Conference terri::cars_uk

Dunno what you mean by a megneto in this context; I always thought that was
a type of ignition system that went out with the ark...

The dynamo/alternator charges the battery, and should provide all the
electricity you need while on the move.  The battery is there for starting
(if you have an electric start) and to power lights, etc, when the engine
isn't running.

If things used to work, and now don't, either there's a faulty connection in
the wiring, or the alternator/dynamo is broken, or the battery is broken.

Disconnect the battery, charge it up if necessary, then connect your headlamp
across it.  If it lights properly then the battery is probably not at fault.

Check and clean all electrical contacts; grease battery terminals and put
everything back together.  If lights don't work properly when running,
then it's probaby the alternator/dynamo.

Check the bulbs are of the "recommended" wattage; a lower wattage will be
dimmer, not brighter; a higher wattage may blow a fuse!

Also check that all other electrical items are working properly; if something
else is shorted out but doesn't blow a fuse, it could be soaking up your power
and will in time damage the alternator...

Scott

<<< Note 1407.1 by HUGS::AND_KISSES "Time is an illusion; lunchtime doubly so" >>>

>>Dunno what you mean by a megneto in this context; I always thought that was
>>a type of ignition system that went out with the ark...

Or more likely - "went out with the arc..."

:-)

Steve

What sort of "bike" ?

Moped/Motorbike/Bicycle ??

If the two former, surely it has already got a battery, and if the latter,
why aren't you using ordinary household battery lamps ?

    Nope, it's not a wind up...
    
    it's a Motorcycle, but it does not use a battery as standard. It is old
    technology isn't it!
    
    I think I've solved my problems now anyway.
    I needed to power a horn that used more power than the magneto
    produced.
    
    It's possible to buy a battery charging device and a battery holder and
    you just plug it all into the loom! Then I'll run the necessary relays
    and stuff from the battery to the switch and horns.
    
    should be quite simple... ( I hope! )
    
    Thanks for the interest anyways,
    
    James.
    

You should'a just got an air horn...uses compressed air cylinders...

they have the advantage that car/lorry drivers can't help but hear them :-)

    
    Maybe he has got an air horn, but one with a compressor?
    
    Mark

    Re .6
    
    
    hmm... thought about those ones, but it's a bit expensive getting new
    cylinders is it not?
    
    James

    re.7
    I was going to get air horns with a compressor, but it's a bit bulky
    for the size of bike and I suspect people would not think it was me
    making that much of a racket when I used them!
    
    I bought the twin-tone-car-type-horns. Look nice enough but they have
    _no_ fitting instructions! . . . 
    
    	"Dad! can you come and give me a hand please!"
    
    ;^)
    
    James.

Ahhh,  Is it by any chance an old Rally Runabout?

My brother started 'biking' on one of those. He ended up (literally) with a 
Suzy 250 X7 (sewing Machine soundalike). He now drives a Lada

Them where the days.

Re: .10

Kept to type then !

:-)

    Nope it's not a 'Rally Runabout'...
    
    It's an old Lambretta (Vega 75s).
    
    James.
    

re .11   :-)))

Re: -.something...

If you are trying to fit a horn to a small bike with lighting powered direct
from the flywheel magneto (common practice on very lightweight machines,
mopeds etc.) you will probably need the correct type of AC horn.

Normal horns are 12 volt DC powered, but the flywheel magneto winding on these
machines produces alternating current (AC), so you need a special AC horn.

It is normal for the lights to dim considerably when the horn is used since the 
output from the flywheel magneto is completely unregulated. In addition the
wattage of the bulbs should not be altered due to the lack of regulation - for
instance if you change the headlamp bulb from 35 watts to 25 watts you may find
that the tail lamp or speedo bulb will blow due to the unregulated voltage
rising too high due to the reduced load - once one blows the rest follow in 
pretty short order!!!

- John.

    Yup, the problem with blowing lights is definately a common one with
    this bike.
    It's only the rear-brake light though... none of the others *ever* go.
    It's due to two things - 
    	* they don't sell twin filament bulbs in a wide enough variety of
    	  wattages anymore
    
    	* When this guy made a loom for me, he neglected to put in a small
    	  bit for a speedo light (which I discovered while taking out an 
    	  old loom on another vega) so there's too much power running
    	  around all the time!
    
    Thanks for the point about the AC electrics.
    
    I had a think though... If I'm _just_ powering the horn by a battery
    and charging the battery from the magneto (via the correct electrical
    bits) then I shouldn't have any problem with the wrong type of current
    should I?
    
    James.

    re.14
    
    By the way, it is possible to regulate the voltage by putting a Zener
    Diode (I think! - long time since I heard this) in the loom. I
    supposedly chops the top off the power if it rises too high.
    Other small bikes I have owned have devices that do this but
    unfortunately I don't have any manuals to hand to study the wiring
    diagrams.
    
    James
    
    

    Seem to remember having to ahve a Zener Diode fitted to my
    Lamberetta to stop the back light blowing too ... them were
    the days !!!

Unfortunately if you want to charge the battery on a magneto powered AC system
you will have to install a rectifier to get DC for the battery. To complicate
matters you will also have to arrange that when the lights are off the power
from the magneto is fed to the rectifier and thence to the battery for charging
purposes. When the lights are on - you will have to arrange your switching such
that the charging circuit is disconnected and all power is fed to the lights.

The reason for this complication is the fact that the magneto output capability
is closely matched to the lighting load and if you have the lights and the
battery charging circuit in operation at the same time, and the battery was not
fully charged, your lights would probably just glow very dimly. For the same
reason you cannot convert the whole system to work off of the battery since if
it were not pretty well fully charged it would load the magneto down and result
negligable charge and dim lights.

The Zener diode used on some machines, is a cheap way to regulate a more
powerful alternator/rectifier combination. Again, the alternator is designed
to be able to supply a full electrical load (headlight, tail, speedo, ignition
etc) plus 'a bit' left over for trickle charging the battery. Consequently if
you switch off the lights the alternator would overcharge the battery. To stop
this happening a 14 Volt zener is strapped across the battery and effectively
shorts the excess current to ground. The alternator is designed to accept this
type of abuse (so Joe Lucas - 'Prince of Darkness', maintains) by having a
relatively high source impedance and the ability to run at full load all the
time.

The zener diode only works on DC systems.

- John.