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Current reversal in 2 connected car batteries?

Discussion in 'Electrical Engineering' started by Alex Coleman, Sep 13, 2006.

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  1. Bill Janssen

    Bill Janssen Guest

    Because it's the NEW standard. All (or most) of the auto manufactures
    are on board this new standard.

    Bill K7NOM
     
  2. Adrian

    Adrian Guest

    () gurgled happily, sounding much like they were
    saying :
    There's rather a lot more electrickery in your average new 7-series than
    just the starter motor...
     
  3. We were somewhere around Barstow, on the edge of the desert, when the
    Are you serious? I was referring to a standard jumpstart with the
    operator not being a clueless fool.
     
  4. Duncan Wood

    Duncan Wood Guest


    It doesn't need the higher voltage, but the higher voltage lets you get
    away with thinner cable & smaller relays, which is cheaper & lighter. &
    makes things like tailgate motors much more practical.
     
  5. Duncan Wood

    Duncan Wood Guest

    Given he diidn't need a new battery straight away that would seem to be a
    reasonable assumption.
     
  6. Duncan Wood

    Duncan Wood Guest

    There's not actually any extra battery weight, as you need less current
    for the same power you end up with only a fractionally larger battery for
    the same power to the starter motor.
     
  7. Roy Lewallen

    Roy Lewallen Guest

    I see some real benefits in establishing a new voltage standard for cars.

    Until it becomes common, aftermarket radios, headlights, and a large
    host of other products won't work in the new cars, so dealers can charge
    what they want for parts.

    As it becomes more common and the parts market increases, all auto parts
    dealers will have to buy a whole new inventory of higher voltage parts,
    from radios to headlights, other lights, and probably even fuses, while
    retaining their current inventory of 12 volt parts. So it's a great deal
    for the auto manufacturers and a great deal for the parts manufacturers.

    I don't see any real benefit to the consumer, but hey, since when was
    that a concern?

    Roy Lewallen
     
  8. Skenny

    Skenny Guest

    Right.
    I can also see an opportunity for manufacturers of 24 (or whatever they go
    to) vdc to 12 vdc converters.
    But they will probably be overly complicated to allow a larger price tag..
     
  9. Bill Janssen

    Bill Janssen Guest

    As I understand the plan there will be two voltages used at least
    initially. !2 volts will be available for
    those after market accessories and 42 volts for the built-in loads.
    Suppliers are designing (cheap)
    converters to get 12 volts from the 42 volts

    There is consideration of using electrical motors for such things a
    breaks and steering. And of
    course as some one mentioned there is the hybrid car and it's power
    requirement.

    Bill K7NOM
     
  10. We were somewhere around Barstow, on the edge of the desert, when the
    For this particular episode, 12V neg ground.
    Car to car, both fairly ordinary vehicles. At this time in the UK, the
    only other common higher-voltage use is 24V on heavy trucks. 42/48/50V
    vehicles are extremely rare. Of course, he could have attempted it from
    a milk float or forktruck - it wouldn't surprise me.

    As for hooking it up wrong; well, that's a possibilty, but he'll be more
    careful next time.
     
  11. Duncan Wood

    Duncan Wood Guest

    The number of Positive gnd , 6v or 24V Mitsubishi Shoguns is pretty
    negligible. You're more likely to encounter a dead short than an non 12V
    neg gnd car which isn't covered in warning signs or driven by someone who
    knows it.
     
  12. We were somewhere around Barstow, on the edge of the desert, when the
    <bored now>

    The whole comment I made was predicated on the assumption that the OP
    wasn't a total idiot and knew that both cars were 12V neg ground.
    Recall that there was another party involved in the jumpstarting and he,
    at least, probably had more clue than the OP.
     
  13. BillW50

    BillW50 Guest

    When I was younger and sometimes today, we still jump 6V (either
    positive or negative ground) with 12V negative ground equipment.
    Although all of this equipment uses generators instead of alternators. I
    would not try this with something that uses an alternator or all. And
    gosh does a 6V starter turn over an engine really fast with 12V
    connected to it. Even hard to start engines generally pop off really
    quickly. :D
     
  14. BillW50

    BillW50 Guest

    Hahahaha... I knackered my car battery trying to start a semi truck in
    cold weather. Just simply jumping, my car battery didn't have enough
    current to turn over the diesel engine. So it had taken me 20 minutes
    using my car's alternator to charge up four of the huge 12V batteries
    enough to give it enough boost to finally start the truck.

