On Sun, 22 Apr 2018 21:48:46 +0100, Jim K wrote:

Chris Green Wrote in message:
I am trying to work out how the wiring on a newly acquired (secondhand)
mower works. I have what are supposed to be the wiring diagrams for it
but none matches exactly.

The current (ha, ha) conundrum is the meaning of the letters on the
regulator. It's a Hatz diesel engine and has an alternator with a
separate external regulator. I have the Hatz manual but that is no
more forthcoming than the mower wiring diagram.

The regulator has terminals marked with the letters G G L C W. I can
work out that the G G terminals are for the output from the alternator
but the others have me rather stumped. The W terminal is not connected
in any of the wiring diagrams I have. The C connector seems (in most
cases) to be connected to switched battery +ve, i.e. it will get 12v on
it when the ignition is turned on. The L connector has me totally
confused, it's connected to the engine hours meter and thence via an 82
ohm resistor to something that will be at 12v when things are running
normally. The regulator is connected to ground/0v by its case. The
alternator has a connection direct to battery +12v in addition to its
two G G connections.

The Hatz engine is German so the letters may mean something in German.

I'm not at home at the moment so I can't provide a picture or much more
detail.

Any information or pointers would be most welcome.

--
Chris Green ·


Shurely if it is an alternator there's no need for a separate
regulator as such?

Although every car alternator I've seen incorporates the regulator into
the alternator itself, that's not necessarily true of the 24v alternators
used on trucks and HGVs. I used such an alternator obtained from a
scrapyard as a replacement to the dynastart on the 2 cylinder auxiliary
petrol engine on my father's 30 foot ocean going sloop some forty odd
years ago.

This engine also had provision for a standard electric starter motor
with which it had been equipped so the dynastart was only being used for
the dynamo function alone. Dynamos being the inefficient things that they
are, it seemed a good idea to uprate this aspect of battery charging with
an alternator to reduce fuel consumption when running the engine just to
top up the battery and power the electrical systems (radio, navigation
lights etc).

The battery power system on the sloop was just your standard 6 cell 12v
LA type but this wasn't a problem since I merely had to design and build
a 12v (14v actually) regulator box to connect to the alternator. The main
six diode 3 phase full wave rectifier pack with the usual additional 3
auxiliary regulator diodes were, as with all such alternators, built into
the alternator itself so it was simply a matter of making connections
from the regulator box to the two slip ring brushes and the auxiliary
rectifier, along with a common earth connection, with the negative side
of the ignition light that had formerly gone to the dynamo's regulator
now being connected to the auxiliary diode's connection on the regulator
box swiftly modified with an extra on/off switch for a reason that will
shortly become apparent.

The dynastart double V grooved pully was only about 2 or 3 inches in
diameter[1] and was driven by just a single V belt, rather than the two
required to handle a starting torque load, wrapped around about an 18
inch diameter flywheel. This gave something like a six to one speed
advantage for the dynamo function whilst providing the converse torque
advantage for the now unused starting function. The gearing up was
necessary because, iirc, the engine maxed out at a mere 1800rpm or so,
maybe ticking over around the 3 to 4 hundred rpm mark. This meant we
needed to run the engine at a wastefully higher than normal idle speed
just to recharge the battery despite the six fold faster rpms of the
dynamo, circa two or three thousand rpm to get maximum output.

Using an alternator designed to produce some 28v for charging a truck's
24v battery meant we could get a useful charge at the normal tickover
speed without wasting as much fuel. Obviously, the torque loading from
generating current at such slow tickover meant the engine actually had to
do a little more work than merely overcome its own frictional and pumping
losses (and that of the drive belt) but we only had to open the throttle
a tad extra to compensate whilst running no faster than the normal idling
speed which was a way more efficient and quieter way to generate
electricity than before.

The only issue was that if the alternator load was allowed to kick in
straight away on startup, it would usually bog the engine down due to one
of the cylinders failing to fire up straight from cold. Without such
loading the engine could get up to tickover speed, allowing the reluctant
cylinder to start firing shortly thereafter. The solution was that
additional on/off switch to prevent the regulator exciting the field
winding via the slip ring connections, thus eliminating the torque
loading otherwise produced when trying to send charging current to the
battery.

It was an effective modification since it took only a minute to warm the
engine up, especially if we throttled up to a higher tickover speed and
then enabled the alternator since the torque loading reduces with speed
for a given current output and we'd have both cylinders working with a
productive load to both help accelerate the warm up period at a still
modest engine speed and swiftly replenish the battery of the energy just
taken by the starter motor.

We hadn't suffered such a problem with the dynamo since it needed a very
fast tickover to get its regulator to kick in to start generating any
current at all. The use of a 24v alternator to generate 12v meant it was
producing at least as much as the dynamo could do at full chat, if not
more at tickover speed alone.

Not a major problem if *both* cylinders were firing at that speed but
since it placed a torque drag loading at less than idling speed, it was a
problem I'm happy to say since it demonstrated we were getting more
efficient use out of the engine when it was being used just to produce
electricity. Having to fit a switch to overcome this cold starting issue
was a tiny price to pay in upgrading the battery charging system
efficiency. :-)

As for those GGLCW connections, I would guess GG are the slip rings, and
of the remainder one will be the 60 to 120 amp rectifier output terminal
(obvious from the sheer size of the nut and thread used), another will be
the auxiliary diode output to energise the field winding excitation
circuit and provide the voltage reference to regulate the voltage on the
main rectifier output. The leftover terminal might be a thermally
operated output indicator (I have a vague recollection of such a 5th
terminal on some alternator connection diagrams but it was a good forty
years ago since I last saw such diagrams - perhaps I should try a search
engine? :-)

I've just checked out a pdf on truck alternators and there was mention
of a connection to an AC output terminal intended to operate a relay (of
the thermal class since it works just as well with ac as with dc) or else
a tacho sensor (presumably as an alternative method to the classic
ignition light confirmation that the alternator is being driven and
producing output).

In reading that pdf, I noticed mention of variations such as a seperate
negative output terminal and a sense wire option terminal so it can all
become rather more complicated than that truck alternator I was using 40
odd years ago. If two of those terminals are both equally large heavy
duty types, that would suggest seperate positive and negative output
connections rather than the use of the casing as a common ground
connection.

[1] The truck alternator's pulley was, I think, a little larger in
diameter, maybe 4 inches or so and, of course, just a single V groove.
Nevertheless, this was going to be running some 5 times faster than the
engine, allowing it to produce useful output even at tickover, unlike the
dynamo half of the dynastart unit it was replacing.

--
Johnny B Good