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External Power and electrical system

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nuckollsr(at)cox.net
Guest

Posted: Fri Jul 14, 2006 5:02 am Post subject: External Power and electrical system

At 09:47 PM 7/13/2006 +0200, you wrote:



 	  Quote: 	
		  

<michele.delsol(at)microsigma.fr>



Listers,



I have been planning on adding external power to my system (one alternator,

one battery, PMag IO360). My original design was pretty simple, hook it

straight onto the battery such as one does when jump starting a car.


	


   That works.



 	  Quote: 	
		    Then I

added a relay so that the external power terminals would not be hot when not

connected to external power.


	


   What is the added value? What risks are mitigated by this?

   Is your external power INTENDED to crank an engine with a

   compromised battery . . . or just to run electro-whizzies on

   the ground, or just charge a battery, or just maintain a battery?



   Settling on one of these design goals drives the size of your

   hardware ranging from a tiny wall-wart charger and 24AWG connecting

   leads up to 2AWG welding cable plugged in through a very fat connecto.



 	  Quote: 	
		  Then some knowledgeable fellow builders told me

that I should only use external power for starting the engine  nothing

else.


	


    If that was their design goal, that's correct. What's your design

    goal?

 	  Quote: 	
		    Then some other knowledgeable builders told me that I could install a

cigar lighter jack in parallel as an external power connector for recharging

the battery.


	




    Yup, that's another achievable design goal . . .



 	  Quote: 	
		    Then there was the issue as to external power not being clean

DC current and consequently liable to play havoc with some of my sensitive

equipment.


	


    If you have a battery on the bus any time ground power is

    applied, then externally conducted noises are not an issue.

    The battery is the airplane's best firewall against any and

    all perturbations of bus voltage.

 	  Quote: 	
		  Based on this I proceeded to design a circuit which would

automatically disconnect all electricals except for the starter solenoid,

current to the PMags and current to my fuel pump. Whereupon another

knowledgeable person suggested that I should remember the KISS principle  I

may be over designing my system.


	


    Again, depends on your design goals. What do YOU want this

    ground power system to do for you?

 	  Quote: 	
		  What do you guys suggest  isolate my electrical system when external power

is hot or just hook it up onto the battery via a relay?


	


    Start with the article at:



http://aeroelectric.com/articles/grndpwr.pdf



    This is typical of ground power jacks installed on

    type certificated aircraft with a few AEC enhancements

    added as described in the text.



    This installation may be used for just about every purpose

    other than battery maintenance because you need to close

    a contactor to get connection between external power and

    the battery.



    Let's start with what you want the connection to do and

    then tailor it to that task. Most of what you were told

    is inaccurate and/or incomplete.



    Bob . . .

chaztuna(at)adelphia.net
Guest

Posted: Sat Jul 15, 2006 5:30 am Post subject: External Power and electrical system

 	  Quote: 	
		   >

 ><michele.delsol(at)microsigma.fr>

 >

 >Listers,

 >

 >I have been planning on adding external power to my system (one alternator,

 >one battery, PMag IO360). My original design was pretty simple, hook it

 >straight onto the battery such as one does when jump starting a car.

>  Then I added a relay so that the external power terminals would not be hot when not connected to external power.


	


Michele,

 Earlier you said that you intended to place your battery on the right side behind the firewall. It seems to me, that in this location, you can access the battery on your RV8 by simply opening the front baggage door and reaching down. With this location, why add weight and complexity when there is such a simple and obvious solution? What am I missing?

Charlie Kuss

brian

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

Posted: Sat Jul 15, 2006 8:05 am Post subject: External Power and electrical system

It can be difficult to effectively asses one's needs when doing an  

initial design. For the most part, whenever I have said to myself, "I  

won't need that," I have found that indeed I eventually needed "that".



As others have said, there are three reasons for ground power:



1. starting the engine when the battery charge is too low;

2. to operate the electrical equipment on the ground without  

discharging the battery;

3. to charge the battery.



If I were going to craft a ground-power plug I would ensure that it  

was usable for all three functions.



Now for an anecdote. At OSH in 2000 I was supposed to fly my CJ6A in  

the mass warbird formation on Friday. (I had already flown on opening  

day on Wednesday as I recall.) At the proper time we hopped in our  

airplanes. It was at that moment I discovered that someone had been  

in my airplane and had turned on every switch, including the battery  

master. My battery was dead. If I had had a ground power plug I might  

have been able to put an initial charge on the battery and start the  

engine and still fly in the shoe. As it was, I couldn't.



I considered trying to get some jumpers in there but, as the battery  

was back in the empennage under the baggage compartment floor, it was  

inconvenient and a rogue jumper cable was likely to do damage to  

something. So I very carefully pulled the battery and hauled it up to  

the warbird maintenance area were we were able to put it on a charger.



