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measuring peak voltage

Discussion in 'Electronic Basics' started by Andy C, Mar 22, 2007.

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  1. Andy C

    Andy C Guest

    hi there,
    we have a batch of voltage regulators for motorcycles which are meant to
    regulate the battery charging voltage to approx 14volts max... i suspect
    they are occasionally putting out 'spikes' of higher voltage which keeps
    blowing bulbs on the bikes they are fitted to...
    can anyone think of an inexpensive way (or already available kit or
    instrument perhaps) whereby we can fit something to a bike... take it for a
    ride... and it will record the peak voltage so we can prove they are faulty
    many thanks !
  2. John Fields

    John Fields Guest

    I'd do something like this: (View in Courier)

    | | |
    | | |

    Any spikes on the 12V line will charge the capacitor quickly, but it
    will discharge slowly through the voltmeter's internal resistance
    (10 megohms for nearly all DVMs)allowing the DVM to acquire it
    before it decays significantly.
  3. chuck

    chuck Guest

    It might be easier and cheaper to simply fix the problem than to analyze it. A 15 volt zener diode at the bulb would surely do it. Higher voltage spikes don't strike me as a likely cause of bulb failure. Vibration and bulb design are more likely candidates. What about an LED replacement for the incandescent bulb(s)?

  4. Andy C

    Andy C Guest

    hi there,
    it. A 15 volt zener diode at the bulb would surely do it. Higher voltage
    spikes don't strike me as a likely cause of bulb failure. Vibration and bulb
    design are more likely candidates. What about an LED replacement for the
    incandescent bulb(s)?
    Hi Chuck,
    thanks for that - we are having a nightmare with this ! the problem is
    occuring on a whole batch of bikes from one specific manufacturer, they seem
    to have in common that they all have the same voltage regulator and similar
    wiring loom.
    on some of the bikes the bulbs will blow every 15 or 20 mins.... on a test
    bike i've tried LED bulbs and they seem to fix the problem except for the
    headlight bulb for which i presume there is no LED possible replacement...
    to try to eliminate vibration and bulb quality as the possible cause i've
    previously tried physically soldering a halogen headlight bulb directly into
    the wiring and mounting it solely (but securely) with silicone... this
    lasted a little longer but still blew after a while - i can only think it is
    the regulator... the regulators charge the battery at 14.8 volts - other
    bike regulators seem to be more like 14.0... do you think 14.8 is too high?
    how would the 15 volt zener diode work ?
    many thanks again,
  5. Either the bulbs aren't rated for the voltage or the charging voltage is too
    high. Spikes would be way down on the possibles list.

    If the connection to the battery is unreliable that will make the voltage go
    high and burn out the lamps.

    Try good quality bulbs. If they fail, you need to look at the regulator or
    the wiring. How many amps is the regulator charging at?
  6. Andy C

    Andy C Guest

    thanks john, that makes perfect sense - even to me !
    i only have a cheap multimeter with no peak hold - time to upgrade i think..
    do you think that one will do the job ? looks as if it has peak hold - do
    you think the pc software and interface will let me display a voltage graph
    whilst i go for a ride? any other recommendations ?
    thanks again,
  7. John Fields

    John Fields Guest

  8. Jamie

    Jamie Guest

    check the battery connection.
    if you lose the connection the alternator will run wild.
    make sure the accessory line to th rest of the bike is
    secure from the battery connection. it's possible the
    alternator is connected to the battery higher up in the
    circuit. a bad module plug can also cause this.
  9. Phil Allison

    Phil Allison Guest

    "Andy C"

    **Consider that the bikes have been fitted with defective batteries that are
    vibration sensitive.

    Under vibration, the internal cell to cell connections come apart.

    Explains your observed symptoms.

    Try replacing a few.

    ........ Phil
  10. chuck

    chuck Guest

    Hello Andy,

    The zener was suggested to clip the peaks (if any). Bulbs should not blow every 15 or 20 minutes, of course. Someone suggested ensuring a tight battery connection: that is vital. I would say that 14.8 volts (I assume you have measured this at idle and at some moderate engine rpms) is probably on the high side, but I would still not expect the results you're seeing.

    Is the regulator electronic or mechanical? What kind of bike is it (just curious).

  11. Andy C

    Andy C Guest

    i hadn't thought of this.... so if the batteries are defective (we have had
    problems with defective batteries before) the alternator could run 'wild' as
    in jamie's post above...
    why would the regulator not be able to cope with the battery not connected
    though ? the regulator has 2 wires going in (approx 50volts ac) and has 2
    wires going out (12v dc) would it still not keep the circuit regulated to
    ~14volts with the battery disconnected?
  12. Phil Allison

    Phil Allison Guest

    "Andy C"

    ** As several other posters have indicated, electronic regulators cannot
    function with a missing or defective battery.

    Just a fact.

    ........ Phil
  13. It's possible. The regulator has limits on what it can control - works OK
    with a good battery and wiring, but what happens at no load? It may send out
    brief pulses at 50 volts!
  14. The battery is like a big capacitor with a smallish resistor inside.
    Without it, the alternator output is going to look allot like the output of
    a bench power supply would without it's internal caps. Most linear
    regulators need a cap and a small load to work right, otherwise they make
    nice oscillators. ;-)
  15. Andy C

    Andy C Guest

    ok, thanks everyone - i have plenty of leads to work with now !
  16. jasen

    jasen Guest


    can you post a schenatic showing the interconnects?

    is this a permanent magnet altenator?

    are the lights DC powered?

  17. Andy C

    Andy C Guest

    hi jasen,
    i'll post a wiring diagram ! might not be able to until monday tho
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