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Van's Aircraft Statement

 
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user9253



Joined: 28 Mar 2008
Posts: 1907
Location: Riley TWP Michigan

PostPosted: Fri Feb 12, 2021 8:43 am    Post subject: Van's Aircraft Statement Reply with quote

Here is a quote from Van's Aircraft FLIGHT TRAINING SUPPLEMENT:
https://www.vansaircraft.com/wp-content/uploads/2020/10/RV-12iS-FTS-4.pdf page 6-6
Quote:
The Rotax 912 iS is equipped with two voltage regulators, one for each generator on the engine. These regulators reject any unused electrical power as heat. Allowing the power usage to fall below 7 amps for extended periods of time may damage the regulators, especially on hot days.

That can not be true can it? Suppose that 21 amps are available but not
used by the aircraft electrical system. 21 amps x 14 volts = 300 watts
of heat that must be dissipated by the voltage regulators.
Don't modern permanent magnet voltage regulators work by shutting off the
output during part of the AC cycle using SCRs that are in series with the output?


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PostPosted: Fri Feb 12, 2021 9:18 am    Post subject: Van's Aircraft Statement Reply with quote

Pretty sure I've read all of the current  rotax manuals and bulletins
for that engine and there is no such information or caution anywhere. 
(and it doesn't make sense anyway for something this large as Joe has
indicated).  The temperature limit on the regulators is 80*C and rotax
insists that it be installed in the engine compartment.  While there is
an optional additional heat sink available for regulator B it's still an
order of magnitude too small to handle that kind of heat.
Ken

On 12/02/2021 11:43 AM, user9253 wrote:
Quote:


Here is a quote from Van's Aircraft FLIGHT TRAINING SUPPLEMENT:
https://www.vansaircraft.com/wp-content/uploads/2020/10/RV-12iS-FTS-4.pdf page 6-6

> The Rotax 912 iS is equipped with two voltage regulators, one for each generator on the engine. These regulators reject any unused electrical power as heat. Allowing the power usage to fall below 7 amps for extended periods of time may damage the regulators, especially on hot days.
That can not be true can it? Suppose that 21 amps are available but not
used by the aircraft electrical system. 21 amps x 14 volts = 300 watts
of heat that must be dissipated by the voltage regulators.
Don't modern permanent magnet voltage regulators work by shutting off the
output during part of the AC cycle using SCRs that are in series with the output?

--------
Joe Gores


Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=500656#500656




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Ceengland



Joined: 11 Oct 2020
Posts: 378
Location: MS

PostPosted: Fri Feb 12, 2021 10:57 am    Post subject: Van's Aircraft Statement Reply with quote

On 2/12/2021 10:43 AM, user9253 wrote:
Quote:


Here is a quote from Van's Aircraft FLIGHT TRAINING SUPPLEMENT:
https://www.vansaircraft.com/wp-content/uploads/2020/10/RV-12iS-FTS-4.pdf page 6-6

> The Rotax 912 iS is equipped with two voltage regulators, one for each generator on the engine. These regulators reject any unused electrical power as heat. Allowing the power usage to fall below 7 amps for extended periods of time may damage the regulators, especially on hot days.
That can not be true can it? Suppose that 21 amps are available but not
used by the aircraft electrical system. 21 amps x 14 volts = 300 watts
of heat that must be dissipated by the voltage regulators.
Don't modern permanent magnet voltage regulators work by shutting off the
output during part of the AC cycle using SCRs that are in series with the output?

--------
Joe Gores
Easy enough to test empirically, if you have the system.


IIRC, early rectifier-regulators really were 'shunt' style regulators,
that would align with the warning from Van's. Newer regulator designs do
seem to use 'switcher' style voltage control, which should function like
typical semiconductors and get hotter as more current flows to the load.

No idea what's used in the iS, but you'd hope it would be the more
modern type.

Charlie

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