Connect with us

Newbie - Basic battery charging question

Discussion in 'Misc Electronics' started by Hake, Dec 6, 2006.

Scroll to continue with content
  1. Hake

    Hake Guest

    Hi All,

    I use a lead acid battery to power my bicycle lights. It is 6v & needs
    replacing (it is only working for 45 mins now instead of hours).

    I have been pondering using a 6v Dynamo to put charge back in whilst I am
    cycling. Now would be a good time to test this as the battery is at the end
    of it's life span & dos not matter if I kill it completly.

    My questions are;

    I am guessing as a dynamo is basically, a motor, I will need something to
    stop electricity flowing back & powering the dynamo as a motor. I think for
    this I need a Diode - is this correct, and if so, what type of Diode do I
    need to ask for?

    If I wire the dynamo to the battery in parrallel with the lights, If I have
    the dynamo charging whilst the lights are switched on, what happens? I am
    guessing this should not blow the bulbs in the same way an alternator is
    charging a caar battery all the time (unless some sort of regulator is
    involvd?)(6v rated) - is this correct?

    ANy thoughts? Or is this a daft idea?

    Many thanks in advance,

  2. You'll notice the drag.

    IME you are better off with dry cells and a dirty DC recharger. You can
    carry a couple of spare sets with little weight penalty.
  3. default

    default Guest

    It is doable within limits. Find out what voltage your dynamo
    generates under load and no load - presumably you'd do some peddling
    during the day and that could be used to recharge the battery.

    Good solution if you are camping for months on end with your bike.

    Dynamos output AC and the rectifier diodes you'd need to convert to DC
    to charge the battery would prevent discharge. A switch or two on the
    handlebar would give you some flexibility on whether to use battery or
    dynamo - or you could just use a steering diode - dynamo voltage goes
    lower than the battery and voltage flows from the battery to the lamp.

    It can be made lots more complicated - but a switch(s) and diodes and
    you're home free at little expense with good control of the system.

    Now - while you're at it reduce the current demands of your lighting
    system. Switch to leds if you can. I mounted 56 white LEDs under my
    motorcycle headlight and it is more than enough at night for bicycle
    speeds (50-75 feet) - uses a measly 3 watts and looks brighter than
    the headlight in daytime - just doesn't have the same beam spread only
    20 degrees. Headlight consumes 50 watts. Leds set me back $7 and the
    resistors and potting compound works out to about 9-10 total for the

    Consider Nickel Metal Hydride rechargeable packs or Lithium also - may
    be able to lower the weight some.

    Finally if you haven't already bought a dynamo; consider an in-hub
    one. The thingees that rub against the wheels add a lot more drag and
    abrade the tires over time. The in-hub dynamos start producing
    earlier and are current regulated to some extent (not good for battery
    charging- but saves light bulbs on an all dynamo system) The friction
    types will pop a bulb at over 15 mph.

    In-hub dynamos cost, but are well worth it if you drive in the dark a
    lot. Requires a new wheel or some new spokes and re stringing the
    wheel. Since you would have some bucks invested in the front wheel
    ditch the skewers and use rounded lock nuts so the wheel isn't stolen.

    To get power from the dynamo to the battery the dynamo has to produce
    enough voltage to overcome the diode drops point six volts or so plus
    a few tenths of a volt over the resting battery voltage (6.3 volts for
    lead acid - so figure 6.6 volts - more is better) which works out to
    7.2 volts. - a 12 volt system will be more efficient at around (14.5
    volts for charging)

    I was writing to some guy in France awhile back who has an automatic
    system for charging and lighting - he camps in the mountains and uses
    the battery for lighting the way and reading at night.
  4. Hake

    Hake Guest

    Whilst I appreciate your name Homer, I dont belive the drag would be a
    problem - if for no other reason than that the dynamo would not be able to
    excert eenough pressure on the tyre before it skidded. I may be wrong, but i
    do not think that even a direct short across the dynamo would cause this -
    and I am just intereste din trickle charging.

    Weight is not a problem. My interests lie in low cost & resiliant lighting
    which can be charged from my own power.

  5. Hake

    Hake Guest

    Thanks for all the Ideas, I shall spend some time trying find and price
    components - I like the Idea of a LED system, but I am in the UK &
    generally, we are ripped of for electronic components - but i shall

    Its interesting to hear of the guy in France - thats the sort of thing I had
    in mind, I just have to get a bit of knoweledge to acheive it.

    TO further the Idea, when I have nothing better to do I d like to buy a
    excersise bike, connect it to a a alternator from a car & attempt to use my
    excersising to cpower lighting and other things in the home - I know its a
    bit crazy & doesnt really save much, but it just sounds fun!

    If I take the bike thing any further, I will post how I get a long, I havent
    got as much time as I would like though!

    Thanks very much for the pointers,


  6. default

    default Guest

    I bought the LEDs on line from Hong Kong, the shipping was free 100/$12 shipping is air mail and takes ~10 days
    Prices shown in USD regardless of currency

    A set of three 1 watt LEDs at $30 would give a little more light and
    out to the sides, 120 degree beam spread - but this works for me I
    just don't want the guys at intersections to pull out and test my
    driving skills or brakes and the LEDs seem to be doing that.
    He was rectifying the AC from a hub dynamo and regulating it with
    SCR's to charge the battery when there was excess power to be had.

    I've used both hub dynamos and friction types. Hub has it all over
    friction style for performance, and friction over hub for price.

    Another guy is marketing a flashing LED bike light that works off a
    frame mounted coil and a magnet affixed to the spokes - don't know if
    that can do much more then keep one from getting run over in the dark.
    Put a lot of very strong magnets on the spokes and it might equal a
    dynamo for less money.
    What's crazy? - makes a lot of sense to power the TV while watching
    it, lot healthier. There's satisfaction, knowledge, bragging rights,
    in the project with exercise for a side effect - sound like reasons to
  7. psdayama

    psdayama Guest

    Hake wrote:

    It is true that dynamo on cycle is AC type. So use a bridge
    rectifier not diode.
    That will kill dynamos magnet in long run.
    If U have lights on while charging then not much happens than U
    will huffing and
    puffing within a KM of cycling. If U switch off lights (in day time)
    may be after 20-30kms
    U will overcharge battery if U haven't put a current limiter after
    bridge. By the way U havent
    mentioned what battery AHs are. I think it is mostly 4.5 AH used in
    most of bikes.
    It has limit of 1.2Amps of charging so U have to put small resistor
    like 0.5ohm in serries.
    As somebody else has mentioned it is better to use LEDs as they dont
    pop off with excess
    voltage but for that condition U have to get speed like going downhill.
    With battery bulb
    doesnt popoff but if it is old battery then with overcharge its voltage
    may go beyond
    8Volts and kill both the bulb and battery.

    I have seen that people using friction dynamo have to change tyres
    frequently and hope
    U better get those axle dynamo.
    Best way would be to use small car alternator with some attchment to
    it. Alternator has battery charging regulator. U will also need smaller
    12V 4AH battery or get
    a pack of LI-ion batteries which are better than lead acid type.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day