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Saggy bus voltage on Cessna 182
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alec(at)alecmyers.com
Guest

Posted: Thu Jun 02, 2016 6:03 am Post subject: Saggy bus voltage on Cessna 182

Hello all,



I wonder if I could get some ideas on fixing an electrical issue with my 1975 Cessna 182. 



The issue is that the bus voltage sags under load. With the engine running and no electrical load the voltage is approximately 13.8V, dropping to 13.2V with daytime load (beacon, avionics, engine monitor, electrical TC, autopilot) and with night time lighting (add strobes, position lights, LED landing and taxi lights, instrument lights) it drops to 12.8V. 



During flight the battery isn't fully charging and the engine start for the next flight I would describe as "reluctant". If I top off the battery from a line voltage charger for a few hours the next engine start is "enthusiastic". 



I have had the alternator serviced, and I have replaced the regulator. I have put a 'scope on the bus with the engine running and I see steady dc with about 50mV pp of ripple. I have a photograph of the scope trace, not sure how best to make it visible to list readers, but the ripple looks like a rectified AC waveform with no gaps (gaps I think would indicate a failed diode).



Can anyone suggest where I could look next?



Thanks for any suggestions



Alec

ceengland7(at)gmail.com
Guest

Posted: Thu Jun 02, 2016 8:25 am Post subject: Saggy bus voltage on Cessna 182

On Thu, Jun 2, 2016 at 8:08 AM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)>

 

 

 Hello all,

 

 I wonder if I could get some ideas on fixing an electrical issue with my 1975 Cessna 182.

 

 The issue is that the bus voltage sags under load. With the engine running and no electrical load the voltage is approximately 13.8V, dropping to 13.2V with daytime load (beacon, avionics, engine monitor, electrical TC, autopilot) and with night time lighting (add strobes, position lights, LED landing and taxi lights, instrument lights) it drops to 12.8V.

 

 During flight the battery isn't fully charging and the engine start for the next flight I would describe as "reluctant". If I top off the battery from a line voltage charger for a few hours the next engine start is "enthusiastic".

 

 I have had the alternator serviced, and I have replaced the regulator. I have put a 'scope on the bus with the engine running and I see steady dc with about 50mV pp of ripple. I have a photograph of the scope trace, not sure how best to make it visible to list readers, but the ripple looks like a rectified AC waveform with no gaps (gaps I think would indicate a failed diode).

 

 Can anyone suggest where I could look next?

 

 Thanks for any suggestions

 

 Alec



	
Can you get voltmeter probes *directly on* the alternator B lead post & case? Not on the bolts, clamps etc, but directly on the post. Measure voltage there with the engine running & loads off, then on.

Sounds like the alternator is supplying ~the right voltage (possibly just a bit low). But if you have high resistance connections anywhere between the alternator and the loads (on the B+ side *or* the ground side paths), the loads may not be seeing the full alternator voltage. If you have an issue with high resistance connections, the voltage from alternator B terminal to case will still be at 13.8 but your bus (and battery) voltage will be lower, due to voltage drops in the high resistance connections.Â 

Secondary possibility would be the same issue, but in the field circuit from regulator to field terminal on the alt.Â 

Charlie

clr(at)redingaviation.com
Guest

Posted: Thu Jun 02, 2016 8:37 am Post subject: Saggy bus voltage on Cessna 182

Im not an expert but I would look for corrosion around grounds. Make sure all of your grounds are good. 



Craig



 	  Quote: 	
		   On Jun 2, 2016, at 9:08 AM, Alec Myers <alec(at)alecmyers.com> wrote:

 

 

 

 

 Hello all,

 

 I wonder if I could get some ideas on fixing an electrical issue with my 1975 Cessna 182. 

 

 The issue is that the bus voltage sags under load. With the engine running and no electrical load the voltage is approximately 13.8V, dropping to 13.2V with daytime load (beacon, avionics, engine monitor, electrical TC, autopilot) and with night time lighting (add strobes, position lights, LED landing and taxi lights, instrument lights) it drops to 12.8V. 

 

 During flight the battery isn't fully charging and the engine start for the next flight I would describe as "reluctant". If I top off the battery from a line voltage charger for a few hours the next engine start is "enthusiastic". 

 

 I have had the alternator serviced, and I have replaced the regulator. I have put a 'scope on the bus with the engine running and I see steady dc with about 50mV pp of ripple. I have a photograph of the scope trace, not sure how best to make it visible to list readers, but the ripple looks like a rectified AC waveform with no gaps (gaps I think would indicate a failed diode).

 

 Can anyone suggest where I could look next?

 

 Thanks for any suggestions

 

 Alec

art(at)zemon.name
Guest

Posted: Thu Jun 02, 2016 8:56 am Post subject: Saggy bus voltage on Cessna 182

I hate it when that happens. It's bad enough when old pilots sag but we should be able to depend on our airplanes staying __. ðŸ˜‹ 

Â Â Â  -- Art Z.

