1. Battery Voltage Boost Regulator
Solving the Mary Gomez Park Incident
Don Steinbach, AE6PM

2. The Mary Gomez Park Incident
Yaesu FT-840 transceiver received bad (terrible) signal quality reports on CW after being operated on battery power for an extended period of time.
Believed to be a result of the dc input voltage being out-of-spec low.
Actual battery voltage was near 11V
FT-840 Spec is 13.5V +/- 10% (12.15 to 14.85)
Don Steinbach, AE6PM

3. Specification Review Battery Specs (100% SOC Voltage)
Deep Cycle (Johnson Controls)
2.11 V/cell or V
Sealed Lead-Acid (Power Sonic)
2.15 V/cell or 12.9 V
Transceivers Specs
Yaesu FT-840
13.5 V ± 10% (12.15 to V)
Yaesu FT-847
13.8 V ± 10% (12.42 to V)
Alinco DX-70TH, ICOM IC-706MKIIG, Kenwood TS-2000, Yaesu FT-857
13.8 ± 15% (11.73 to V)
Don Steinbach, AE6PM

4. Possible Solutions
Add a second battery (or a cell) in series with the primary battery
Raise primary battery dc voltage to 14 or 18 or 24 volts and regulate down to 13V
Use a modified/enhanced computer UPS
Let the primary battery power the UPS and let the UPS power the transceiver ac power supply
Use a dc/dc converter and regulator
Use a conventional dc/dc converter to provide 18V then regulate down to 13V
Use a boost supply in series with the battery
Add a differential voltage to the primary battery voltage
Don Steinbach, AE6PM

5. QST to the Rescue QST Article
A 12V dc Boost Regulator for Battery Operation
Daniel R. Kemppainen, N8XJK
November 2004, page 37
Quote from the article:
“A dc-dc boost switching converter is the answer to low voltage battery problems for mobile, portable or emergency-power operation”
Don Steinbach, AE6PM

6. Step 1 – Check the Current Status
Contacted the author regarding availability of bare PC board
Author responded that circuit had been redesigned and that farcircuits had PC boards for sale
Author also stated that he has uploaded the new design to the ARRL website
Don Steinbach, AE6PM

7. Step 2 – Build It Procure the PC board and the components FAR Circuits
PCB, E-core and bobbin, toroid core
Digikey
Filter capacitors, power MOSFETs, Schottkey dual diode
Anything that needs to fit the PCB layout
Anchor Electronics
Miscellaneous ICs, semiconductors, resistors, capacitors
Wind the transformer
Wind the filter inductor
Stuff and solder the PC board
Cut, bend and drill some aluminum
Final electrical/mechanical assembly and heat sinking
Test
Don Steinbach, AE6PM

8. The Finished Product
Don Steinbach, AE6PM

9. PCB Top
PC Board (Top)
Don Steinbach, AE6PM

10. PCB Bottom PC Board (Bottom) Note the 18 SMT capacitors installed
Don Steinbach, AE6PM

11. Transformer could be salvaged from a PC power supply and rewound
Don Steinbach, AE6PM

12. N8XJK Schematic
Don Steinbach, AE6PM

13. Power Supply 101
Don Steinbach, AE6PM

14. Battery Boost Configuration
Don Steinbach, AE6PM

15. N8XJK Design Concept
The circuit is best visualized starting with a full-wave power supply using a transformer with a center tapped secondary.
The center tap, rather than being grounded, is connected to the high side of the battery so that the power supply adds to the battery voltage.
Feedback from the total output voltage back to the full-wave power supply causes the power supply to modulate its output voltage to keep the sum of the battery voltage plus the power supply voltage constant.
The power supply that supplies the additional voltage is a switch-mode design that operates from the same battery that is supplying the baseline power.
The IC that drives the switch-mode power supply provides the regulation by modulating the pulse width.
Don Steinbach, AE6PM

