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Max Johansson
Joined: 09 Jan 2006
Posts: 25
Location: Helsinki, Finland
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 Posted: Tue May 20, 2008 11:20 pm Post subject: part of the 701 wiring question - 912 master warning |
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RE
"if one turns the MASTER everything should turn off"
Note that the standard Rotax 912 rectifier/regulator
made by Ducati is damaged when running the engine without
connection to any battery. This is one of the reasons
the 22000 uF capacitor is fitted but unfortunately this
is not a perfect solution as a big electrolytic capacitor
often fails in frigid conditions and also generally
looses its capacitance with age.
Have a look at the rectifier/regulator unit itself.
The warning against batteryless running is stamped into
the metal case of the unit both in Italian and English...
So make it a habit not to disconnect the battery
by operating the master before the propeller has
stopped turning.
regards
Max
flying and wiring in Helsinki and
building a 912s ch701sp on a-floats
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_________________
Max
Max Johansson, Helsinki, Finland
Building a CH701SP-912S
on CZAW amphibian floats |
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ashontz
Joined: 27 Dec 2006
Posts: 723
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| Posted: Wed May 28, 2008 12:07 pm Post subject: Re: part of the 701 wiring question - 912 master warning |
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So how do you turn the master off in an emergency without damaging the rectifier? Sounds like a safety issue to me in that someone who may in fact need to turn the master off for safety reasons would be less inclined to, thinking they're going to have an expensive fix on their hands and instead winds up with a cockpit fire.
One could argue that to turn off the master isn't just turning off the stuff, but rather isolating the high amperage (aka dangerous welding potential) battery from the everything else.
| Max Johansson wrote: | RE
"if one turns the MASTER everything should turn off"
Note that the standard Rotax 912 rectifier/regulator
made by Ducati is damaged when running the engine without
connection to any battery. This is one of the reasons
the 22000 uF capacitor is fitted but unfortunately this
is not a perfect solution as a big electrolytic capacitor
often fails in frigid conditions and also generally
looses its capacitance with age.
Have a look at the rectifier/regulator unit itself.
The warning against batteryless running is stamped into
the metal case of the unit both in Italian and English...
So make it a habit not to disconnect the battery
by operating the master before the propeller has
stopped turning.
regards
Max
flying and wiring in Helsinki and
building a 912s ch701sp on a-floats |
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Max Johansson
Joined: 09 Jan 2006
Posts: 25
Location: Helsinki, Finland
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| Posted: Wed May 28, 2008 3:08 pm Post subject: part of the 701 wiring question - 912 master warning |
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Andy, this is not at an emergency issue, but
some student pilots have been seen to switch
off the master before killing the ignition...
With low rpm and a good capacitor nothing
will happen to the rectifier-regulator even
if the battery and all other loads have been
disconnected. But with higer rpm and/or a faulty
capacitor the module is in danger of being
damaged just as the manaufacturer warns.
In my opinion both the Ducati rectifier/regulator
design as well as the Rotax wiring instructions
are minimal and marginal.
rgrds,
Max
RE ....912 master warning
| Quote: | Zenith701801-List message posted by: "ashontz" <ashontz(at)nbme.org>
So how do you turn the master off in an emergency without
damaging the rectifier? Sounds like a safety issue to me in
that someone who may in fact need to turn the mater off for
safety reasons would be less inclined to thinking they're
going to have an expensive fix on their hands and instead
winds up with a cockpit fire.
Max Johansson wrote:
>
> RE "if one turns the MASTER everything should turn off"
>
> Note that the standard Rotax 912 rectifier/regulator made by
> Ducati is damaged when running the engine without connection
> to any battery. This is one of the reasons the 22000 uF capacitor
> is fitted but unfortunately this is not a perfect solution as a big
> electrolytic capacitor often fails in frigid conditions and also
> generally looses its capacitance with age.
>
> Have a look at the rectifier/regulator unit itself.
> The warning against batteryless running is stamped into the
> metal case of the unit both in Italian and English...
>
> So make it a habit not to disconnect the battery by operating
> the master before the propeller has stopped turning.
>
> regards
> Max
>
> flying and wiring in Helsinki and
> building a 912s ch701sp on a-floats
--------
Andy Shontz
do not archive
CH601XL - Corvair
www.mykitlog.com/ashontz
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_________________
Max
Max Johansson, Helsinki, Finland
Building a CH701SP-912S
on CZAW amphibian floats |
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ashontz
Joined: 27 Dec 2006
Posts: 723
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| Posted: Wed May 28, 2008 3:25 pm Post subject: Re: part of the 701 wiring question - 912 master warning |
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"Andy, this is not at an emergency issue"
My point is, "It could be."
