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Deceptive Voltage?

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bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Sun Jul 11, 2010 2:38 pm Post subject: Deceptive Voltage?

7/11/2010



Hello Bob Nuckolls and other Electrical Gurus,



Suppose you ran your battery down by spinning your first time to be started 

O-540 Lycoming engine with the starter in order to preoil the engine in your 

nearly finished RV-10. And maybe you did some other things that ran the 

battery down.



Then you connected your small amperage output battery charger to the battery 

and you attempted to start the Shower of Sparks equipped engine without 

success. The engine was cranked OK, but the starting vibrator just was not 

putting out.



A check of the system voltage in appropriate points with a separate volt 

meter while cranking the engine showed 13 plus volts.



Is it possible that the voltage being seen was in fact the voltage being put 

out by the battery charger as it attempted to recharge the run down battery, 

but the amperage being put out by the run down battery and battery charger 

together just was not enough current flow to run the starting vibrator as 

well as crank the engine?



'OC' Baker Says: "The best investment we can make is the time and effort to 

gather and understand knowledge."

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jul 12, 2010 7:01 am Post subject: Deceptive Voltage?

At 05:36 PM 7/11/2010, you wrote:




7/11/2010



Hello Bob Nuckolls and other Electrical Gurus,



Suppose you ran your battery down by spinning your first time to be 

started O-540 Lycoming engine with the starter in order to preoil the 

engine in your nearly finished RV-10. And maybe you did some other 

things that ran the battery down.



Then you connected your small amperage output battery charger to the 

battery and you attempted to start the Shower of Sparks equipped 

engine without success. The engine was cranked OK, but the starting 

vibrator just was not putting out.



A check of the system voltage in appropriate points with a separate 

volt meter while cranking the engine showed 13 plus volts.



    This number appears bogus. A battery is incapable

    of delivering energy at more than about 12.5 volts

    lightly loaded . . . a few amps. Given that most

    batteries offer an internal resistance on the order

    of .007 to .010 ohms, a 200A starter draw would be

    expected to drop the battery terminal voltage by

    perhaps 2 volts. So a terminal voltage of 10.5 or

    lower is expected.

Is it possible that the voltage being seen was in fact the voltage 

being put out by the battery charger as it attempted to recharge the 

run down battery, but the amperage being put out by the run down 

battery and battery charger together just was not enough current flow 

to run the starting vibrator as well as crank the engine?



    No, if the engine cranked at some speed you would

    EXPECT to start it, then the battery is fine. The

    shower-of-sparks system is designed to do two things:

    (1) increased intensity of the sparking energy by

    offering a repeating train of battery-supported

    sparks and (2) DELAYING the delivery of ANY sparks

    until just after TDC such that potential for kickback

    is eliminated.



    If your engine cranks but doesn't start, the battery

    is fine and the SOS system is suspect. This article might

    be of value in your quest for making all things right

    with the world:



http://www.aeroelectric.com/articles/Shower-of-Sparks/ShowerOfSparks.pdf





        Bob . . .

                    ////

                   (o o)

    ===========o00o=(_)=o00o=========

    < Go ahead, make my day . . .   >

    < show me where I'm wrong.      >

    =================================

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bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Tue Jul 13, 2010 4:38 am Post subject: Deceptive Voltage?

7/13/2010



Hello Again Bob Nuckolls, Thank you for the prompt response copied below, 

but my specific electrical theory question about the battery charger output 

voltage possibly masking the battery's output voltage capability was not 

answered.



In response to the statement: "...... a separate volt meter while cranking 

the engine showed 13 plus volts."



You wrote: "This number appears bogus. A battery is incapable of delivering 

energy at more than about 12.5 volts.........."



But what about the battery charger that is connected to the system, turned 

on, and providing a higher than normal battery output voltage in its attempt 

to recharge the battery while the engine was being cranked and the volt 

meter readings were taken?



My electrical theory question is: "Could that battery charger output voltage 

be affecting the reading obtained by the separate volt meter and indicate 

that the battery is more capable than it really is in putting out amperage?" 

Thank you.



'OC' Baker Says: "The best investment we can make is the time and effort to 

gather and understand knowledge."



PS: Thank you also for writing and passing on the link to the article about 

Shower of Sparks.



http://www.aeroelectric.com/articles/Shower-of-Sparks/ShowerOfSparks.pdf



I will pass that along to the RV-10 builder and his helpers.



