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blowing bulbs- revisited !

Discussion in 'Electronic Basics' started by Andy C, Apr 1, 2007.

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  1. Andy C

    Andy C Guest

    hi all,
    please could anyone who is bored enough have a look at these 2 wiring
    diagrams for me...
    they are both for the same motorbike, but one is an old one and the other
    one is a later (factory modified) one...
    the older one is prone to blowing headlight and tail-light bulbs (even LED
    ones) but the newer one is much better...
    the main difference seems to be that in the later one the 4-wire regulator
    has been replaced with a 5-wire one and a bleed resistor added which is used
    only when the lights are off...presumably to help protect the regulator by
    ensuring there is always a load on it...
    i'm not 100% certain that this is the only reason the bulbs are blowing on
    the older bikes (e.g. the older ones might have crapper batteries for
    example)... but if this is the reason... why would the 5-wire regulator be
    the better system ?
    if you look at the extra (black) wire on the 5-wire regulator it simply
    joins directly with the red wire anyway if you follow the circuit (so long
    as the ignition is on).. so what is the point of the extra wire... is the
    different regulator probably not the solution ?
    both regulators charge the battery at peak ~14.8volts on a long run using
    the system for measuring peak voltage which someone previously suggested on
    this group -
    many thanks !
  2. Kim Clay

    Kim Clay Guest

    sure - I've got lots of ramblings - had a bike where the batt ground
    wire broke at its frame ground. Driving 45mph down the road (of course
    at night) & the low-beam pops out - switch to high-beam & pop its gone.
    305 Sky-Hawk Scrambler I think.

    Has anyone tried replacing the regulator on a "old" bike that has the
    problem? Did it fix it? Do all of the old bikes suffer the same problem?
    Has this problem always been there (people always had to replace the
    lights frequently?).
    The permanent-magnet alternator, by design, will produce increased power
    output as its rpm is increased. The only way to tame this increase is to
    utilize the excess power somewhere. This "bleed resistor" is a simple
    way to "waste" the same amount of energy as the lighting system would
    consume. Thus either the lighting system is "on" or the "bleed resistor"
    is "on" & the combination of both options provides a constant load to
    the permanent-magnet alternator.

    The lighting circuit will consume about 2/3 the total (12V) power of the
    It appears that the "new" regulator has two outputs that get connected
    together when the ign. sw. is "on". One of the outputs has a direct
    connection to the battery for better charging of the battery at low rpm.
    The other output runs directly to its main load, the lighting circuit.

    The lighting output does get tied to the battery charging output but the
    run is long & the wiring resistance will be quite high compared to the
    "direct connections" limiting the effects of being tied together.
    First is to identify the problem...

    It is difficult to design a charging ckt. using a permanent-magnet
    alternator that works equally well for slow speeds/short trips as well
    as high speed/long trip conditions (& do it as cheap as possible).

    To keep it simple the OEM used a PM alternator (cheap). This alternator
    has to be powerful enough to run full lighting, around town, at low rpm
    & still recharge the battery on every trip.

    Once the battery is recharged, the regulator must get rid of the excess
    power by wasting it as heat, as there is no way to reduce the power
    output of the PM Alternator. Usually short-trip/in-town-driving barely
    keeps the battery charged so little heat needs to be wasted.

    But on longer/high-speed (rpm) trips the battery quickly recharges &
    LOTS more power must be wasted to keep the voltage down (<15V).

    A single regulator could be designed to work properly in all
    circumstances, but it might be cheaper to build a regulator with 2
    outputs :) The "new" design appears to have done just this. Each output
    only needs to carry 1/2 the load of a single output regulator.

    By including a "bleed resistor" to replace the lighting load (when the
    lights are off) the designers found a cheap/simple way to regulate much
    of the 12V power circuit. Now, the regulator only needs to handle (waste
    as heat) the excess battery charging current & the excess power produced
    at the higher rpms.

    Now back to what I think was your original problem - burning out
    14.8V is at the top end for 12V lights!
    14.8V on the battery terminals will cause it to boil water slowly. Brief
    periods should not hurt it as long as water is added when needed.

    On a old bike with the problem try a new battery & _really_ inspect
    _all_ the connections. All clean? Tight? Fuse holder & fuse very clean &
    the fuse clamps very secure? Ground wire attached to the frame & the
    wiring harness OK? No frayed wires at its connector? Bullet connectors
    are very clean & tight?

    If after doing the above the bike still has the same problems then
    perhaps the OEM design is faulty. After all they did redesign it in
    later models.

    A couple of things you could try... Get an electronics friend involved
    if you want to try any mods. Or be certain you know what you are doing

    If the old voltage regulators are just regulating at a higher than
    normal voltage, then perhaps adding a single diode in series will help.
    It will drop the voltage ~0.7V.

    Depending where it is installed, either...
    the whole system voltage will become ~14.1V, including the battery float
    (install in series with the regulator Pos. output Red lead)

    or just the lighting load voltage will become ~14.1V
    (install in series with the Red lead going to the Ign. sw.).

    The new schematic shows a 15A fuse in the batt lead so a 25-30A
    stud-mount diode should be ok. Mounted on a heatsink & very well
    insulated/protected from ground.

    The other idea would be to use a "new" model voltage regulator in a
    "old" bike by connecting the two output leads together at the regulator
    & treating it as a 4-lead regulator.

    I would really try to find out how the new regulator was designed first.
    It does have two outputs but its possible that they are regulated
    somewhat differently.

    BUT, after all that, why do both old & new designs show the same battery
    charging voltage of 14.8V? I dunno. It kinda suggests that the "old"
    bikes have other problems causing lamp burnout. Perhaps it is the length
    of time the battery voltage is held at 14.8V?

    Keep us posted & good luck!

    To reply add xyzzy to subject line.
  3. Andy C

    Andy C Guest

    hi kim,
    many thanks, that has some really helpful ideas in there - i will email you
    shortly if you don't mind!
  4. Kim Clay

    Kim Clay Guest

    Sure :) E-mail addr is valid.

    Ignore the "To reply add xyzzy to subject line."
    It was left over from previous testing.
  5. Kim Clay

    Kim Clay Guest

    Some notes I found out about this fifth wire...

    Initially I suggested the regulator might have two outputs but more
    likely is that the fifth wire is an external sense lead the voltage

    The 4-wire regulator would have its sense lead tied (internally) to the
    Pos Batt output wire.

    The fifth-wire sense lead should terminate where the voltage needs to be
    regulated - the battery - to keep the battery properly charged.

    The wiring diagram for the bike will show the actual routing of this
    wire. The schematic just shows what is connected to what, not the actual
    wiring layout.

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