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car battery and windshield wiper motor

Discussion in 'Electronic Basics' started by Pat Kilgore, Apr 8, 2005.

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  1. Pat Kilgore

    Pat Kilgore Guest

    For an art piece, I would like to be able to anticipate about how long a
    standard car battery would drive a car windshield wiper motor hooked
    directly to it, if the wiper motor is activated for one cycle every ten
    minutes. This is not in the manual.
    Thanks for any input.

    pat
     
  2. Lord Garth

    Lord Garth Guest

    The answer specifically depends on the motor. The demand of the motor
    depends on the mechanical load. The mechanical load changes as the amount
    of water & dirt and the drag of the rubber change, then there is the motor
    speed
    to consider. Also, pausing for 10 minutes between strokes is plenty of time
    for
    the battery to recover....

    I would say there are plenty of undefined variables so the only answer is,
    a while. Give it the acid test...hook it up and run it until the battery
    reaches
    10.5 volts. This is considered a dead battery, it is not good to deep cycle
    a
    battery to this point regularly. Deep cycle batteries can handle this
    better but they cost more.
     
  3. Ban

    Ban Guest

    Around one week at least. 5s*20A = 100As each cycle. The battery has maybe
    54Ah capacity of which you can use around 50% to not degrade it.
    27*3600/100= 972 activations.
     
  4. Chris

    Chris Guest

    Warning -- as someone said earlier on s.e.d., there's a law that
    requires at least one boneheaded obvious math error in any post
    dependent on arithmetic to make a point. Caveat emptor.

    Hi, Pat. By chance, a surplus wiper motor for 2000/2001 Saturns is
    being sold at All Electronics. It's a 2-speed job, and the blurb says
    it uses 4 amps for hi-speed at 106 RPM and less than 1 amp for low
    speed at 41 RPM.

    http://www.allelectronics.com/cgi-bin/category.cgi?category=400400&item=DCM-171&type=store

    Not a bad deal for 16 bucks. Let's assume lo-speed. 41 RPM = about
    1.5 seconds at 0.91 amps. Round it off to 1 amp * 1.5 seconds = 1.5
    a-s (amp-seconds, a-s = amp * seconds).

    Now, even a small car battery is good for 40 a-H (amp-hours), but even
    for marine and deep discharge batteries, you shouldn't take more than
    half of that. So lets assume 20 a-H capacity, which means 72,000 a-s
    capacity. This will give you 48000 shots, and at 6 per hour, you're
    talking about 333 days of use. Of course, as a practical matter, the
    battery will self-discharge and go flat well before that, and the above
    didn't take into account the work that will have to be done by the
    motor. Short story, though, is you'll probably be OK for a month,
    maybe two months with this motor, but not 333 days, or forever.

    I would lean toward using a marine, R-V or wheelchair-type battery
    instead of a car battery. Although they're somewhat more expensive,
    they are made to handle deep discharges better. Also, if you ask
    around, you can find batteries with better room temperature a-H ratings
    (battery sellers and manufacturers have this data -- they just don't
    want to publicize it for some reason). Higher a-H rating is better.

    No matter what, stay away from used car batteries, unless you know it's
    less than a couple of years old and hasn't been in a car with
    electrical problems. Old car batteries are almost always a
    disappointment, even for starving artists who have made disillusionment
    their very sustenance.

    Remember -- your 10 minute timer drives a relay, transistor, or SSR to
    start the motor, and use a cam microswitch to stop it at exactly the
    same place every time. (These are also available at
    Allelectronics.com)

    <Safety Man> By the way, try to get a sealed lead-acid battery, and be
    sure to clamp or bolt down the battery well. Spilled acid can ruin
    someone's day (possibly a kid -- be careful). Also, make sure the
    terminals and any exposed wiring is insulated -- people use (and drop)
    the darnedest things when setting up and taking down displays. It
    might be better to get one of those batteries with the built-in
    carrying handle, and install the battery after the display has been
    moved.</Safety Man>