 

Sent from my phone so please excuse typos and brevity.

kjashton(at)vnet.net
Guest

Posted: Thu Jun 02, 2016 9:42 am Post subject: Saggy bus voltage on Cessna 182

To add to what Charlie said, It sounds like a battery load-test is in order.  A place like Batteries Plus can do one for you.  Also Skytec has a good explanation of how to check for a high resistance that results in voltage drop.

http://www.skytecair.com/troubleshooting.htm

-Kent



 	  Quote: 	
		   On Jun 2, 2016, at 11:37 AM, Charlie England <ceengland7(at)gmail.com> wrote:

 

 

 

 On Thu, Jun 2, 2016 at 8:08 AM, Alec Myers <alec(at)alecmyers.com> wrote:

 

 

 

 Hello all,

 

 I wonder if I could get some ideas on fixing an electrical issue with my 1975 Cessna 182.

 

 The issue is that the bus voltage sags under load. With the engine running and no electrical load the voltage is approximately 13.8V, dropping to 13.2V with daytime load (beacon, avionics, engine monitor, electrical TC, autopilot) and with night time lighting (add strobes, position lights, LED landing and taxi lights, instrument lights) it drops to 12.8V.

 

 During flight the battery isn't fully charging and the engine start for the next flight I would describe as "reluctant". If I top off the battery from a line voltage charger for a few hours the next engine start is "enthusiastic".

 

 I have had the alternator serviced, and I have replaced the regulator. I have put a 'scope on the bus with the engine running and I see steady dc with about 50mV pp of ripple. I have a photograph of the scope trace, not sure how best to make it visible to list readers, but the ripple looks like a rectified AC waveform with no gaps (gaps I think would indicate a failed diode).

 

 Can anyone suggest where I could look next?

 

 Thanks for any suggestions

 

 Alec

 

 Can you get voltmeter probes *directly on* the alternator B lead post & case? Not on the bolts, clamps etc, but directly on the post. Measure voltage there with the engine running & loads off, then on.

 

 Sounds like the alternator is supplying ~the right voltage (possibly just a bit low). But if you have high resistance connections anywhere between the alternator and the loads (on the B+ side *or* the ground side paths), the loads may not be seeing the full alternator voltage. If you have an issue with high resistance connections, the voltage from alternator B terminal to case will still be at 13.8 but your bus (and battery) voltage will be lower, due to voltage drops in the high resistance connections. 

 

 Secondary possibility would be the same issue, but in the field circuit from regulator to field terminal on the alt. 

 

 Charlie

user9253

Joined: 28 Mar 2008
Posts: 1938
Location: Riley TWP Michigan

Posted: Thu Jun 02, 2016 11:00 am Post subject: Re: Saggy bus voltage on Cessna 182

If the regulator has I A S F terminals, measure the voltage between terminal S and the regulator case with the engine running.  If 14 to 14.5 volts, the regulator and alternator are working OK.

 With engine running and all electrical loads turned on, measure the voltage between the positive battery terminal and the alternator "B" terminal.  The voltage drop should be less than a few tenths of a volt.   If more, then check all connections between alternator B terminal and battery positive.  Also check all ground connections, especially regulator ground, engine ground strap and battery ground.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 02, 2016 11:45 am Post subject: Saggy bus voltage on Cessna 182

At 10:37 AM 6/2/2016, you wrote:



 

  	  Quote: 	
		  On Thu, Jun 2, 2016 at 8:08 AM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:

   --> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)>



 

  Hello all,



  I wonder if I could get some ideas on fixing an electrical issue with my 1975 Cessna 182.



  The issue is that the bus voltage sags under load. With the engine running and no electrical load the voltage is approximately 13.8V, dropping to 13.2V with daytime load (beacon, avionics, engine monitor, electrical TC, autopilot) and with night time lighting (add strobes, position lights, LED landing and taxi lights, instrument lights) it drops to 12.8V 	
 

   The factory spec set point for those regulators

   is 14.2 +/- 0.2 volts . . .  After engine start

   and before turning on any additional loads, the

   BUS voltage should be within those limits.



  	  Quote: 	
		    .



  During flight the battery isn't fully charging and the engine start for the next flight I would describe as "reluctant". If I top off the battery from a line voltage charger for a few hours the next engine start is "enthusiastic". 	
 

   This observation rules out soggy battery. Given

   the voltages you've reported, battery performance

   sans external supports is understandable. A

   battery will not accept significant energy

   at bus voltages below 13.8 . . . and even at 13.8

   it would take HOURS to top it off. This is why

   the slightly excessive set-point is the legacy

   value of 14.2 was selected for flooded lead-acid

   batteries . . . 'slight' overcharge that quickly

   tops off battery without serious 'damage'.



