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1. 05:00 AM - RotaxEngines-List Digest: Capacitor ()
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| Subject: | RotaxEngines-List Digest: Capacitor |
Gilles,
I am not saying that the capacitor is not needed,
only that it does not have any significant role
in the regulation process if the battery is close,
and can in this case as well be left out, with
the further advantage that overvoltage will not
be possible if the battery is switched off
while the engine is still running.
Of concern is the overvoltage that might occur
in two situations. The first (1) is handled by
an overvoltage relay and the other (2) is not.
(1) Constant overvoltage will occur if one of the
silicon controlled rectifiers will die shorted out
for example because the module gets too hot during
flight. In this case the overvoltage relay will
save the day (and the avionics) after the battery
has taken the brunt of the initial attack.
(2) If the wiring is such that when the battery
accidentally is switched off and the capacitor charge
is still available, then the controlled rectifiers
will fire because the voltage on the sense terminal
is under the treshold. For how many cycles they will
fire I do not know, they anyhow are always fired
simultaneously but only the one having the G voltage
forward biased will actually conduct.
The information above and in my previous message
is based on the schematic you have provided yourself.
To my knowledge nobody else has come forward with
another reasonable explanation for the overvoltage
experienced by some 912 users, so I will still not
install a capacitor if the charged battery is close.
Regarding the Harley-Davidson alternative - no, I have
912 or 912S in all my aircraft, but the majority of
all PM-generator rectifier-regulators in the world
are used in snowmobiles and certain motorbikes like
the Harley-Davidson, so we should not discount the
experience these users have gained. To my knowledge
they do not need a capacitor for their regulator
if a battery is fitted.
best regards
Max
RE
>As you know, our perception of the working of the regulator
>is not similar to yours. It took us several bench test sessions
>to get a clear notion. Is your opinion based on data we are not
>aware of, or did you make deductions from existing data ?
>
>> On the other hand, moving the capacitor behind the battery
>> switch might slowly burn the switch or relay with its
>> inrush current.
>
>Not sure I clearly understand the circuit you are referring to.
>Bob Nuckolls' figure Z provides anything that is needed to
>design a safe and efficient Rotax circuit with OV protection,
>and no damage to the ship's circuits, whatever the action
>on the master switch in flight.
>
>> Well, this is a controversial subject, but in my opinion
>> the capacitor is not needed
>
>The electricity experts I submitted the regulator to do not agree
>with this statement. I would be really willing to publish any
>additional study or data you have collected to support this.
>
>> Does anybody know if Harley-Davidson uses any capacitor
>> in their similar style PM-generator regulator ?
>>
>You really trying to design your aircraft circuits the
>Harley-Davidson way ?
>
>Regards,
>Gilles
>http://contrails.free.fr
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