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Charging system failure

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dreel(at)cox.net
Guest

Posted: Wed Apr 26, 2006 11:50 am Post subject: Charging system failure

I was flying along, 7.8 hours total so far, minding my own business, =

getting ready to do some climb testing when a blinking red light alerted =

me to low voltage.  I switched the master off and the essential bus feed =

on ( wrong order by the way) & was relieved to see the system voltage =

perk up to 12.4v.  I returned to Manassas without further incident but =

am now looking for a way to make the charging system more reliable.  =

Here's what I found on the ground:



The alternator field coil main fuse, 7.5amp, was blown.  This feeds a 5 =

amp circuit breaker which did not trip.  Hypothesis: the overvoltage =

crowbar shorted the field coil circuit to ground.  To test this I =

replaced the fuse, pulled the breaker, started the engine & set to =

1,000rpm, and then watched the voltmeter as I reset the breaker.  =

Voltage gradually increased from the 11.7volts battery voltage to =

14.3volts that I am used to seeing in about 10 seconds.  So, the VR166 =

external voltage regulator and Vans 35 amp alternator were working =

again.



Now I'm back home looking at my Z12 wiring diagram & I'm realizing a =

couple of things.  I used 18awg wire to feed the circuit breaker so I =

can increase that feedline fuse to 10amps.  Hopefully, this will let the =

circuit breaker trip before the fuse blows.  That would make an =

overvoltage event a lot more tolerable as I could try a reset in the =

air.  I see that Z-23 uses a 22awg fuse link instead of a fuse to feed =

the field coil circuit.  Would that be even less likely to blow than a =

10 amp buss fuse?



Second, my engine monitor is connected to the essential bus so it =

routinely shows about a 1/2 volt difference between voltage when the =

master is on and feeding it through the isolation diodes and voltage =

when the essential bus feed is on.  That means my charging voltage is =

probably 14.8volts.  Do you think that is high?  Should I be thinking of =

replacing the VR166 voltage regulator with one I can set lower?  Might =

reduce overvoltage event frequency & put less stress on the Panasonic =

LC-RD1217P battery?  I'll take the voltmeter and measure the actual =

charging voltage next time out.



Lastly, I wonder if I need to change the crowbar module.  I've heard a =

lot about nusiance trips.  The unit I have came pre-assembled from B&C & =

encased in black shrink tubing.  It was purchased 2-21-2003.  Is it =

likely to be one of the questionable ones I have heard about?  What's =

the likely voltage required to trip?  I seem to remember 16volts.  Not =

far above 14.8volts.



Anyway, I'll increase the fuse size, measure actual charging voltage, & =

wait for any clarification Bob or others on the list can provide =

relative to the other questions.



Dave Reel - RV8A

fvalarm(at)rapidnet.net
Guest

Posted: Wed Apr 26, 2006 1:16 pm Post subject: Charging system failure

Dave,



I'm sure you will get some help here with your situation from other much

more qualified than I.  I am trying to follow your description and are

wondering what the use of = is.  Maybe I'm missing something here but what

does = mean?



Bevan 



--

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Wed Apr 26, 2006 2:55 pm Post subject: Charging system failure

On Apr 26, 2006, at 12:46 PM, DAVID REEL wrote:

 	  Quote: 	
		  

 The alternator field coil main fuse, 7.5amp, was blown.  This feeds  

 a 5 =

 amp circuit breaker which did not trip.


	


Well, of course the fuse blew first. Why do you have a fuse and a  

breaker? You don't need the fuse. But if you want redundant  

protection then the fusible link is the right answer.



So, lose the fuse, install a fusible link, and go fly again.

Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

 Antoine de Saint-Exupry

_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

rv8ch

Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

Posted: Wed Apr 26, 2006 9:05 pm Post subject: Charging system failure

B Tomm wrote:

 > I'm sure you will get some help here with your situation

 > from other much more qualified than I.  I am trying to

 > follow your description and are wondering what the

 > use of = is.  Maybe I'm missing something here but what

 > does = mean?



Hi Bevan,



The = signs at the end of each line in his note are

artifacts from his E-mail client.  He has it set to

send HTML, and the Matronics server didn't strip out

all the HTML properly.  HTML is best left to web

pages, and not used in E-mail.



