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Extending the range of an electric bike...

Discussion in 'Electronic Design' started by [email protected], Apr 7, 2007.

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  1. Guest

    Hi,

    In the last few days,
    I've bought a 22 inch electric bike 2nd hand for £120.

    It's been pretty impressive so far imho.

    Problem is,
    as people probably already know, is the battery...

    At the moment,
    it does 12 miles at 17 mph quite comfortably with no input from the
    rider.
    (36v 12 amp lead acid battery)

    Just curious to what you think of this idea of extending the range.

    A leisure battery from a scrap yard 12v 110 amp - £30
    A fast charger 22amp from Argos - £40
    A 12v to 36 dc to dc convertor - £70
    A current limiting diode.

    ie 12v at 110amps,
    probably equals 36 volt at 30amp = 2 times as far = 25 miles,
    (taking into account the extra weight and the loss of electric
    convertion)

    but I reckon it should be good for an approx range of 30 miles of
    effortless riding.

    Any comments? Ideas?

    Thanks,
    Dave
     
  2. Rich Grise

    Rich Grise Guest

    To me, it sounds like a complete non-starter. Don't EVER get a scrap
    battery and expect to do anything but pay somebody to haul it away.

    You'd be better off to just get another 36V battery just like the
    one you have, slap it in parallel with the existing one, and either
    beef up the charger or charge it twice as long.

    Or, get THREE of the big 12V honkers, and wire them for 36V, and
    just be done with it.

    Although, you still have the weight issue. Other people might have
    other ideas about battery technology/power density, etc, but I'm
    at my limit here. :)

    Good Luck!
    Rich
     
  3. Do you mean 12 Amp-hours?
    Are you planning on replacing the existing battery with the above? Or
    paralleling the converter output with it?

    What exactly do you mean by 'current limiting diode'? A blocking diode
    for parallel operation?
    You could replace the 110 Ah, 12V battery with 3 40 Ah batteries in
    series (giving you 36V) and do away with the dc-dc converter, its losses
    and weight.

    One thing you might want to consider before investing $$ (or ££) in a
    lot of range enhancing hardware: Test the existing battery capacity
    first. You said you bought this thing second hand and its possible that
    its battery capacity has diminished.

    Hook up a voltmeter, ammeter and a suitable load (a couple of 12V
    headlights) and plot the battery current and voltage over time. No sense
    in re-engineering the whole contraption until you have established a
    good baseline for performance.
     
  4. kell

    kell Guest

    If you want extra watt hours, get a bigger 36 volt battery or just add
    another 36 volt battery in parallel with the one you already have.
     
  5. Is not putting Lead Acid in parallel creating the possibility for giga-amps
    egalization currents?
     
  6. MassiveProng

    MassiveProng Guest

    "egalization"???

    Also, if "wired for 36 volts"... that would be series, not parallel.

    This is very unlike you Pan Janteltge! ;-] Have you been drinking?
     
  7. kell

    kell Guest

    Yeah, they say you should only parallel identical batteries of the
    same amp hours/brand/batch/age (new, in other words).

    I owned a diesel Suburban with two batteries hard-wired in parallel.
    Must have been many thousands of those vehicles on the road, and I
    imagine a lot people ended up putting dissimilar batteries together,
    so I guess it's not a huge danger.

    I know I would want to make sure at least that both batteries are in
    good condition, similar amp hour ratings and well charged before
    making the connection.
     
  8. MooseFET

    MooseFET Guest

    12 miles at 17mph takes: 0.7 hours

    36V * 12AH = 432WH

    432WA / 746 = 0.579 HpHr

    0.579/0.7 = 0.8Hp

    You have huge losses somewhere in the system. Making a bike go at
    17MPH takes less than 1/4HP.
     
  9. skenn_ie

    skenn_ie Guest

    Does it use regeneratice braking ? If not, employ it, if it does, it
    may not be very effective. Either way, MooseFET has a good point.
    Does it use resistive speed control, or PWM ?
     
  10. Pump up the tyres


    martin
     
  11. MooseFET

    MooseFET Guest


    It may not have any control at all other than on/off.

    A system for running on 12V, 24V or 36V is better than simple PWM but
    requires more smarts from the driver.
     
  12. ehsjr

    ehsjr Guest

    You must know some things no one else knows. :)
    Like: the weight of the rider & the bike, rolling resistance,
    the slopes encountered in the 17 miles, headwinds and tail winds,
    the state of charge at the end of 17 miles, how much energy
    was extracted from the battery etc.

    In other words, we have no idea of the work done
    nor the energy expended.