The devil is in the details.
Usually not one thing leads to an accident, or post accident mishaps, but a series of things. And one thing like the master left on, when it really should have been off, forgotten about, and then you crash, even fairly gently, and then everything comes loose and BOOM.
Something like comparing and contrasting the benefits of turning off the master (ie. $300 for a new generator) vs the chances of an electrical fire/fuel explosion changes in 15 seconds, but in that 15 seconds of an emergency (ie. yeah, I really am going down) you could easily forget about the master switch because you're original thinking 15 seconds earlier was preserving that month's savings. It really is an potential emergency situation.
| Max Johansson wrote: | Andy, this is not at an emergency issue, but
some student pilots have been seen to switch
off the master before killing the ignition...
With low rpm and a good capacitor nothing
will happen to the rectifier-regulator even
if the battery and all other loads have been
disconnected. But with higer rpm and/or a faulty
capacitor the module is in danger of being
damaged just as the manaufacturer warns.
In my opinion both the Ducati rectifier/regulator
design as well as the Rotax wiring instructions
are minimal and marginal.
rgrds,
Max
RE ....912 master warning
| Quote: | Zenith701801-List message posted by: "ashontz" <ashontz>
So how do you turn the master off in an emergency without
damaging the rectifier? Sounds like a safety issue to me in
that someone who may in fact need to turn the mater off for
safety reasons would be less inclined to thinking they're
going to have an expensive fix on their hands and instead
winds up with a cockpit fire.
Max Johansson wrote:
>
> RE "if one turns the MASTER everything should turn off"
>
> Note that the standard Rotax 912 rectifier/regulator made by
> Ducati is damaged when running the engine without connection
> to any battery. This is one of the reasons the 22000 uF capacitor
> is fitted but unfortunately this is not a perfect solution as a big
> electrolytic capacitor often fails in frigid conditions and also
> generally looses its capacitance with age.
>
> Have a look at the rectifier/regulator unit itself.
> The warning against batteryless running is stamped into the
> metal case of the unit both in Italian and English...
>
> So make it a habit not to disconnect the battery by operating
> the master before the propeller has stopped turning.
>
> regards
> Max
>
> flying and wiring in Helsinki and
> building a 912s ch701sp on a-floats
--------
Andy Shontz
do not archive
CH601XL - Corvair
www.mykitlog.com/ashontz
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Max Johansson
Joined: 09 Jan 2006
Posts: 25
Location: Helsinki, Finland
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| Posted: Wed May 28, 2008 4:14 pm Post subject: part of the 701 wiring question - 912 master warning |
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Andy,
you are right in that the pilot should not need to consider what can be
damaged if switching off the master in the air and consequently might
forget to switch off somewhat later when it really would be needed if
the situation necessitates an emergency landing.
But whe have the equipment we have. It is good practice to switch off
only after the Rotax has stopped. It is as well good practice to check
the capacitor regularly as it can be faulty without any indication that
this is the case. And if you have expensive avionics then an overvoltage
relay (that cuts the generator alternating current) is a good investment
that will also allow operating the master at any time.
regards
Max
[quote]--
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_________________
Max
Max Johansson, Helsinki, Finland
Building a CH701SP-912S
on CZAW amphibian floats |
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txpilot
Joined: 26 Feb 2007
Posts: 87
Location: Houston, TX
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| Posted: Fri May 30, 2008 4:02 pm Post subject: Re: part of the 701 wiring question - 912 master warning |
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| Quote: | So how do you turn the master off in an emergency without damaging the rectifier? Sounds like a safety issue to me in that someone who may in fact need to turn the master off for safety reasons would be less inclined to, thinking they're going to have an expensive fix on their hands and instead winds up with a cockpit fire.
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If it's that big a concern, purchase a Cessna-like master switch that prevents switching off the battery and leaving the alternator on-line.
http://www.aircraftspruce.com/catalog/elpages/cessnasplit.php
You can wire a relay to the alternator side of the switch that would take the alternator off-line when the relay is de-energized. See Bob Nuckoll's diagram Z-16 on how to do this:
http://www.aeroelectric.com/articles/Rev11/AppZ_R11M.pdf
Problem solved.
Dan Ginty
N787DG
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