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Battery Voltage Boost Regulator

Battery Voltage Boost Regulator

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Battery Voltage Boost Regulator

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  1. Battery Voltage Boost Regulator Solving the Mary Gomez Park Incident

  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)

  3. Specification Review • Battery Specs (100% SOC Voltage) • Deep Cycle (Johnson Controls) • 2.11 V/cell or 12.66 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 14.85 V) • Yaesu FT-847 • 13.8 V ± 10% (12.42 to 15.18 V) • Alinco DX-70TH, ICOM IC-706MKIIG, Kenwood TS-2000, Yaesu FT-857 • 13.8 ± 15% (11.73 to 15.87 V)

  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

  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”

  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 • www.farcircuits.net • Author also stated that he has uploaded the new design to the ARRL website • www.arrl.org/files/qst-binaries/

  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

  8. The Finished Product

  9. PCB Top PC Board (Top)

  10. PCB Bottom PC Board (Bottom) Note the 18 SMT capacitors installed

  11. Transformer could be salvaged from a PC power supply and rewound

  12. N8XJK Schematic

  13. Power Supply 101

  14. Battery Boost Configuration

  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.

  16. N8XJK Schematic

  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

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

  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)

  20. Test Results • Test Duration: 6 minutes, continuous • Input Voltage: 12.16 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

  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

  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

  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 $100.00 (I’ve spent $81.58) • Jameco may also be a source

  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

  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

  26. The End Mary Gomez Park Incident Solved