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Peer Review of Schematic

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Noah

Joined: 02 Jul 2009
Posts: 18
Location: Rhode Island

Posted: Thu Apr 08, 2010 7:08 pm Post subject: Peer Review of Schematic

Greetings-  



I am requesting comments on the following dual alternator single battery schematic using Plane Power 60A and B&C SD-20 alternators using an external SB-1B regulator.



http://img88.imageshack.us/img88/4748/100408.png



Plane is an RV which will be equipped with a magneto and an EI, so engine is not electrically dependent.  Mission is multi-day X-country with occasional IFR. Avionics suite will include EFIS/EM, IFR GPS, and autopilot.  Backup flight instruments (AI, ALT, AS) are planned.  EFIS and AI will contain internal backup batteries.   Design goal is to keep it as simple as the mission allows.



Thanks in advance for your thoughts and consideration.

_________________
Highest Regards,

Noah Forden
RV-7A
Rhode Island

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Apr 09, 2010 6:07 am Post subject: Peer Review of Schematic

At 10:08 PM 4/8/2010, you wrote:

 	  Quote: 	
		  



Greetings-



I am requesting comments on the following dual alternator single 

battery schematic using Plane Power 60A and B&C SD-20 alternators 

using an external SB-1B regulator.



http://img88.imageshack.us/img88/4748/100408.png


	


    When you post a customized power distribution diagram

    it would be most helpful if you also include design

    goals you expect to achieve that are over and above

    what was published in the nearest Z-figure match.



    One presumes that some design goal deficiency is

    perceived with an existing z-figure. This would prompt

    development of a new configuration. Without knowing

    what those deficiencies are, it's difficult if not

    impossible to evaluate effectiveness of the new

    configuration for meeting design goals.



    What drove the decision to use an SD-20 in lieu

    of the lighter and much less expensive SD-8?



    Bob . . .

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Fri Apr 09, 2010 8:58 am Post subject: Re: Peer Review of Schematic

Noah,



Thanks for posting your schematic. As you know, I'm doing something similar because Z-13, with an SD-8, does not meet the needs of my all electric plane with high  Ebus loads. I opted for a 40a Alt over the SD-20 largely because of cost and a small weight penalty.



Questions:

1. Why the HE sensor and the shunt for the SD-20?

2. Part # for the HE sensor?

3. What kind of device is "Midi 30"?

4. "AFS"?



Thanks,

John

Glasair IIS-TD

Noah

Joined: 02 Jul 2009
Posts: 18
Location: Rhode Island

Posted: Fri Apr 09, 2010 1:44 pm Post subject: Re: Peer Review of Schematic

 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 10:08 PM 4/8/2010, you wrote:

    When you post a customized power distribution diagram

    it would be most helpful if you also include design

    goals you expect to achieve that are over and above

    what was published in the nearest Z-figure match.



    One presumes that some design goal deficiency is

    perceived with an existing z-figure. This would prompt

    development of a new configuration. Without knowing

    what those deficiencies are, it's difficult if not

    impossible to evaluate effectiveness of the new

    configuration for meeting design goals.



    What drove the decision to use an SD-20 in lieu

    of the lighter and much less expensive SD-8?



    Bob . . . 	




Bob, didn't we already hash these questions out?

http://forums.matronics.com/viewtopic.php?p=288883#288883

_________________
Highest Regards,

Noah Forden
RV-7A
Rhode Island

Noah

Joined: 02 Jul 2009
Posts: 18
Location: Rhode Island

Posted: Fri Apr 09, 2010 2:03 pm Post subject: Re: Peer Review of Schematic

 	  jonlaury wrote: 	
		  Noah,



Thanks for posting your schematic. As you know, I'm doing something similar because Z-13, with an SD-8, does not meet the needs of my all electric plane with high  Ebus loads. I opted for a 40a Alt over the SD-20 largely because of cost and a small weight penalty.



Questions:

1. Why the HE sensor and the shunt for the SD-20?

2. Part # for the HE sensor?

3. What kind of device is "Midi 30"?

4. "AFS"?



Thanks,

John

Glasair IIS-TD 	




Thanks for the questions John.



1.  The Hall Effect Sensor on the SD-20 B-Lead is actually part of the SB1B regulator kit.  With this regulator, the alternator is only brought to life if the bus voltage falls to around 13V (main alternator failed/offline).  The HE sensor will trigger the regulator to continuously flash the annunciator light if B-Lead current exceeds 20A, signaling to the pilot to reduce load.  If B-Lead current is below 20A, the annunciator will remain steady-lit.  The second current sensor on the B-Lead goes to the Advanced Flight Systems (AFS) to indicate current load to the pilot, which can not be determined via the HE sensor on the regulator (unless all you want to know is whether B-Lead load is <>20A).



2. Part of SB1B-14 kit.



3. Midi 30 fuses:

http://www.littelfuse.com/data/en/Data_Sheets/498.pdf

I like these fuseblocks since they are rugged and covered for protection.  And McMaster-Carr sells the fuseblocks, P/N 9180K6.



