Chapter 4: Appendix; Theory Of Operation - MacDon R113 Installation Instructions Manual

Chapter 4: Appendix

• For the general theory of operation of the power limiter module, refer to
4.1 Theory of Operation, page 19.
• For troubleshooting and electrical harness schematics, refer to
4.2 Troubleshooting and Harness Schematics, page 21.

4.1 Theory of Operation

The power limiter module protects the rotary disc header from overspeed. This module is part of the harness and module
assembly (MD #256653) supplied in the kit.
With the power limiter module installed in the header drive speeds control circuit, the maximum allowable current able to
be delivered to header pumps FORWARD speeds pulse width modulation (PWM) control is limited. In normal operation the
disc speed is controlled via a feedback loop from the disc speed sensor to a predetermined maximum disc speed of (R85)
(2600-2650 rpm). However if (without limiter module installed) and the feed back from the disc speed sensor is lost
(damaged sensor / harness disconnected / damaged or broken wire / header ID) the disc speed is maintained via the
internal look up table within the header profile. The values established for the look up table (disc speed versus pump
output and PWM current) are built around the size (volume) of the standard motor on the R85 rotary disc header, which
required 273 L/min (72 gpm) for a disc speed of 2650 rpm. The R113 is equipped with a motor which requires 151 L/min
(40 gpm) to deliver the 2600 rpm disc speed. Under normal operation the feedback from the disc speed sensor will be used
to regulate the disc speed to a maximum of 2600–2650 rpm (M205 operates the R113 under the R85 header profile).
However if the disc speed is lost (not present for any reason) the disc speed control will revert to the internal look up table
to establish an approximate disc speed versus pump output for given PWM current, which is 273 L/min (72 gpm) (for the
R85 rotary disc header) NOT 151 L/min (40 gpm) (the maximum required for the R113 rotary disc header). If unchecked
this could cause the disc speed of the R113 header to turn at 1.75 times the maximum speed. To reduce this possibility the
power limiter module limits the maximum current supplied to the PWM valve for the header forward function of the
header drive pump thereby limiting the maximum output of the header drive pump (and subsequent disc speed) to the
maximum desired speed (2600–2650 rpm).
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