actually both! a manufacturer designs the needed pulley diameters for what
ever reason to be specific sizes. there may actually be only 1 or 2 or 3
difrent tachometers as far as internal componentry(there are a bunch of
color variants and number designs as far as the face you see in the car.
but just like over driven or under driven in blower pulleys goes, so
similarly applies the size of the generator pulley diameter to what gear
reduction may be required per specific aplication.
an engine capeable of turning very high rpm's may require a much larger
diameter pulley to slow down the armature speed to keep the windings from
literally being centrifugally thrown into the field coils (this was a huge
problem with generators of the 50's / 60' when high revving engines came
into their own!) , resulting in obvious catastrophic failure! while an
engine of much lower top rpm's may require a smaller generator pulley to
increase the generator's output while still remaining within the
generator's operable "pre-grenade" rpm range. the gear reduction units
job is to read the specific pulley diameters resulting armature speed and
report to the tachometer engine rpm's .
and to mess up the equations, if you change the mfgr's crank pulley
diameter this absolutly throws off evrything the generator may be reporting
to your gauge! :)
and that is why the old race spridgets used gutted generators having all
the armature windings cut off the armature! at high rpm, the windings
would fly out and shear or sieze in the generator leaving the car without a
tachometer. ( i'm not even venturing into the early days of weight
savings!)
chuck.
> [Original Message]
> From: Robert E. Shlafer <pilotrob@webtv.net>
> To: <spridgets@autox.team.net>
> Date: 02/10/2006 11:59:19 AM
> Subject: Gen. driven Tach Gearboxi
>
> Ignore my prior post on this, Chuck.
>
> The light finally went on upstairs...you're
> talking about "different applications" as to
> gen. pulley sizes?
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