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Z12 Alternator Amps

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RV7ASask

Joined: 25 Jan 2006
Posts: 36

Posted: Fri Jul 06, 2012 5:44 am Post subject: Z12 Alternator Amps

I have been flying my RV7A for 38 hours and all has been going well. The electrical architecture Z12, is installed stock and is also working well.

 

After start with only the Skyview and two Light Speed Ignitions drawing current the main alternator shows 14.7 volts and 8 amps. As part of the “After Start Check” I test the Aux Alternator by switching the Main Alternator off. The battery takes over and as the voltage drops to 12.7 volts the Aux Alternator comes on line. It will maintain 12.7 volts, so far so good.

 

As I have only one amp indicator on the Skyview I have a switch to monitor the Main Alternator or Aux Alternator amps. The Aux Alternator amps climb up to and sit around 16 amps with no change in the load. 



Questions: why is the amperage showing double for the Aux Alternator? Should I be concerned? 



Warmest regards

David Lamb

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jul 06, 2012 6:22 pm Post subject: Z12 Alternator Amps

--> AeroElectric-List message posted by: "RV7ASask" <rv7alamb(at)sasktel.net>



 I have been flying my RV7A for 38 hours and all has been going well. The electrical architecture Z12, is installed stock and is also working well.

  

 After start with only the Skyview and two Light Speed Ignitions drawing current the main alternator shows 14.7 volts and 8 amps. As part of the “After Start Check” I test the Aux Alternator by switching the Main Alternator off. The battery takes over and as the voltage drops to 12.7 volts the Aux Alternator comes on line. It will maintain 12.7 volts, so far so good.



  You don't mention engine RPM during your cited observations. The SD-20 alternator on a vacuum pump pad will develop full output at 3500 shaft RPM . . . with a 1.4:1 pad ratio, you need about 2500 engine RPM to get full output from the SD-20. At 2700 redline on the engine, you can get more . . . the SD-20 is REALLY a 40A alternator de-rated for limits to available pad speeds. Your observed drop to 12.7 is consistent with the SD-20 being essentially relaxed at low engine RPMs and the battery is picking up the loads. Under this condition, I would expect the alternator load amps to be small if not zero.

  The only time I would attempt to test the SD-20 on the ground is during engine run-up where you can get a substantial output but still less than 20A during the mag-check. Same thing goes for the SD-8 alternator. With the high pulley ratio on belt driven alternators folks are very accustomed to seeing substantial output from the main alternator and bus voltages that do not sag to the point that a battery is asked to support ship's loads.  

 As I have only one amp indicator on the Skyview I have a switch to monitor the Main Alternator or Aux Alternator amps. The Aux Alternator amps climb up to and sit around 16 amps with no change in the load. 



 Questions: why is the amperage showing double for the Aux Alternator? Should I be concerned?   Something is wrong. I would expect to see very few amps from the SD-20 at ramp RPMs on the engine. How does it perform in flight?

  After say 30 minutes of flight when you know that the battery is topped off, first reduce total ship's loads as much as possible and switch between the two alternators. See that both support the bus at similar voltage readings ABOVE 14 volts. Then add small loads and compare the two alternator output readings. Readings of 20A or less on the main alternator should be mirrored on the aux alternator.



  However, as long as the bus remains above 14 volts with either alternator, my best guess is that the SD-20 is fine and you've got an instrumentation problem.



 

  Bob . . .     [quote][b]

RV7ASask

Joined: 25 Jan 2006
Posts: 36

Posted: Sat Jul 07, 2012 8:26 pm Post subject: Re: Z12 Alternator Amps

I went flying today and did an Aux alternator check as you suggested Bob. After turning most of the electrical load off, once again I was left with 8 amps and 14.4 volts on the Main Alternator. 



Cruising at 2400 RPM I selected the Main Alternator Off. Voltage dropped to 12.9 and the Aux Alternator came on line with a steady 12.9 volts. The amps then slowly climbed up to and settled down at 20 amps, more than double the reading of the Main? To the best of my knowledge everything is wired correctly.



Any suggestions?



Regards

David Lamb

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Jul 08, 2012 7:04 am Post subject: Z12 Alternator Amps

At 11:26 PM 7/7/2012, you wrote:




I went flying today and did an Aux alternator check as you suggested 

Bob. After turning most of the electrical load off, once again I was 

left with 8 amps and 14.4 volts on the Main Alternator.



Cruising at 2400 RPM I selected the Main Alternator Off. Voltage 

dropped to 12.9 and the Aux Alternator came on line with a steady 

12.9 volts. The amps then slowly climbed up to and settled down at 20 

amps, more than double the reading of the Main? To the best of my 

knowledge everything is wired correctly.