   The sealed vented lead-acid (SLVA) likes to be

   charged more aggressively . . . excerpts from

   the Hawker data says:



 [img]cid:.0[/img][/b]



   This fact drives the B&C policy decision to factory

   set their regulators to 14.6 volts.  



 

  	  Quote: 	
		    I have had the alternator serviced, and I have replaced the regulator. I have put a 'scope on the bus with the engine running and I see steady dc with about 50mV pp of ripple. I have a photograph of the scope trace, not sure how best to make it visible to list readers, but the ripple looks like a rectified AC waveform with no gaps (gaps I think would indicate a failed diode).



  Can anyone suggest where I could look next? 	
 

    Yes . . . and it is simple . . . just not easy. You need

    to get a voltmeter reading at the "S" and "F" terminals

    of your regulator with the engine running. "VS" should

    be the 14.2 +/- 0.2 volt value (or what ever is presently

    presented on the regulator's name-plate) and "VF" should

    be substantially larger than zero but NOT pegged against

    the bus . . . if it is pegged, then increase RPM to see

    if the voltage comes off the peg.



 I have had the alternator serviced, and I have replaced the regulator. I have put a 'scope on the bus with the engine running and I see steady dc with about 50mV pp of ripple. I have a photograph of the scope trace, not sure how best to make it visible to list readers, but the ripple looks like a rectified AC waveform with no gaps (gaps I think would indicate a failed diode).



 

    This reading is WAAaayyy low. It should be on the order

    of 1.5 volts pk-pk.  3 phase rectified DC is predicted

    to have an RMS ripple voltage on the order of 4% of the DC

    output. Hence 14 X 0.04 = 560 mVrms and approx 3x that

    pk-pk. 



    If the bus voltage is that 'clean' then I think you're going

    to find that the field voltage is essentially zero. Depending

    on what you fine for "VS", there's probably a wiring disconnect

    somewhere along the path from Bus through the alternator switch

    to the OV sensor, out to the regulator and on to the alternator

    "F" terminal.



    Having the voltage measurements I suggested will 'divide' the

    enemy in the battle toward submission.



    Finally, once the stock regulator is working, you may want

    to consider a more modern ADJUSTABLE device that can be

    set to accommodate the special needs of SVLA batteries.

   



 

   Bob . . .

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alec(at)alecmyers.com
Guest

Posted: Fri Jun 03, 2016 6:22 am Post subject: Saggy bus voltage on Cessna 182

I started by looking at the voltage at the regulator terminals, which is a thousand times easier to reach than the alternator. I took four measurements, at idle RPM and 1600RPM, lights off and lights on.

idle (lights off/lights on)

V_bus  13.6 / 13.2

V_F  5.56 / 9.09

V_S  12.87 / 12.34

V_A  13.89 / 13.79

1600RPM (lights off/lights on)

V_bus  13.6 / 13.2

V_F  4.02 / 7.72

V_S  12.77 / 12.38

V_A  13.99 / 13.78



It's a 14v regulator.

Note: the bus voltage is displayed on the engine monitor, the others are measured with my Fluke.

Does this shed any light?





On Jun 2, 2016, at 15:43, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

  At 10:37 AM 6/2/2016, you wrote:



 

  	  Quote: 	
		  On Thu, Jun 2, 2016 at 8:08 AM, Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)> wrote:

   --> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)>



 

  Hello all,



  I wonder if I could get some ideas on fixing an electrical issue with my 1975 Cessna 182.



  The issue is that the bus voltage sags under load. With the engine running and no electrical load the voltage is approximately 13.8V, dropping to 13.2V with daytime load (beacon, avionics, engine monitor, electrical TC, autopilot) and with night time lighting (add strobes, position lights, LED landing and taxi lights, instrument lights) it drops to 12.8V 	
 

   The factory spec set point for those regulators

   is 14.2 +/- 0.2 volts . . .  After engine start

   and before turning on any additional loads, the

   BUS voltage should be within those limits.



  	  Quote: 	
		    .



  During flight the battery isn't fully charging and the engine start for the next flight I would describe as "reluctant". If I top off the battery from a line voltage charger for a few hours the next engine start is "enthusiastic". 	
 

   This observation rules out soggy battery. Given

   the voltages you've reported, battery performance

   sans external supports is understandable. A

   battery will not accept significant energy

   at bus voltages below 13.8 . . . and even at 13.8

   it would take HOURS to top it off. This is why

   the slightly excessive set-point is the legacy

   value of 14.2 was selected for flooded lead-acid

   batteries . . . 'slight' overcharge that quickly

   tops off battery without serious 'damage'.



   The sealed vented lead-acid (SLVA) likes to be

   charged more aggressively . . . excerpts from

   the Hawker data says:



 <ea42f08.jpg>



   This fact drives the B&C policy decision to factory

   set their regulators to 14.6 volts.  