4. Advanced Flight Systems - EFIS/Engine Monitor.

_________________
Highest Regards,

Noah Forden
RV-7A
Rhode Island

rckol

Joined: 14 Nov 2008
Posts: 36

Posted: Sat Apr 10, 2010 7:14 am Post subject: Re: Peer Review of Schematic

Noah,



I don't see any wiring errors.



I am planning to use the same architecture but with a couple of different details you might consider.



1. I am going to eliminate the two shunts and run both alternator B leads through one Hall Effect transducer.  This eliminates the need to add switching for the shunts.  The AFS manual that I have (about 2 years old) shows provisions for only one shunt.



2. I am going to use an LR3C regulator instead of the SB1B.  With the install kit, the SB1B is $308 more than the LR3C and the I don't see that the extra features it has add any value in this application.  



You will have a main alt out annunciator light, plus voltage and current reading on the AFS, plus you can probably program alarms for a low voltage condition in the AFS, so the automatic turn on feature is not adding any value in my opinion.



You will also be able to read the voltage and standby alt current on the AFS, so the blinking current warning light is also redundant.



Great features for adding to an old TC aircraft, but you already have their functions well covered.



Just my 2 cents.



Dick Kaehler

_________________
rck

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Sat Apr 10, 2010 2:44 pm Post subject: Re: Peer Review of Schematic

Noah,

Here are some suggestions for weight savings.

12AWG (or maybe 14) is big enough for the aux alternator and E-Bus.

Have you done a load analysis on the E-Bus, adding the actual amperage of individual loads (not individual fuse sizes)?

The main power bus feed is not normally protected by a fuse.  If you want to, that is OK.  But one ANL60 can protect both the alternator B lead and the main power bus feed wire from excessive battery current.  The alternator can not put out much more than 60amps, so it is not necessary to use a fuse between the alternator and main power bus.

6AWG is big enough for the main alternator unless you expect that the aircraft load will continuously draw 60amps.

Joe

_________________
Joe Gores

Noah

Joined: 02 Jul 2009
Posts: 18
Location: Rhode Island

Posted: Sat Apr 10, 2010 3:30 pm Post subject: Re: Peer Review of Schematic

 	  rckol wrote: 	
		  Noah,



I don't see any wiring errors.



I am planning to use the same architecture but with a couple of different details you might consider.



1. I am going to eliminate the two shunts and run both alternator B leads through one Hall Effect transducer.  This eliminates the need to add switching for the shunts.  The AFS manual that I have (about 2 years old) shows provisions for only one shunt.



2. I am going to use an LR3C regulator instead of the SB1B.  With the install kit, the SB1B is $308 more than the LR3C and the I don't see that the extra features it has add any value in this application.  



You will have a main alt out annunciator light, plus voltage and current reading on the AFS, plus you can probably program alarms for a low voltage condition in the AFS, so the automatic turn on feature is not adding any value in my opinion.



You will also be able to read the voltage and standby alt current on the AFS, so the blinking current warning light is also redundant.



Great features for adding to an old TC aircraft, but you already have their functions well covered.



Just my 2 cents.



Dick Kaehler 	




Appreciate the comments Dick.



#1 is a good idea.  I actually meant to show a 2nd hall effect sensor on the aux B-Lead vice a shunt.  You're right that AFS does not have provision for two shunts, but they do have provision for a shunt and a HE sensor.  I have struggled with how much instrumentation on current is enough or too much.  I debated having a single current sensor at the battery ground cable.  AFS' software can not presently deal with negative current flow signals (battery charging) so this is why I ended up with this configuration.  Never thought of having two alternator B-Leads going thru one HE sensor.  I like this.  But if you have two LR3 regulators, doesn't that mean they will both be online simultaneously (load sharing)?  Or are you dialing the voltage setting down on one of them so that it only comes alive in case of failure of the primary?  Or, are you keeping the aux alternator field switch normally open, and only switching the aux alt on in case of primary alt failure?



One thing I should have mentioned is that standard operating procedure is to have both bus switches in the full on position during flight (both alternators available).  One thing I like about this is that no pilot action is required in case of a primary alternator failure - the aux alternator just comes online and no switching is immediately required.  You might want to eventually turn off the main bus / battery contactor depending on loads.



Anyway, some thought provoking comments so thank you.

_________________
Highest Regards,

Noah Forden
RV-7A
Rhode Island

Noah

Joined: 02 Jul 2009
Posts: 18
Location: Rhode Island

Posted: Sat Apr 10, 2010 4:00 pm Post subject: Re: Peer Review of Schematic

 	  user9253 wrote: 	
		  Noah,

Here are some suggestions for weight savings.

12AWG (or maybe 14) is big enough for the aux alternator and E-Bus.

Have you done a load analysis on the E-Bus, adding the actual amperage of individual loads (not individual fuse sizes)?

The main power bus feed is not normally protected by a fuse.  If you want to, that is OK.  But one ANL60 can protect both the alternator B lead and the main power bus feed wire from excessive battery current.  The alternator can not put out much more than 60amps, so it is not necessary to use a fuse between the alternator and main power bus.