    And I let my car run another 5 minutes after disconnecting to charge my
    car battery up enough so I could start it later. Well 12 hours later, I
    went to start it and my battery was dead. Used the truck to now start me
    up. All was well after that. What a PIA! lol

    Oh but I do have a story about jumping someone else that could cost you
    or someone plenty. My dad and his friend jumped a vehicle and the
    battery blew up in my dad's friend's face. They had a garden hose right
    there and thus hosed him down with water and he turned up okay
    afterwards. Thank goodness. Just some cuts on his face.

    I have jumped hundreds of vehicles and I have never seen this ever
    happen. I have heard these stories though for decades. This was the
    first time my dad has seen this happen too from hundreds of jumps.

    The safe idea though is to connect up the last connection to ground and
    far enough away from the battery so that the spark doesn't ignite the
    battery vapors. Although with most things made of plastic and having
    plastic shell covers on everything. And everything metal is also painted
    if you can find the real metal, this is getting harder and harder to do
    on some makes and models. :(
     
  15. BillW50

    BillW50 Guest

    All of the big trucks that I know only uses 24v just for starting. As
    everything else is still 12v. Like lights, radios, fans, etc. That is
    why they use batteries in multiples of 2 (12v batteries) i.e. 2, 4, or 6
    batteries. They change the battery configuration from parallel to in
    series by using simple starter relays.

    And why pick 42v if you are going to change from 12v? As in series that
    would take three 12v and one 6v batteries in series to produce that. Why
    not use 48v or 36v? That way you could use 4 or 3 12v batteries.

    The big advantage of 12v is that you normally can't get shocked. Well
    sticking your tongue on it you can, but normally no. Now using 42v, this
    is now a shock hazard. You can feel that most of the time. So if you are
    going to raise it that high, why not go to 120/240AC? This makes more
    sense running electric motors off of this vs. 42vdc. And you can plug in
    your laptops, TVs, stereos, etc. off of this as well.

    How much watts does one need to push an electric car at highway speeds
    anyway? 1200 watts? 2400 watts? 12vdc to 120vac inverters should work
    nicely if it isn't very much.
     
  16. AIUI, they settled on 42V for safety reasons. Anything below 48V
    is considered "low voltage". A 42V battery will nominally be just
    under 48V.
    Standards. See above.
    1HP is about 746 watts. Figure out how many you need.
     
  17. Guy King

    Guy King Guest

    The message <ADRUg.7368$>
    You could do it with a flywheel but the output frequency would droop as
    it slowed down - unless you got all clever with synthetic AC which
    rather defeats the object. It'd be nice to have regenerative braking
    though.
     
  18. BillW50

    BillW50 Guest

    I don't know? :(
    As far as the ignition, starter, instruments and other normal things
    found in cars for decades could still use 12v battery. But things like
    lights would last longer on AC vs. DC. And I would think electric motors
    for the electric car side is more efficient being run from AC vs. DC.
    Yes I too have ran cars from a faulty charging system. You can usually
    run the engine for many hours off of a good car battery. :D
     
  19. Roy Lewallen

    Roy Lewallen Guest

    One horsepower is 746 watts, very nearly 3/4 kilowatt.

    Maybe some of the readers recall the little 50 cc Honda motorcycles at
    the tip of the Japanese bike invasion. They were alleged to develop 5
    HP, or about 3700 watts. With a single rider they could do about 40 mph
    wide open on flat ground (although their speedometer would indicate
    about 60).

    All the hybrid vehicles I've seen use voltages of 100 volts or more -- a
    new one reviewed in Saturday's paper used 300. This makes sense for the
    power levels involved for propulsion. But it makes no sense to run the
    remainder of the electrical system at that level. As far as I know, all
    the hybrids use 12 volts for the electrical systems.

    Roy Lewallen
     
  20. BillW50

    BillW50 Guest

    Grrrr! There ain't much of a difference between 42v and 48v to really
    matter. Yet someone controlling the standards says there is. :(

    [snip]
    Isn't every 50cc of a gasoline engine roughly 1HP? I know 49cc can
    travel at speeds of 30MPG (mopeds). Thus my '72 Honda 350cc motorcycle
    must be like 7HP and I know I can exceed 70MPG on that thing. And my '95
    Honda 1100cc motorcycle must be like 22HP. And I don't know what the top
    speed of it yet. lol

    Now the old VW Beetles were around 1200cc and usually traveled at a top
    speed of 83MPG. So that would be like 24HP to do the same. And if 746
    watts is correct, pushing the old VW would be roughly 17,904 watts. Wow!
    *gulp*

    Anyway I forgot how they vary the speed of AC motors? Doesn't it require
    different windings for every RPM? If so, that wouldn't work anyway. :(
    Although just thinking about adding a torque converter and we are back
    in business! :D
     
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