5 Station Battery Charger

Magnavox 706841-801

Brooke Clarke 2001 - 2007



General Information

This charger has provision to hold up to five NiCad batteries.  The label specifies to use with Magnavox battery 548103-801.  Thes is a combined battery and battery housing unlike other PRC-68 family squad radio batteries that require the use of a separate housing.  Also this battery has a test point to allow reading the internal resistor that is temperature dependent.  Because of the test point pin on the charger it can not be used on conventional two terminal batteries.

The source voltage is selected by the construction of the power cord.

Photos

Front Panel -
One of the five Printed Circuit Boards - showing the nomenclature used in the schematic, pin 1 is on the bottom
Schematic diagram of one board - circled numbers correspond to the pin numbers (1 to 10) on the edge of the board.
Inside Left - showing printed circuit boards on bottom and battery wire terminal strips and power transistor on pack.

Operation

The primary power source is connected to the charger by means of a power cord made for that source.
The main power switch is turned on. All 5 LOW LEDs will turn on and the amber ON light will light.
Connect a battery to one of the battery connectors and place the battery in the corresponding hole on top of the charger.
Press the RESET button that corresponds to the hole where the battery is connected. The red HIGH LED for this battery will light and the green LOW LED will turn off.
When the battery is fully charged the red HIGH LED will turn off and the green LOW LED will turn on.
The battery is being float charged when the green LOW LED is on.

Input Power Options

THIS IS MY BEST GUESS
Input Power Schematic Diagram - showing the three different power cord wirings.

The connector on all the following power cables is the AMP Division of TYCO Series 1,  p/n 206708-1 (Digikey A1302-ND)
This is a size 13 shell that uses the 206966-1 (Digikey A1331-ND) cable clamp.
The female sockets are p/n 66360-2 (Digikey A1321-ND)

105 to 125 Volts, 47 to 63 Hz

Neutral to 1
Hot to 2 and 4
Jumper 3 to 9
Ground to 5 and 8
Jumper 6 (+28) to 7 (+28 distribution buss)

210 to 250 Volts, 47 to 63 Hz

Neutral to 1
Hot to 4
Jumper 2 to 3
Ground to 5 and 8
Jumper 6 (+28) to 7 (+28 distribution buss)

28 Volts DC, 2 Amps

Hot (+28 VDC) to 7
Ground to 8

AC Input Connection.pdf  from Power One

Theory of Operation

The test point on the battery has a temperature sensing resistor that goes to the positive battery terminal.  Aprox 80 k Ohms at 40 deg F and 32 k Ohms at 72 deg F.
When the RESET button is pressed the charging current is at it's high value (about 310 mA), Z1 is operational and U2 is comparing the voltage set by P1 to temperature compensated output from the battery.  When the temperature compensated output gets to the threshold set by P1,  U2 will pull it's output down, stopping the HIGH mode.

U1 compares the Battery voltage and the temperature compensated terminal voltage to control the amount of charge current going to the battery.

Parts

The printed circuit boards and parts have a conformal coating. R2 appears to have some black markings that were caused by the heat cooking the coating.  This also makes it very difficult to probe anywhere on the board, since everything is covered with an insulator that is clear and thin.
Power One HN28-3 Linear Supply
Winchester Electronics - Battery Connector

Reference Information

There is  another version 706841-802 that did not hove the third temperature sensor terminal to charge the BB-588 and p/n 588103-804 Batteries.
This unit was made on a 1987 contract.
The BB-588 is a battery that goes into the regular battery housing, it's a 0.6 AH NiCad.


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