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voltage fluctuations

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erich weaver

Joined: 16 Jun 2016
Posts: 11

Posted: Mon Nov 06, 2017 11:44 am Post subject: voltage fluctuations

I have my RV-7A wired per Z-13/8.  I sometimes observe rapidly fluctuating voltage, varying from approximately 13.0 to 14.0 V, as indicated on my EFIS display.  I figured it was just a loose connection at the EFIS, but I hooked up a voltage meter to the battery terminals and ran the engine and observed similar occasional fluctuations, so the problem lies elsewhere.  I then tested voltage at pin 6 on my B&C LRC voltage regulator with the engine off and the  master on, and observed a voltage of about 11.9 V.  However, when I remove the wire from my master switch that feeds pin 6 and test voltage on it, I get the expected 13 V.  The voltage drop is only observed after connecting the wire to the voltage regulator.  B&C specs say the voltage drop should be 0.2V or less.  Is my regulator bad and is this the cause of my voltage fluctuations?



thanks



Erich

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Nov 06, 2017 2:14 pm Post subject: Re: voltage fluctuations

If I am interpreting your voltage measurements correctly, it sounds like the master switch contacts or terminals have high resistance.  Make sure the terminals are tight and cycle the master switch on and off many times to wear away corrosion.

_________________
Joe Gores

erich weaver

Joined: 16 Jun 2016
Posts: 11

Posted: Mon Nov 06, 2017 5:24 pm Post subject: Re: voltage fluctuations

No, when I measure voltage at the regulator end of the wire, but with it disconnected from the regulator, I see the full 13 V.  When I reconnect the wire to the regulator and measure the voltage again at the pin 6 terminal, it drops to 11.9 V.  Measurements were repeated several times to confirm.



Erich

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Nov 06, 2017 5:43 pm Post subject: Re: voltage fluctuations

OK Erich.  That confirms my interpretation.  There is a problem with the master switch or its connections.  If you do not believe me, connect that wire to a test lamp instead of to regulator terminal 6.  The lamp should be as high wattage as possible without blowing the fuse or tripping the breaker.  If the voltage drops at the end of that wire, then there is resistance someplace in the circuit.  If the connections are all good, then replace the master switch.

_________________
Joe Gores

ceengland7(at)gmail.com
Guest

Posted: Mon Nov 06, 2017 6:37 pm Post subject: voltage fluctuations

If his VOM has a 10 amp DC current range, he could just put it in series 

with that wire & check the current going through the regulator.



(I agree that it's probably a bad switch, or crimp, etc.)



On 11/6/2017 7:43 PM, user9253 wrote:

 	  Quote: 	
		   



 OK Erich.  That confirms my interpretation.  There is a problem with the master switch or its connections.  If you do not believe me, connect that wire to a test lamp instead of to regulator terminal 6.  The lamp should be as high wattage as possible without blowing the fuse or tripping the breaker.  If the voltage drops at the end of that wire, then there is resistance someplace in the circuit.  If the connections are all good, then replace the master switch.



 --------

 Joe Gores


	




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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Nov 07, 2017 7:20 am Post subject: voltage fluctuations

At 01:44 PM 11/6/2017, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "erich weaver" <erich.weaver(at)aecom.com>



 I have my RV-7A wired per Z-13/8.  I sometimes observe rapidly fluctuating voltage, varying from approximately 13.0 to 14.0 V, as indicated on my EFIS display.  I figured it was just a loose connection at the EFIS, but I hooked up a voltage meter to the battery terminals and ran the engine and observed similar occasional fluctuations, so the problem lies elsewhere. 	


   I am presuming that this is a new condition . . . that

   you've enjoyed some period of normal operations from

   your alternator system.



   What was the voltage when the system was operating normally?

   The legacy choice of set point for lead-acid systems and

   RG batteries if 14.2 to 14.6V



  	  Quote: 	
		    I then tested voltage at pin 6 on my B&C LRC voltage regulator with the engine off and the  master on, and observed a voltage of about 11.9 V.  However, when I remove the wire from my master switch that feeds pin 6 and test voltage on it, I get the expected 13 V.  The voltage drop is only observed after connecting the wire to the voltage regulator.  B&C specs say the voltage drop should be 0.2V or less.  Is my regulator bad and is this the cause of my voltage fluctuations? 	


    Voltage drop in pin 6 power generally

    don't cause large excursions of bus voltage.

    This is power pin for field current . . .

    not bus voltage sensing.



    As an experiment, disconnect pins 6 and 3

    from ship's wiring. Jumper 6 and 3 together.

    Put a 10A fuse in a temporary line from

    3/6 to the alternator B-terminal.



