Battery%20Voltage%20Boost%20Regulator

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Battery Voltage Boost Regulator

• Solving the Mary Gomez Park Incident

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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)

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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)

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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

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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

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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/

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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

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The Finished Product
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PCB Top
PC Board (Top)
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PCB Bottom
PC Board (Bottom) Note the 18 SMT capacitors
installed
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Transformer could be salvaged from a PC power
supply and rewound
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N8XJK Schematic
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Power Supply 101
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Battery Boost Configuration
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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.

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N8XJK Schematic
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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
13.8 Vdc
9-12 Vdc
Pulse Width Modulator (PWM) U1
Output voltage sensing R3, R4, R5, R16
Low battery protection U2, Q7
5.0V
Reference voltage divider R1, R2, C15
2.5V
RF detect Q9, Q8, Q7
RF Sample
PWM IC compensation C17
PWM Enable
PWM operating frequency C16, R6
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N8XJK Schematic (simplified)
RF sense/PWM enable
Low battery protection/PWM disable
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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)
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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

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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

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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

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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 (dont 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 (Ive spent
  81.58)
• Jameco may also be a source

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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

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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

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The End

• Mary Gomez Park Incident Solved