Mickey

-- 

Mickey Coggins

http://www.rv8.ch/

#82007 finishing

do not archive

_________________
Mickey Coggins
http://www.rv8.ch/

john(at)ballofshame.com
Guest

Posted: Wed Apr 26, 2006 10:11 pm Post subject: Charging system failure

Okay, I'll bite.  My experience with fuses vs. circuit breakers is that in general it's a race 

to see which one will blow first....in the case of a short anyhow (i.e. crowbar tripping in 

this case).  I agree the fuse is unnescessary (or the CB...either one), but what am I 

missing that would make it likely for the fuse to blow first?



-John Coloccia

www.ballofshame.com

On 26 Apr 2006 at 21:27, Brian Lloyd wrote:

 

 	  Quote: 	
		   Well, of course the fuse blew first. Why do you have a fuse and a  

 breaker? You don't need the fuse. But if you want redundant  

 protection then the fusible link is the right answer.

 

 So, lose the fuse, install a fusible link, and go fly again.

 

 

 Brian Lloyd                         361 Catterline Way

 brian-yak AT lloyd DOT com          Folsom, CA 95630

 +1.916.367.2131 (voice)             +1.270.912.0788 (fax)

 

 I fly because it releases my mind from the tyranny of petty things . . .

  Antoine de Saint-Exupry

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Thu Apr 27, 2006 6:35 am Post subject: Charging system failure

On Apr 26, 2006, at 11:03 PM, john(at)ballofshame.com wrote:



 	  Quote: 	
		   



 Okay, I'll bite.  My experience with fuses vs. circuit breakers is  

 that in general it's a race

 to see which one will blow first....in the case of a short anyhow  

 (i.e. crowbar tripping in

 this case).  I agree the fuse is unnescessary (or the CB...either  

 one), but what am I

 missing that would make it likely for the fuse to blow first?


	


It depends on the kind of breaker. Magnetic breakers are almost as  

fast as fuses but thermal breakers like the ones we have in our  

airplanes are *much* slower. The thermal mass of the fusible link in  

the fuse is a lot less than the thermal mass in the circuit breaker  

so it will reach its melting point much more quickly.



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

 Antoine de Saint-Exupry

nuckollsr(at)cox.net
Guest

Posted: Thu Apr 27, 2006 7:05 am Post subject: Charging system failure

Agreed. The 14.8 V regulation setpoint is a bit

    high too. How long has this system been in place?

    The design deficiency for nuisance tripping issues

    with B&C OVM were resolved years ago.



    Know too that with an external regulator that shares

    field supply wire with the voltage sense wire, there

    is a potential for regulation instability. This is why

    modern regulator philosophies use a separate remote

    voltage sense lead (like the B&C regulators).



    The VR-166 style regulator isn't inherently evil

    because of the common power/sense lead but it does

    offer another avenue of investigation as to why

    your system behaved as it did.



    The fuse needs to come out and the fusible link

    needs to go in. Also, tell us where your regulator

    is mounted and what size wires run the pathway between

    bus and the regulator's "A" and "S" terminals.



    Bob . . .





 	  Quote: 	
		  Well, of course the fuse blew first. Why do you have a fuse and a

breaker? You don't need the fuse. But if you want redundant

protection then the fusible link is the right answer.



So, lose the fuse, install a fusible link, and go fly again.

Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

  Antoine de Saint-Exupry

--

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        Bob . . .

      ---------------------------------------------------------

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

      ---------------------------------------------------------

john(at)ballofshame.com
Guest

Posted: Thu Apr 27, 2006 6:37 pm Post subject: Charging system failure

Yes, good point.  I was definitely thinking along the lines of magnetic 

breakers.



-john



On 27 Apr 2006 at 7:32, Brian Lloyd wrote:



 	  Quote: 	
		   

 

 On Apr 26, 2006, at 11:03 PM, john(at)ballofshame.com wrote:

 

 > 

 >

 > Okay, I'll bite.  My experience with fuses vs. circuit breakers is  

 > that in general it's a race

 > to see which one will blow first....in the case of a short anyhow  

 > (i.e. crowbar tripping in

 > this case).  I agree the fuse is unnescessary (or the CB...either  

 > one), but what am I

 > missing that would make it likely for the fuse to blow first?

 

 It depends on the kind of breaker. Magnetic breakers are almost as  

 fast as fuses but thermal breakers like the ones we have in our  

 airplanes are *much* slower. The thermal mass of the fusible link in  

 the fuse is a lot less than the thermal mass in the circuit breaker  

 so it will reach its melting point much more quickly.

 

 Brian Lloyd                         361 Catterline Way

 brian-yak AT lloyd DOT com          Folsom, CA 95630

 +1.916.367.2131 (voice)             +1.270.912.0788 (fax)

 

 I fly because it releases my mind from the tyranny of petty things . . .