Several hours later the battery was charged and I was in the process  

of reinstalling it. I was being extremely careful to keep the  

terminal from touching any of the control cables but it was dark back  

in there. I had avoided the rudder and elevator control cables but  

missed seeing the much smaller trim cable. Of course I managed to get  

the trim cable across the battery terminals. The trim cable failed  

with a most satisfactory flash and bang. (Yes, the damned thing  

literally exploded in my face.) I bashed my head against a bulkhead  

and uttered the immortal words. I managed to extricate my temporarily- 

blinded eyes from the baggage compartment only to have the pilot next  

to me say, "So Sparky, having a bit of trouble, are we?" From then on  

my call-sign was "Sparky".



So, yes, I want my ground power plug to be able to do it all. I  

consider it to be a safety issue now.



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-Exupéry

_________________
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

michele.delsol(at)microsi
Guest

Posted: Thu Jul 20, 2006 9:57 am Post subject: External Power and electrical system

Thanks Bob - as usual it is back to basics. This is what I want to

accomplish :



1 - Jump start the engine because the battery does not have enough juice

left. Would it be OK to just hook in onto the existing battery, turn the

master on, and push on the starter or should all electrics be isolated

except for PMags, fuel pump and starter solenoid?



2 - Charge the battery - cockpit shut, baggage door shut. Here I can leave

the main contactor off to isolate all circuits.



3 - Run electrical equipment in the airplane for testing as I assemble the

electrical circuit - for this one I guess I could just as well hook up an

external source onto the battery terminals or onto the main bus over the

rails. I don't really need an external power source to accomplish this. 



Thanks,

Michele



--

michele.delsol(at)microsi
Guest

Posted: Thu Jul 20, 2006 9:58 am Post subject: External Power and electrical system

I've been debating whether to put the battery up front in the forward

baggage area or in the rear. The roar in favor of the rear has been so

strong that I finally capitulated and shall indeed be putting it in the

rear, but I shall prepare the front baggage well to receive the battery and

contactors if my CG permits it after all.



As for external power, Ill wait 'till the battery issue gets finalized.



Thanks,

Michele



--

mprather(at)spro.net
Guest

Posted: Thu Jul 20, 2006 12:38 pm Post subject: External Power and electrical system

Hello Michele,



Though it is common to 'jump start' airplanes (and cars, etc.), doing so

may likely cause the battery to have a significantly shortened life.  As

soon as the engine is running at a speed (RPM) which allows the alternator

to put out it's rated current, the battery will be charged at that rate

(minus whatever operating load is on the system).  Lots of people talk of

using a 60Amp (or greater) alternator.  Dumping 50Amps+ into the battery

may heat it significantly (not to mention putting a heavy load on the

alternator)...

Regards,



Matt-



[quote] 

 <michele.delsol(at)microsigma.fr>



 Thanks Bob - as usual it is back to basics. This is what I want to

 accomplish :



 1 - Jump start the engine because the battery does not have enough juice

 left. Would it be OK to just hook in onto the existing battery, turn the

 master on, and push on the starter or should all electrics be isolated

 except for PMags, fuel pump and starter solenoid?



 2 - Charge the battery - cockpit shut, baggage door shut. Here I can leave

 the main contactor off to isolate all circuits.



 3 - Run electrical equipment in the airplane for testing as I assemble the

 electrical circuit - for this one I guess I could just as well hook up an

 external source onto the battery terminals or onto the main bus over the

 rails. I don't really need an external power source to accomplish this.



 Thanks,

 Michele



 --

nuckollsr(at)cox.net
Guest

Posted: Thu Jul 20, 2006 5:11 pm Post subject: External Power and electrical system

At 07:54 PM 7/20/2006 +0200, you wrote:



 	  Quote: 	
		  

<michele.delsol(at)microsigma.fr>



Thanks Bob - as usual it is back to basics. This is what I want to

accomplish :



1 - Jump start the engine because the battery does not have enough juice

left. Would it be OK to just hook in onto the existing battery, turn the

master on, and push on the starter or should all electrics be isolated

except for PMags, fuel pump and starter solenoid?


	


   See http://aeroelectric.com/articles/grndpwr.pdf



    With the battery on line, you can have any equipment running

    that you wish. I'd wait a minute or two after plugging

    in ground power and charging the battery before you power

    up the airplane for cranking.

 	  Quote: 	
		  2 - Charge the battery - cockpit shut, baggage door shut. Here I can leave

the main contactor off to isolate all circuits.


