PRC-25, -74, -77 Batteries

© Brooke Clarke, N6GCE

Background
257577BA Battery Adapter
2577BA Battery Adapter (obsolete)
BA-386/PRC-25 The granddaddy
BA-3386 Zinc Carbon
BA-4386/PRC-25 Magneasium 
BA-5598/U Half Size LiSO2 
BB-586/U Ni-Cad
PRC-74 Battery Options
Links

Background

The PRC-25 is a solid state radio with the exception of the final transmitter tube.  The filament of this tube is only turned on when the radio is in transmit mode and requires 3 Volts at about 375 mA.  The "LITE" position of the function switch checks the 3V battery supply.  The rest of the radio runs from the 15 Volt battery supply.

The PRC-77 is an all solid state radio and only needs a 15 Volt battery.  The "LITE" position of the function switch checks the 15 V battery supply.

There are a number of ways that these radios can be powered, either through the POWER connector or by means of a battery connected to the bottom of the radio and housed in the battery box.
 

257477BA

This adapter is an improved version of the 2577BA.  I can be used in the PRC-25, PRC-77 battery boxes without removing the foam strips and also fits into the CY-6314/PRC-74 battery boc (But not the CY-6314A/PRC-74 box).

2577BA

This was my first battery adapter for the PRC-25 and PRC-77 radios.  No longer being made.

BA-386/PRC-25

This is a classical Zinc Carbon chemistry dry cell battery. 15 AH rating.

BA-3386

These are plastic cased primary Alkaline batteries.  About 15 AH rating.

BA-4386/PRC-25

The TM for the PRC-74 says that two of these in parallel provide 15 V and 14 AH meaning that each BA-4386 is a 7 AH battery.
The Battery Handbook shows the 1LM cell as being 22.8mm dia x 84.2 tall and a capacity of 4.5 AH.  Since two of these are in parallel for all of the 15 Volt section the capacity would be 9 AH.  The 3 Volt section uses 6 cells total, 3 in parallel in series with 3 more in parallel.  The 15 Volt section shares the filament section.

The 14 AH rating may be due to the current draw of the PRC-74?

  This is a Magneasium chemistry battery that developes voltage after a load is applied.  When testing you need to wait up to 10 seconds prior to running the test.
WARNING - This battery out gasses Hydrogen gas as a normal part of its chemistry.
It MUST be used with a battery box that has the vent!  If an unvented battery box is used,
when the latches are released the box may shoot off of the radio and cause personal injury.  \
Mike Murphy experienced this in person. Also the Hydrogen gas may explode.

Caution - I got one of these on eBay that was new in the sealed plastic wrap and in the cardboard box. with an expiration date of 07/99.  When tested on 27 Nov. 2001 is was about or really dead.
See the first part of the Power Out vs. DC Supply Voltages table on the PRC-25 web page.  Buyer beware.
A web page about "MILITARY RADIO BATTERY PRC-25/77 BA4386 FRESH "

BA-4386 Inside
              View  Inside there are 18 cells (each about 1.75 Volts) about 0.85" dia x 3.3" tall.  There are two groups of three cells in parallel (1.75 V) and these are in series (3.5 V) for the filament.  For the +14 Volts there are six groups of two cells (1.75 V)  in series (10.5 v) and these are connected on top of (in series with) the filament cells (10.5 + 3.5 = 14 V).  The wires from the battery to the connector for the ground and +14 are about 18 gauge BUT the for the filament it is #30 wire wrap wire and is about 5" long.  This is either to add resistance and/or act as a fuse?  It measures 1.28 Ohms resistance, so it may be a current limiting resistor for when the final tube has a cold filament.  If the tube filament draws 375 mA the drop across the wire under normal operation would be 0.375 * 1.28 = 0.48 volts, (3.5 - 0.48 = 3.02 Volts across the tube filament).

If the PSM-13 Battery Test Set is used to check this battery, it will show the "fresh" eBay out of date batteries to be dead.