    Good luck
    Chris
     
  5. Bob Masta

    Bob Masta Guest

    As an addendum to what others have posted, I'd just like
    to note that windshield wiper motors can have an
    astonishing amount of starting torque. As a student
    engineer at Cadillac Motor Car in the late 1960s, I used
    a wiper motor to drive a test fixture (for something else
    I don't recall now). In order to test the rotation direction,
    I held the motor in my hand while connecting it to a big
    bench supply. Big mistake! Jerked right out of my grip
    and whacked me with the mounting ears of the motor
    housing. So, 1) be careful! and 2) the starting current
    may be a whole lot more than the run current, and in
    your case you have a high proportion of starting current.

    Best regards,





    Bob Masta
    dqatechATdaqartaDOTcom

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
     
  6. Pat Kilgore

    Pat Kilgore Guest

    Thanks everybody for the replies. That's more than I knew about
    batteries put together already
    What we have used in the past to control timing and switching is time
    delay relays. http://www.ssac.com/catalog/TDR01A01.pdf(tdr1b12 is the
    one i would use here) With this one current is always on and the timer
    switches the relay on and off. Little pricey at fifty bucks but I didn't
    see a switch timer combo I could use hooked up to a 12 volt battery at
    allelectronics.com. I know squat about reading the specs on switches and
    cam microswitches, etc. You think I could do a lot better than $50?

    Pat
     
  7. Lord Garth

    Lord Garth Guest

    The only current that is on all the time is that which runs the timer. I'm
    sure this is very low. Given that you don't work with electronics, this
    $50 part is probably a good approach.
     
  8. Chris

    Chris Guest

    Hello again, Pat. SSAC makes very good products. I would guess you
    can save at least half of that $50 by doing a home brew, but given your
    level of electronics expertise, buying a packaged solution and avoiding
    the hassle might be worth the extra $30.

    One question: You said you need one cycle every 10 minutes. What do
    you mean by that? I guess I assumed in your OP you meant you needed
    precisely 1.00 revolution of the motor. If not, the SSAC relay is a
    great idea. If you need the motor to stop at the same place every
    time, you're going to need a better solution, particularly a cam on the
    motor shaft and a microswitch to sense the cam bump to stop the motor.
    At least you don't have to worry about the power supply.

    (By the way, I don't believe there's reverse-polarity protection on
    those Solid State interval timers. If it's possible to reverse-connect
    the battery terminals, you should think about using a protection diode
    to keep from smoking your SSR. It's shown as "D" below. Use a 1N4002
    for D, and a 1N5402 for D2 if the motor uses less than 3 amps.)

    `
    ` + Battery -
    ` o o
    ` | Microswitch |
    ` | (Use N.C. Contact) D2 |
    ` | .---|<----o
    ` | -o | |
    ` | __--o-----------o _ |
    ` o------o | / \ |
    ` | o--( M )--o
    ` | | \_/ |
    ` | .-------------. | |
    ` | 1| |3 | |
    ` o----oRLY RLYo---' |
    ` | |COM SSR N.O.| |
    ` | 2| Timer |7 |
    ` o->|-o+ -o-------------o
    ` | D | | |
    ` | '-------------' |
    ` | |
    `created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    Every ten minutes or so, your SSAC TDR1B12 timer will close the relay
    contacts for about 0.3 second, long enough to turn on the motor and get
    the motor shaft cam off the microswitch. Since the N.C. microswitch
    contact will now allow power to go to the motor, it will continue to
    run until the motor comes around, and the cam pushes on the microswitch
    again, removing power from the motor. D2 is necessary to absorb the
    inductive kick of the motor when the microswitch turns it off. If you
    don't have it, you'll get an arc on the microswitch which will reduce
    its life. Simple & easy. Heck, windshield wipers used to be wired up
    with a microswitch this way, except the dashboard wiper switch was used
    instead of the SSR. That way the wipers would always stop down.

    Post again if you've got more questions.

    Chris
     
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