  Antoine de Saint-Exupry

dreel(at)cox.net
Guest

Posted: Thu Apr 27, 2006 6:57 pm Post subject: Charging system failure

I'm back from the airport & have some further info about this problem.



With a digital voltmeter across the battery, I read charging voltage of 15.3

volts.  It was very unstable, jittering around a lot by about +/- a half a

volt.  Replaced the VR166 with a NAPA VR428 and now the charging voltage is

pretty stable at 14.8.  Jitters are gone.  The Panasonic battery spec sheet

calls for charging voltages from 14.5 to 14.9.  I'm working on a fusible

link replacement for the fuse but I'm still curious whether a 10 amp buss

fuse is likely to blow before a 5 amp circuit breaker.  Comparing meter

readings, the drop through the isolation diode amounts to 1 volt, not the .5

volts I previously thought as the engine monitor now reads 13.8v.



To answer other questions that came up, the wire size is 18awg from main bus

to circuit breaker, 20awg everywhere else.  The system worked for 7.8 engine

hours til it tripped the crowbar which I now think worked properly.  The

regulator is mounted on the upper right side of the firewall in the engine

compartment & depends on the firewall for it's ground return path.



Dave Reel

klehman(at)albedo.net
Guest

Posted: Fri Apr 28, 2006 2:52 am Post subject: Charging system failure

DAVID REEL wrote:



 	  Quote: 	
		  



I'm back from the airport & have some further info about this problem.



With a digital voltmeter across the battery, I read charging voltage of 15.3

volts.  It was very unstable, jittering around a lot by about +/- a half a

volt.  Replaced the VR166 with a NAPA VR428 and now the charging voltage is

pretty stable at 14.8.  Jitters are gone.  The Panasonic battery spec sheet

calls for charging voltages from 14.5 to 14.9.  I'm working on a fusible

link replacement for the fuse but I'm still curious whether a 10 amp buss

fuse is likely to blow before a 5 amp circuit breaker.



Yes Dave.  I'd suspect even a 20 amp fuse would likely blow before the 
	


breaker.  These C/B's are much much slower than these fuses even though 

there might be way over 20 amps flowing.  



I got away with a 10 amp fuse feeding a 2.5 (two point five) amp breaker 

with an internal VR alternator but that won't work for your situation. 

 Especially at cool temperatures, I'd consider 14.8 volts to be normal. 

And I agree with your diagnosis that the OVM probably worked properly. 

My OVM are set to trip at 16.3 volts.



Ken



 	  Quote: 	
		    Comparing meter

readings, the drop through the isolation diode amounts to 1 volt, not the .5

volts I previously thought as the engine monitor now reads 13.8v.



To answer other questions that came up, the wire size is 18awg from main bus

to circuit breaker, 20awg everywhere else.  The system worked for 7.8 engine

hours til it tripped the crowbar which I now think worked properly.  The

regulator is mounted on the upper right side of the firewall in the engine

compartment & depends on the firewall for it's ground return path.



Dave Reel

william.p.dube(at)noaa.go
Guest

Posted: Mon May 01, 2006 10:15 am Post subject: Charging system failure

There are all kinds of fuses and circuit breakers. Each has a different 

time delay. Some are designed to open very quickly at just above the 

rated current, others will delay for a very long time before opening. 

There are slow blow style fuses and breakers. There are fast blow fuses 

and circuit breakers.

    Fuses are not precision devices. The fuse holder plays a significant 

role too. If you load a fuse continuously for much more than about 70% 

its rating, it may well open.

    The 15.3 volts is quite high. Your electronics can be damaged at 

this high voltage. The battery won't much care for continuous operation 

at this voltage either.

    Bill Dube'

Ken wrote:

 	  Quote: 	

DAVID REEL wrote:

>

>

>I'm back from the airport & have some further info about this problem.

>

>With a digital voltmeter across the battery, I read charging voltage of 15.3

>volts.  It was very unstable, jittering around a lot by about +/- a half a

>volt.  Replaced the VR166 with a NAPA VR428 and now the charging voltage is

>pretty stable at 14.8.  Jitters are gone.  The Panasonic battery spec sheet

>calls for charging voltages from 14.5 to 14.9.  I'm working on a fusible

>link replacement for the fuse but I'm still curious whether a 10 amp buss

>fuse is likely to blow before a 5 amp circuit breaker.

