Motor Controllers - FAQs

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I am not familiar with SepEx, what can you tell me about it?
SepEx or Separately Excited DC motor belongs to the family of the wound field DC motors including; Series, Shunt, and Compound. It is a 4 terminal motor where the armature (A1 and A2) and field windings (S1 or F1 and S2 or F2), are brought out the like a Series motor. But unlike a Series motor, a SepEx motor field is wound with finer gauge wire of many turns, and has to be independently driven by a SepEx motor speed controller. Since all Curtis SepEx controllers offer full bridge control of the motor field, this will make changing in direction of travel quiet and seamless without the use of direction contactors.
What are some of the benefits for choosing a SepEx controller?
The benefits include smooth response at any speed, increase usable battery energy per battery charge, extend life of motor by reducing brush wear, reduce motor loss, and small package size. In addition, it is easy to install and service is simple.
What is Multimode?
Multimode is a feature commonly available in all SepEx controllers to allows user to instantly change an entire set of parameters, such as speed, acceleration, deceleration and current limits to preset levels for up to four different vehicle operating modes.
Can Series motors be converted to SepEx motors?
Yes, generally but require lots of time and effort. The large gauge wire, low turns field winding can be replaced by a small gauge wire, high turns field winding. When doing so, the field must be designed to draw the required current but not higher than the controller’s maximum field current at low battery, when the motor is hot.
How do losses compare between Series motors and SepEx motors?
Losses in the field are a function of the square of the current (I2R). Typical losses in a Series motor field might be 0.020 ohms x 400 amps squared = 3200 watts. Typical losses in a SepEx motor field might be 0.32 ohms x 50 amps squared = 800 watts. Similarly we can expect less losses in a SepEx controller compared to a Series controller.
Does the higher inductance of the SepEx motor field cause any problems?
The higher inductances of the field is not a problem for Curtis controllers. The increased inductance does slow the transition between forward and reverse, but this can be tuned by changing the parameter settings in a SepEx controller.
I heard that Series motors produce more torque than SepEx motors.
This is not true when an electronic motor controller is used. A motor controller will limit the current to a Series motor, effectively limiting its torque to the controller’s maximum current rating. A Series motor will only provide more torque than an equivalent SepEx motor if the Series motor is connected directly to a battery without any current limiting. In this case, the stalled motor current would be very high due to zero armature back EMF. However, once the motor got spinning, the torque would rapidly decrease.
What is the difference between neutral braking and regenerative braking?
Neutral braking simulates the feel of “compression braking” that occurs when the operator led off the accelerator pedal of an internal combustion engine car. On the other hand, regenerative braking occurs when current generated by the motor during braking is allowed to flow back into the batteries.
What does it mean when a SepEx controller is available with CAN?
A few SepEx controllers are available with CAN (Controller Area Network) option to accommodate CAN-based truck application. In such application, a CAN interface and its simple wiring harness are used to replace a more complex wiring harness between a tiller head or “man-up” platform and Curtis controller. This means all normal input signals received by the motor controller may be replaced by CAN messages, thus freeing up multiple inputs and outputs to be wired to a variety of customer-specific needs.
Can a SepEx controller’s performance be adjusted and what equipment do I need?
All Curtis SepEx controllers are fully programmable through a Curtis 1311 handheld programmer allowing the operator to change the controller’s parameter settings. Use of the programmer also provides diagnostic and quick test capability. The programmer is powered by the controller, which makes it very portable and convenient to use anywhere.
Are there any SepEx controllers specifically designed for pump application?
There are a few controllers (i.e. 1254 & 1297) designed to provide finer control for pump motor than traction motor controllers with special features tailored for lifting and lowering operations.
When the vehicle is on a ramp or a hill, the vehicle tends to roll backward before the brake engaged. How can the rolling be prevented?
The parameter Restraint determines how strongly the controller will attempt to limit the vehicle speed to the existing throttle setting. This feature will help hold the vehicle on a ramp and the mechanical or electromagnetic brake has not engaged.
My controller doesn’t work. What is wrong with it?
