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Chronically low voltage

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Randy.McFarland(at)novell
Guest

Posted: Wed Jan 24, 2007 10:54 am Post subject: Chronically low voltage

I was really hoping not to have to ask this question, but I'm at the end of

my electron understanding, so...



I have a 2 year old PC680 Battery and a 60amp IR alternator on my 7A. With

Avionics on my Buss voltage is 12.6 or greater as shown on my Engine

montitor. When I add Nav and Strobes I get a fluctuating 12.4 to 12.6 volts

which is just enought to trigger the Lo/Ov module light. Drives me crazy

after awhile. When I add either Landing or Taxi light to the load I get

steady Lo voltage light. Alternator seems to be putting out up to 28 +/-

amps as needed so my guess is that I have not maintained the battery very

well during the 18 months or so it sat in the airplane while installing /

testing the avionics. 



What sequence of tests would help me narrow the reasons this may be

happening?



Randy

mprather(at)spro.net
Guest

Posted: Wed Jan 24, 2007 12:21 pm Post subject: Chronically low voltage

Hello Randy,



When you observe the problem, is the engine running and if so, at what

RPM?  If it's at idle, this might be normal behavior.  If the engine is

turned off, what you describe is normal.



If the battery has enough energy to start the engine fairly well, I'd

guess the battery isn't dragging the buss down - the battery is

essentially healthy though maybe having reduced capacity.



How did you deduce that the alternator is putting out "28 +/- amps"?  It

seems theoretically possible that the internal regulator has a problem -

regulated voltage too low.  Or maybe a diode in the rectifier has gone

bad.

Matt-



 	  Quote: 	
		   

 <Randy.McFarland(at)novellus.com>

 I was really hoping not to have to ask this question, but I'm at the end

 of

 my electron understanding, so...



 I have a 2 year old PC680 Battery and a 60amp IR alternator on my 7A. With

 Avionics on my Buss voltage is 12.6 or greater as shown on my Engine

 montitor. When I add Nav and Strobes I get a fluctuating 12.4 to 12.6

 volts

 which is just enought to trigger the Lo/Ov module light. Drives me crazy

 after awhile. When I add either Landing or Taxi light to the load I get

 steady Lo voltage light. Alternator seems to be putting out up to 28 +/-

 amps as needed so my guess is that I have not maintained the battery very

 well during the 18 months or so it sat in the airplane while installing /

 testing the avionics.



 What sequence of tests would help me narrow the reasons this may be

 happening?



 Randy

N1DeltaWhiskey(at)comcast
Guest

Posted: Wed Jan 24, 2007 12:28 pm Post subject: Chronically low voltage

Randy,



You left out a lot of info.  Is your voltage reading with the engine 

(alternator) running or not.  IF the alternator is not running, why are you 

concerned?  Do you normally run those lights with the alternator off?  While 

running, your alternator should provide around 14v, so the battery does not 

come into question until you approach/exceed the alternator output.  With 

the alternator running, do you have the same problem.



If this is with alternator off, why are your concerned about it?  If you 

were flying at night and lost the alternator, you would want to switch off 

the lights anyway to preserve battery until you can make a field to land as 

Bob has suggested many times.



But to your question.  E=IR, or voltage = current times resistance.  Look at 

your circuits - they form a loop from the minus side of the battery to the 

plus side.  Lights, switches, connectors, connections, wire size, and the 

battery itself are all possible points of resistance around the loop.



Check the battery first, with no load, by measuring the voltage at the 

battery terminals; then turn on all your loads and repeat the reading - what 

do you get?  You can calculate the resistance of the battery by R=E/I.  This 

should be quite small, and should be available from battery performance 

charts.  Now you know the equivalent resistance of the battery.  (Do you 

know the load current, or just estimating?)



To calculate other resistances, measure from BAT ground to various points 

along the circuit. The resistance can be determined by the delta-V between 

the points.  Compare the resistance in the wire to theoretical charts to see 

if there is something going on there.  There will be some resistance across 

connectors/connections, but this should be almost none existent, but you can 

check one side to the other.



If you really have a problem, this process should be able to identify where 

it is at.



Regards, and good hunting,



Doug Windhorn





---

Randy.McFarland(at)novell
Guest

Posted: Wed Jan 24, 2007 1:17 pm Post subject: Chronically low voltage

Sorry, the Lo V status occurs at cruise power and rpm.

The battery seems to start the engine ok, but I think with electronic

ignition it seems to start much easier than with only the Mag.

I have a Grand Rapids Engine Monitor that shows the current output of the

alternator. This is the 60amp Nippon Denso alternator that has gotten so

much discussion recently. My original 60a alternator failed witnin 20 hours

of operation, so this is a replacement alternator.

Randy



--

john(at)ballofshame.com
Guest

Posted: Wed Jan 24, 2007 1:34 pm Post subject: Chronically low voltage

I'm gonna go out on a limb and say that the 12.4 to 12.6 volts isn't a

real reading.  Your battery would practically never charge.  Personally,

first thing I would do is whip out a VOM and sanity check the readings. 

Maybe they're correct but it seems weird.  At least rule that out first.



-John

www.ballofshame.com

[quote] 

 <Randy.McFarland(at)novellus.com>



 Sorry, the Lo V status occurs at cruise power and rpm.

 The battery seems to start the engine ok, but I think with electronic

 ignition it seems to start much easier than with only the Mag.