   There's no reason for the currents to

   be that different. I'd forgotten about the lower

   setpoint for the standby regulator. 12.9 is a bit

   low, it should be about 1 volt lower than your

   main alternator regulator. 14.5 for main, 13.5

   for aux.



   You say that the aux alternator amps 'climbed slowly'

   where did it start from? I'd tweak the aux alternator

   regulator up to 13.5 volts and see how the behavior

   changes. Sounds like the battery is taking on part of

   the aux loads and reduces its share as the terminal

   voltage drops.



   The aux alternator should support all ships loads up

   to 20A at some voltage just above that which will cause

   the battery to share the load. This has to be above

   13.0 volts.

   Bob . . .

RV7ASask

Joined: 25 Jan 2006
Posts: 36

Posted: Sun Jul 08, 2012 7:36 pm Post subject: Re: Z12 Alternator Amps

Thanks Bob,



You asked about the amps climbing slowly. When I switch the main alternator off and switch the amps monitor switch to Aux Alternator the Aux will show zero amps. As the Aux comes on line the amps slowly build from zero to 20 amps and it takes about 20 to 30 seconds. I am not sure if this is the Skyview indicating system or is the battery slowly allowing the load to be taken up by the alternator? I do not have the ability to monitor the amps being drawn by the battery as the two indicator inputs come off the shunts as per Z12.



I will not be flying until the end of the week but I will adjust the aux regulator and let you know how the next test goes.



Regards

David Lamb

maca2790

Joined: 26 Jan 2011
Posts: 59
Location: Australia

Posted: Mon Jul 09, 2012 3:53 pm Post subject: Re: Z12 Alternator Amps

As Bob says it would seem that you have a load of at least 20 amps or more on the electrical system and because the Aux Alt output Voltage

is so low some of the load is being shared with the Battery.



As the battery terminal voltage starts to reduce because of current being drawn from it, the load on the Aux Alternator is slowly increasing. Hence you see the increase in indicated Aux Alt output.



If 20 amps is the rated output of the AUX Alt you need to turn off unneeded equipment to get the load down to say 16 or 17 amps and so give you some headroom for battery charging.



cheers



John MacCallum

RV10 #41016

steve(at)tomasara.com
Guest

Posted: Tue Jul 10, 2012 5:58 am Post subject: Z12 Alternator Amps

Regarding the unexpected slowly rising to too high current reading when 

switching to the backup alternator,  one thing I would check for is that 

the wrong shunt is in the alternate alternator current patch (leading to 

the high, but I suspect false, reading) and that the 

indicator/glass-panel has a very strong low-pass response (leading to 

the slow rise).



Steve Stearns

Boulder/Longmont, Colorado

CSA,EAA,IAC,AOPA,PE,ARRL,BARC (but ignorant none-the-less)

Restoring (since 1/07) and flying again (8/11!): N45FC O235 Longeze 

Cothern/Friling CF1 (~1000 Hrs)

Flying (since 9/86): N43732 A65 Taylorcraft BC12D

RV7ASask

Joined: 25 Jan 2006
Posts: 36

Posted: Wed Jul 11, 2012 2:31 pm Post subject: Re: Z12 Alternator Amps

I managed to get flying again today after turning the Aux Alternator regulator voltage up three turns. This worked. The voltage now shows 13.3 volts with the Main Alternator off.



The high Amps, however, did not change. Prior to switching the Main Alternator off it was reading 8 Amps as before and adding up what was on, this was about right. With the Main off the Aux Alternator is still reading 20 Amps. 



At this point I do not think it has anything to do with the battery charging and I think everything is wired correctly.



Still head scratching.



Regards

David Lamb

Bob McC

Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON

Posted: Wed Jul 11, 2012 3:39 pm Post subject: Z12 Alternator Amps

David;



Amperage cannot just mysteriously appear or disappear. Are you sure that the

shunt being used to measure this amperage is the correct one?? and that the

instrument reading it is properly set up to interpret the shunt voltage

correctly?? (your measurement instrument measures the voltage across the

shunt then translates that into an amperage indication. The incorrect shunt

will result in an erroneous indication as will a faulty translation

calculation setup.)



Bob McC



[quote] --

_________________
Bob McC
Falco #908
(just starting)

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jul 11, 2012 4:09 pm Post subject: Z12 Alternator Amps

At 05:31 PM 7/11/2012, you wrote:

 	  Quote: 	
		  



I managed to get flying again today after turning the Aux Alternator 

regulator voltage up three turns. This worked. The voltage now shows 

13.3 volts with the Main Alternator off.



The high Amps, however, did not change. Prior to switching the Main 

Alternator off it was reading 8 Amps as before and adding up what 

was on, this was about right. With the Main off the Aux Alternator 

is still reading 20 Amps.


	


    Does it now go immediately to 20A instead of

    'drifting up'?

 	  Quote: 	
		  



At this point I do not think it has anything to do with the battery 

charging and I think everything is wired correctly.



