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Ideas For 675 Ah 48 volt Battery Bank Charger?

Discussion in 'Electronic Basics' started by Ulysses, Jun 22, 2007.

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  1. Ulysses

    Ulysses Guest


    I have a 48 volt battery bank (675 Ah) supplying my Outback Inverters which
    are connected to my house wiring. I am looking for a way to charge the
    batteries until I get the cash to get some solar panels. Right now I am
    using one inverter to supply AC and another one only to charge batteries.
    The problem is that it will only charge at up to about 20 amps.

    Are there plans somewhere that would show me how to build a regulated
    battery charger in the 100 amp range? If not a battery charger then perhaps
    a power supply? It would need to be able to go up to about 62 volts. So
    far I've only built little 12 volt, 1 1/2 supplies. If I can't get 100 amps
    can I get 50?

    Would it be possible just to use a step-down transformer from 120 VAC to
    about 60 VAC or so and rectify it? Would one 12,000 uF capacitor be enough
    to smooth out the AC ripple? I've read that deep cycle wet cells do not
    like ripple.

    Another possibility might be a DC generator and the voltage could be
    adjusted by engine speed. If I was to acquire a permanent magnet DC motor
    is there a simple way to determine how many amps it would put out at what
    voltage at what RPM? I've looked at many online and something in the 1725
    RPM range seems like it would be easier on a small engine (and quieter if
    the engine is running at half speed) but so far I've not seen any motors
    rated at more than about 30 amps.

    If all else fails I'd consider building a permanent magnet alternator from
    scratch. I've read about building PMAs for wind generators and it sounds
    like to get more current I would need to wind the coils with larger diameter
    wire and fewer turns to reduce resistance. All of the plans I've seen call
    for six coils but I'm thinking 9 might work better for higher current. Most
    of them also call for two rotors containing 12 magets each but I'm thinking
    that is just so there is more output at low wind speeds and if I'm using an
    engine then 1800 rpm or higher is not a problem so I was thinking six
    magnets might work. Anyone know it it can be built with 9 (or more) coils
    and fewer magnets?

    Any other ideas?

  2. BobG

    BobG Guest

    I'd start out trying to use a BIG variac with a BIG bridge rectifier
    and a couple BIG caps. Manually adjust the voltage. Might need a 50A
    shunt. Big DC amp meters are pricy. You can get all this stuff at
    Skycraft Parts and Surplus in Winter Park Florida (
  3. Jasen

    Jasen Guest

    You want plans for a 6KW charger ?
    AFAIK no capacitor is needed.
    that's news to me.

    A big inductor might work better.
    ask the maker? measure it?

  4. Ulysses

    Ulysses Guest

    Um. I don't know what I was thinking when I wrote that. I guess I wasn't.
    Let's make that 60 amps which would almost be the C10 charge rate and could
    run from a 5000 watt generator.
    I've also read that they do, but that was a long time ago.

    I've been looking at surplus stuff and usually the current draw, running
    speed, and voltage are indicated but I don't know if that transforms into
    the same thing if driven by an engine and used as a DC generator.
  5. Ulysses

    Ulysses Guest

    I like that idea. Thanks.
  6. Jasen

    Jasen Guest

    60A into 55V is 3300W, that should work.

    if you don't need isolation go with the variac plan.

    not even close. that'd reduce the ripple amplitude by about 1V (based
    on guessed parameters)
    I guess it's possible ( but capacitors are bad. they reduce the power
    factor of the load, meaning you'd need a stronger 120V supply, variac,
    and possibly a bigger rectifier

    the inductor works to smooth the charging current this will knock the
    peaks off reducing ripple to the battery and improving the power factor
    to the source.

    a large 24V (automotive) altenator run at 7200rpm should be able to
    produce the current and voltage you want. you'd need to replace the
    24V regulator with one designed for 48V batteries, possibly you'd need
    to replace the rectifier too.

    if it's a used, one while you're at it fit new brushes and bearings etc.
    dead brushes are a hassle but a bearing failure is a disaster.

    the automotive altenators have two advantages over a single phase
    120Vac supply

    the voltage is independant of the motor speed and easy to control,
    the output frequency is higher so the ripple is easier to filter out,
    and they're three phase so there's much less ripple to start with.

    not all that suprising that they are so suitable considering that
    they were designed to charge lead acid batteries....

  7. Ulysses

    Ulysses Guest

    Someone tried to explain to me how to use a Delco 10S1 12 volt alternator by
    removing the voltage regulator, using external heat-sinked diodes, and using
    resistors to make an external regulator think that 48 volts was 12 volts and
    regulating accordingly. The problem I have with that idea is that I don't
    know what to do with the F and R tabs. One senses the battery voltage but
    I'm not sure which one, and then what to do with the other tab. I succeeded
    it getting about 30 volts output by putting a resistor in series with the F
    tab and Positive but it did not increase with speed. I have been told that
    if I do this right I can get about 63 amps @ 48 volts from my existing
    alternator. I've also been told the internal diodes will not withstand as
    much as 24 volts.

    So far I understand how the 3-phase works, how to connect the diodes to both
    positive and negative, and probably how to remove the internal voltage
    regulator. I just don't understand the F and R terminals.

  8. Jasen

    Jasen Guest

    I'm not familiar with that altenator, so I can't help with details
    there I did a quick google for Altenatoe 48V mod with no success,

    Automotive Alternator Schematic on the other hand got me this one:

    which looks promising, you's need to change a few things for it to
    work on 48V though, mainly replacuing Z1 and Z2 with a combination of
    zener diodes that come closer to your target voltage. r3 and r4 should
    probably be increased to about 4 times the resistance, (eg:) 3.9K and 470K

    a power resistor of upto three times the resistance of the altenator
    field winding winding resistance between tr4+r4 and DF+D3 might help

    the transistors are kind of marginal too, a load dump at the wrong
    time would destroy them.

    here's that schematic translated to ascii with zome of the components

    .--------------------+------------+---------------------- "48"V
    | | |
    \ | |
    / 2.2K + |
    \ / |
    / |< BC557 |
    +-----[1K]---+----| |
    | | |\ |
    | | \ /
    \-+-\ | + |<
    / \ | || | |<-|
    T +---||--+-+----| |\ BD902
    | 1N4750 | || | |\ \
    | | 150nF | \___|
    | | | |
    \---\ +---------|--[470K]--+--R?--+------> --.
    / \ | | |
    T \ --- |-| altenator
    | 1N4750 / 3.9K / \ |\| field
    | \ T |-| winding
    | / | |
    | | | |
    `----------------------+-----------------+----------+------- 0V

    the two 27v zener diodes put the switching point somewhere near 56v
    if that's too high use a different combination

    the bc557 and BD902 transistors should probably be repaced with
    higher voltage versions, but I'm not sure what to rceccomend

    the 3.9K resistor should be a 1W or larger it'll get hot.
  9. Ulysses

    Ulysses Guest

    Great. thanks!
  10. If the alternator was wound for 12 volts, and this regulator
    goes full on, for any reason from failure to slightly low
    battery voltage, the alternator field will be quickly fried,
    of something else doesn't burn out first.

    I think it would be much easier to start over and make a
    crude switching regulator with a 0 to 14 volt output to feed
    the field coil, with the output voltage determined by the
    error in the 48 volt battery voltage.
  11. neon


    Oct 21, 2006
    the transformer to 60 v is easy to implement efficiency about probably 80 85% why a cap batery love pulseting dc for charging. i would recomend a current limiting thought. 100 amps 48 vthat 4800watts that is a lot of heat battery do not like heat
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