    Start the engine. Alternator will come on

    line immediately. Observe bus voltage. If

    not 14.2 minimum, adjust LR regulator to

    achieve 14.4 volts.



    Turn on system loads and observe that

    bus voltage is still 14.0 to 14.4 volts.



    This will confirm/deny proper opreation of

    your B&C equipment.



 

   Bob . . .

erich weaver

Joined: 16 Jun 2016
Posts: 11

Posted: Tue Nov 07, 2017 2:55 pm Post subject: Re: voltage fluctuations

yes, I didnt see such fluctuations in the past, at least not as large.  Ive noticed it recently because my EFIS warns me when voltage falls to 13 V.



I dont understand the logic behind the earlier posts indicating that there is likely a problem in the master switch or the the wire from it to pin 6 of the regulator.  Not saying thats wrong, just that I dont understand it.  The wire clearly is not at fault because I see no voltage drop from one end to the other when disconnected from the regulator; voltage drop only occurs when connected to the regulator.



As currently wired, there is a jumper between pin 3 and 6.  During past "normal" operation I believe my indicated operating voltage was somewhere in the 13.5-14.0 range.  I attributed the slightly low values to diodes within the Grand Rapids EFIS and/or EIS that dropped the voltage slightly.  Not entirely sure that is correct however.



I will try Bob's suggestion of the temporary wire to the alternator B-terminal and monitoring buss voltage this weekend and report back.



thanks guys



Erich

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Tue Nov 07, 2017 4:49 pm Post subject: Re: voltage fluctuations

The logic is based on ohms law.  E=IR  In other words, voltage drop is equal to current times resistance.  There should be very little resistance between the battery and terminal 6 of the voltage regulator.  Let's call it zero ohms.  So the voltage drop is equal to current times zero, or zero voltage drop.  Since the voltage drop is actually 1 volt or more, then the resistance is not zero between the battery and terminal 6.  The most likely places to find resistance is the master switch or its terminals or else a fuse or circuit breaker, whatever is in the circuit.  The easiest way to find the voltage drop (and resistance) is with a voltmeter.  Of course the voltage regulator needs to be turned on during this test.  Connect the black meter lead to terminal 6 and probe the circuit with the red meter lead backwards towards the battery.  If the voltmeter displays more than a couple of tenths of a volt, then the problem has been located.

_________________
Joe Gores

ceengland7(at)gmail.com
Guest

Posted: Tue Nov 07, 2017 5:12 pm Post subject: voltage fluctuations

The logic is that if there's high series resistance (flaky contacts in a 

switch, bad crimp, corrosion in a joint, etc), then there will be 

voltage drop across that resistance when a load is applied. The amount 

of the voltage drop will depend on the current demanded by the load. 

When the load is removed completely (wire disconnected from the load), 

there will be no voltage drop across the resistance.



Here's another check you can make for high resistance in that circuit: 

While the system is on and operating, use your voltmeter to measure 

between the a/c main bus and pin 6 of the regulator. You should measure 

near zero volts. If the measurement is anything higher than a tenth of a 

volt or so, you've got high resistance somewhere between the supply and 

the regulator.



On 11/7/2017 4:55 PM, erich weaver wrote:

 	  Quote: 	
		   



 yes, I didnt see such fluctuations in the past, at least not as large.  Ive noticed it recently because my EFIS warns me when voltage falls to 13 V.



 I dont understand the logic behind the earlier posts indicating that there is likely a problem in the master switch or the the wire from it to pin 6 of the regulator.  Not saying thats wrong, just that I dont understand it.  The wire clearly is not at fault because I see no voltage drop from one end to the other when disconnected from the regulator; voltage drop only occurs when connected to the regulator.



 As currently wired, there is a jumper between pin 3 and 6.  During past "normal" operation I believe my indicated operating voltage was somewhere in the 13.5-14.0 range.  I attributed the slightly low values to diodes within the Grand Rapids EFIS and/or EIS that dropped the voltage slightly.  Not entirely sure that is correct however.



 I will try Bob's suggestion of the temporary wire to the alternator B-terminal and monitoring buss voltage this weekend and report back.



 thanks guys



 Erich




	




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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Nov 07, 2017 6:14 pm Post subject: voltage fluctuations

 	  Quote: 	
		  As currently wired, there is a jumper between pin 3 and 6. 	


   Aha!  You really want to consider running separate

   wires for Field supply (pin 6) and bus sense (Pin 3).

   Separate power and sense paths are essential for meeting

   the regulator's design goals. Furhter, if you trip the

   ov system in the regulator with 3 tied to 6, you loose

   low voltage warning.



