View Full Version : Resistors for G504 and wiring for PK296A2A-SG7.2 motors (unipolar)

Fri 13 November 2009, 18:33
I am ready to solder up the DB9 connectors for the G504 and the PK296A2A-SG7.2 motors (to be wired unipolar) and need confirmation on the size and location of the resistors. The spec sheet for the G540 says "the current set equals 1,000 Ohms per Amp of motor current."
The Spec sheet for the OM PK296A2A-SG7.2 motors shows the "Current per Phase (A/phase)" as "3" [unipolar] So I assume I need a 3K resistor soldered across pins 1 and 5 of each DB9 assembly, right? Does it make any difference how the resistor is oriented? (i.e., is there an current direction consideration)

Also, recalling Gerald's very helpful instructions in Post #2

"...With a 6-wire motor you can wire them either:
- UNIpolar (use half the motor), Diagram B, using yellow and white wires (center-taps), and then using black or green, and red or blue. ie. use half-windings only.
- BIpolar series (UNIvoltage X 1.4 and UNIcurrent 1.4) Diagram C. Yellow and white not connected
(only 4 wires will be connected - 2 wires will not be connected)"

I assume I would wire:

Yellow wire to DB9 pin #6
Black wire to DB9 pin#7
White wire to DB9 pin#8
Red wire to DB9 pin #9

(The above assumes the Phase A and Phase B motor wires are interchangeable for this purpose)

And that would complete to a cable for this configuration of driver and motor. Can anyone confirm all this for me? Thanks (I know nothing about electricty except where to find the switch and when to pay the bill.:D)

Fri 13 November 2009, 18:54
All of your thinking and pins are correct. I'm not close enough to my shop right now to confirm the resistor value and the colors of the wires, but I'll try to check tomorrow on what I'm using exactly.

I chose to take the leads from my motors, place them inside a short piece of clear plastic tubing, and run them to a DB9 connector with the resistor inside. So the motor can be set on a bench within a foot or so of the G540 and tested. Then I made sheilded DB9 extension cables that run through the trays and ways of my mechmate. This means that my extension cables carry 6 conductors inside a shield braid where they could only carry 4, but I had access to the wire cheap.

Fri 13 November 2009, 23:01
Brad: Thanks for the confirmation. Let me know about that resistor value when you get a chance. Joe

Sat 14 November 2009, 12:33
Joe, I indeed have:

white, red, yellow, black on 6,7,8,9 (your wiring will work just as well)
and an ORG BLK RED resistor across 1 - 5 = 3K = 3amps on the Gecko

Sat 14 November 2009, 13:30

Sun 15 November 2009, 18:46
Brad: One more question on resistors. How close do they have to be. The local Radio Shack only has 3.3K resistors. Is that within permissible limits when I need 3K?

Sun 15 November 2009, 19:09
The 3.3K resistors will give you 3.3 A. If you want a little less, I would suggest the 2.7K which is also a standard resistor value and would give you a little less current at 2.7A

Sun 15 November 2009, 19:16
Heath is correct. I think you'll be okay either way. A third option would be to place resistors in series, for example, 3 1K resistors would do it, and be available at RS.

For the record, resistors come with a tolerance factor of 10% or 5%, or 1% ... That's what the fourth band color represents. So a nominal 3.3K resistor of radio shack quality may range from 3K to 3.6K. You could meter this out if you were paranoid.