6AWG is big enough for the main alternator unless you expect that the aircraft load will continuously draw 60amps.

Joe 	




Thanks for the input, Joe.



I am in process of sizing wires, fuses, and breakers so what is listed is preliminary.



I was under the impression that separate ANL fuses were used on both the B-lead and the bus feed so that a short in either would not take down the other?



Although now that I think about it some more, if configured as you indicate, a significant enough fault in either the primary B-lead or main bus feed would open the single ANL fuse, which would take both the primary alternator and the main bus offline.  But the E-bus would not be affected, so maybe this is a good trade off.  Those ANL carriers ARE large and heavy.  Why bother carrying the weight?



I'm gonna have to sleep on this one.



Thanks again for your comments Joe.

_________________
Highest Regards,

Noah Forden
RV-7A
Rhode Island

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Apr 10, 2010 4:14 pm Post subject: Peer Review of Schematic

 	  Quote: 	
		  

 >     What drove the decision to use an SD-20 in lieu

 >     of the lighter and much less expensive SD-8?

 >

 >     Bob . . .

Bob, didn't we already hash these questions out?


	


  Sorry. I have so many conversations going I have trouble

  keeping track of them. Ignore all the above.



  Bob  . . .

Noah

Joined: 02 Jul 2009
Posts: 18
Location: Rhode Island

Posted: Sat Apr 10, 2010 4:17 pm Post subject: Re: Peer Review of Schematic

I should have posted some notes along with the schematic.  Most have been covered.  One that has not involves the E-bus feed diode.  I selected a Power Schottky from Ixys.  Cheapest outlet I found was Future Electronics:

http://ixdev.ixys.com/DataSheet/l227.pdf



The forward voltage drop for this diode is quite low, 0.29V at 20A, so the power dissipated is also low, only <5.8W at 20A.  Also, the diode comes in a form factor which really includes two diodes (half of a bridge rectifier, I believe).  Although not shown on my initial schematic, I plan to connect both of these diodes in parallel - for three reasons:  first for redundancy – if one fails, the other might still be ok.  Second, to reduce current (and therefore overall voltage drop) across the diode(s).  And third, to reduce junction temperature and spread the heat load more evenly in the component.  I expect that with such a low heat dissipation and a robust package, just bolting this device to any piece of convenient aluminum will provide sufficient heatsinking.



Since standard operating procedure will be to have both bus switches closed in flight, this eliminates any potential for current flow through the diode, and any associated power losses & heat dissipation as well.  Only if the E-Bus switch is in the off position (or there is a failure in the main E-Bus feed) will the diode(s) see current flow and temperature rise.  Should this occur, no pilot action is required to maintain power to the E-Bus.

_________________
Highest Regards,

Noah Forden
RV-7A
Rhode Island

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Sat Apr 10, 2010 5:02 pm Post subject: Re: Peer Review of Schematic

Noah,

   You pointed out a good reason not to connect the main power bus to the same fuse as the alternator.  I do not think that any of the Z-drawings have a fuse in the wire supplying power to the main bus.  The theory is that a short circuit in the wire will burn away the aluminum sheet metal and thus electrically isolate the heavy copper wire once again.  If you do a good job of wiring, and I am sure you will, then the likelihood of a short circuit is remote, especially if the wire is double insulated where it passes through the firewall or bulkheads.

  The main purpose of the ANL fuse is to protect the battery and wires in case the alternator shorts out (a rare occurrence).  But if it does short out, one would not want 400 amps draining the battery and heating wires.

   	  Quote: 	
		  Second, to reduce current (and therefore overall voltage drop) across the diode(s). 	


That is true, but not by a significant amount.  Diode redundancy and heat dissipation are good reasons for using both diodes in the package, IMHO.  Heat conducting grease should be used between the diode and heatsink.

  I do not see a problem with always having the E-bus alternate feed turned on.

   You might consider having the aux-alternator on a separate switch so that you can control it independently of the E-bus.  If I remember correctly, Bob N. said that connecting two alternators in parallel causes problems unless the voltage regulator for the aux unit is set well below the set point of the main alternator.

Joe

_________________
Joe Gores

rckol

Joined: 14 Nov 2008
Posts: 36

Posted: Sat Apr 10, 2010 7:04 pm Post subject: Re: Peer Review of Schematic

Noah,



If you use an LR3C instead of the SB1B, the normal operating condition would be with the Aux alternator and alt battery feed off.  You would be feeding the E-bus through the diode under normal conditions. 



With your scheme using  the SB1B and the associated switch always on, I think your E-bus would end up getting most of its power back through the relay, since that will be the lower resistance path.  I don't think the diode would be doing much of anything unless the main contactor is on and the alt-feed relay is off.



I think the auto-on feature of the SB1B would be a great thing on an aircraft with a volt or ammeter stuck down on the bottom of the panel where you might not notice the problem until it manifested itself after the battery had run down and the gizmos started going on the fritz.  I heard one such first hand dark and stormy night story from my CFII.   With all the low voltage signaling you have, I would personally not be worried about missing the event or having to throw the switch(s).  



Dick

_________________
rck

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