>

>    

>

Yes Dave.  I'd suspect even a 20 amp fuse would likely blow before the 

breaker.  These C/B's are much much slower than these fuses even though 

there might be way over 20 amps flowing.  

I got away with a 10 amp fuse feeding a 2.5 (two point five) amp breaker 

with an internal VR alternator but that won't work for your situation. 

 Especially at cool temperatures, I'd consider 14.8 volts to be normal. 

And I agree with your diagnosis that the OVM probably worked properly. 

My OVM are set to trip at 16.3 volts.

Ken

> Comparing meter

>readings, the drop through the isolation diode amounts to 1 volt, not the .5

>volts I previously thought as the engine monitor now reads 13.8v.

>

>To answer other questions that came up, the wire size is 18awg from main bus

>to circuit breaker, 20awg everywhere else.  The system worked for 7.8 engine

>hours til it tripped the crowbar which I now think worked properly.  The

>regulator is mounted on the upper right side of the firewall in the engine

>compartment & depends on the firewall for it's ground return path.

>

>Dave Reel

> 

>

>    

>

dreel(at)cox.net
Guest

Posted: Thu May 04, 2006 1:51 pm Post subject: Charging system failure

To continue the saga, 45 minutes into my first flight with the new voltage

regulator, I got another overvoltage crowbar event.  A 10 amp fuse blew

before the 5 amp circuit breaker that protects the alternator field circuit.

Back on the ground I replaced the fuse with a 22awg 5" long fuselink made up

from one of Bob's kits.  Then I ran the engine to see what the voltage

regulator was doing.  The starting battery voltage was 12.6.  After a few

minutes idling the buss voltage settled to 14.3 volts.  Pretty steady.  Then

I turned on some loads, my only significant one being the Whelen strobe

lights.  The voltage became unstable, jumping up to 14.6 and back down to

14.3.  I'm thinking this relates to Bob's remark about the unstability of

regulators that use the field circuit to sense bus voltage.  I wonder if

anyone can explain the mechanism for this instability.  In particular, I'm

wondering if, as the battery gets a full charge & stops providing a large

proportion of the load, a varying load such as the strobes could cause it to

burp up to 16 volts or more occasionally?  This regulator seemed to settle

on 14.8 volts when the battery was fully charged.



I've just recieved Van's variable voltage regulator & will be installing

this.  Think I'll set it low, maybe 13.8v, to try and eliminate these

crowbar events.  Certainly, 14.8 volts seems to start overcharging the

battery almost immediately & is way overkill.  Have others used lower

charging voltages successfully?



Dave

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Fri May 05, 2006 6:54 am Post subject: Charging system failure

On May 4, 2006, at 2:44 PM, DAVID REEL wrote:

 	  Quote: 	
		   ...

 I turned on some loads, my only significant one being the Whelen =20

 strobe

 lights.  The voltage became unstable, jumping up to 14.6 and back =20

 down to

 14.3.  I'm thinking this relates to Bob's remark about the =20

 unstability of

 regulators that use the field circuit to sense bus voltage.  I =20

 wonder if

 anyone can explain the mechanism for this instability.  In =20

 particular, I'm

 wondering if, as the battery gets a full charge & stops providing a =20=


	


 	  Quote: 	
		   large

 proportion of the load, a varying load such as the strobes could =20

 cause it to

 burp up to 16 volts or more occasionally?  This regulator seemed to =20=


	


 	  Quote: 	
		   settle

 on 14.8 volts when the battery was fully charged.



 I've just recieved Van's variable voltage regulator & will be =20

 installing

 this.  Think I'll set it low, maybe 13.8v, to try and eliminate these

 crowbar events.  Certainly, 14.8 volts seems to start overcharging the

 battery almost immediately & is way overkill.  Have others used lower

 charging voltages successfully?


	


Dave, I hate to say this but I think you are approaching the problem =20

the wrong way. Frankly, getting a variable VR and putting it in is a =20

band-aid and not a real fix. Of course, this is assuming that your =20

original VR is working properly -- you need to test it.



Frankly, there is no reason for the voltage to wander around much =20

even as you change loads. The fact that you see a relatively high =20

buss voltage of 14.8V worries me too. Can these two symptoms be =20

related? I think so. They can if the VR is not really sensing bus =20

voltage but rather bus voltage after a drop.