    Ed
     
  13. MooseFET

    MooseFET Guest

    Yes I know lots and lots of things.
    It just about doesn't matter within the normal range for adult
    humans. The width across the shoulders matters more. I am on the
    large end of the scale and assumed that since the person had not said
    anything about the subject they were not abnormally wide.
    All bikes weight 50 pounds.
    A 10 pound bike needs a 40 pound lock and chain
    A 20 pound bike needs a 30 pound lock and chain
    A 30 pound bike needs a 20 pound lock and chain
    A 40 pound bike needs a 10 pound lock and chain
    A 50 pound bike doesn't need a lock and chain.
    I assumed that the bike was a normal bike and that the tires were
    pumped up and that the various bits hadn't rusted together.
    There may be light poles and phonepoles but there were no math poles
    enclosed during the ride.
    I assumed the wind did not change and that it was low enough not to be
    remarked on.
    The OP told us the "range" was 17 miles. The battery was discharged
    at the end.
    Almost all the energy that could be.

    What's this "we" paleface. I made a fairly good estimate based on
    what I know from experience.
     
  14. Well, that rating is for a longer discharge time. Maybe 5Hr but
    proabably 10Hr or 20Hr. The useable capacity with a 3/4 Hr discharge
    will be lower, probably substantially lower.

    Robert
     
  15. Jeff L

    Jeff L Guest

    Hi,

    In the last few days,
    I've bought a 22 inch electric bike 2nd hand for £120.

    It's been pretty impressive so far imho.

    Problem is,
    as people probably already know, is the battery...

    At the moment,
    it does 12 miles at 17 mph quite comfortably with no input from the
    rider.
    (36v 12 amp lead acid battery)

    Just curious to what you think of this idea of extending the range.

    A leisure battery from a scrap yard 12v 110 amp - £30
    A fast charger 22amp from Argos - £40
    A 12v to 36 dc to dc convertor - £70
    A current limiting diode.

    ie 12v at 110amps,
    probably equals 36 volt at 30amp = 2 times as far = 25 miles,
    (taking into account the extra weight and the loss of electric
    convertion)

    but I reckon it should be good for an approx range of 30 miles of
    effortless riding.

    Any comments? Ideas?

    Thanks,
    Dave


    Check the capacity of your batteries, they may be aging - other similar
    bikes running on 36V get a lot more range, see the link below (12V, 12Ah
    batteries weigh a little over 4 kg, this one has 14 kg of battery, so about
    a 36V 12 Ah battery). Do a google search for many more hits

    http://www.bicycle-mountain-bike-cycle.co.uk/index.php/product/LB01-dd.html

    New batteries are fairly cheap (likely around £50 - 60) - don't waste your
    time with used batteries (especially don't waste your time with car / truck
    starting batteries for storage), mixing batteries, or voltage converters.
    Doing so will not give the expected results and could be dangerous. Ever see
    what happens when a car battery shorts out? They are capable of sustaining
    several thousand amps of current into a direct short. This is enough power
    to turn a section of the frame of your bike into a red hot chunk of steel,
    or vaporize a wire shorting it out. High power DC to DC converters are not
    likely a good answer. There are several very good reasons why a 36V system
    was initially used, and there is no reason to change it to a lower voltage.
     
  16. Tim Williams

    Tim Williams Guest

    Nope, it all factors out. It's just a comparison.

    Do you honestly know of any bicyclist who can put out 0.8HP for 42 minutes?
    The typical human can do about 1/4HP as I recall, making that figure a good
    basis for the power consumed at 17MPH. Depending on bearing quality/tire
    pressure, wind resistance, "uphill both ways", etc., of course.
    Presumably, the energy expended was 432Wh, since the OP implied that 12
    miles is the maximum range on the given batteries.

    It's all just math and makes sense when looked at. Of course, facts don't
    produce such comments as:
    which reflects badly on his attitude...

    Tim
     
  17. FWIW the average human can produce about 3w/Kg body weight, so about
    200W for about an hour.


    martin
     
  18. MooseFET

    MooseFET Guest

    A bike racer can put out more, but they go a lot faster than 17MPH.

    [....]
    That was an attempt at humor.
     
  19. MooseFET

    MooseFET Guest

    I think that is a bit optimistic. The problem is with "average". You
    have to include a lot of the very unfit, the sick and the elderly if
    you say "average".
     
  20. MooseFET

    MooseFET Guest

    This would be part of the losses of the total system, as would the
    losses in the motor. All together it is a rather poor efficiency.
     
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