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small, simple 48 volt battery charger for lead acid batteries

Discussion in 'Electronic Basics' started by yeswedeliver, May 18, 2006.

  1. yeswedeliver

    yeswedeliver Guest

    I'm disabled, don't drive a car - but I have a 48 volt electric scooter
    that I use to get around town - it's just great. It runs on 4 12 volt
    lead acid batteries. I have a nice charger for when I"m home - but need
    to build a durable, simple, small one to take with me, on the scooter,
    for long trips...
    Does anyone have any schematics or plans that come to mind that that
    you can share or that you could point me toward? A quick steady charge
    for a [near] full charge on a return trip...
    Thanks alot - happy building...
    Jerry
     
  2. BobG

    BobG Guest

    How about a 60V PV panel and an MPPT controller?
     
  3. Chris

    Chris Guest

    Hi, Jerry. Sorry to say, a home-brew charger cobbled together from
    advice on the internets probably isn't a good idea. Here's a link from
    a European supplier of portable wheelchair rechargers that goes into a
    little non-technical detail on what you'd have to look at if you were
    going to make one of these:

    http://www.ladac.no/dbLadac/brosj/MF026UK.pdf

    You can smoke your batteries or the drive electronics if this is done
    wrong. The potential cost of getting stuck and having to arrange
    emergency repairs while you're away from home far exceeds any potential
    cost savings.

    A paraplegic friend of mine has a secondary market portable switching
    power supply charger which works well for her (she does drive, and can
    take it with her), and might be small enough to carry under the chair
    itself. But making one is definitely not hobbyist level work.

    Cheers
    Chris
     
  4. kell

    kell Guest

    http://www.fieldlines.com/story/2006/5/8/6559/50626
    This guy uses a dimmer.
    If you have experience doing this sort of thing, you might try it.
    If you don't have experience, you are just going to ruin your
    batteries, injure yourself.
     
  5. Chris

    Chris Guest

    This link is hilarious. Thanks for the humor.

    I particularly like how he's got it set up on a board on the grass,
    with strategically placed cinder blocks and prefab shed in the
    background.

    Best quote: "My big problem is seeing through my cheap helmet. I am
    going to get those solar powered helmets that auto darken."

    The only things missing from the page are a tailless one-eyed hound dog
    and a Pontiac Trans-Am on the cinder blocks.

    Needless to say, the charging method shown in the post is, if not
    suicidal, definitely insane.

    If I were on a desert island, it was a life-or-death situation, there
    were no other way, I had good eye and face protection and a nearby
    tidal pool to jump into to wash off the acid after the battery
    explosion, and I was guaranteed I'd never have to use the batteries for
    anything again whether it worked or not, I might try it, but I'd think
    'er over, first. And ask the hound dog.

    Cheers, and thanks again for the laugh, Kell. You made my morning.

    Chris
     
  6. ehsjr

    ehsjr Guest

    Hmmm.... What part(s) do you find a problem with:
    1) Pulse charging
    2) Charging a 36 volt bank to 40 volts?
    3) Charging at 1.02 amps
    4) The "hay-wire" setup?
    5) Or ?

    Ed
     
  7. Chris

    Chris Guest

    Hi, Ed. The whole thing:

    DO NOT DO THIS!
    UNSAFE CIRCUIT! Bridge
    Rectifier
    .---------------. .-----.
    | | | |
    o---o Lamp Dimmer o----o~ +o--------o-------.
    | | | | | +|
    120VAC '---------------' | | | ---
    | | | -
    o------------------------o~ -o---. | | Wheelchair
    | | | | | Lead--Acid
    '-----' | | +| Battery
    | / \ --- Bank
    | ( V ) - to be
    | \_/ | "Charged"
    (sadly)
    | | |
    | | +|
    | | ---
    | | -
    | | |
    | '-------o
    | / \
    | ( I )
    | \_/
    | |
    | |
    '------------'
    (created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

    I'm not sure how many ways this is bad practice, especially for an
    application where safety and the reliability of the batteries are the
    primary concerns.

    The cheapie DVM is reading average voltage, not peak. The other
    cheapie DVM can't see peak current, either. The pulses are just blips
    that are averaged out over the whole line cycle. If there's a voltage
    surge or sag, even BillyBob the former NASCAR driver would take a
    second to adjust the lamp dimmer. A voltage spike -- forget it. Of
    course, then you just chuck the battery on the pile out back, and go
    get another one after the boneyard closes. No problem if you're using
    batteries for arc-welding out back of the shed. They die on him all
    the time.

    Controlled pulse charging is good. Obviously you have to raise the
    battery voltage above nominal to charge it. Controlled current can
    (and should) be more than 1 amp if you want a successful overnight
    charge. But there's no control here except the guy out back on the
    collapsible lawn chair with the dimmer dial in one hand and a Pabst in
    the other. There is no pulse-to-pulse control here.

    There's way too much that can go wrong. Although it's possible you
    might get a somewhat successful charge, it's every bit as likely you'll
    also end up with a somewhat damaged battery with reduced life after
    even the first charging cycle, even if you are trying your best.
    You'll probably end up with both. Battery life should be progressively
    lessened on subsequent charges.

    And you're really depending way too much on the series resistance of
    the light dimmer, the house wiring, and the fusebox here (as well as
    the 200' extension cord chain going from out back of the house to the
    shed).

    A wheelchair is actually a living space. I can see a battery explosion
    here. Welcome to your nightmare, especially if you're away from home
    and dependent on service people (most of whom are actually nice guys
    who are OK with taking care of the disabled -- it's their sponsoring
    companies who are unprintables).

    Of course, BillyBob could always throw the wheelchair on the pile out
    back, and wait for the boneyard to close to get another one.

    Cheers
    Chris
     
  8. kell

    kell Guest

    Do I detect self-aggrandizement?
     
  9. Chris

    Chris Guest

    Hi, Kell. Nope, just trying to lighten things up a bit.

    Didn't mean to be offensive or have it reflect on you personally.
    Looking back on my posts, though, I could see where you might have
    taken it that way. Sorry.

    Chris
     
  10. kell

    kell Guest

    Just for that I'll have to let you come over for a PBR and let you pet
    my one-eyed, three-legged, tailless hound dog!
     
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