Running Geckos at 80V

[amishx64]

I would like to run my new Gecko 203V as close to the 80V ceiling as possible, but I don't want to trip it with line fluctuations.

How close should I run it? I was thinking 76 or 77 Volts. If it helps, I will also be running the 7A limit.

[morestuff]

The G203V does not "trip" at 80 volts, it is just
rated at 80 volts. This rating is based on the
voltage tolerance of the components inside and
reasonable engineering decisions about their
expected lifetime. Running higher voltages than
specified, especially at maximum current will
reduce life expectancy. Voltages higher than 80
volts will shorten lifetime as the voltage gets
higher that the design value. The limiting value
is somewhere above 100 volts where the lifetime
becomes milliseconds. If you want to push the
G203V as far as possible, consider the following:

1) Use a power supply that will not produce
greater than 80 volts output, even if the mains
voltage goes above what is expected. You can
achieve this with an unregulated power supply
by setting a target voltage that allows for enough
margin to allow for the mains voltage to exceed
the expected voltage by 10 percent or more. We
typically recommend 70 VDC as the nominal supply
output voltage.

2) Use a power supply whose output voltage is
regulated. This can be expensive, but will allow
you to run at 80 volts without worrying about
mains voltage fluctuations.

3) If you will have situations where the motors
will have to decelerate a large moving mass, then
provide a clamp or dump circuit that can absorb
the energy returned by the motors so that they
do not drive the DC supply voltage up by pumping
energy back in to the supply.

4) Provide the G203V drivers with good heatsinking
to keep component temperatures down. The
mounting surface of the heatsink plate must be
flat and a thermal coupling medium such as white
thermal grease or a compliant thermal gasket should
be used between the G203V and the heatsink. Fans
can help cool the heatsink, but make provisions for
making sure the fans are working and that dust or
other debris does not block the air flow.

The principal advantage of a higher supply voltage
is faster motor speed. A supply that delivers 80 volts
will result in the motors being around 11% faster than
with a supply rated for 70 volts. Is this really worth
all the cost and risk?

Regards,
Steve Stallings
www.PMDX.com

[amishx64]

Steve,

I greatly appreciate the response. Thanks for clearing up the 80V trip confusion. Plenty more to think about now.

11% really isn't much. I think I'll go with your recommendation of 70V. I also already have a dump circuit that just needs put together.

To top it off, I have mega (~8"x8"x6" or something) heatsinks I got for a very good price that I plan on using.

I think all this should fit the bill.

Again, thanks!

[morestuff]

Oops, my bad, the speed difference between 80
volts and 70 volts would be around 14%. It is
directly proportional to voltage, i.e. 80 divided
by 70 gives 1.14 or 14% more speed.

Regards,
Steve Stallings
www.PMDX.com

[amishx64]

Oops, my bad, the speed difference between 80
volts and 70 volts would be around 14%. It is
directly proportional to voltage, i.e. 80 divided
by 70 gives 1.14 or 14% more speed.

Regards,
Steve Stallings
PMDX.COM - Products for CNC and motion control applications

Eh that's still pretty small. The way things turn out, I may bump the voltage a bit due to my DIY transformer, but that's alright.

[asuratman]

Hi Steve,
Just to clarify that for motor, if we use higher voltage for example kelling DC servo motor rated 90 VDC, if we run at higher voltage about 100 vdc, it will not hurt the motor. But it will damage control.

Is it recommended to run at higher voltage above motor rated voltage for example I use granite device 160 VDC, so I can run motor w/100 vdc that is above motor rated voltage (90 vdc).

[ger21]

I believe that if you run servos over their rated voltage, they will be destroyed.

[morestuff]

The voltage rating of a servo motor is voltage across
its input terminals. The voltage output by a servo
motor driver will typically be slightly less that the
power supply voltage, so it is common to see 90
volt servo motors using servo amps connected to
a 100 volt power supply in order to get the most
out of them.

Gecko servo motor drivers would not likely live
very long if you tried to run them at 100 volts,
they are rated for an 80 volt power source.

The ratings on servo motors are mainly about
the following issues:

1) voltage - Sets the rated voltage to achieve the
rated speed. Servo motors will have a speed
limit beyond which they fail mechanically, but
this is often greater than their rated speed.
This is because the rated speed is stated as
a lower value in order to correlate to other
desirable properties that are specified at that
speed. You may be able to run the motor faster
but with lower torque for example. Don't take
this as an excuse to run a 3000 RPM motor at
10,000 RPM - that would likely kill the motor,
but running a 1500 RPM motor at 2000 RPM
might work as long as you accepted lower
torque as a side effect.

2) continuous torque - This is the rating that relates
to heat generated inside the motor. It is also
directly related to current. Usually the motor
driver is set up to allow short bursts of peak
torque, but limit the average continuous torque
to avoid overheating the motor.

3) peak torque - This is where servos have their
advantage over steppers. Most will allow short
bursts of torque 3 to 5 times their continuous
rating. This allows more power when needed
for quick acceleration. "Short" in this case is
in terms of the thermal time constant of the
parts of the motor that can be damaged by
heat and usually refers to only a few seconds
in duration. As before, peak torque is directly
related to peak current. Current in excess of
the peak rating can cause mechanical damage,
erode brushes, and for some older designs, can
cause the permanent magnets to be partially
demagnetized and weaker.

Servo motors, like most electromechanical devices,
can be pushed beyond their ratings, but you must
accept the fact that their useful life will be shortened
by doing so.

Regards,
Steve Stallings
www.PMDX.com