  	  Quote: 	
		    During past "normal" operation I believe my indicated operating voltage was somewhere in the 13.5-14.0 range.  I attributed the slightly low values to diodes within the Grand Rapids EFIS and/or EIS that dropped the voltage slightly.  Not entirely sure that is correct however. 	


   Are you running an e-bus? Is the EFIS on the main bus or e-bus?

   The e-bus normal operating voltage is 0.5 to 0.7 volts LOWER than

   the main bus so perhaps your EFIS does not speak with forked tongue.



  	  Quote: 	
		  I will try Bob's suggestion of the temporary wire to the alternator B-terminal and monitoring buss voltage this weekend and report back. 	


   Okay, that's MAIN bus voltage, not E-BUS



 

   Bob . . .

erich weaver

Joined: 16 Jun 2016
Posts: 11

Posted: Tue Nov 07, 2017 10:19 pm Post subject: Re: voltage fluctuations

Ok, will revise wiring to eliminate the pin 3 to pin 6 jumper.  Did the wiring back in 2007 or so, and don't remember my reasoning for using the jumper, but I didn't make deviations from B&C instructions on a whim. Not important now.



The EFIS is powered from the e-bus, which I realize now will have a slight voltage drop due to the diode, so I should expect somewhere around 13.7 to 14 V at the buss with engine running.  Still not sure if there would be additional voltage drop from a diode internal to the EFIS.  



Thanks 

E.

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Nov 08, 2017 7:23 am Post subject: voltage fluctuations

At 12:19 AM 11/8/2017, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "erich weaver" <erich.weaver(at)aecom.com>



 Ok, will revise wiring to eliminate the pin 3 to pin 6 jumper.  Did the wiring back in 2007 or so, and don't remember my reasoning for using the jumper, but I didn't make deviations from B&C instructions on a whim. Not important now. 	


   Jumpering 3/6 together will allow the LR3

   to emulate a 3-wire, 'ford' regulator . . .

   which is not necessarily bad . . . but it

   fails to exploit a design feature of the

   LR series regulators that improves regulation

   performance -AND- wards off the 'galloping

   ammeter' syndrome.



  	  Quote: 	
		  The EFIS is powered from the e-bus, which I realize now will have a slight voltage drop due to the diode, so I should expect somewhere around 13.7 to 14 V at the buss with engine running.  Still not sure if there would be additional voltage drop from a diode internal to the EFIS.  	


   No, they wouldn't do that. The bus voltage sample

   to the EFIS will be a straight pipe line from

   sample point to the analog/digital converter.

   But unless there is a separate input pin labeled

   "bus sense" or similar, then the EFIS has no

   choice but to monitor and display the voltage

   applied to the system power pin. 



   In this instance, powering from the e-bus would

   produced an expected, normal voltage somewhat

   lower than main bus . . . not a big deal 'cause

   you KNOW what the drop is.



   As part of the experiment, you can CLOSE the

   alternate feed switch for the E-Bus which

   would bypass the normal feed path diode.



   The voltage drops you observe on the field supply

   are a separate issue . . . but related to the

   overall investigation. However, when 3/6 are tied

   together, then a voltage drop on that line would

   fool the LR3 into believing that the bus voltage is

   LOW whereupon the regulator would BOOST the

   bus, not depress it.



   So there are things we still don't know/understand

   about your observations. Let's confirm integrity

   of the regulator/alternator hardware first.

   



 

   Bob . . .

erich weaver

Joined: 16 Jun 2016
Posts: 11

Posted: Mon Nov 20, 2017 1:20 pm Post subject: Re: voltage fluctuations

I was able to work on this last weekend and found that there was indeed some voltage loss between main bus and master switch.  Got that taken care of, got rid of the jumper between pins 3 and 6 on voltage regulator and added a dedicated bus voltage sense wire, and then monitored voltage at a number of locations with the engine running using my trusty Radio Shack multimeter:  14.08 V at battery; 14.06 at battery bus, 14.05 at main bus, and 13.31 at e-bus that is fed through a diode.  With the e-bus alternate feed switch turned on, e-bus voltage jumps to 13.96.  Voltage readings are now steady at the battery and bus locations.



EIS and two EFIS screen voltage values are only indicated in tenths of volts on the screens, and these values seem to fluctuate by 0.1 or 0.2 V; not sure why that is, but perhaps that isnt really a concern.



EIS (fed from e-bus) = 13.5 V

pilot EFIS, primary power source (fed from e-bus) 13.4 V

pilot EFIS, secondary power source (fed from main bus & TCW power stabilizer  =13.8 V.  So looks like my intended secondary power source for covering engine-start brown-outs is actually serving as my primary power source due to its higher voltage.