===========================================================



Time: 08:01:28 AM PST US

From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

Subject: Re: Deceptive Voltage?



At 05:36 PM 7/11/2010, you wrote:



7/11/2010



Hello Bob Nuckolls and other Electrical Gurus,



Suppose you ran your battery down by spinning your first time to be

started O-540 Lycoming engine with the starter in order to preoil the

engine in your nearly finished RV-10. And maybe you did some other

things that ran the battery down.



Then you connected your small amperage output battery charger to the

battery and you attempted to start the Shower of Sparks equipped

engine without success. The engine was cranked OK, but the starting

vibrator just was not putting out.



A check of the system voltage in appropriate points with a separate

volt meter while cranking the engine showed 13 plus volts.



    This number appears bogus. A battery is incapable

    of delivering energy at more than about 12.5 volts

    lightly loaded . . . a few amps. Given that most

    batteries offer an internal resistance on the order

    of .007 to .010 ohms, a 200A starter draw would be

    expected to drop the battery terminal voltage by

    perhaps 2 volts. So a terminal voltage of 10.5 or

    lower is expected.

Is it possible that the voltage being seen was in fact the voltage

being put out by the battery charger as it attempted to recharge the

run down battery, but the amperage being put out by the run down

battery and battery charger together just was not enough current flow

to run the starting vibrator as well as crank the engine?



    No, if the engine cranked at some speed you would

    EXPECT to start it, then the battery is fine. The

    shower-of-sparks system is designed to do two things:

    (1) increased intensity of the sparking energy by

    offering a repeating train of battery-supported

    sparks and (2) DELAYING the delivery of ANY sparks

    until just after TDC such that potential for kickback

    is eliminated.



    If your engine cranks but doesn't start, the battery

    is fine and the SOS system is suspect. This article might

    be of value in your quest for making all things right

    with the world:



http://www.aeroelectric.com/articles/Shower-of-Sparks/ShowerOfSparks.pdf

        Bob . . .

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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klehman(at)albedo.net
Guest

Posted: Tue Jul 13, 2010 5:05 am Post subject: Deceptive Voltage?

OC

The thing is the battery voltage during cranking is the highest possible 

voltage in the system during cranking. The charger voltage must be 

pulled down to the same value unless you are measuring near the charger 

and there is is high resistance between where you are measuring the 

voltage and the battery. That would mean you have a second wiring issue. 

So Bob really did answer the question. The 13 volt reading is 

bogus/wrong/not related to you shower of sparks problem and is 

meaningless/impossible unless you have the above mentioned second issue 

or a large (100 amp ?) charger. Hope that helps a bit.



The answer to your electrical theory question is "No"

BTW I do enjoy your posts.



Ken



bakerocb(at)cox.net wrote:

 	  Quote: 	
		   

 

 7/13/2010

 

 Hello Again Bob Nuckolls, Thank you for the prompt response copied 

 below, but my specific electrical theory question about the battery 

 charger output voltage possibly masking the battery's output voltage 

 capability was not answered.

 

 In response to the statement: "...... a separate volt meter while 

 cranking the engine showed 13 plus volts."

 

 You wrote: "This number appears bogus. A battery is incapable of 

 delivering energy at more than about 12.5 volts.........."

 

 But what about the battery charger that is connected to the system, 

 turned on, and providing a higher than normal battery output voltage in 

 its attempt to recharge the battery while the engine was being cranked 

 and the volt meter readings were taken?

 

 My electrical theory question is: "Could that battery charger output 

 voltage be affecting the reading obtained by the separate volt meter and 

 indicate that the battery is more capable than it really is in putting 

 out amperage?" Thank you.

 

 'OC' Baker Says: "The best investment we can make is the time and effort 

 to gather and understand knowledge."

 

 PS: Thank you also for writing and passing on the link to the article 

 about Shower of Sparks.

 

 http://www.aeroelectric.com/articles/Shower-of-Sparks/ShowerOfSparks.pdf

 

 I will pass that along to the RV-10 builder and his helpers.

 

 ===========================================================

 

 Time: 08:01:28 AM PST US

 From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

 Subject: Re: Deceptive Voltage?