Let me address your question about instability and sensing the field =20

current. First, the VR works by increasing alternator field current =20

when it senses a reduction in bus voltage. The logic is simple; if =20

the voltage goes down it is probably because something is drawing =20

more current and therefore we need more output from the alternator. =20

The problem arises because the designers of most VRs figured that, =20

since the VR needed power from the bus in order to drive the field =20

and they needed a wire to the bus to sense the voltage, they could =20

save time, effort, and money by using the same wire to perform both =20

functions. Good idea -- NOT!



The problem is, every wire and connection is a resistor. When you put =20=



more current through it the voltage across it increases too (ohms =20

law). This "voltage drop" makes the voltage at the end of the wire =20

lower than at the beginning of the wire. Now lets think about our =20

alternator system. The VR senses the voltage between the ground and =20

input (bus) terminals on the VR. It does NOT sense bus voltage but =20

rather the voltage AFTER it has traversed the wiring from bus through =20=



the fuse through the breaker and through several intervening =20

connections. Now we put the field current through that wire, =20

typically up to about 3A at high output. That means that the voltage =20

at the input (bus) terminal of the VR is LOWER than the voltage on =20

the bus. The VR doesn't care. It turns on the alternator harder until =20=



the voltage comes up to what it wants to see. This increases field =20

current which increases drop which makes the VR sense a lower voltage =20=



which increases field current which increases drop which makes the VR =20=



sense a lower voltage which increases field current which increases =20

drop which makes the VR sense a lower voltage ...



Do you get the picture? This is the instability Bob was referring to. =20=



This is called positive feedback and can cause the alternator system =20

to eventually break into oscillation (up and down and up and down and =20=



up and down and ...).



Now in a properly designed VR there is a separate wire that senses =20

the voltage. This gets connected to the bus and has little or no =20

current flowing through it as it doesn't have all that field current. =20=



It can proper sense the bus voltage without any drop and therefore =20

does a MUCH better job of keeping the voltage stable. OK, that is the =20=



better way to do it.



Now let's work with what you have and see if we can make it good =20

enough. The first thing to do is to eliminate as many drops as =20

possible. That means you need to get rid of any extra and extraneous =20

connections and devices that drop too much voltage.



Step 1: LOSE THE FRICKING FUSE



That fuse and fuse holder are a serious source of voltage drop when =20

current flows through them. The fuse is a resistor designed to drop =20

current and get hot enough to melt. (So is the breaker but you have =20

to have the breaker.) Add to that the extra connections and the poor =20

connections in the fuse holder to the fuse and you have a serious =20

source of voltage drop. Bad. Bad bad. Bad bad bad. No flight for you!



So, task one is to lose the fuse and use an unbroken piece of 18AWG =20

wire from your bus to your field breaker and then an unbroken piece =20

of 18AWG wire from breaker to the input of your VR. That will =20

minimize any "movement" (voltage change) of the VR input terminal =20

when the VR decides to change the field current.



OK, so you want some protection for your 18AWG wire between the bus =20

and the breaker. If you must have this (frankly, I wouldn't put it =20

in) use a fusible link that is properly soldered and protected.



And you want this lead as close to the positive terminal of the =20

battery as possible. You don't want any more voltage drops to occur =20

between the battery's positive terminal and the input to the VR. This =20=



means you want to move the VR input wire as close to the battery's =20

positive terminal as is humanly possible. This probably means putting =20=



it right at the battery contactor if possible. (I am trying to =20

eliminate as many drops as possible here folks.) You know that point =20

on the battery contactor where the alternator 'B' lead connects and =20

where your bus distribution wire connects? Yeah, right there.



Now you have minimized any drop between the battery and the VR.



But there is also another source of change in the voltage sensed by =20

the VR. That is the ground wiring to the VR. Remember that the VR =20

senses the voltage between its input terminal and ground terminal? =20

Well, if your ground terminal can move around (electrically speaking) =20=



the VR will change the field current to compensate. If the voltage =20

change sensed by the VR is the result of any voltage drops associated =20=



with the ground circuit, you end up with yet another source of =20

instability. This is where the whole single-point-ground concept =20

comes in. We need to make sure that the ground terminal of the VR is =20

electrically as close as it can be to the negative terminal of the =20

battery. Now since you can't actually connect it to the negative =20

terminal of the battery (it would be just too inconvenient), it needs =20=



to connect to where the negative terminal of the battery connects to =20

the aircraft ground system. You are using a single point ground, =20

right? If not (more bad on you), you need to connect it to the same =20

bolt where you connect your battery's negative terminal to the airframe.



