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Steve Kelly

Joined: 08 Jul 2016
Posts: 18

Posted: Sat Aug 06, 2016 9:20 am Post subject: Battery charging

I have a small 9ah sealed lead-acid battery in the back of my plane that I use mainly to operate some things on the ground without having to use the main battery which is on the firewall.  It is also available, should I need it in flight to power a  few items such as the com or the flight display.

  This battery feeds buss #2 with a #14 wire, again coming from the back of the plane.  

  I have been charging this with a battery charger, but would like to be able to charge it off the main buss when the engine is running.

  My thoughts are to run another wire back to the battery from the main buss with a diode and a resistor of some sort to limit the current so the wire (or fuse) doesn't burn up.  Am I on the right track here?

  I have some 3A diodes here and hopefully can use a #20 wire.  No idea what to use for a resistor value or if this would even work.

  I would appreciate any feedback on this idea.

Thanks, Steve

_________________
Steve

user9253

Joined: 28 Mar 2008
Posts: 1924
Location: Riley TWP Michigan

Posted: Sat Aug 06, 2016 11:01 am Post subject: Re: Battery charging

How about connecting buss #1 & #2 together with a DSS 2x121-0045B Schottky diode?

Doing that will be electrically the same as your proposal, except that the wire will be shorter and no additional fuse or resistor is used.

It is unlikely that the fuse protecting the existing 14 AWG wire will ever blow from charging current, unless the aux battery is completely run down or defective.  Have you ever seen the aux battery charging current go above 15 amps?

The diode will drop about 0.3 to 0.35 volts at your intended load current.

_________________
Joe Gores

racerjerry

Joined: 15 Dec 2009
Posts: 202
Location: Deer Park, NY

Posted: Sun Aug 07, 2016 3:04 am Post subject: Re: Battery charging

Long #14 wire from Aux Battery to main buss.



It's early yet, but my first thoughts revolve around a hypothetical short to ground in the middle of the wire.  Would not you need a fuse at both ends to adequately protect the wire?



Or am I full of crap?

_________________
Jerry King

Steve Kelly

Joined: 08 Jul 2016
Posts: 18

Posted: Sun Aug 07, 2016 4:14 am Post subject: Re: Battery charging

Joe,

  I think that would work to charge the battery, but I'm not sure that would do what I want.  My intention here is to be able to turn on this small accessory buss without turning on the main and lighting up the entire electrical system just to use a few items while on the ground.  This is something I always disliked with factory planes where everything comes on with the master switch just so you could run cockpit lites or listen to ATIS.  

  The way I have it set up is through an on-off-on switch.  This switch feeds buss #2 and power comes into the switch from both batteries.  The buss can only be fed from 1 battery at a time.  The master switch must be on to get power from battery #1.  And there is a fuse at both feeds to the switch.

  Also, there already is an extra #20 wire in place that I could use to charge the battery if you think that might work.  

 Thanks for the input, Steve

_________________
Steve

kjashton(at)vnet.net
Guest

Posted: Sun Aug 07, 2016 5:22 am Post subject: Battery charging

 	  Quote: 	
		   On Aug 6, 2016, at 1:20 PM, Steve Kelly <amsk22(at)gmail.com> wrote:

 

 

 

 I have a small 9ah sealed lead-acid battery in the back of my plane that I use mainly to operate some things on the ground without having to use the main battery which is on the firewall.  It is also available, should I need it in flight to power a  few items such as the com or the flight display.

  This battery feeds buss #2 with a #14 wire, again coming from the back of the plane.  

  I have been charging this with a battery charger, but would like to be able to charge it off the main buss when the engine is running.


	


It seems like this could all be automated using Bob’s diagrams something like so:



- Charge both the main and 2nd battery from the alternator with the 2nd battery being fed through a 30V 9A Schottky diode that allows to to charge but isolates the 2nd battery unless you select your essential bus.



- Setup a main and essential bus.  Feed the E-bus from the main bus through a diode.  I have set up Main & E-bus arrangements a couple of ways (using fuseblocks).  Once I used a large (14 fuse?) bussman fuse block and a small 6-fuse block and connected them with the diode.  Another time I used a large bussman fuse block, opened it up and cut the center conductor to make two separate fuseblocks.  I brazed a tab on the smaller end which became the E-bus side and the other side became the main bus side.  Then I fed the E-bus side with a diode from the main side.



- When you need the E-bus items, throw a switch that powers the E-bus from the 2nd battery.



- If either battery needs a charge, put the charger on the common charging circuit.



-Kent

user9253

Joined: 28 Mar 2008
Posts: 1924
Location: Riley TWP Michigan

Posted: Sun Aug 07, 2016 6:14 am Post subject: Re: Battery charging

Steve,

There is more than one way to accomplish your goal.  Both Jerry and Kent offer good suggestions.  And your plan will work too.  Since there are two power sources, fuse the 20 AWG wire at both ends and use a Schottky diode because it has a lower voltage drop.  The aux battery will not charge if the diode drops too much voltage.  You do not need a resistor.  That 20 gauge wire has enough resistance.  If the fuse protecting it blows, no harm will be done.  It will just be back in the same situation that it is in now without that 20 gauge wire.

_________________
Joe Gores

Steve Kelly

Joined: 08 Jul 2016
Posts: 18

Posted: Mon Aug 08, 2016 3:46 am Post subject: Re: Battery charging

Some interesting ideas.  What exactly is a schottky diode.  Is it different than a standard diode.  

 If the small battery was very low in charge how much current do you think could flow in the 20 wire?  



