Simple Shunt Solar Controller

version 1A (May 2001)

Alan Biocca
WB6ZQZ

This 9 part design uses a Voltage Monitor IC to control an FET shunt
that cuts off solar panel current when the battery reaches full charge.


Parts List

Q1 IRLZ34 FET 55V 30A 0.035 ohms
Q2 ZM33164 5V Voltage Monitor

D1 MBR1045 10A 45V Schottky Diode, 0.75V@10A
D2 1N4148 diode

R1 6800 1/4 watt
R2 2000 20 turn trimpot
R3 4700 1/4 watt
R4 100K 1/4 watt

C1 22uF 16V or better Electrolytic capacitor (not critical)


Brief Assembly Instructions

Read all instructions before starting. The order of installation list is later
in these instructions.

Refer to the color photographs (in jpg format) to place components correctly.

Observe static electricity safety to protect the components (work on a
grounded conductive surface and use a grounded soldering iron).

Use a low power or thermally regulated soldering iron designed for
electronics work to avoid damaging components or the printed circuit
board. Use quality electronics type solder.

Be careful to install D2 with the cathode (banded) end in the proper
direction.

Be careful to install the Voltage Monitor with the flatted side in the
proper direction.

The Q1 FET is especially static sensitive - use anti-static procedures 
when handling.

The heatsinks should be attached between the devices and the PC board with
4-40 hardware. Heatsink compound between the device and the sink is
recommended. Bend the device leads gently to fit in the circuit board
holes.

The heatsink on D1 should be installed with the notch pointing off the
pc board to provide clearance for the trimpot R2.

Do not solder any components until all components have been fitted to the
PC board. Bend the leads slightly to hold them in place.


Recommended component installation order:

  Terminal Block
  R2 Trimpot
  Voltage Monitor IC (to-92 package, like a small transistor)
  fixed resistors
  D2 1N4148 diode
  C1 capacitor
  Q1 FET and heatsink
  D1 Schottky diode and heatsink


Connecting to System

  Use a 10 amp fuse inline on each side of the controller.

  Connect as follows:


  PV+ ---------------*       *------------------ Battery +
                     |       |
                     |       |
                     I   G   O <- Controller Terminals
                         |
                         |
  PV- -------------------*---------------------- Battery -


Adjusting the Voltage

  The R2 potentiometer controls the voltage switching point. There is 
some hysteresis (approx 0.6V) between turn-off and turn-on. A good way to 
set this is to (temporarily) connect a large capacitor on the battery terminals (instead of a battery), and
a solar panel on the panel input side. The system will charge the
capacitor until the shutoff voltage is reached. A resistor or a short
can be used to discharge the capacitor and start a new cycle after
adjusting the pot. Adjust the pot and discharge-charge the capacitor
until the final voltage is the desired value. 14.2V is recommended.


Warnings

  Do not connect a battery to the Input side of the controller.

  Do not reverse the polarity on either input or output.

  Do not use without fusing, especially toward the battery side.

  Be careful if connected to a solar panel and not connected
    to a battery. In this situation the controller cycles on
    and off. This may cause heating in the FET heatsink. The
    switching rate may be lowered by increasing the value of C1,
    which in turn lowers the heating.


-- Alan

