Today's Message Index:
----------------------
1. 10:18 AM - Re: 220vac diode? (jonlaury)
2. 02:57 PM - electrical system planning (Ryan Brown)
3. 04:00 PM - Re: Newbie with PM alternator feed question (blues750)
4. 06:01 PM - Re: Newbie with PM alternator feed question (user9253)
5. 06:38 PM - Re: Newbie with PM alternator feed question (blues750)
6. 07:46 PM - Re: Newbie with PM alternator feed question (user9253)
Message 1
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| Subject: | Re: 220vac diode? |
Hey All,
Thanks for your suggestions on how to isolate the mains from the back-up power
so no one gets fried when BU pwr is on. The system works well and is safe in all
configurations. Also thanks for cluing me in on diodes only being for DC.
Now back to aviating.
Cheers,
John
Do not archive.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=445781#445781
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| Subject: | electrical system planning |
I'm working on figuring out the system architecture for my plane.
It's an rv9 with all glass panel and an O320 with electrically dependent
fuel injection (EFII).
The mission is typically cross countries including some night flight and
IFR, though it would typically be going through a layer of clouds to VFR on
top.
Here's what I've got for my load analysis:
Fuel pump: 5 A
Ignition/Fuel injectors: 5 A
So already the SD-8 is out.
For minimal comfortable flight I'd add:
Primary EFIS: 3.1 A
Transponder: 0.4 A
Total: 13.5
Add in the rest of the avionics for normal flight:
gtn650 nav/com 2.2A
intercom 0.1A
adsb in 0.2A
Backup efis 3.1 A
(total 19.1)
Then 10A for pitot heat, and lights:
strobes 2.5A
position lights 1.2A
landing lights 1.8A
I'm not including the motors for trim, flaps, or auto pilot here. Also I'm
assuming the comms aren't transmitting. Are these the right assumptions for
the load analysis?
It seems like Z-12 is the best option for me here. I have to use a 20-30
amp backup alternator to keep the engine running. That gives me enough
juice to keep nearly everything running, so Z-13/8 doesn't seem useful.
Z-12 shows an SD-20 backup alternator with it's own switch. I'm assuming
normal operation is with Master on ALT and Aux Alternator on OFF. When you
get low volts warning, you switch Master to BAT and Aux Alternator to ON.
Is there some advantage to wiring it this way instead of having the standby
alternator take over automatically when the voltage drops? Or is that
actually what Z-12 is showing, and you'd normally fly with Aux Alternator
ON?
Also I see that Z-12 shows Battery, Master, and Endurance busses. What's
the point? It seems I'd put the minimum equipment on the battery bus, and
everything else could be on master. It's probably just as many switch flips
to shed load on the master bus as it is to reconfigure the endurance bus.
I guess the endurance bus also give you an extra route to the battery if
the master switch or battery contactor fails, but why not just put the
important devices on the battery bus?
Message 3
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| Subject: | Re: Newbie with PM alternator feed question |
Follow on questions...
Having trouble reconciling the tinyurl link wiring that you posted versus the wiring
diagram for the B&C OVPM package (505-500) I planned on using. Appear to
be only one relay to control on/off of the alternator via the capacitor and
R/R versus your sketch with two relays for two of three phases. Also, why the
need to fuse each phase of the alternator prior to the R/R as depicted in the
B&C diagram? I feel like I'm missing parts of the big picture [Embarassed]
Thanks for indulging my queries!
Dave
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http://forums.matronics.com/viewtopic.php?p=445797#445797
Attachments:
http://forums.matronics.com//files/505_500_rev_j_191.pdf
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| Subject: | Re: Newbie with PM alternator feed question |
Bob's drawing uses two relays because they switch the AC from the dynamo. B&C
uses only one relay because it switches the rectified DC. Either way will work.
It is not a good idea to put fuses or circuit breakers in series. The B&C drawing
has 3 in series: the 40 amp battery fuse, the 30 amp breaker, and the 20
amp fuses. A short circuit that trips the 30 amp breaker is likely to also blow
the 40 amp fuse. Not only would dynamo power be lost, but also the battery.
The 20 amp fuses are not necessary because dynamo current is self limiting.
What really needs protection are the dynamo wires and aircraft battery. The 30
amp breaker satisfies that requirement in the B&C drawing, as does the 40 amp
fuse in Bob's drawing.
Joe
--------
Joe Gores
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| Subject: | Re: Newbie with PM alternator feed question |
user9253 wrote:
> Bob's drawing uses two relays because they switch the AC from the dynamo. B&C
uses only one relay because it switches the rectified DC. Either way will work.
> It is not a good idea to put fuses or circuit breakers in series. The B&C
drawing has 3 in series: the 40 amp battery fuse, the 30 amp breaker, and the
20 amp fuses. A short circuit that trips the 30 amp breaker is likely to also
blow the 40 amp fuse. Not only would dynamo power be lost, but also the battery.
> The 20 amp fuses are not necessary because dynamo current is self limiting.
What really needs protection are the dynamo wires and aircraft battery. The
30 amp breaker satisfies that requirement in the B&C drawing, as does the 40
amp fuse in Bob's drawing.
> Joe
Thanks Joe...
(1) Is dynamo current "self limiting" a characteristic of all 3 phase PM type alternators?
(dynamos?) Would gladly eliminate those three 20 amp c/b's if not
required!
(2) Was planning on a 40A ANL type fuse for the 10 ga wire from the relay to the
primary bus.
(3) Was not planning on fuse/circuit protection from the battery to the primary
bus.
Appreciate all thoughts and input. I hope to post my schematic as an attachment
as soon as I have an idea of what I'm doing [Shocked]
Dave
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| Subject: | Re: Newbie with PM alternator feed question |
All alternators and dynamos are self current limiting. They can only do so much
work. If loaded to much more than their rated capacity, the voltage will start
to drop. Another concern is heat. If fully loaded, an alternator could get
too hot if not adequately ventilated.
--------
Joe Gores
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http://forums.matronics.com/viewtopic.php?p=445802#445802
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