16. N8XJK Schematic
Don Steinbach, AE6PM

17. N8XJK Block Diagram Input fuse & filter F1, F2, C1-C4
Switching transistors
Q1/Q3/Q6 and Q2/Q4/Q5
Transformer and rectifier
T1, D7
Low pass filter
L1, C5-C12
9-12 Vdc
13.8 Vdc
Low battery protection
U2, Q7
Pulse Width Modulator (PWM) U1
Output voltage sensing
R3, R4, R5, R16
5.0V
Reference voltage divider
R1, R2, C15
2.5V
RF Sample
RF detect
Q9, Q8, Q7
PWM IC compensation
C17
PWM Enable
PWM operating frequency
C16, R6
Don Steinbach, AE6PM

18. N8XJK Schematic (simplified)
RF sense/PWM enable
Low battery protection/PWM disable
Don Steinbach, AE6PM

19. User Comments/Modification
Battery protection circuit
Reacts too quickly (false alarms)
Can only be reset by removing input power
RF detection/enable
Boost power supply turned on only during transmit
Different voltage during transmit and receive
Not recommended IMHO
Quiescent current is only 22 mA
I disabled battery protection & RF detection by removing U2 and grounding emitter of Q7 (jumper U2-1 to U2-12)
Don Steinbach, AE6PM

20. Test Results Test Duration: 6 minutes, continuous
Input Voltage: V dc
Output Voltage: 13.0 V dc
Output Current: 16 A dc
Maximum Temperatures (IR Thermometer):
Transformer: 145 deg F
Diode area: 180 deg F
Heat sink area: Very hot to touch
Filter capacitors: Slightly warm
Switching Frequency: 40 kHz
Ripple voltage: 17 mV p-p
Don Steinbach, AE6PM

21. Test Results (Continued)
Quiescent current (no load)
Input = 12 Vdc, Output = 13.4 Vdc
Input current = 21.8 mA
Output voltage range adjustment (no load)
Input = 12 Vdc
Output voltage = 11.9 Vdc to 15.3 Vdc
Minimum input voltage for 13.4V output (no load)
7.6 Vdc
Don Steinbach, AE6PM

22. Parts Selection
This power converter operates at about 40 kHz, not 120 Hz
Conventional aluminum electrolytics are ineffective as filter capacitors
Use low impedance (ESR) capacitors as specified
The traditional 2N3055 NPN silicon transistor cannot switch fast enough
Also power dissipation
Use HEXFET Power MOSFET as specified
The rectifier diodes need to be low forward voltage drop (desired) and fast switching (required)
Use Schottky rectifier as specified
SMT capacitors added by the author (18 total) indicate probable RFI issues fixed
Don Steinbach, AE6PM

23. Parts Selection (Continued)
FAR Circuits has the double-sided PCB (for new design) for $17.00
Add $8.00 for the T1 E-core and the L1 toroid core
Or scavenge the cores from a defunct PC power supply
Order C1 thru C12 from DigiKey (don’t substitute)
Order U1 from DigiKey (limited availability)
Order Q5, Q6 and D7 from DigiKey (limited availability)
Order C13 thru C15 from DigiKey (Panasonic parts)
Order C17, C18, C21 from DigiKey (Kemet parts)
Order R16 from DigiKey (fits the PCB)
Remaining ICs, transistors, resistors and capacitors can be purchased from Anchor Electronics in Santa Clara for less than $9.00
Total cost will be under $ (I’ve spent $81.58)
Jameco may also be a source
Don Steinbach, AE6PM

24. Design Comments
C1 thru C12 voltage ratings are marginal (16V in 13V circuit)
Probably ok since problem was input voltage too low
And the output voltage is regulated
Input has capability for two fuses in parallel
Added by author in response to user requests
This can be risky since load sharing is not guaranteed
Why use 2.5V reference for comparator input when 5V would provide more sensitivity to output voltage variations?
Apparently older versions of the LM3524 were not suited for a reference input voltage as high as 5V
Don Steinbach, AE6PM

25. MFJ-4416 Version Commercial version from MFJ
Note adition of series RC “snubbers” and crowbar circuit
Redesigned LV & RF detect
Shipped with battery protection circuit disabled
~ $139.95
Don Steinbach, AE6PM

26. Mary Gomez Park Incident Solved
The End
Mary Gomez Park Incident Solved
Don Steinbach, AE6PM