Johnny B Good wrote:
On Mon, 23 Apr 2018 10:02:33 +0100, Chris Green wrote:

Chris Green wrote:

[snip boring description of problem]

I outlined the problem to someone else as well and, as very often
happens, I think that has led me to the answer:-

G G - these terminals are the alternator field coil which the

Aha! So my initial guess was right, then! :-)

regulator drives to vary the alternator's output. The alternator
has a separate B+ output which actually charges the battery.

So no other similar heavy duty terminal for the B- output then, just
relying on the alternator frame to provide the common ground connection?

No, just a big lump of screwed together aluminium castings (not always
absolutely reliable in my experience).


C - This is the switched +12v feed from the battery, it provides
power for the regulator electronics and also tells it the battery
voltage.

That's normally the function of the L connection in the typical truck
and motorcar usage case.


L - This is L for L[amp]. It would normally have a lamp between it
and the C terminal. When ignition is turned on there is 12v on the
C terminal and 0v on the L terminal so the lamp lights. When the
engine runs L goes up to 12v and the lamp goes out. On my Hatz

That corresponds to the auxiliary diode pack output that provides a
lower current rated duplicate of the main rectified voltage output of
the alternator to both act as the voltage feedback needed to regulate the
output voltage and to provide the energy required by the regulator to
drive whatever current is needed to excite the field winding on the rotor.

When the ignition is switched on, the ignition warning lamp provides
current which the regulator passess to ground via the slip rings and the
3 or 4 ohm field winding which saves the need to kick start the self
excitation process by revving the ******** off the engine to ultilise the
rather weak residual magnetism, if any, in the rotor core.

It's this, typically 180mA, lamp current which bootstraps the build up
of voltage to the regulator's power/voltage sense input terminal. Once
bootstrapped, the voltage on both sides of the lamp equalises and the
lamp extinguishes.

OK, yes, I agree. 12 volts across 82 ohms is around 160mA.


there is an 82 ohm resistor instead of the lamp (between L and C)
and L is also connected to the hours meter. The hours meter is thus
only running when 'the lamp is out', i.e. when the engine is running
and the alternator producing output.

W - I still don't know what this is.

That will almost certainly be an ac output as surmised by Tim and Bill
who mentioned frequency/tacho connection and, from my vague recollection
from 40 years ago, a reference to the use of a thermally operated relay
to sense when the alternator is turning and producing power instead of
relying on the traditional ignition warning lamp circuit. I suspect in
this case it's simply surplus to requirements and unused (BICBW).


I don't know why 'G' means field, translating to German doesn't help.
L for Lamp makes some sense, C for battery +ve doesn't.

I only surmised slip-ring field connections from the fact that there was
a pair of them and only the field connections, whose polarity is entirely
arbitrary in this case, made up a pair of anything to be found on an
alternator without a - or + subscript. :-)

BTW, just how big is this diesel powered mower that it needs what seems
to be a full size car/truck alternator? :-)

It's not particularly big but it is verging on commercial. The Hatz
1B50 engine is 8.5kW output (around 11 BHP). It drives a three rotor
125cm wide cutting deck but there are loads of electrical accessories.
The cutting height is electrically adjustable, there's a cruise
control (!), an electrically operated rear PTO and a power connection
for a sand spreader.

--
Chris Green
·