26 July 2002 - When doing testing on the 2577BA using an Electronic Load I compared the Energizer E95 Alkaline, Rayovac renewal and the BA-4386. (I'm waiting for the Radio Shack 23-519 NMH cells to charge).  It turns out that when the BA-4386 is loaded with 1 Amp on the 15 Volt section the output is lower than when it is tested at 1 amp after a load of 3 amps for 20 seconds.  Applying a heavy load to the BA-4386 activates the chemistry better than a light load, like that of the PRC-25 radio.

BA-5598/U

  This is a modern Lithium disulphide (LiSO2) chemistry battery that provides about the same capacity as the BA-4386 in 1/2 the space.  It has both the 3V filiment voltage and the 15 Volt main supply so appears to be designed for both the PRC-25 and PRC-77 radios.  But the Army PS magazine has had a couple of articles saying "don't use the BA-5598/U in a PRC-25".  I think there is a design problem with the BA-5598/U that makes it unusable on the PRC-25.
Lithium Battery is Taboo for PRC-25 - The reason that the PRC-25 may not work with the BA-5598 is because of the diode inside the battery dropping its voltage.  The voltage to the radio may be too low to operate the final tube.
(I heard that this was the problem with early design BA-5598s, diode in series with the +3 line)

450-44 - PM Tips - "Never use a lithium battery in an AN/PRC-25's RT-505 receiver-transmitter.  This type battery will damage the radio's tube. Only use the magnesium battery."

(Then when the +3 V diode was removed the tube burnout problem surfaced.  The diode in series with the +15 V section is still there to prevent charging.)  The diode dropped too much voltage but provided some current limitation.  With the diode removed and no provision for current limiting the very stiff LiSO2 cells over stressed the filament.

Construction

Warning - LiSO2 cells contain Sulfur Dioxide gas that is under enough pressure to make it a liquid (maybe up to 45 psi).  If you puncture any of these cells the gas is dangerous.  Use a lot of safety precautions when opening any of these batteries.


  Inside there are 5 each LiSO2 3 Volt cells connected in series.  There is a tap on the bottom battery providing 3 Volts for the PRC-25 final tube filament. BUT THERE IS NO PROVISION FOR CURRENT LIMITING!
 

  There is also a small printed circuit board and a thermal circuit breaker in addition to the socket.  The 2 position DIP switch is activated by the "ATTENTION Before disposal remove this label and push switch" battery draining function.
Once all the cells have been depleted the battery becomes safe land fill.  LiSO2 chemistry has a shelf life of 10 years, so a partially depleted battery is hazardous material.

Wires between cells and PCB:

Wires between PCB and socket:

Printed Circuit Board

The PCB supports a number of functions:
  • holds the battery depleat switch
  • Holds 2 each 2.25 A slow blow fuses, one for the 3 Volt output and one for the 15 Volt output
  • Holds the battery depleation resistor
  • Holds the diode that is in series with the 15 Volt output to prevent charging current from being applied
Note that all the wiring appears to be normal stranded hookup wire of maybe 20 AWG.  There is not any 30 AWG wire used and there is not any provision to add resistance in series with the 3 Volt output.

My estimate is that the cold inrush current will go to 15 to 30 Amps unless the battery or external circuitry has some limiting action.  The BA-4386/U and the Bren-Tronics Alkaline batteries BT-70245 (the BT-70240 is a 15V only version for the PRC-77 and not the PRC-25) have a 1 Ohm resistor in series with the 3V output.

There is no provision to limit the cold inrush current going to the PRC-25 filament.  If this is true then using the BA-5598/U in a PRC-25 may lead to premature filament burn out an/or weakining of the filiment function decreasing the tube output.

Very Difficult to Test BA-5598/U

Because of the very low internal resistance (and associated very flat discharge curve) it takes a very special tester (or a computer controlled test system) to determine the State Of Charge of any LiSO2 battery.  See my State Of Charge web page form more in the LS 91 (TS-4403/U) and the BA-5590/U web page for more on this.

