Sepex Motors explained for dummies (like me) by JohnnieB

[JohnnieB]

Originally Posted by georgia088

Does this mean (in your opinion) these “general” field maps for carts with no speed sensor could weaken the current sent to the field windings in order for the cart to gain more speed?

They all do, that is how a sepex motor is transformed from a higher torque motor to a higher speed motor on the fly.

The DCS is the only sepex drive that I know of that didn't have a speed sensor (There may be others, but I'm not aware of them if there are) and the Alltrax DCX controller was designed to be a plug-n-play replacement for the stock DCS controller (Curtis 1206SX - which had some issues that were corrected in the DCX).

A DCS had a higher top speed with a DCX controller than it had with a stock DCS controller. One reason was because it had a user selectable "Turbo" mode that further reduced the field amps when specific conditions are met. (Below is a cut and paste from the Controller-Pro manual)

Turbo – DCX models only

This feature enables a turbo boost mode when enabled. It only goes into and stays in turbo mode when two conditions are met. The throttle position is at 100% for at least 1 second and the controller is not in current limit. The controller will adjust the field map to allow for extra speed while those conditions are met.

The field map Alltrax used for a DCS motor might have been pushing the envelope closer to the field weakening limitations then the field map Curtis used in the 1206SX. If so, that would be another reason the DCS was faster with a DCX than with a 1206SX.

I ran my PDS cart with a DCX controller and an adapter kluge and no speed sensor and know my motor got really hot when I ran at top speed. I eventually exploded my stock PDS motor and replaced it with the D&D motor I'm running now, which I ran with a DCX until the XCT was introduced in 2015.

The Field Weakening Limitations Map (attached) for my ES-76-51 motor indicates a minimum of 3A for any armature amp flow below 100A, but I have data logs from the XCT showing field amps of 1A and less, so I suspect the Alltrax guys might have played a little fast and loose with motor manufacturer's recommendations with the DCX field maps also.

I can see both sides technically. The motor manufacturer want to keep the field amps high so the motor runs cooler and the controller manufacturer wants to reduce the field amps more so the cart will go faster with their controller installed.

FWIW: The term "Field Map" might a shortening of the term "Field Weakening Limitations Map" that some motor manufacturers use.