 

  	  Quote: 	
		    I have had the alternator serviced, and I have replaced the regulator. I have put a 'scope on the bus with the engine running and I see steady dc with about 50mV pp of ripple. I have a photograph of the scope trace, not sure how best to make it visible to list readers, but the ripple looks like a rectified AC waveform with no gaps (gaps I think would indicate a failed diode).



  Can anyone suggest where I could look next? 	
 

    Yes . . . and it is simple . . . just not easy. You need

    to get a voltmeter reading at the "S" and "F" terminals

    of your regulator with the engine running. "VS" should

    be the 14.2 +/- 0.2 volt value (or what ever is presently

    presented on the regulator's name-plate) and "VF" should

    be substantially larger than zero but NOT pegged against

    the bus . . . if it is pegged, then increase RPM to see

    if the voltage comes off the peg.



 I have had the alternator serviced, and I have replaced the regulator. I have put a 'scope on the bus with the engine running and I see steady dc with about 50mV pp of ripple. I have a photograph of the scope trace, not sure how best to make it visible to list readers, but the ripple looks like a rectified AC waveform with no gaps (gaps I think would indicate a failed diode).



 

    This reading is WAAaayyy low. It should be on the order

    of 1.5 volts pk-pk.  3 phase rectified DC is predicted

    to have an RMS ripple voltage on the order of 4% of the DC

    output. Hence 14 X 0.04 = 560 mVrms and approx 3x that

    pk-pk. 



    If the bus voltage is that 'clean' then I think you're going

    to find that the field voltage is essentially zero. Depending

    on what you fine for "VS", there's probably a wiring disconnect

    somewhere along the path from Bus through the alternator switch

    to the OV sensor, out to the regulator and on to the alternator

    "F" terminal.



    Having the voltage measurements I suggested will 'divide' the

    enemy in the battle toward submission.



    Finally, once the stock regulator is working, you may want

    to consider a more modern ADJUSTABLE device that can be

    set to accommodate the special needs of SVLA batteries.

   



 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jun 03, 2016 8:16 am Post subject: Saggy bus voltage on Cessna 182

At 09:21 AM 6/3/2016, you wrote:

 I started by looking at the voltage at the regulator terminals, which is a thousand times easier to reach than the alternator. I took four measurements, at idle RPM and 1600RPM, lights off and lights on.



 idle (lights off/lights on)



 V_bus  13.6 / 13.2

 V_F  5.56 / 9.09

 V_S  12.87 / 12.34

 V_A  13.89 / 13.79



 1600RPM (lights off/lights on)



 V_bus  13.6 / 13.2

 V_F  4.02 / 7.72

 V_S  12.77 / 12.38

 V_A  13.99 / 13.78



 It's a 14v regulator.



    Interesting . . .



    Okay, the fact that your field voltages are responding

    to load changes and not 'stuck on a rail' says the

    regulator is actively controlling alternator behavior.

    Voltage behaviors for loads-off/on suggest that the

    alternator is shouldering the loads albeit at magnitudes

    less than ideal.



    If I recall correctly, Vs comes through the ov

    protection module which explains the approx

    1 volt lower value than Va which comes directly from

    the bus.



    Va and Bus voltages should be closer together,

    You might get a reading of bus voltage with

    the Fluke to compare with what's displayed

    on the engine monitor . . . but the difference

    doesn't explain the chief complaint.



    The fact that your Va value (bus sense to

    the regulator) is so close to 14.0 (lower limit

    of spec) suggests that this regulator may

    have passed acceptance testing at the factory

    but given that it IS low yet actively controlling

    the alternator suggests that it's simply set

    too low . . . but not as low as bus volts reading

    on your engine monitor suggests.



    Do you have the service manual for this airplane

    hence, access to the applicable alternator wiring

    diagram?  My recollections are 40+ years old

    and may indeed be in error.  If you don't have

    the applicable wiring diagram, I can call my

    'mole' at Textron and get the drawing. It would

    also be useful to get the part number off the

    regulator.



    I'm puzzled by the 'scope readings you cited but

    again, given the values you collected above,

    the ripple numbers are not germane to the

    chief complaint either.



    Given that this is a new regulator, I'm not

    ready to jump on the defective regulator diagnosis

    quite yet but the numbers sure do point in

    that direction . . .



    How old is your battery and what type . . .

    flooded or RG? What is the s/n of the

    airplane?



 



 

   Bob . . .

alec(at)alecmyers.com
Guest

Posted: Fri Jun 03, 2016 11:30 am Post subject: Saggy bus voltage on Cessna 182

I'm going to look for a high impedance connection between the A terminal of the alternator and the bus: the regulator is seeing 13.8V at A, but with the load current flowing from A to the bus the bus voltage is 0.6v lower, at the other end of a thick cable and 60A breaker.