Do Not Use the PSM-13 in an attempt to check the BA-5598/U!
 

New Old Stock BA-5598/U from Fair Radio

Using the Chemtronics State of Charge tester on a NOS BA-5598/U from Fair Radio showed it to have 100 % capacity.  The expiration date on the box is 10/95, Lot 2, MFD 1090A (Oct. 1990?). CAGE 7X634 (Saft).   This is good news for PRC-77 users, but this model battery should not be used in the PRC-25.  When I ordered these Fair had them listed as BB-5598/U, but there is no such battery.  This is interesting in that LiSO2 is said ot have a shelf life of 10 years, and here is a case of a battery that's at full capacity after 12 years.

BB-586/U

BB-586 Top

BB-586 Front
                  Label
BB-586 End
                  w/Fuse

9.5 long x 3 5/8 wide x 1 3/16 high. 

The 15 Volt output socket terminals has an internal diode in series with the positive lead so that you can NOT charge the battery using the output terminals.  The socket where the BA-4386 has it's 3 Volt output is missing.  The other two sockets that are not used on the BA-4386 are used here as charging terminals.    The negative charging terminal goes through a thermal switch at opens at about 110 deg F.   There is a 10 Amp 32V "311" fast blow fuse connected to the battery internal positive terminal that's in both the normal output and the charging circuits.  The fuse holder is on one end and a spare fuse is on the other end.
Label:

Battery, Rechargable BB-586/U
Nikel Cadmium, Selaed
13.2 Volts, 4.0 Ampere-Hours
at 0.8 Ampere
NSN: 6140-01-084-1460
DAAB07-91-D-R015
DATE 0991
Bren-Tronics, Inc. FSCM 51828
Commack, New York
Serial # 10866
Charging Instructions:

Charge through Connector Pins marked "charging only (+) and (-)".
Recommended charge rate is 1 AMP for 5
to 6 hours.  Charging temperature should be 4ºC (40ºF) to 32ºC (80ºF).  Unit con-
tains Thermal Switch which will prevent charging above approximately 43ºC (110ºF).

On the first attempt at load testing after charging, the battery did not make it through 1 cycle (50 ma Rx 9 min then 1.1 Amp for 1 min Tx).
Will try discharge charge cycle to recondition the memory.  It took a few discharge - charge cycles, but the battery did come back to life.
The Load test using my PRC-25 profile (9 min @ 50 ma, 1 min. @ 1.1 Amps) shows a little over 20 hours of operation and 20.9 AH output.  See the table on my Batteries web page for comparison to other battery options.  The internal resistance looks to be about 0.5 Ohms.

PRC-74 Battery options

All the battery boxes supply 15 Volts (fresh) to 11 Volts (discharged) to the radio.
Based on the 14 AH spec in the PRC-74 manual for a pair of BA-4386 batteries and the 24 hours operation with a 9:1 Rx:Tx ratio, I assume the Rx  current is in the 0.2 to 0.4 Amp range and the Tx current is in the 2 to 4 Amp range.

A self resettable fuse that holds at 4 Amp and trips at 8 Amp might be suitable. (Jameco 200053 RB400-30)

CY-6314/PRC-74 Dry Battery Box

Holds 2 each BA-4386/PRC-25 or equivalent batteries.
Plate with 4 wing nuts.
The plug on the movable plate can be retracted to allow isntallation and removal of the nearest battery.
 

CY-6314A/PRC-74 Dry Battery Box

Holds 2 each BA-4386/PRC-25 or equivalent batteries.
Hinged seperator between the two batteries.

CY-6121/PRC-74 Wet Battery Box

Holds 10 each BB-418 wet NiCad stoarge cells
13.x volts full charge, radio degraded performance at 11 Volts
30 "D" cells may fit into this box.
Fair Radio photo -

CY-4880

Holds 70 each BA-30 ("D" cells) in 7 series strings of 10 cells each for 15 Volts and about 58.45 Amp Hours.

Links

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