Copilot EFIS, primary power source (fed from e-bus) = 13.2 V (a bit low)

There is no secondary power source connected for the copilot EFIS.



So, all good overall, although thinking I should adjust the voltage regulator until I get 14.2 V at the battery so that it recharges a  bit faster.



Thanks for the assistance guys.  



Erich

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Nov 20, 2017 3:23 pm Post subject: Re: voltage fluctuations

Good going Erich.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Nov 21, 2017 9:37 am Post subject: voltage fluctuations

I was able to work on this last weekend and found that there was indeed some voltage loss between main bus and master switch.  Got that taken care of, got rid of the jumper between pins 3 and 6 on voltage regulator and added a dedicated bus voltage sense wire, and then monitored voltage at a number of locations with the engine running using my trusty Radio Shack multimeter:  14.08 V at battery; 14.06 at battery bus, 14.05 at main bus, and 13.31 at e-bus that is fed through a diode.  With the e-bus alternate feed switch turned on, e-bus voltage jumps to 13.96.  Voltage readings are now steady at the battery and bus locations.



   Very good. This validates our hope that there

   are no problems with the hardware.



 EIS and two EFIS screen voltage values are only indicated in tenths of volts on the screens, and these values seem to fluctuate by 0.1 or 0.2 V; not sure why that is, but perhaps that isnt really a concern.



   ALL digital dispalys are subject to some

   degree of 'bobble' in the least significant

   digit. Which has to do with the manner in which

   DC votlages are filtered, sampled and converted

   to binary values for furhter processing. Then

   there are the effects of naturally occuring

   variations in the bus votlage itself.



   Unless the designer has gone to the trouble to

   oversample, do running averaging or perhaps

   convert to more digits and toss out the last

   one . . . you're going to see this bobble.



   As much as plus or minus two counts in the

   least significant digit is of no concern.

   Back in the days when the best voltmeters 

   installed might look like this:



 

   

  



 

   You couldn't see the fluctuations . . . but they

   were still there.



 

 EIS (fed from e-bus) = 13.5 V

 pilot EFIS, primary power source (fed from e-bus) 13.4 V

 pilot EFIS, secondary power source (fed from main bus & TCW power stabilizer  =13.8 V.  So looks like my intended secondary power source for covering engine-start brown-outs is actually serving as my primary power source due to its higher voltage.



 Copilot EFIS, primary power source (fed from e-bus) = 13.2 V (a bit low)

 There is no secondary power source connected for the copilot EFIS.



 So, all good overall, although thinking I should adjust the voltage regulator until I get 14.2 V at the battery so that it recharges a  bit faster.

  

    14.4 volts is not out of line. Reading from the

    Hawkjer-Enersys manual on Odyssey batteries:



 [img]cid:.0[/img]



    It sounds like the power management philosophy for

    the 'secondary power sources' could use some

    refinement. Without detailed schematics describing

    just how electrons are being herded through the

    system, it's not possible to offer a detailed

    assessment.



    The take-away from this exercise was predicted

    by one of my heros:



 "When you can measure what you are speaking about, and

 express it in numbers, you know something about it; but

 when you cannot measure it, when you cannot express it in

 numbers, your knowledge is of a meagre and unsatisfactory

 kind; it may be the beginning of knowledge, but you have

 scarcely in your thoughts advanced to the stage of science,

 whatever the matter may be." -Lord Kelvin- 1864 



 



 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Nov 21, 2017 12:50 pm Post subject: voltage fluctuations

I almost forgot . . .



  	  Quote: 	
		  So, all good overall, although thinking I should adjust the voltage regulator until I get 14.2 V at the battery so that it recharges a  bit faster.

  

    14.4 volts is not out of line . . . 	


 When setting your voltage regulator, adjust

 for the desired magnitude AT THE REGULATOR'S

 SENSE POINT.



 In this case, at the main bus. Adjusting

 for voltage at the battery does not account

 for inevitable VARIATIONS in voltage drop

 between the sense point and the battery. If

 the battery is taking a charge, current through

 the charge path DEPRESSES voltage at the

 battery . . . which approaches zero as the battery

 charges.



 A fully charged battery's terminal voltage and

 the sense point at the bus will be essentially

 equal. So while cranking on the little screw, measure

 from the bus.



 

 

   Bob . . .

erich weaver

Joined: 16 Jun 2016
Posts: 11

Posted: Thu Nov 23, 2017 4:51 pm Post subject: Re: voltage fluctuations

Got it, thanks Bob.

Reading this forum and the Connection gave me the courage to wire my plane myself, something I’ve never regretted.



Erich

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