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Frequently Asked Questions

What is IR compensation on my PMDC control, and why do I need it?

IR compensation is what provides the speed regulation of the control. When the load on a PMDC motor increases, the amount of current that the motor draws also increases. Per the performance characteristics of permanent magnet DC motors, an increase in load will cause a decrease in speed, because of the negative correlation between speed and torque (see speed-torque curve below). The IR compensation increases the voltage going to the motor, thus compensating for changes in the load, in order to maintain a constant speed at the end-user’s setting regardless of load variations.

Can I run 2 permanent magnet DC motors on one permanent magnet DC control?

No, you cannot run 2 PMDC motors/gearmotors on one PMDC control. The IR compensation in the control cannot communicate with 2 motors. PMDC applications require a one:one ratio of motor:control.

I have a type WPM control. I’m measuring voltage across A1 and A2 and I’m not getting 130V across (I see a very low voltage). Does this mean I have a defective control?

No, it does not. A voltage measurements across A1 and A2 (if the motor/gearmotors is not loaded) on our type WPM controls will result in low voltages because of the transistors on the output of the control that turn power on and off for the PWM signal. Because of these transistors, you must be connected to a load to see the expected 0-130VDC.

Are there replacement boards available for the enclosed type FPM controls? Or do they use the same boards as the chassis type FPM controls?

Our enclosed type FPM controls use different boards than the chassis type FPM controls. The boards are very similar and have identical functional abilities, but the boards within the enclosures have some physical characteristics that are not on the chassis control. There are replacement boards available for the standard enclosed type FPM controls.

      The part numbers are as follows:

      Models 81X (X = 5,6,8) – part no. 43100451

      Models 83X (X = 5,6,8) – part no. 43100483

      Models 85X (X = 5,6,8) – part no. 43100485

Contact an authorized distributor to purchase these replacement boards. A distributor locator is available online at

Can I use the 5VDC power supply (S3) on the type WPM control to power external circuitry?

The 5VDC supply on our type WPM controls was not designed to do much more than provide power to the main speed potentiometer. You may use it to power something else, but will not be able to get much current out of it. We only use .5mA from this supply, which is the optimal maximum current. You may be able to pull 1mA, but at your own risk. If you pull 2mA, you will definitely damage the board. Please proceed with caution if you do plan on using this power supply to source power to any of your components. Note that using this supply as a source of power is out of the rated specifications of this control and will void your Bodine warranty.

What is the difference between a filtered DC control and an unfiltered control?

A filtered control provides the motor with cleaner DC power than the one supplied by the unfiltered control. Also, when used with an unfiltered control vs. a filtered one, the motor will most likely run hotter (at the same load point) and will have shorter life. The unfiltered control provides a 130VDC motor with a maximum voltage of 90VDC, which means that the speed of the motor will not reach the nameplate rating, it will be 9/13th of that.


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