On Jun 3, 2016, at 12:13, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

  At 09:21 AM 6/3/2016, you wrote:

 I started by looking at the voltage at the regulator terminals, which is a thousand times easier to reach than the alternator. I took four measurements, at idle RPM and 1600RPM, lights off and lights on.



 idle (lights off/lights on)



 V_bus  13.6 / 13.2

 V_F  5.56 / 9.09

 V_S  12.87 / 12.34

 V_A  13.89 / 13.79



 1600RPM (lights off/lights on)



 V_bus  13.6 / 13.2

 V_F  4.02 / 7.72

 V_S  12.77 / 12.38

 V_A  13.99 / 13.78



 It's a 14v regulator.



    Interesting . . .



    Okay, the fact that your field voltages are responding

    to load changes and not 'stuck on a rail' says the

    regulator is actively controlling alternator behavior.

    Voltage behaviors for loads-off/on suggest that the

    alternator is shouldering the loads albeit at magnitudes

    less than ideal.



    If I recall correctly, Vs comes through the ov

    protection module which explains the approx

    1 volt lower value than Va which comes directly from

    the bus.



    Va and Bus voltages should be closer together,

    You might get a reading of bus voltage with

    the Fluke to compare with what's displayed

    on the engine monitor . . . but the difference

    doesn't explain the chief complaint.



    The fact that your Va value (bus sense to

    the regulator) is so close to 14.0 (lower limit

    of spec) suggests that this regulator may

    have passed acceptance testing at the factory

    but given that it IS low yet actively controlling

    the alternator suggests that it's simply set

    too low . . . but not as low as bus volts reading

    on your engine monitor suggests.



    Do you have the service manual for this airplane

    hence, access to the applicable alternator wiring

    diagram?  My recollections are 40+ years old

    and may indeed be in error.  If you don't have

    the applicable wiring diagram, I can call my

    'mole' at Textron and get the drawing. It would

    also be useful to get the part number off the

    regulator.



    I'm puzzled by the 'scope readings you cited but

    again, given the values you collected above,

    the ripple numbers are not germane to the

    chief complaint either.



    Given that this is a new regulator, I'm not

    ready to jump on the defective regulator diagnosis

    quite yet but the numbers sure do point in

    that direction . . .



    How old is your battery and what type . . .

    flooded or RG? What is the s/n of the

    airplane?



 



 

   Bob . . .

alec(at)alecmyers.com
Guest

Posted: Fri Jun 03, 2016 6:35 pm Post subject: Saggy bus voltage on Cessna 182

I worked through the wiring from the B lead post on the alternator. The wiring goes from the alternator post, to some kind of filter bolted to the engine side of the firewall (which doesn't appear in the Cessna service manual wiring diagrams) then to the 60 amp alternator CB, then to the bus.



The voltage on the alternator B lead post is the same 13.9V (13.8V with heavier load) that I see on the A terminal of the regulator.



I looked at the voltage drop along the B current path: it's about 100mV per terminal - there doesn't appear to be one connection that's any worse than the others. 



There's also about 150-200mV drop across the 60 amp CB, when the bus is loaded up. The terminal screw also gets hot - nearly too hot to touch. Is this expected? It's a thermal-type breaker but I don't know how warm they are intended to get, outside an overload condition.



I'm stumped on two questions:



Why, although the regulator field terminal voltage is well within normal operating range (4-7v), the regulated voltage is low at 13.8 to 13.9V. This is the case with two different regulators. 



Secondly why I'm losing 0.6V, distributed equally across four crimp terminals and a CB. I'm going to estimate the current at 20 amps, including LED landing and taxi lights, halogen position and beacon lights, strobes, pitot heat and full avionics bus, and recharging the battery soon after cranking. Is this to be expected?

On 2Jun2016, at 11:37 AM, Charlie England <ceengland7(at)gmail.com> wrote:



Can you get voltmeter probes *directly on* the alternator B lead post & case? Not on the bolts, clamps etc, but directly on the post. Measure voltage there with the engine running & loads off, then on.



Sounds like the alternator is supplying ~the right voltage (possibly just a bit low). But if you have high resistance connections anywhere between the alternator and the loads (on the B+ side *or* the ground side paths), the loads may not be seeing the full alternator voltage. If you have an issue with high resistance connections, the voltage from alternator B terminal to case will still be at 13.8 but your bus (and battery) voltage will be lower, due to voltage drops in the high resistance connections. 



Secondary possibility would be the same issue, but in the field circuit from regulator to field terminal on the alt. 



Charlie

millner(at)me.com
Guest

Posted: Fri Jun 03, 2016 7:36 pm Post subject: saggy bus voltage on Cessna 182

>> to some kind of filter bolted to the engine side of the firewall 

(which doesn't appear in the Cessna service manual wiring diagrams)



  Cessna only installed that filter on airplanes that had the "avionics" 

package... so the filter is found in the "Avionics" manual for your year 

range of airplane. The Avionics manuals were typically for the entire 

100 series (150/152, 172, 177/RG and 182). Some manuals covered two or 

three model years. There are free scans online, include lots of little 

details you won't find elsewhere.



