Voltage regulator highish

Discussion in 'UK Motorcycles' started by Chris Malcolm, Feb 9, 2006.

  1. An old battery I left alone on my bike for a couple of months has
    comprehensively died and will not climb above 11.5V on charging. It
    could have been the age of the battery, but a surprising amount of
    electrolyte seemed to have been gassed away in rather a short time.
    Investigating the bike's charging system I find it seems to be
    regulated to hit the battery with something between 14.5 and 14.6
    volts, depending on revs. The bike's spec says it should be 14.5V. But
    web sites about modern battery care and maintenance suggest that a
    regulator output of 14.0V would be kinder to batteries. I note that
    later models of my bike (CX500) did indeed reduce the regulator
    voltage to 14.0V.

    The regulator is a sealed unadjustable unit. and regulators are a bit
    pricey. It occurs to me that I could cheaply drop the output of my
    bike's regulator by about 0.5V by interposing a suitably robust diode
    between reg output and battery.

    Has anyone tried this? Would it work?

    What I'm trying to do, having invested in a new battery, is to extend
    its life without spending more than the cost of a new battery :)
    Chris Malcolm, Feb 9, 2006
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  2. Probably not.

    Why don't you just leave such circuit design considerations to the
    electrical engineers
    who know what they are doing?

    I know a tiny bit about electrical generating systems and voltage
    regulating systems and batteries. I have worked on generators that
    produce all the way from 50 watts to generators that put out 1.5
    megawatts of power.

    I wouldn't recommend changing the resistance between the positive
    output from the regulator to the battery. You might wind up buying a
    new regulator because you've defeated the voltage sensing circuit by
    adding resistance.

    If your voltage regulator is a shunt type, there are two possible ways
    for the votlage sensing circuit to work. One way is to sense directly
    off the battery, the other way is to sense voltage off of one of the AC
    input leads.

    One would think that the AC input is a lot higher than 14.0 to 14.5,
    but it isn't. When the relatively low-powered alternator is attached to
    the battery through a diode bridge, the AC output voltage is dragged
    down to battery voltage or a few volts more as the engine is revved up.

    The shunt regulator uses the sensing voltage I described above to
    trigger a silicon control rectifier. The SCR is like a power transistor
    which has its output grounded. It has enough internal resistance to
    dissipate excess power as heat. If you do anything to change the
    sensing voltage, it may never rise high enough to trigger the zener
    diode that sends voltage to the SCR gate.

    So the diodes in the rectifier bridge will have to pass more current
    constantly instead of having that current be shunted to ground.
    Something as simple as a dirty battery cable can reduce the sensing
    voltage to the point where the zener diode/SCR shunt circuit doesn't

    If you have an excited field alternator (brush type or brushless),
    adding resistance to the voltage sensing circuit can cause the
    alternator to try to bootstrap itself. The more voltage is reduced, the
    more current goes to the field windings. The resistance you've added to
    the circuit dissipates the extra current as heat, and the voltage in
    the sensing circuit drops.

    So the regulator increases the current to the exciter field and you
    have an endless input of error to your voltage regulator. The regulator
    cannot tell what the true battery voltage is if you mess with the
    circuit resistance!

    Don't even ask how I know all this. Just trust your charging system as
    designed, keep up the battery *electrolyte* level, and keep the
    connections clean and tight.
    Battery electrolyte is a 50/50 mixture of water and sulfuric acid. If
    your battery keeps boiling off its water, and a hydrometer shows that
    the battery is full charged half and hour after a ride, that's the time
    to add more *electrolyte* instead of water!

    This is especially true of brand new batteries. When you first fill up
    a brand new battery, some of the electrolyte is absorbed into the
    fibrous separators between the
    lead plates. I always fill a new battery to the top level line, and
    then trickle charge the
    battery as recommended. If, after my first long ride, I see that the
    *electrolyte* level is low, I add *electrolyte* not water.

    But I would bet that you religiously add *water* to your battery,
    diluting the electrolyte and wondering why the water keeps boiling off!

    I learned about batteries from working in the battery shop at Edwards
    Air Force Base.

    We literally had hundreds of lead acid batteries on charge at all
    times. I would walk around all day with a hydrometer and a 2-sided
    container. One side had distilled water, the other side had electrolyte
    in it.

    I was trained to add the water to batteries that were still charging,
    if the battery was low on electrolyte. But I was trained to add
    *electrolyte* to batteries that were finished charging.

    I am amazed that almost nobody but me knows this simple fact about
    maintaining battery electrolyte level! And some kibitzer is sure to
    reply with an URL to a "battery maintenance FAQ" that never mentions
    adding electrolyte to a lead acid battery.