 I have a Grand Rapids Engine Monitor that shows the current output of the

 alternator. This is the 60amp Nippon Denso alternator that has gotten so

 much discussion recently. My original 60a alternator failed witnin 20

 hours

 of operation, so this is a replacement alternator.

 Randy



 --

Erich_Weaver(at)URSCorp.c
Guest

Posted: Wed Jan 24, 2007 2:30 pm Post subject: Chronically low voltage

Randy:



I note that you refer to both a low/over voltage module and a GRT Engine

Monitor  in your previous posts.  These seem somewhat redundant since the

EIS indicates  voltage and warns you if you are under/over your designated

limits - no separate module is necessary.  If the EIS is NOT warning of any

limit exceedance, perhaps something is screwy with the voltage module?

Perhaps Im not understanding this completely.



regards

Erich Weaver

nuckollsr(at)cox.net
Guest

Posted: Wed Jan 24, 2007 7:44 pm Post subject: Chronically low voltage

At 10:52 AM 1/24/2007 -0800, you wrote:



 	  Quote: 	
		  

<Randy.McFarland(at)novellus.com>

I was really hoping not to have to ask this question, but I'm at the end of

my electron understanding, so...



I have a 2 year old PC680 Battery and a 60amp IR alternator on my 7A. With

Avionics on my Buss voltage is 12.6 or greater as shown on my Engine

montitor. When I add Nav and Strobes I get a fluctuating 12.4 to 12.6 volts

which is just enought to trigger the Lo/Ov module light. Drives me crazy

after awhile. When I add either Landing or Taxi light to the load I get

steady Lo voltage light. Alternator seems to be putting out up to 28 +/-

amps as needed so my guess is that I have not maintained the battery very

well during the 18 months or so it sat in the airplane while installing /

testing the avionics.



What sequence of tests would help me narrow the reasons this may be

happening?


	


    What architecture are you using? How do you measure alternator

    output amps?  With voltage readings like that, it sounds like

    the alternator is not even coming on line. It the alternator is

    working, 14.2 to 14.6 is more normal.



    Bob . . .

nuckollsr(at)cox.net
Guest

Posted: Wed Jan 24, 2007 7:48 pm Post subject: Chronically low voltage

At 01:16 PM 1/24/2007 -0800, you wrote:



 	  Quote: 	
		  

<Randy.McFarland(at)novellus.com>



Sorry, the Lo V status occurs at cruise power and rpm.

The battery seems to start the engine ok, but I think with electronic

ignition it seems to start much easier than with only the Mag.

I have a Grand Rapids Engine Monitor that shows the current output of the

alternator. This is the 60amp Nippon Denso alternator that has gotten so

much discussion recently. My original 60a alternator failed witnin 20 hours

of operation, so this is a replacement alternator.

Randy


	


    Put a battery maintainer or other smart charger on

    the battery and wait until its green light comes on

    stating that the battery is fully charged.



    Start the engine but leave EVERYTHING electrical

    turned off except battery and alternator. The engine

    monitor should IMMEDIATELY show 14.2 or more volts

    and alternator output current should peak up but

    come down pretty quickly . . . probably under 10

    amps in a minute or so.



    If you don't have 14 volts but do have some measurable

    output current, the alternator is bad.



    Bob . . .

khorton01(at)rogers.com
Guest

Posted: Thu Jan 25, 2007 2:42 am Post subject: Chronically low voltage

On 24 Jan 2007, at 22:48, Robert L. Nuckolls, III wrote:



 	  Quote: 	
		   

 <nuckollsr(at)cox.net>



    Start the engine but leave EVERYTHING electrical

    turned off except battery and alternator. The engine

    monitor should IMMEDIATELY show 14.2 or more volts

    and alternator output current should peak up but

    come down pretty quickly . . . probably under 10

    amps in a minute or so.



    If you don't have 14 volts but do have some measurable

    output current, the alternator is bad.


	


This appears to assume that the engine monitor is on a bus that sees  

the full alternator voltage.  If the engine monitor is on a bus that  

gets its power via a conventional diode, then you can subtract about  

0.6 volts from the above values.



Kevin Horton         RV-8 (finishing kit)

Ottawa, Canada

http://www.kilohotel.com/rv8

nuckollsr(at)cox.net
Guest

Posted: Thu Jan 25, 2007 4:35 am Post subject: Chronically low voltage

At 05:40 AM 1/25/2007 -0500, you wrote:



 	  Quote: 	
		  



On 24 Jan 2007, at 22:48, Robert L. Nuckolls, III wrote:



>

><nuckollsr(at)cox.net>

>

>    Start the engine but leave EVERYTHING electrical

>    turned off except battery and alternator. The engine

>    monitor should IMMEDIATELY show 14.2 or more volts

>    and alternator output current should peak up but

>    come down pretty quickly . . . probably under 10

>    amps in a minute or so.

>

>    If you don't have 14 volts but do have some measurable

>    output current, the alternator is bad.



This appears to assume that the engine monitor is on a bus that sees

the full alternator voltage.  If the engine monitor is on a bus that

gets its power via a conventional diode, then you can subtract about

0.6 volts from the above values.


	


   Good put sir! Thanks.



   Bob . . .

Randy.McFarland(at)novell
Guest

Posted: Thu Jan 25, 2007 8:37 am Post subject: Chronically low voltage

Thanks all. Off to the hangar to measure / test as suggested. Will report

back the results.

R



--

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