 

 

 

 At 05:36 PM 7/11/2010, you wrote:

 

 7/11/2010

 

 Hello Bob Nuckolls and other Electrical Gurus,

 

 Suppose you ran your battery down by spinning your first time to be

 started O-540 Lycoming engine with the starter in order to preoil the

 engine in your nearly finished RV-10. And maybe you did some other

 things that ran the battery down.

 

 Then you connected your small amperage output battery charger to the

 battery and you attempted to start the Shower of Sparks equipped

 engine without success. The engine was cranked OK, but the starting

 vibrator just was not putting out.

 

 A check of the system voltage in appropriate points with a separate

 volt meter while cranking the engine showed 13 plus volts.

 

    This number appears bogus. A battery is incapable

    of delivering energy at more than about 12.5 volts

    lightly loaded . . . a few amps. Given that most

    batteries offer an internal resistance on the order

    of .007 to .010 ohms, a 200A starter draw would be

    expected to drop the battery terminal voltage by

    perhaps 2 volts. So a terminal voltage of 10.5 or

    lower is expected.

 

 

 Is it possible that the voltage being seen was in fact the voltage

 being put out by the battery charger as it attempted to recharge the

 run down battery, but the amperage being put out by the run down

 battery and battery charger together just was not enough current flow

 to run the starting vibrator as well as crank the engine?

 

    No, if the engine cranked at some speed you would

    EXPECT to start it, then the battery is fine. The

    shower-of-sparks system is designed to do two things:

    (1) increased intensity of the sparking energy by

    offering a repeating train of battery-supported

    sparks and (2) DELAYING the delivery of ANY sparks

    until just after TDC such that potential for kickback

    is eliminated.

 

    If your engine cranks but doesn't start, the battery

    is fine and the SOS system is suspect. This article might

    be of value in your quest for making all things right

    with the world:

 

 http://www.aeroelectric.com/articles/Shower-of-Sparks/ShowerOfSparks.pdf

 

 

        Bob . . .

- The Matronics AeroElectric-List Email Forum -

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nuckollsr

Joined: 24 Mar 2009
Posts: 95
Location: Medicine Lodge, KS

Posted: Tue Jul 13, 2010 6:06 am Post subject: Re: Deceptive Voltage?

 	  Quote: 	
		  But what about the battery charger that is connected to the system, turned on, and providing a higher than normal battery output voltage in its attempt to recharge the battery while the engine was being cranked and the volt meter readings were taken?



My electrical theory question is: "Could that battery charger output voltage be affecting the reading obtained by the separate volt meter and indicate that the battery is more capable than it really is in putting out amperage?" 	




 My apologies, I did miss that one. A battery charger is simply another energy source. It has characteristics common to all energy sources in terms of potential power, open circuit voltage, ability to deliver current (internal impedance), noise, etc.  A charge may be considered equivalent to a noisy battery (because its got artifacts of internal electronics noise and/or rectified ac mains) with a high internal impedance. The charger can produce no more output current than its designers provided. Unless the charger is specifically designed for cranking engines . . . see:



http://tinyurl.com/385snfg



then the effects of an operating charger on system voltage while cranking is insignificant. It's not unlike paralleling a 60A alternator with an SD-8 alternator. As long as you don't draw more than 8-10A, and SD-8 with a HIGHER regulation setpoint might happily assume all the load and boost the voltage high enough to cause the larger alternator to simply relax.



But as soon as the demand (in this case a cranking motor) exceeds the load carrying capabilities of the source with the higher setpoint (in this case a charger), the voltage sags to the point where the battery is willing and able to shoulder some load . . . in this case, about 12.5 volts or lower. So the short answer is, unless were talking about a boss-hogg charger that is capable of supporting engine cranking loads at 13.0 volts (I don't think such a critter exists), then the cited reading raises some questions as to measurement technique, quality of the instrument, etc. I would not dispute what the individuals observed but I will suggest that the reported readings raise more questions than they answer and beg some explanation that will come from data we do not yet have.



I will suggest that the voltmeter be tested against another instrument believed to be good. They should agree to within a 0.2 volts or so at 13v. Then connect the voltmeter right at the battery terminals to watch the battery's ability to pick up the cranking loads. Do the test with the charger connected, then repeat with the charger disconnected. I suspect that voltage readings while cranking under the two conditions will be under 12.5 volts and not significantly different from each other.



Bob . . .

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