Curtis Companion Pre-Charge Controller

A motor controller needs large capacitors to smooth out the current going to the motor. When power is first applied to a controller, these capacitors will charge up causing a huge inrush of current from the batteries, which can cause damage to many components. To avoid this a "pre-charge" circuit is used to turn-on the controller but very slowly and limit the current flowing into the capacitors until they are done charging. Curtis recommends a very primitive precharge circuit be added when installing their controllers. We have designed an advanced packaged solution that solves this problem and in addition provides other important features.

Our Curtis Companion is a micro-processor based system that uses three inputs to control a contactor that is placed before the negative terminal of the battery pack. The operation of the controller works as follows:

• Initiates operation when 12v power is applied, which would be tied to car key-on switch.
• Waits for the throttle-off switch to turn on.
• Turns on the precharge relay to allow battery current to flow through a 50ohm resistor.
• Monitors the precharge current and waits for it to stop flowing.
• If the precharge current does not stop after 10 seconds, a fault is reported.
• The main contactor is now activated with full 1-amp 12v power to its coil, and the car can now operate.
• The 12v power to the main contactor is reduced to 600ma to conserve battery energy.
• The main battery current is now monitored and reported
• The throttle-off switch is monitored, if the throttle goes off and battery current continues to flow, the main contactor is turned off and a fault is reported.
• The RPM sensor is monitored and if RPM ever exceeds 6000rpm, the main contactor is turned off and a fault is reported.

We have placed all the components into a convenient self-contained water-tight plastic PVC box.

There is full isolation between the battery pack and the 12v circuitry. Looking at the gory details inside, you can see most of the key components, starting with the LEV200 contactor. This has an Allergo Micro ACS755 hall-effect current sensor between it and the ground terminal that measures main battery current. The circuit board has a DC-DC converter that provides 3v power to the precharge relays and the microprocessor board. There are two small blue 3v relays for the 144v precharge across the contactor main contacts into a 50ohm resistor (which is not visible, it is at the base of the enclosure). There is an ACS730 15amp hall-effect current sensor after the relays the measures the precharge current, a transistor that is activated by the micro to allow power to the precharge relay coils. There is a high-side driver chip that drives a N-channel transistor for power to the contactor coil. The microprocessor is not visible because its located on a daughterboard under the yellow board, you can just see its 2.4ghz wireless portion and antenna that is used to transmit status information to a wireless display located on the dashboard.