 >> There's also about 150-200mV drop across the 60 amp CB, when the bus 

is loaded up. The terminal screw also gets hot - nearly too hot to 

touch. Is this expected?



Nope... sure sign of resistance there. You can start by breaking both 

connections to the breaker, cleaning them up to shiny, and reassembling 

them wetted with ACF50 or CorrosionX. But the breaker itself may be 

developing high resistance, and needs replacement. There's a series of 

service bulletins on that breaker... it was a problem. Aircraft Spruce 

and others have aftermarket breakers for that service.



Paul

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jun 04, 2016 4:25 am Post subject: Saggy bus voltage on Cessna 182

At 02:29 PM 6/3/2016, you wrote:

  	  Quote: 	
		  I'm going to look for a high impedance connection between the A terminal of the alternator and the bus: the regulator is seeing 13.8V at A, but with the load current flowing from A to the bus the bus voltage is 0.6v lower, at the other end of a thick cable and 60A breaker. 	


   Yea, that seems excessive. An easy experiment

   to run is install a simple, 4AWG welding cable

   jumper from alternator b-lead to the hot side

   of the starter or battery contactors (I believe

   your battery is up front in that a/c?). Bypass

   the normal ships wiring and see what the effects

   are.



 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jun 04, 2016 4:44 am Post subject: Saggy bus voltage on Cessna 182

At 09:30 PM 6/3/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com>



 I worked through the wiring from the B lead post on the alternator. The wiring goes from the alternator post, to some kind of filter bolted to the engine side of the firewall (which doesn't appear in the Cessna service manual wiring diagrams) then to the 60 amp alternator CB, then to the bus. 	


   b-lead filters were marginally effective

   in suppressing some noises in the ADF.

   The capacitors on most wiring diagrams

   of that era were flagged as part of the

   ADF installation kit and often did not

   show on the production line as-manufactured

   documents.



 

  	  Quote: 	
		  The voltage on the alternator B lead post is the same 13.9V (13.8V with heavier load) that I see on the A terminal of the regulator.



 I looked at the voltage drop along the B current path: it's about 100mV per terminal - there doesn't appear to be one connection that's any worse than the others. 



 There's also about 150-200mV drop across the 60 amp CB, when the bus is loaded up. The terminal screw also gets hot - nearly too hot to touch. Is this expected? It's a thermal-type breaker but I don't know how warm they are intended to get, outside an overload condition. 	


   At the current levels you're running during

   ground tests, that breaker shouldn't warm up

   to the touch.  Those were the least expensive

   breaker Cessna could put their hands on and

   with all due respect, the one in your airplane

   has probably delivered fair value.



   If this were my airpalne, I'd do a 337 mod

   to take the b-lead to the starter contactor

   through an ANL60 current limiter per common,

   modern practice. Dump the filter . . . even

   if there IS some observable noise in your ADF,

   it's unlikely to be a performance issue for

   its utility.



   That would reduce the number of joints and

   greatly reduce the voltage drop from b-lead

   to bus.



 

  	  Quote: 	
		  I'm stumped on two questions:



 Why, although the regulator field terminal voltage is well within normal operating range (4-7v), the regulated voltage is low at 13.8 to 13.9V. This is the case with two different regulators. 	


   I'm with you. Are these 'original' electro-mechanical

   regulators or an aftermarket, electronic replacement?



 

  	  Quote: 	
		  Secondly why I'm losing 0.6V, distributed equally across four crimp terminals and a CB. I'm going to estimate the current at 20 amps, including LED landing and taxi lights, halogen position and beacon lights, strobes, pitot heat and full avionics bus, and recharging the battery soon after cranking. Is this to be expected? 	


   No . . . that's a lot more than factory new.

   Recall that the 'galloping ammeter' phenomenon

   common to those aircraft has root cause in

   the build up of resistance in the bus to regulator

   "A" terminal that eventually forces a negative

   resistance in the dynamics of the voltage regulator

   loop. This is common on older airplanes where

   voltage sense -AND- field supply current share

   the same feed wire.



   Many mechanics replace something . . . often

   the split rocker switch . . . and the problem

   goes away. The customer is momentarily satisfied

   that the ammeter stops hopping around. But the

   fix is temporary in that the fix reduces the loop

   resistance just below the point of instability.

   The problem will return. The elegant fix is to

   renew every metallic joint in that loop from

   bus bar to "A" terminal. THEN the problem is 

   held off for another 30-40 years.



   I suspect your 60A breaker is demonstrating

   effects of age with increased resistance that

   promotes the heating you've observed.



   The REAL fix is to install an after market

   regulator with separate Field Supply and

   Bus Sense leads. 



   If your old and new regulators are electro-mechanical,

   there may be a case for long term storage 

   drift of set point in a downward direction.

   I've never had occasion to study the effects

   of long term storage on new old-stock components.