Look for the LED flash code on top of the controller. If it is not flashing then you probably have lost the power to the control system. In which case check for charged batteries, good connections and intact fuses. If the flash code is one single flash then the controller is operational but has yet to receive a full set of drive signals. i.e. Keyswitch, interlock, direction and throttle. A different flash code indicates a system fault which may or may not be controller related. This flash code should be checked against the diagnostics table in the controller manual which may be downloaded from the Curtis website.
The main contactor pulls in then drops out again and then the controller shows a contactor did not close (Contactor DNC) fault. What is wrong?
As part of the controller initialization routine the voltage on the B+ supply to the controller is tested to ensure that the contactor is not welded and to ensure the contactor has closed. If the voltage does not rise to a preset level within a certain time then the contactor is released. The cause is likely to be very low battery voltage or contaminated or damaged contactor tips. Never force a main contactor closed as this may lead to controller damage and personal injury.
My controller is showing welded contactor even though the contactor is open. Why is that?
The controller determines that the contactor is welded by measuring the voltage on the B+ terminal with the contactor coil switched off. Before doing this test the controller capacitor bank connected to B+ is discharged by energizing the motor armature. If the armature has an open circuit winding then the capacitor bank remains charged and the controller assumes that the contactor is welded. Alternatively there is an electrical short circuit on the system where the main contactor is bypassed.
Why do the brushes on my SepEx motor wear down so quickly?
SepEx controllers are able to regenerate the braking energy by using the motor as a generator. However if the regen braking current is set too high then the commutator can suffer from flashover and an electric arc is set-up which can vaporize the carbon brushes. Regeneration is more likely to induce this due to the raised voltage across the motor. The regen current should be reduced to a lower level.
Why does my controller fault code shows Contactor Missing yet the contactor is there?
If the main contactor coil is OK and the wiring is intact, check that the auxiliary contactor driver is turned off if unused and also the electromagnetic brake driver is turned off if unused. Both of these are tested as part of the contactor check routine.
Why does my Curtis controller run so much cooler than other manufacturers products?
Well that is a good question. Many people can produce a controller, sometimes at a lower cost, but Curtis have many years experience and invest a great deal of effort in fine tuning the power switching circuits. This understanding of the fundamental intricacies of power switching PWM ensures greater reliability due to lower component temperatures, and a lower system cost due to much reduced heatsink and cooling fan requirements.
Can I run a dual drive system with SepEx?
Yes, a pair of SepEx controllers with integral CANbus interface can be used with the Curtis 1310 vehicle system controller. The 1310 vehicle system controller, reading the vehicle speed, steering angle and mast height can calculate the control vectors which are then sent via the CANbus to the controllers.
Is the Regen Braking only effective at high speed?
No the Curtis controller can regen current into the battery almost to zero vehicle speed. This is enabled by using the motor Armature windings as a charge pump circuit. At low speeds the Armature is shorted allowing the current to rise. When Armature circuit short is released the high voltage generated from the collapsing magnetic field allows the current to flow into the battery.
Is the SepEx system closed loop?
Not entirely in the fact that there is no speed encoder feeding information back into the controller. However the voltage applied and the current flowing into the field and armature circuits is measured using high precision hall effect sensors and used by the motor drive algorithms to ensure the highest possible performance.
What voltages can you run the SepEx controllers at?
The smallest SepEx controller is the 24V 200Amp model 1243 and the largest is the 80V 600Amp model 1244. Two of these in a dual drive system would give you 80V @ 1200 Amps or 96kW. That’s enough for the majority of applications!
Can I get controller status information out to a dashboard?
Yes you can, either by using an 840 Spyglass display which connects to the serial interface or via the CAN bus, or by hard wiring the fault code LED drivers to a dashboard indicator lamp.
What causes a controller to fail?
In the vast majority of cases the controller will detect a fault and shutdown safely to protect itself and the user. A catastrophic motor failure such as a burst Armature or the brush gear working loose will cause an Armature to Field short and destroy the controller. With good maintenance of the vehicle the controller will out live the application.