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Boost-Buck Regulator Device

Discussion in 'Electronic Design' started by RST Engineering \(jw\), Dec 4, 2005.

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  1. Well, after twenty-five years of "borrowing" a miniscule amount of power
    from a county power pole, some enterprising young building inspector noticed
    the fairly well disguised extension cord going to some thirty hangars and
    pulled our plug on the battery trickle chargers we use to keep the airplane
    battery from going dead in the slow-flying part of the year and the coldest

    Be that as it may. Harbor Freight has a pretty nice solar trickle charger
    for under $20, but it is possible for this 150 mA device to overcharge a
    $150 aircraft battery and make another dandy paper weight.

    Of course, in the grismal weather of winter, it is possible for this solar
    panel to put out LESS than the 13.4 volts that the battery likes, so we've
    got the worst of all possible panels putting out between 8
    and 18 volts to charge a 12 volt (13.4 volt) battery.

    Does anybody have a "pet" device that will take 8-18 vdc and put out 13.4
    regulated volts at up to 150 mA? Preferably from a manufacturer that the
    usual easy to access parts houses (Mouser, Digi-Key, etc.) stocks?

  2. John B

    John B Guest

    The good old MC33063 will do the trick. Look at

    or the original app note is available at:
  3. Of course. I had forgotten about that old warhorse.

  4. Forgot the "and thanks" in the previous reply.

  5. While you *can* use a boost-buck device, its hardly worth it for the
    application. A silicon solar panel acts mostly like a constant voltage
    source ( typically around 18 volts ) in series with a resistor. The
    resistor value is inversely controlled by the solar radiation. At
    radiation levels where the available voltage is less than your required
    13.8 volts, the energy available is so low it not worth trying to capture.

    Your main concern should be a really reliable way of limiting the float
    voltage to stop overcharging, and a linear series regulator does that
    pretty well.


    Adrian Jansen adrianjansen at internode dot on dot net
    Design Engineer J & K Micro Systems
    Microcomputer solutions for industrial control
    Note reply address is invalid, convert address above to machine form.
  6. John B

    John B Guest

    No Problem. Before I retired, I used the 33063 in every uP design I did
    as 24V->5V converter. Very robust chip and despite all sorts of abuse
    we never had a failure. Blew up a few current limiting resistors but
    never managed to torch the 33063.
  7. Terry Given

    Terry Given Guest

    I stuck one in a 1,000,000W 3-phase light dimmer (oh OK, soft-starter).
    it worked well.

  8. Rich Grise

    Rich Grise Guest

    I'm a consultant, and I'll design, build, and install a solar-powered
    airplane battery charging system for you in exchange for as many dollars
    as the cost of the electricity you've been stealing for the last 25 years.
    What's that, maybe $10,000? $25,000?

    Plus parts, of course.

    You can email me by concatenating my first and last name, Rich Grise, and
    appending the usual shift-two and "".

    Looking forward to hearing from you!
  9. Gee, I dunno, let's do the math. About half the time I go into the hangar
    the "charge" light is on with the linear design I did 25 years ago, so I
    think a 50% duty cycle would probably be a good approximation.

    And I current limited the charger at 150 mA at 13.4 volts, or about 2 watts
    when on; 50% duty cycle reduces that to an average watt.

    So 1 watt an hour 24 hours a day times 365 days a year times 25 years is 219
    kWh times $0.10 per kWh is $21.90.

    You're on. Of course I expect on-site service for this sum.
    No problem. Radio Shack is just down the road.

    Lesson #1 in business ... never bullshit with a bullshitter.

  10. No, but the more I think about it, the more I'm just going to go with a buck
    switching converter. THis turkey solar cell is going to have enough trouble
    keeping up with leakage current with a winter sun than enough and I can't
    afford to throw linear power away during periods of good sunshine.

  11. Terry Given

    Terry Given Guest


  12. JeffM

    JeffM Guest

    Lesson #1 in business ... never bullshit with a bullshitter.
    Switching from boots to waders. :cool:
  13. jw\ wrote...
    In many cases you may find only a small advantage gained in the end
    from a smart power converter between the solar cells and the battery.
    Go ahead if you wish, but if you're working with a substantial number
    of small stations, the direct connection with a diode may prove best.
  14. Joerg

    Joerg Guest

    Hello Jim,
    8-18V in would require SEPIC. I usually do that with the LM3478 but I
    guess the MC33063 might work as well. The MC won't go above 100kHz
    though IIRC.

    The real pros squeeze the last drop of electricity out of solar via
    maximum point point tracking (MPPT) but that would go a bit far here. A
    2nd panel is probably cheaper than a uC doing MPPT.

    Heck, you could turn this into a hot seller and make one for mounting on
    top of the fuselage, for airplanes in the tie-down area. Of course,
    you'd have to get STC and all that ...

    Regards, Joerg
  15. Joerg

    Joerg Guest

    Hello Win,
    However, Jim said that 150mA trickle could already fry an airplane
    battery over time. Which really surprised me.

    So there would have to be some kind of precise voltage limit. If a
    linear regulator drops too much a shunt regulator around a TLV431 might
    work. Maybe some circuit that routes the excess into a large resistor or
    light bulb. The only thing I'd never do again is an LDO since the
    stability of some of those is the pits.

    Regards, Joerg
  16. Absolutely not. If the device has to be removed before flight, there isn't
    even a requirement for a logbook entry, much less an STC.

    Rutan beat me to it by twenty years. He used to sell a small solar cell
    that mounted on the top of the forward fuselage when you were parked to keep
    the VariEZ battery charged. He simply chose a solar cell that didn't have
    enough poo to overcharge the battery.

  17. Well, it has to work the same in winter AND summer. Say you get a nice
    couple of weeks in June and July where you get 10 hours of decent sunlight a
    day. 150 mA over a 10 hour span is 1.5 amp-hours. Over 10 days this is 15
    amp hours on a battery that is only 35 amp hours to begin with. And gas
    recombinant (sealed) to boot. With only a few mA per day of keep-alives
    like clocks and such. I have seen damage like this under the right

  18. Consultant: Abreviation of Con and Insulting ....
  19. At colder temperatures the voltage a solar panel
    delivers is higher than when hot.

  20. Joerg

    Joerg Guest

    Hello Jim,
    Sure but that is cumbersome. A 'no worries' product would be nice where
    people can tie down their aircraft and just forget about battery self
    discharge. But AFAICT the regulatory burden and cost is so high that
    many of those ideas never make it. One method of getting a foot in the
    door would be to begin marketing in countries with lesser bureaucratic
    hurdles. That's how we do it in medical.

    Regards, Joerg
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