   The real acid test would be to run the regulator

   on a test stand independent of all effects

   of aged wiring in the a/c.  But it IS a

   vexing puzzle.



 

   Bob . . .

alec(at)alecmyers.com
Guest

Posted: Sat Jun 04, 2016 6:01 am Post subject: Saggy bus voltage on Cessna 182

Alas, Canadian airplane so no 337 type process available...

Both old and new regulators are Lamarr, solid state. 

With "lights on", I used the service manual electrical loads table to calculate the current draw on the alternator at close to 50amps (vice my previous estimate at 20): pitot heat, strobes, position lights, beacon and avionics all use more current than I thought.

Paul Milner kindly pointed me to the Cessna service kit to replace the 60 amp CB, which involves shortening the bus bar so the replacement breaker will fit. I think the approved breaker is $400 or thereabouts, so if it does need replacing, does anyone know a PMA alternative?



On Jun 4, 2016, at 08:42, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

  At 09:30 PM 6/3/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com (alec(at)alecmyers.com)>



 I worked through the wiring from the B lead post on the alternator. The wiring goes from the alternator post, to some kind of filter bolted to the engine side of the firewall (which doesn't appear in the Cessna service manual wiring diagrams) then to the 60 amp alternator CB, then to the bus. 	


   b-lead filters were marginally effective

   in suppressing some noises in the ADF.

   The capacitors on most wiring diagrams

   of that era were flagged as part of the

   ADF installation kit and often did not

   show on the production line as-manufactured

   documents.



 

  	  Quote: 	
		  The voltage on the alternator B lead post is the same 13.9V (13.8V with heavier load) that I see on the A terminal of the regulator.



 I looked at the voltage drop along the B current path: it's about 100mV per terminal - there doesn't appear to be one connection that's any worse than the others. 



 There's also about 150-200mV drop across the 60 amp CB, when the bus is loaded up. The terminal screw also gets hot - nearly too hot to touch. Is this expected? It's a thermal-type breaker but I don't know how warm they are intended to get, outside an overload condition. 	


   At the current levels you're running during

   ground tests, that breaker shouldn't warm up

   to the touch.  Those were the least expensive

   breaker Cessna could put their hands on and

   with all due respect, the one in your airplane

   has probably delivered fair value.



   If this were my airpalne, I'd do a 337 mod

   to take the b-lead to the starter contactor

   through an ANL60 current limiter per common,

   modern practice. Dump the filter . . . even

   if there IS some observable noise in your ADF,

   it's unlikely to be a performance issue for

   its utility.



   That would reduce the number of joints and

   greatly reduce the voltage drop from b-lead

   to bus.



 

  	  Quote: 	
		  I'm stumped on two questions:



 Why, although the regulator field terminal voltage is well within normal operating range (4-7v), the regulated voltage is low at 13.8 to 13.9V. This is the case with two different regulators. 	


   I'm with you. Are these 'original' electro-mechanical

   regulators or an aftermarket, electronic replacement?



 

  	  Quote: 	
		  Secondly why I'm losing 0.6V, distributed equally across four crimp terminals and a CB. I'm going to estimate the current at 20 amps, including LED landing and taxi lights, halogen position and beacon lights, strobes, pitot heat and full avionics bus, and recharging the battery soon after cranking. Is this to be expected? 	


   No . . . that's a lot more than factory new.

   Recall that the 'galloping ammeter' phenomenon

   common to those aircraft has root cause in

   the build up of resistance in the bus to regulator

   "A" terminal that eventually forces a negative

   resistance in the dynamics of the voltage regulator

   loop. This is common on older airplanes where

   voltage sense -AND- field supply current share

   the same feed wire.



   Many mechanics replace something . . . often

   the split rocker switch . . . and the problem

   goes away. The customer is momentarily satisfied

   that the ammeter stops hopping around. But the

   fix is temporary in that the fix reduces the loop

   resistance just below the point of instability.

   The problem will return. The elegant fix is to

   renew every metallic joint in that loop from

   bus bar to "A" terminal. THEN the problem is 

   held off for another 30-40 years.



   I suspect your 60A breaker is demonstrating

   effects of age with increased resistance that

   promotes the heating you've observed.



   The REAL fix is to install an after market

   regulator with separate Field Supply and

   Bus Sense leads. 



   If your old and new regulators are electro-mechanical,

   there may be a case for long term storage 

   drift of set point in a downward direction.

   I've never had occasion to study the effects

   of long term storage on new old-stock components.



   The real acid test would be to run the regulator

   on a test stand independent of all effects

   of aged wiring in the a/c.  But it IS a

   vexing puzzle.



 

   Bob . . .

millner(at)me.com
Guest

Posted: Sun Jun 05, 2016 3:22 pm Post subject: Saggy bus voltage on Cessna 182

- Paul Millner kindly pointed me to the Cessna service kit to     replace the 60 amp CB, which involves shortening the bus bar so the     replacement breaker will fit. I think the approved breaker is $400     or thereabouts, so if it does need replacing, does anyone know a PMA     alternative?