    But, it's discussed in my Suzuki shop manual. So, there actually are
    engineers in Japan that understand the liquid diet required by the
    humble plastic cube.

    People who discover that the coolant level in the radiator is low seem
    to know that they need to add *coolant*, not water. So, why can't they
    understand that a battery needs *electrolyte*, not water?

    New batteries are *far less expensive* than regulators and alternators!
    It would be nice if you could find a sealed maintenance-free battery
    *and* a voltage regulator that would allow your original equipment
    alternator to reach about 16 volts before cutting off field excitation
    or shunting excess current to ground.

    Maintenance free batteries have higher internal cell resistance, so
    they need higher charging voltage.

    Your problems might be over with such a set up, or you might discover
    some unforeseen problem comes out of the woodwork and your great idea
    comes to an expensive failure.
    Binder Dundat, Feb 9, 2006
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  3. Believe it or not, the electrical engineers at Honda and their
    suppliers did have some idea of what they were doing when they selected
    charging and lighting components.

    The lights and battery and charging system are usually balanced very
    well and the system works well when the wiring (and associated
    connectors) are new and the battery is new.

    Where Honda and all the other manufacturers err is in having too damned
    many electrical connections for ease of parts replacement.

    If the electric connectors begin to corrode and the resistance
    increases, the connector will get hot and they will burn up more
    electrical energy. The hotter they get, the higher the resistance and
    the connectors will melt.

    If you add electrical load in the form of higher wattage light bulbs,
    you risk damaging your wiring harness conectors and your battery may
    have an even shorter life than it had when you didn't try to out think
    the engineers.

    About the best I can recommend for a lead acid battery is to buy a
    Yuasa with
    Sulf-Stop technology. I had such a Yuasa last for five years in my
    GSXR-750, which has an excited field alternator. I was amazed at the
    longevity. My Suzukis which had
    permanent magnet alternators would kill a battery every year, probably
    due to leaky diodes in the rectifier regulator.
    Binder Dundat, Feb 9, 2006
  4. Chris Malcolm

    Kevin Seal Guest

    Yes, it will. The forward volt drop of an ordinary silicon rectifier is
    of the order of 0.6 volts.
    Kevin Seal, Feb 9, 2006
  5. Chris Malcolm

    Pip Luscher Guest

    Umm. At the sort of current we're talking about, probably closer to 1V

    TBH the voltages don't look too bad; my Guzzi's regulator is spec'd at
    between 14.0 & 14.6V.
    Pip Luscher, Feb 9, 2006
  6. Chris Malcolm wrote
    So it appears to be less than 0.007% outside the manufacturers stated
    tolerance? If only the carbs were the same eh?
    steve auvache, Feb 9, 2006
  7. I think you want a new regulator. Not sure if you really need the
    mfr unit or if an aftermarket one could be made to work. You
    ought to look into this. Electrexusa.com has some good advice
    and might have a component.

    For about $6, you can get a Radio Shack "battery/alternator tester".
    This is a 6 LED unit which gives you a decent idea what voltage
    you're running at. They're pretty easy to mount permanantly on
    the bike. This would give you a good idea when you might be
    Rob Kleinschmidt, Feb 9, 2006
  8. Chris Malcolm

    Eatmorepies Guest

    So what's the resistance of a forward bias diode when it's conducting? I
    thought diodes were frequently used for dropping 0.7V or for clamping
    outputs. Shows what I know.

    Eatmorepies, Feb 9, 2006
  9. Maybe so, but like every other bugger in the automotive design side,
    they had to watch as their carefully crafted wiring system was pared to
    the bone by the beancounters.
    Agreed, up to a point. Everything works well when in lovely condition,
    but the measure of a design is how it continues to work in foreseeable
    use. In the case of most bike electrics, that's not at all well once a
    few years have passed.
    Agreed. Outwit the beancounters, you mean. Keepers of ShiteOldBikes
    should be cleaning and protecting their connecters at the end of every
    summer if they intend to use the bike all year round.
    My last battery in my GS lasted at least 7 years in the PM Suzi charging
    system, but that was running with a front light on and all charging
    wires switched in permanently. In this case, you *can* outsmart the
    The standard reg/rec on the PM Suzis is total shit. A Honda reg/rec
    extends the life of the standard alternator and battery by years. Often
    by that stage the original reg/rec has taken out the original alternator
    by way of its banzai charge.
    GS850x2 XS650 SE6a
    I demand nothing of you except that you amuse me.

    [email protected] Team UKRM
    Grimly Curmudgeon, Feb 10, 2006
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