The Knowledge - Velocette Owners Club

trouble but I don't ride with lights on very often.
#4126 The Podtronic regulator that I fitted for a friend seemed just the job, price from memory was
around £24 but I know some places charge more. Ill dig up the source if anyone wants it. The
regulation was really good at around 14 volts, very stable. I shall convert mine soon and get rid of the
Zerner and rectifier, indeed some high output alternators call for two Zerners to be fitted, even more
expense and messing around with the wires. Has anyone used the podtronic in anger for extended
periods, I know this USA regulator gets good comments in the USA press
#4128 Permanent magnet alternators look pretty much like current sources - the faster they go the
more current they supply up to a limit set by their leakage inductance and the revs - the higher the revs,
the higher the frequency and the more the inductance limits the current. Above certain revs this means
they generate a constant current and the voltage is undetermined - could be quite high - 40 or 50 volts.
Unregulated lighting sets as used on bicycles ,cheap mopeds etc rely on this constant current designed
to feed their quota of bulbs correctly. But if one bulb blows the current remains the same and the volts
go up, so you'll blow the rest pretty soon. You're quite right about Zerner-controlled alternators such as
the old Lucas design - they generate power proportional to engine revs ( i.e. constant current and volts
proportional to revs) , and the power is distributed between the Zerner and the various bike loads. They
were cheap and simple, but wasteful of power and didn't control the battery volts very well- an old
triumph of mine always had to have it's battery topped up regularly. And of course if the Zerner failed
you boiled the battery thoroughly and blew the lights the moment they were turned on. Early Ducati
twins had a permanent magnet alternator like Lucas, but used a clever thyristor regulator such that
each cycle of the ac output was only turned on for long enough to hold the battery at 14 volts. With no
load this took very little time on, with heavier loads more. It's this style of reg I offered to design for
Criterion. I don't know what Harleys use(d). Might be a simple series pre-regulator but this misses the
point as the inductive reactance is lossless ( approx) . Don't know - can only guess. Modern bikes use
wound field alternators just like cars, with similar control units. Glad your VW regulator works OK - but if
designed for 12v it won't limit the field voltage and hence you risk over-dissipating the field and burning
it out.
#4130 Sounds a bit like the old Ducati thyristor-switching regs I mentioned in my previous. I properly
done should work very well. Less load on the engine, almost no wasted power so nothing gets hot.
regards.
#4132 A brief follow up on the JG Unit. I called Dave Lindsley this morning and had a long chat. The
problem I'm having is with a E3N 48 watt short generator mounted in a, wait for it, a 49 AJS. (the JG
Unit in my '66 VMT works Great!!!). The JG Unit will frequently fail to "wake up" and begin to charge
unless I blip the throttle and really boost the revs, like 4K RPM. Mr. Lindsley walked me thru the control
strategy and gave me great ideas for locating the problem. His view is the air gap may be too wide on
the newly rewound armature. Large air gap means the residual magnetism in the pole shoe man not be
sufficient to begin exciting the field coil unless the dynamo is spun faster than normally required. The
difficulty in correcting the air gap problem lies with either replacing the armature with a "newer"
armature that may not have been skinned after rewinding, or shimming the pole shoe. Either option
require removing the entire primary drive and tin ware to pull the dynamo out of an AJS. (I know, I
know, this a Velocette list). I've a PODtronics 6-12PE unit on hand and may swap out the JG Unit
before removing and stripping the dynamo. I'm seeking the path of least resistance! I've some testing to
do. In any event, I really appreciated Mr. Lindsley's patience with me and help in finding some
resolution. This is a vendor I will continue to support! One of his answers may be of interest to the
group. The JG Unit does send approximately 14 volts to the field coil but limits the current to avoid over
heating the field coil and the possibility of reducing the life of the field coil.
L #4161 My MAC is getting nearer completion and I have an Alton Alternator to fit. I have fitted
some neat little indicators and want to use a larger, more modern headlamp. I have a Honda
Superdream unit that fits OK but my query is, do I need the ammeter? No modern machine has one
and if the Alton is all it is cracked up to be, why would I need an ammeter at all. I am using the
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