     

     Nowadays, we consider breakers standard electrical parts, and under     the advisory circular guidance, they don't require special     approvals. I understand Transport Canada may not have gotten to that     point yet. That said, Aircraft Spruce (even the Canadian flavour of     same) have several attractive offerings... You don't have to buy     your wire and PIDG terminals from Cessna with PMA do you?

     

     BTW, at least one of the service bulletins is:          SE76-15-Replacement of Alternator Circuit Breakers     (S1596-60L)

     

     Paul 

     



          



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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 08, 2016 7:07 pm Post subject: Saggy bus voltage on Cessna 182

At 08:59 AM 6/4/2016, you wrote:

  	  Quote: 	
		  Alas, Canadian airplane so no 337 type process available... 	


   Fooey . . . 



 

  	  Quote: 	
		  Both old and new regulators are Lamarr, solid state. 	


   Aha! Are they not adjustable?



 

  	  Quote: 	
		  With "lights on", I used the service manual electrical loads table to calculate the current draw on the alternator at close to 50amps (vice my previous estimate at 20): pitot heat, strobes, position lights, beacon and avionics all use more current than I thought.



 Paul Milner kindly pointed me to the Cessna service kit to replace the 60 amp CB, which involves shortening the bus bar so the replacement breaker will fit. I think the approved breaker is $400 or thereabouts, so if it does need replacing, does anyone know a PMA alternative? 	


   Hmmmm . . . your most economical route

   would be to 'refurbish' . . . replace

   as much of the parts with made-up, metal

   to metal joints from the bus to the b-terminal.



 



 

   Bob . . .

alec(at)alecmyers.com
Guest

Posted: Wed Jun 08, 2016 7:43 pm Post subject: Saggy bus voltage on Cessna 182

There is an adjustment inside the regulator. The newer regulator has the lid riveted on, but the older one (same part code) has the lid secured by screws, so the trim pot can be reached. Set to maximum, I now get a bus voltage of 14.2V under no load, and 13.8 with everything energized. Which is a big improvement.

I have sourced a new breaker - as you pointed out, it's a standard electrical part - I'll let you know what the results are when it's installed.

On Jun 4, 2016,:00, Robert L. Nuckolls, III e <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

  At 08:59 AM 6/4/2016, you wrote:

  	  Quote: 	
		  Alas, Canadian airplane so no 337 type process available... 	


   Fooey . . . 



 

  	  Quote: 	
		  Both old and new regulators are Lamarr, solid state. 	


   Aha! Are they not adjustable?

  	  Quote: 	
		  With "lights on", I used the service manual electrical loads table to calculate the current draw on the alternator at close to 50amps (vice my previous estimate at 20): pitot heat, strobes, position lights, beacon and avionics all use more current than I thought.



 Paul Milner kindly pointed me to the Cessna service kit to replace the 60 amp CB, which involves shortening the bus bar so the replacement breaker will fit. I think the approved breaker is $400 or thereabouts, so if it does need replacing, does anyone know a PMA alternative? 	


   Hmmmm . . . your most economical route

   would be to 'refurbish' . . . replace

   as much of the parts with made-up, metal

   to metal joints from the bus to the b-terminal.



 



 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 09, 2016 6:34 pm Post subject: Saggy bus voltage on Cessna 182

At 10:29 PM 6/8/2016, you wrote:



  	  Quote: 	
		  There is an adjustment inside the regulator. The newer regulator has the lid riveted on, but the older one (same part code) has the lid secured by screws, so the trim pot can be reached. Set to maximum, I now get a bus voltage of 14.2V under no load, and 13.8 with everything energized. Which is a big improvement. 	


  But still too low . . . it shouldn't sag

  that much under load.



 

   Bob . . .

alec(at)alecmyers.com
Guest

Posted: Thu Jun 09, 2016 6:57 pm Post subject: Saggy bus voltage on Cessna 182

Tyco quote a resistance of 20mOhms for their 50A breaker. I just put the new 60A (not Tyco) breaker on the bench for a four terminal resistance check, and measure about 30mOhms - at 50A that's a 0.15 volt drop (and 7 watts of heat, which should warm it up). I'm seeing not much more than that on the existing installed original breaker, so I'm not sure how much better the new breaker will be.



On Jun 9, 2016, at 22:32, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

  At 10:29 PM 6/8/2016, you wrote:



  	  Quote: 	
		  There is an adjustment inside the regulator. The newer regulator has the lid riveted on, but the older one (same part code) has the lid secured by screws, so the trim pot can be reached. Set to maximum, I now get a bus voltage of 14.2V under no load, and 13.8 with everything energized. Which is a big improvement. 	


  But still too low . . . it shouldn't sag

  that much under load.



 

   Bob . . .

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