Once you do these things to improve sensing we will know that the VR =20

*can* do its job properly. Put your voltmeter right on the battery =20

terminals. Start the engine and turn on some big loads, e.g. landing =20

light, pitot heat, vacuum tube radios, etc., and run the engine at =20

the lowest RPM that will bring the bus voltage up to normal. (At low =20

RPM the field current is greatest.) Switch the big loads on and off =20

at the same time while watching the voltmeter. It should be at the =20

same voltage whether the loads are on or off. That voltage should be =20

somewhere around 14.2 volts. (Frankly I like an analog expanded-scale =20=



meter or oscilloscope for this. If it is, you have solved your =20

problem. If it is not then NOW you can suspect the VR.



BTW, it is normal for the meter to twitch right at the moment you =20

switch the loads as the alternator system takes a fraction of a =20

second to respond. Regardless, it should settle right back on the =20

same voltage.



So, time to do some homework. Make sure that this part of things are =20

right and then let us know what happens.



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

=97 Antoine de Saint-Exup=E9ry

dreel(at)cox.net
Guest

Posted: Sun May 07, 2006 3:18 pm Post subject: Charging system failure

After Bob and Brian put me on to the stability issue, I replaced the fuse in

the alternator field supply circuit with a fuse link and replaced the

regulator with an adjustable Vans regulator.  Then I set the bus voltage to

13.8 with the engine at 1000rpm and no loads but battery charging & the

master contactor.  Next I added the Whelen strobes & got instability of +2

tenths of a volt.  As I was seeing +3 tenths with the fuse, I believe

replacing the fuse eliminated one third of the resistance in the circuit

outside the regulator.  Then I added nav lights.  The bus voltage went up to

13.95.  Then I added my landing light & the bus went up further to 14.06.

In both cases, the strobe variation appeared to greatly decrease or

disappear.  Since my nav load is 8.5 amps and my landing light load is 4.6

amps, it appears that my bus to regulator input resistance is now in the

neighborhood of .018 to .02 ohms.  Now here come the big questions for Bob

or Brian or anyone else:



Is .02 ohms small enough for reasonable stability?  How much typically comes

from a circuit breaker?



At cruise rpm where field circuit amperage will presumably be less, will

stability increase due to decreased voltage drop?  Or will stability

decrease because the smaller current requires more precise manipulation?



What happens to voltage in the millisecond range which I'd need an

oscilloscope to see?  Will it be much less stable than what I'm seeing on my

digital voltmeter?



I should be able to fly again Tuesday & I guess, should I continue to get OV

trips, I could always fly with nav lights on & see if that solved the

problem.  Ugh!



Dave Reel - RV8A

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Sun May 07, 2006 7:46 pm Post subject: Charging system failure

On May 7, 2006, at 4:12 PM, DAVID REEL wrote:

 	  Quote: 	
		  

 Is .02 ohms small enough for reasonable stability?  How much  

 typically comes

 from a circuit breaker?


	


To be honest, I don't know. The answer is probably, "try it and see."  

The numbers you are now bandying about seem pretty reasonable to me.  

Remember, an alternator is NOT a precision bench supply with .001%  

regulation. I doubt a couple tenths of a volt will make a lot of  

difference.



 	  Quote: 	
		   At cruise rpm where field circuit amperage will presumably be less,  

 will

 stability increase due to decreased voltage drop?


	


I would expect it to.



 	  Quote: 	
		   Or will stability

 decrease because the smaller current requires more precise  

 manipulation?


	


No.



 	  Quote: 	
		   What happens to voltage in the millisecond range which I'd need an

 oscilloscope to see?  Will it be much less stable than what I'm  

 seeing on my

 digital voltmeter?


	


Well, I wasn't thinking of too much in the millisecond range but if  

you want to see how long it takes your alternator charging system to  

settle down after a big load change you aren't going to see it on a  

digital meter and an analog meter may be too slow also. That is where  

a cheap 'scope will help. You can set it to capture a single event at  

something like 100 ms per division and then see what happens. I think  

Bob has posted some of these traces but we are talking about YOUR  

system.



 	  Quote: 	
		   I should be able to fly again Tuesday & I guess, should I continue  

 to get OV

 trips, I could always fly with nav lights on & see if that solved the

 problem.  Ugh!


	


You just keep working at it, fixing one possibility after another  

until everything works right.



If you don't mind hacking the guts of your regulator you might be  

able to pull the sense wire out separately. After all, this is  

EXPERIMENTAL aviation. Just a thought.



Good luck!

Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

 Antoine de Saint-Exupry

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