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MHerder
Joined: 11 Feb 2008
Posts: 143
Location: Fort Worth TX
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 Posted: Sun Dec 26, 2010 1:12 pm Post subject: Voltage Regulator Output |
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I am using a Jabiru 3300 with a permanent magnet alternator and a kubota voltage regulator. I have some questions since I don't fully understand the PM alternator output.
1) What does the voltage out of the regulator look like on an oscilloscope? Is it really pure DC or does it have some squiggles that avionics may not do so well with?
2) Jabiru suggests tying the yellow wire (senses voltage and tells whether or not the system needs charge or dumps excess to ground) and the Red wire (charges battery) as close to the positive terminal as possible. I would like to charge and sense voltage at the starter contactor for the following reason... If I have an over voltage situation, I will get an alarm from my EIS and I can simply shut off my master switch which would hopefully prevent a problem.... Take a look at my schematic and let me know what you think.
3) What should the voltage be at say 800 RPM, 1500 RPM and 2800 RPM?
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Zodiac 601 HD
Jabiru 3300
Wood Sensinich 64x47
Finally Flying |
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MHerder
Joined: 11 Feb 2008
Posts: 143
Location: Fort Worth TX
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| Posted: Sun Dec 26, 2010 1:16 pm Post subject: Re: Voltage Regulator Output |
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To clarify, my main concern is with damaging avionics since my charging would rin past the avionics bus on the way to the positive side of my battery. I also have concerns with what happens if the red and yellow are disconnected. Where would the voltage go, or would it just be an open circuit?
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Mon Dec 27, 2010 7:48 am Post subject: Re: Voltage Regulator Output |
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Michael,
The output of the voltage regulator is not pure DC, but rather pulsing DC. Hopefully your avionics are well designed to operate on dirty DC. If not, it might be helpful to add some type of filter.
Your schematic does not show a switch to disable the alternator. Is there a switch? The schematic does not show details, but it appears that the master switch will not disconnect the alternator output from the aircraft load. But the avionics master will isolate the avionics. I recommend that Bob Nuckolls' over-voltage protection module be used. It will react in less than one second. It will take a human 5 or 10 seconds to recognize a high voltage problem and take appropriate action.
Joe
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nuckolls.bob(at)aeroelect
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| Posted: Mon Dec 27, 2010 8:01 am Post subject: Voltage Regulator Output |
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At 03:12 PM 12/26/2010, you wrote:
| Quote: |
<michaelherder(at)beckgroup.com>
I am using a Jabiru 3300 with a permanent magnet alternator and a
kubota voltage regulator. I have some questions since I don't fully
understand the PM alternator output.
1) What does the voltage out of the regulator look like on an
oscilloscope? Is it really pure DC or does it have some squiggles
that avionics may not do so well with?
|
When the regulator is running flat out (switched on hard)
the output current is what one would expect from a full-wave
bridge rectifier driven by a single phase ac source.
As bus voltage achieves the regulation setpiont, the regulator
"throttles back" an if the battery were not present, you would
no doubt see a trashier looking waveform
Noise studies on these power generating sources have
shown that the noise levels (while unique to PM alternators)
are of no more concern than the noise from a wound-field,
3-phase alternator.
| Quote: | 2) Jabiru suggests tying the yellow wire (senses voltage and tells
whether or not the system needs charge or dumps excess to ground)
and the Red wire (charges battery) as close to the positive terminal
as possible. I would like to charge and sense voltage at the
starter contactor for the following reason... If I have an over
voltage situation, I will get an alarm from my EIS and I can simply
shut off my master switch which would hopefully prevent a
problem.... Take a look at my schematic and let me know what you think.
|
Why not add active monitoring and automatic control
for the OV condition as described here?
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z16M.pdf
| Quote: | 3) What should the voltage be at say 800 RPM, 1500 RPM and 2800 RPM?
|
PM alternators are usually "geared" such that full alternator
output is not available until the engine is turning at max
cruise RPM. This is why PM alternators are problematic for
meeting legacy design goals assigned to their larger 3-phase
brothers found on TC aircraft. It's unlikely that any useful
output is achieved at 800 or 1500 engine rpm. The engine
manual is silent on alternator performance data.
http://www.usjabiru.com/images/pdf/manuals/new%20stuff/3300%20Install.pdf
. . . other than to say it's rated for 200W of output
(about 14 amps).
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
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MHerder
Joined: 11 Feb 2008
Posts: 143
Location: Fort Worth TX
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| Posted: Mon Dec 27, 2010 11:23 am Post subject: Re: Voltage Regulator Output |
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Here's my logic... The over voltage scenario is highly unlikely with the PM alternator, in fact the Jabiru manual does not even recommend any protection. It seems that I could either disconnect the master solenoid which would remedy the problem, or just turn on my landing and taxi light which draws a lot of power. Normally the PM alternator can barely keep up with anyway. The master switch disconnect would isolate the regulator and rectifier, however the disadvantage is that I have no power to the main buss or avionics buss. Since I have battery backup up on my EFIS and GPS, I'm not that concerned. I can still land safely, which is all I'm really looking for.
The EIS should give me ample visual and audio warning if I set it for a little lower threshold value, say 13.8V.
Michael,
The output of the voltage regulator is not pure DC, but rather pulsing DC. Hopefully your avionics are well designed to operate on dirty DC. If not, it might be helpful to add some type of filter.
Your schematic does not show a switch to disable the alternator. Is there a switch? The schematic does not show details, but it appears that the master switch will not disconnect the alternator output from the aircraft load. But the avionics master will isolate the avionics. I recommend that Bob Nuckolls' over-voltage protection module be used. It will react in less than one second. It will take a human 5 or 10 seconds to recognize a high voltage problem and take appropriate action.
Joe
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Jabiru 3300
Wood Sensinich 64x47
Finally Flying |
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nuckolls.bob(at)aeroelect
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| Posted: Tue Dec 28, 2010 7:51 am Post subject: Voltage Regulator Output |
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At 01:23 PM 12/27/2010, you wrote:
| Quote: |
<michaelherder(at)beckgroup.com>
. . . .Since I have battery backup up on my EFIS and GPS, I'm not
that concerned. I can still land safely, which is all I'm really looking for.
The EIS should give me ample visual and audio warning if I set it
for a little lower threshold value, say 13.8V.
|
Michael, It's not clear to me that you've acquired
an understanding of the simple-ideas that go into
a recipe for success for your airplane's electrical
system. There's a recommended library of information
but in particular, a chapter on system reliability
published in the AeroElectric Connection. You can
get printed/bound copies for a nominal fee or download
it and print yourself at no cost other than printer
expenses.
You're correct that OV conditions are rare and
one of the least concerns for reducing risk . . .
which is why chapter 17 goes to some length attempting
to order various system frailties and failures in
order of criticality.
The architecture diagrams offered in appendix Z
strive to bring the best legacy design goals from
TC aviation into the new "kitchen". Owner Built
and Maintained aviation is crafting new recipes
specific to what the builder wants/needs . . .
not what the FAA or program managers dictate.
At the same time, we strive to drive risks to
still lower numbers.
If you've not taken advantage of the resources
cited, I would encourage you to do so. It goes
toward increasing your comfort and confidence in
the operation of your airplane.
Happy new year!
Bob . . .
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