Power Supply


Beginning with NIWOT07, TRAM uses a Lambda GEN60-25 programmable power supply.  In addition to being much lighter than the huge linear HP supply (still used on the FLAB test track), the Lambda has an RS-232 port that can be used for both monitoring/logging trolley power and for setting power voltage.  I never implemented the capability to increase voltage on uphills and decrease for downhills (now not necessary with speed control), but still have the ability to kill all system power remotely or under software control if fail criteria should occur.  

The Lambda supply also has the ability to operate in parallel with similar supplies.  This would allow a very long track to be powered by multiple supplies spaced along the track, to reduce the power drops.  To date, this capability has not been needed.  However, starting with the BAO track, I have put the supply in the middle of (a mostly linear) track and powered BOTH turns on this tower.  This should minimize voltage drops.

These days, I run the power supply at about 30VDC.  Pulse-width modulation on the trolley's PIC starts at 75%, which would drop the motor voltage to 22.5VDC.  The PWM signal originates on the PIC, drives a TTL gate that in turn drives a solid-state relay connected to the trolley's motor.   The duty cycle of PWM is changed (with some limit) by the PIC every 0.1s as the PIC compares the present speed with the (changable) set-point.

Current usage at 30VDC is about 0.2A idle, 2A straight-and-level, 10A (6W, 60W, 300W, respectively) powering through turns.  The GEN60-25 specifies an efficiency of 83% for this operation, which would make the input power 7W, 72W, 360W.

In the trolley electronics box is a power daughter board.  This takes the 30VDC and filters it for noise (due to oxidation or dirt on either the cables or trolley power pick-ups) using 5Farads of ultracapacitors.  A 12VDC regulator, combined with another 5F of ultracapacitors cleans up this power and sends it to the PIC board.  Jumpering on the PIC can route 12V to sensors.  The PIC board also has 5V and 3.3V regulators either for sensor or component use.  The PIC itself uses 3.3V.  As mentioned below, the IMU takes more current at 3.3V than the PIC board regulators can supply.  Thus, a daughter board to the power daughter board has been added for this purpose.