	


   The above circuit allows this also but won't work well

   with battery maintainers because of the ground power contactor's

   0.8A draw. If you want to run a battery maintainer, add

   a small connector directly to the battery bus to connect a

   battery maintainer. See:



http://batterytender.com/product_info.php?products_id=4&osCsid=98b86a9d022882459cf6e26026c0edf6



   Street price on these is 25-30 dollars.

 	  Quote: 	
		  3 - Run electrical equipment in the airplane for testing as I assemble the

electrical circuit - for this one I guess I could just as well hook up an

external source onto the battery terminals or onto the main bus over the

rails. I don't really need an external power source to accomplish this.


	


    Use the ground power jack and plug an AC supply into it.

    Here's a nice one that will run just about everything but pitot heat

    and fat landing lights:



http://mpja.com/productview.asp?product=5386+PS

    If it were my airplane I'd have a high current external

    power jack like that described above and a low current

    tap to the battery bus for a battery maintainer.



    Bob . . .

nuckollsr(at)cox.net
Guest

Posted: Thu Jul 20, 2006 5:11 pm Post subject: External Power and electrical system

At 02:31 PM 7/20/2006 -0600, you wrote:



 	  Quote: 	
		  



Hello Michele,



Though it is common to 'jump start' airplanes (and cars, etc.), doing so

may likely cause the battery to have a significantly shortened life.  As

soon as the engine is running at a speed (RPM) which allows the alternator

to put out it's rated current, the battery will be charged at that rate

(minus whatever operating load is on the system).  Lots of people talk of

using a 60Amp (or greater) alternator.  Dumping 50Amps+ into the battery

may heat it significantly (not to mention putting a heavy load on the

alternator)...


	


     While the "loads" cited are real, they're transient

     and not even a minor hazard to an RG battery or an

     alternator.



     Bob . . .

chaztuna(at)adelphia.net
Guest

Posted: Thu Jul 20, 2006 5:44 pm Post subject: External Power and electrical system

At 04:31 PM 7/20/2006, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Matt Prather" <mprather(at)spro.net>



 Hello Michele,



 Though it is common to 'jump start' airplanes (and cars, etc.), doing so

 may likely cause the battery to have a significantly shortened life.  As

 soon as the engine is running at a speed (RPM) which allows the alternator

 to put out it's rated current, the battery will be charged at that rate

 (minus whatever operating load is on the system).  Lots of people talk of

 using a 60Amp (or greater) alternator.  Dumping 50Amps+ into the battery

 may heat it significantly (not to mention putting a heavy load on the

 alternator)...



 

 Regards,



 Matt- 	
snipped



 Matt,

  Providing that your voltage regulator functions properly, you will never damage a battery as mentioned above. As the heavy charge quickly refills the battery, system voltage will rise. The voltage regulator will limit system voltage (and thereby amperage into the battery). This will prevent damage to the battery. 

 Charlie Kuss

glastar(at)gmx.net
Guest

Posted: Thu Jul 20, 2006 8:23 pm Post subject: External Power and electrical system

Hello Matt,



during winter I had to do jump starts 2-3 times on a now 3 year old 

Panasonic, so for the first 2 to 5 minutes I did see on my amp meter a 

load of 11-13 Amps coming, however as load is around 4-5 amps from the 

cockpit an inrush current less then 10 Amps at the beginning has been 

see, a lot more then the std. 1.8 you should charge with. So far I've 

not seen a negative effect but I should do that winter a capacity test 

to see more.



br Werner



Matt Prather wrote:



[quote]



Hello Michele,



Though it is common to 'jump start' airplanes (and cars, etc.), doing so

may likely cause the battery to have a significantly shortened life.  As

soon as the engine is running at a speed (RPM) which allows the alternator

to put out it's rated current, the battery will be charged at that rate

(minus whatever operating load is on the system).  Lots of people talk of

using a 60Amp (or greater) alternator.  Dumping 50Amps+ into the battery

may heat it significantly (not to mention putting a heavy load on the

alternator)...

Regards,



Matt-



  



>

><michele.delsol(at)microsigma.fr>

>

>Thanks Bob - as usual it is back to basics. This is what I want to

>accomplish :

>

>1 - Jump start the engine because the battery does not have enough juice

>left. Would it be OK to just hook in onto the existing battery, turn the

>master on, and push on the starter or should all electrics be isolated

>except for PMags, fuel pump and starter solenoid?

>

>2 - Charge the battery - cockpit shut, baggage door shut. Here I can leave

>the main contactor off to isolate all circuits.

>

>3 - Run electrical equipment in the airplane for testing as I assemble the

>electrical circuit - for this one I guess I could just as well hook up an

>external source onto the battery terminals or onto the main bus over the

>rails. I don't really need an external power source to accomplish this.

>

>Thanks,

>Michele

>

>--

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