Bob,
It is interesting that what was old is new again.
In a 1998 discussion the voltage warning bulb is a grain of wheat bulb or 3
W/12V standard incandescent bulb. It should not be a LED in a Ducati Regul
ator.
Note the older Rotax installation manuals. The new 912 install manual is v
ery poor in describing the electrical installation for some reason. The bui
ld manual Chapter 25 indicates the same to use a 3W bulb.
Long answer Ducati Only:
Battery voltage at B+ is supplied to the regulator and in the circuit the L
or light is connected to the C or control (Bus Voltage) and is to be withi
n .2 Volts of battery. When the regulator C and R, and B+ are powered by t
he battery the light is illuminated because the voltage output of the gener
ator side(also the L) is at Zero volts (basically ground).
When the engine is started the Alternator supplies AC voltage to the Regula
tor via GG and converts it to DC voltage. As the voltage output rises, the
L circuit is powered by the generated output of the Alternator and as the
L and C voltage near equal voltage, the lamp then goes out indicating the a
lternator is generating charging voltage.
In the event the alternator stator fails L goes to ground or less than bat
tery voltage, the light illuminates, warning the pilot of the output failur
e as C voltage is greater than L voltage. Unfortunately if the Regulator f
ails internally, the light will not work leaving your first clue the regula
tor failed is a low voltage warning or dead battery.
Hence the term idiot light.
If you have a LED installed as the alternator warning light, you have a pro
blem. The LED takes 1.2 volts to energize and of course only works one way
as you found out. I have seen them work or not work as this is a temperam
ental current circuit.
I won=92t argue the point. With a Ducati, just put in a grain of wheat bul
b and be done with it. Do not put in a circuit breaker or fuse in the warn
ing light circuit as the 3Watt bulb is the circuit protection. It will blo
w before the wire will fry. 20 or 22 gauge wire is all that is needed to w
ire this circuit, as no fuse is really necessary.
Should you decide on a Schicke GR6 voltage regulator, that solid state unit
does require an LED and a .5 amp fuse in the warning circuit as it is a to
tally different design.
The LAA requires a warning light, however in other parts of the world if on
e has a volt meter or low voltage warning system, a warning light is not re
quired. I am the department of redundant redundancy, I have an idiot light
, low voltage warning on the EFIS and a volt/amp meter. Trouble shooting i
s a breeze.
Regards,
Bud Yerly
Custom Flight Creations, Inc.
Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Window
s 10
________________________________
From: owner-europa-list-server@matronics.com <owner-europa-list-server@matr
onics.com> on behalf of BobD <rjd@bobdawson.plus.com>
Sent: Wednesday, January 24, 2018 7:05:57 PM
Subject: Europa-List: Re: rotax integrated alternator warning light
I discovered the warning light I have used is polarity sensitive, so when I
swapped the wires, the light did indeed come on with the Master Switch. I'
ll take it on faith at the moment that it extinguishes once the engine is r
unning, as I didn't start her up today.
--------
Bob Dawson
XS TG || 912 ULS || G-NHRJ
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