Use a little wall wart if you have to.
The purpose of optoisolators in this type of control is only partly for
protection of the electronics. It would take an outrageous,
catastrophic failure of the controller to actually cause damage to the
computer. ( I'm sure this has happened, but I;ve never run across
it )
Optos are really used to solve ground problems that arise through either
the long lines connecting the equipment OR more frequently, ground
problems caused by the 110v neutral bouncing around, which can and DOES
happen.
When I RE-WIRED my electronics shop, I did it right. I RE-WIRED it
with a single point ground from EACH outlet: a separate wire ran from
each duplex receptacle back to a point on cold water pipe. Previous
to that, I could induce erroneous ( and just plain weird ) readings
using sensitive test equipment and BIG power devices. Problem went
away after the rewire.
Since no one wires their shop this way, not even me ( even though
we all should if we have sensitive electronics and big motors on the
same chunk of wire ), extra care must be taken with grounds.
One more thing .. calculate your maximum step rate, consult your
controller manufacturer for minimum allowable pulse width, then look
HARD at the datasheets for the various optos, specifically, the Ton and
Toff times. Many optos will be too slow for "stepper" use.
Alan
--
Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta