RESISTOR : 8.2 K ohms

DIODE = 1N4004 TO 4007 or any diode at least 1 amp and 200 Volts breakdown voltage.

Preferable to have a 5 to 10 amps diode for better protection in times of fast ON/OFF cycling.

This way any inductance causing oscillations in the line will be clamped to the battery voltage level.

24 or 48 volts ballast controller

For 24 or 48 volts IS BEST to have an isolated buffered supply to the controller.

Disconnect the controller from the Zener and bias resistor and filter capacitor.

Connect the BASE of a NPN power transistor to the junction of the Zener and the bias reistor and filter capacitor, connect the COLLECTOR to the Positive of the battery bank and use the EMITTER as the source power for the controller and add another filter capacitor.

Voila, you have a ballast controller with ample input voltage range.

The power MosFet must have a Voltage breakdown of at least 1.4 times the top battery voltage -- 100 + volts is OK, Current as needed and defined by the load and should be at least 2 times the carrying load.

Voltage reference control

The LM723 Voltage regulator has a 7.15 volts internal reference, so the input voltage at point of control needs to be 7.15 volts

The circuit says use a 1 K ohms pot.

For some the setting may be a bit problematic, so to easy such adjustment:

24 volts battery MEANS the CONTROLLER should be operating at around 28.44 volts and

for 48 volts the same point MEANS to operate at around 56.88 volts .

The best way is to use current in the resistor chain to set the upper resistors.

The ckt shows a 1 k ohm pot and a 3.3 K ohms to ground LETS ASSUME THE POT IS SET TO CENTER AT TRIP POINT
So the net resistor value is 500 + 3300 ohms = 3800 ohms

7.15 volts / 3800 ohms = 1.8815 milliamps

FOR 24 VOLTS : 28.44 - 7.15 = 21.29 volts
21.29 volts / 1.8815 milliamps = 11.314 kilo-ohms

USE 10 KILO-OHMS + 1.2 KILO-OHMS IN SERIES.

FOR 48 VOLTS BEST SOLUTION

28.44 volts / 1.8815 milliamps = 15.114 kilo-ohms - TO BE ADDED IN SERIES TO THE 24 VOLTS STRING .
IF ONE BUILDS THE CIRCUIT for both battery banks, one can select 24 or 48 volts by placing a switch in parallel with the 15.114 Kilohms resistor.

PROBLEM for some : the accuracy or precision of the resistor may CAUSE the setting of the pot PROBLEMATIC AND NOT ATTAINABLE,

SOLUTION : REPLACE : the 10 KILO-OHMS + 1.2 KILO-OHMS IN SERIES as follows :

a 6.4 Kilo-ohms resistor with a 5 Kilo-ohms variable resistor in series, connecting the 6.4 kh to the battery, the opposite side to the brush of the pot, also , brush connected to the Clockwise terminal of the pot, the CCW of the pot to the upper terminal of the shunt setting pot ( 1 Koh).

This way one can attain the proper ranges with resistor values that maybe not precise.

Setting : with the power of set the 5 Koh pot + 6.4 Koh = 11.2 Kohms for initial adjustment.

I hope this helps