Still head scratching.


	


    Okay . . . how about calibration issues. What

    kind of sensors do you have on the alternator

    b-leads, hall effect? . . . or are they shunts?



    What instrument displays the alternator current

    readings. One instruement that watches BOTH

    current signals or does it switch from one to

    the other?

   Bob . . .

RV7ASask

Joined: 25 Jan 2006
Posts: 36

Posted: Thu Jul 12, 2012 7:21 am Post subject: Re: Z12 Alternator Amps

Early this morning I was in the hanger and did some major testing. I disconnected the 20 Amp Shunt I received originally from B&C when I got the 20 Amp Aux Alternator. I then temporarily installed a 40 Amp Shunt I had received from Dynon but had not used. A ground run gave all the correct and expected indications. The Aux Alternator is now showing the same Amps as the Main. 



Thanks to everyone who weighed in on this issue. It looks like I have a solution.



Regards

David Lamb

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jul 12, 2012 9:30 am Post subject: Z12 Alternator Amps

At 10:21 AM 7/12/2012, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "RV7ASask" <rv7alamb(at)sasktel.net>



 Early this morning I was in the hanger and did some major testing. I disconnected the 20 Amp Shunt I received originally from B&C when I got the 20 Amp Aux Alternator. I then temporarily installed a 40 Amp Shunt I had received from Dynon but had not used. A ground run gave all the correct and expected indications. The Aux Alternator is now showing the same Amps as the Main. 



 Thanks to everyone who weighed in on this issue. It looks like I have a solution. 	


    This speaks to calibration issues for switching

    one display between multiple values to be measured,

    converted to 'amps' and displayed to the operator.



    A ammeter shunt in simply a power resistor, usually fabricated

    from manganin (high resistance, low temperature coefficient of

    resistance). Here's a popular example:



 [img]http://t1.gstatic.com/images?q=tbn:ANd9GcQW7N6xQF4wong0qQ9Kg8tffqBzGJOo7GTllyHm0zeMj8mfh3m1Ag[/img]  



   Two terminals for high current, two SEPARATE terminals

   for sampling the voltage dropped across the resistance

   (thin strut between the posts).



   Shunts are always paired with an instrument. The instrument

   will display some reading at full scale when excited by

   a voltage. A legacy convention is to craft ammeters that

   go to full scale with 50 millivolts applied. Accurate

   pairing calls for installing a scale plate with an

   appropriate full scale value (in example below it's

   30 Amps; and then combining it with a shunt that drops

   full scale volts for the instrument when carrying 30

   amps).



   



   When you want to watch two different current flows with

   a single instrument, you pick two shunts large enough

   to cover the largest expected current flow . . . but

   for the display in amps to be accurate, they must be

   identical shunts.



   If the two current flows are widely separated (suppose

   b-lead currents from say a 60A main alternator

   and an 8A SD-8 alternator), then an ammeter that

   reads 60+ amps full scale is not so useful for slicing

   up the output of an 8A alternator.



   This is often handled by not calibrating the ammeter

   in AMPs but in PERCENT of full load for the devices

   being monitored. For example, the ammeter we offer



 [img]cid:.0[/img]



   Is calibrated in percent. We then offer a variety of

   shunts calibrated to the instrument and scaled to the

   load being monitored. For example, an SD-8/60A combo

   would call for a 10A/60A shunts. An SD-20/40A combo

   would be 20/40, etc.



   When you have a digital display like Dynon, it may

   come to you with a FIXED input sensitivity for full

   scale, like a steam-gauge . . . 



   It may be programmable either from a local keyboard

   or USB input. But in any case, it's probably NOT capable

   of different sensitivities. In the situation we're

   considering, 40A, 50mv shunts give accurate readings

   on the Dynon . . . irrespective of the size of the

   device being monitored. 



 

 

   Bob . . .

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bbradburry(at)bellsouth.n
Guest

Posted: Thu Jul 12, 2012 10:10 am Post subject: Z12 Alternator Amps

Isn't the shunt supposed to be the same as the range on the reading

instrument?



Bill



--

Bob McC

Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON

Posted: Thu Jul 12, 2012 11:43 am Post subject: Z12 Alternator Amps

Yes. (or the reading instrument needs to be calibrated to match the shunt. (same thing))



Bob McC

[quote] From: bbradburry(at)bellsouth.net

 To: aeroelectric-list(at)matronics.com

 Subject: RE: Re: Z12 Alternator Amps

 Date: Thu, 12 Jul 2012 14:09:33 -0400

 

 --> AeroElectric-List message posted by: "Bill Bradburry" <bbradburry(at)bellsouth.net>

 

 Isn't the shunt supposed to be the same as the range on the reading

 instrument?

 

 Bill

 

 --

_________________
Bob McC
Falco #908
(just starting)

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