Gerald D
Fri 06 June 2008, 04:08
Copied from Gecko yahoo forum today (http://finance.groups.yahoo.com/group/geckodrive/message/15556):
I suggest you can pretty much ignore winding resistance and winding
voltage. There are only two electrical specifications that matter:
1) Rated motor phase current. This is the more important spec. Use
this rating to select the drive's current set resistor value.
1a) Series or parallel? You have this choice if you have a 6-wire or
8-wire motor. No choice is needed with a 4-wire motor.
6-wire motor wired full winding = 8-wire motor wired in series. For an
8-wire motor use the motor datasheet specified series current rating.
For a 6-wire motor use 1/2 the datasheet specified current.
6-wire motor wired half winding = 8-wire motor wired in parallel. For
an 8-wire motor use the motor datasheet specified parallel current
rating. For a 6-wire motor use the datasheet specified current.
2) Motor inductance. This is the other important spec. It determines
the maximum practical power supply voltage for your motor. That
voltage is 32 times the square root of the motor inductance in
milliHenries. V = 32 * SQRT mH.
6-wire motors:
full winding inductance = 4 times the half winding inductance.
8-wire motors:
series winding inductance = 4 times the parallel winding inductance.
Explanation:
Motor power output doubles when you double the supply voltage. Motor
iron-loss heating quadruples when you double the power supply voltage.
This means motor heating outraces motor power output, placing a
maximum limit on power supply voltage. This limit can be calculated
from the motor specifications.
Back when most step motors were round, expensive and 6-wire, I came up
with a simple calculation that worked well: Maximum supply voltage
equals 20 times the motor's rated voltage. The underlying principle
always was the motor inductance but the equation hid it and the
necessity of pulling a square root. Times have changed.
Motors are square, inexpensive and mostly 8-wire. They are much better
than the best round motors. What makes them inexpensive also crashes
the old, simple equation; winding fill.
The round motors used nearly 100% wire fill (the windings filled
nearly all the available space on the stator). That kept the
resistance to inductance relationship constant (R = L^2). The newer
motors don't have 100% fill because oftentimes a smaller gage wire is
used. This disconnects the resistance to inductance relationship and
makes the '20 times rated voltage' rule inaccurate.
Mariss
I suggest you can pretty much ignore winding resistance and winding
voltage. There are only two electrical specifications that matter:
1) Rated motor phase current. This is the more important spec. Use
this rating to select the drive's current set resistor value.
1a) Series or parallel? You have this choice if you have a 6-wire or
8-wire motor. No choice is needed with a 4-wire motor.
6-wire motor wired full winding = 8-wire motor wired in series. For an
8-wire motor use the motor datasheet specified series current rating.
For a 6-wire motor use 1/2 the datasheet specified current.
6-wire motor wired half winding = 8-wire motor wired in parallel. For
an 8-wire motor use the motor datasheet specified parallel current
rating. For a 6-wire motor use the datasheet specified current.
2) Motor inductance. This is the other important spec. It determines
the maximum practical power supply voltage for your motor. That
voltage is 32 times the square root of the motor inductance in
milliHenries. V = 32 * SQRT mH.
6-wire motors:
full winding inductance = 4 times the half winding inductance.
8-wire motors:
series winding inductance = 4 times the parallel winding inductance.
Explanation:
Motor power output doubles when you double the supply voltage. Motor
iron-loss heating quadruples when you double the power supply voltage.
This means motor heating outraces motor power output, placing a
maximum limit on power supply voltage. This limit can be calculated
from the motor specifications.
Back when most step motors were round, expensive and 6-wire, I came up
with a simple calculation that worked well: Maximum supply voltage
equals 20 times the motor's rated voltage. The underlying principle
always was the motor inductance but the equation hid it and the
necessity of pulling a square root. Times have changed.
Motors are square, inexpensive and mostly 8-wire. They are much better
than the best round motors. What makes them inexpensive also crashes
the old, simple equation; winding fill.
The round motors used nearly 100% wire fill (the windings filled
nearly all the available space on the stator). That kept the
resistance to inductance relationship constant (R = L^2). The newer
motors don't have 100% fill because oftentimes a smaller gage wire is
used. This disconnects the resistance to inductance relationship and
makes the '20 times rated voltage' rule inaccurate.
Mariss