Steve

_________________
Steve

user9253

Joined: 28 Mar 2008
Posts: 1924
Location: Riley TWP Michigan

Posted: Mon Aug 08, 2016 4:05 am Post subject: Re: Battery charging

Yes, a Schottky diode is different than a standard diode, but I have no idea how they are made.  All I know is that they have half of the voltage drop.

  Sorry, I do not know what the maximum charging current will be in a dead 9AH battery.  You could test it to find out.

_________________
Joe Gores

racerjerry

Joined: 15 Dec 2009
Posts: 202
Location: Deer Park, NY

Posted: Mon Aug 08, 2016 7:11 am Post subject: Re: Battery charging

I guess that you can use Ohm's Law to find a resistance that would limit your maximum charging rate.  Let's say you want to limit the charging rate to 3A for a #20 wire NOT in a bundle.  With 14 volts, a 4.7 ohm resistance would do it.  Problem is resistor heat dissipation ability at these values.  Such setup would require a large 42 watt resistor (W=volts x amps).  A 50 Watt 5 ohm resistor would be the nearest commercial size.  Google / Newark Electronics shows several types in the $7 range.



When faced with similar problems, sometimes I use things like an old automotive 12 volt coil ignition resistor to limit current.  Or, on the bench, I use different wattage light bulbs; but remember that actual resistance changes somewhat (increases), as the resistor heats up.



I am almost betting that you could use a small 3A diode at each end of your wire to also serve as the "fuse" because the usual failure mode is that they explode and pop open.  But certain people here, who I highly respect, may yell at me for suggesting this.

_________________
Jerry King

user9253

Joined: 28 Mar 2008
Posts: 1924
Location: Riley TWP Michigan

Posted: Mon Aug 08, 2016 10:47 am Post subject: Re: Battery charging

A lead acid battery is just about dead at 11 volts.  If the charging voltage is 14, then only 3 volts has to be dropped.  The internal resistance of the battery will drop the voltage.  There are too many variables to calculate the current.  I would just wire it without a resistor.  Then discharge the battery and go flying to see if a 7.5 amp fuse blows.  If it does, increase the wire and fuse size.  Or do not run the battery down until it is almost dead.

_________________
Joe Gores

kenryan

Joined: 20 Oct 2009
Posts: 426

Posted: Mon Aug 08, 2016 12:19 pm Post subject: Re: Battery charging

If you do as Joe suggests and the fuse blows, another option would be to run another 20 awg wire (if that would be easier).

Steve Kelly

Joined: 08 Jul 2016
Posts: 18

Posted: Tue Aug 09, 2016 3:28 am Post subject: Re: Battery charging

Ok.  I think I will give that a try.  Is there a particular diode you would recommend to use for this.  

  I am not quite ready to run the engine yet, so I will try to test it using the main battery to charge.  This will make it easier to check current flow at different stages of battery discharge on batt #2.  Do you think the main battery alone will give about the the same current flow as if the alternator was on line.

Steve

_________________
Steve

ceengland7(at)gmail.com
Guest

Posted: Tue Aug 09, 2016 4:55 am Post subject: Battery charging

You can't charge a 12v battery from another 12v battery. You need ~14v to actually charge, which the 12v battery can't deliver.



On Tue, Aug 9, 2016 at 6:28 AM, Steve Kelly <amsk22(at)gmail.com (amsk22(at)gmail.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "Steve Kelly" <amsk22(at)gmail.com (amsk22(at)gmail.com)>

 

 Ok.  I think I will give that a try.  Is there a particular diode you would recommend to use for this.

   I am not quite ready to run the engine yet, so I will try to test it using the main battery to charge.  This will make it easier to check current flow at different stages of battery discharge on batt #2.  Do you think the main battery alone will give about the the same current flow as if the alternator was on line.

 Steve

 

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user9253

Joined: 28 Mar 2008
Posts: 1924
Location: Riley TWP Michigan

Posted: Tue Aug 09, 2016 5:10 am Post subject: Re: Battery charging

I agree with Charlie.

  The diode that I recommended in a previous post, DSS 2x121-0045B Schottky,  has mounting holes, an isolated (insulated) base, two independent diodes in one case, low voltage drop, high current capability.  The disadvantage is that it costs $20 plus shipping.  It is available from Mouser or Digikey.  Other Schottky diodes are available in a TO-220 case for as little as a dollar, but the case might need to be insulated from the aircraft and the terminals are not as robust.

_________________
Joe Gores

ceengland7(at)gmail.com
Guest

Posted: Tue Aug 09, 2016 6:56 am Post subject: Battery charging

Try searching ebay; I've seen some pretty good deals there.



On 8/9/2016 8:10 AM, user9253 wrote:

 	  Quote: 	
		   



 I agree with Charlie.

    The diode that I recommended in a previous post, DSS 2x121-0045B Schottky,  has mounting holes, an isolated (insulated) base, two independent diodes in one case, low voltage drop, high current capability.  The disadvantage is that it costs $20 plus shipping.  It is available from Mouser or Digikey.  Other Schottky diodes are available in a TO-220 case for as little as a dollar, but the case might need to be insulated from the aircraft and the terminals are not as robust.



 --------

 Joe Gores

Steve Kelly

Joined: 08 Jul 2016
Posts: 18

Posted: Wed Aug 24, 2016 4:45 am Post subject: Re: Battery charging

Just a followup on this thread.

  The question was how to charge an "accessory" battery off the main buss.

  I ran about 16' of #20 wire, with the schottky diode and a 7.5 amp fuse in line from the main buss to batt #2.  

  Since the airplane is not running yet , I used the charging system on my car to test.

  With the #2 battery discharged down to 10.7 volts the draw was 5.7 amps.  The initial surge was 6.8.  At 12 volts the draw was 4.2 amps.  So it looks like this will work.  

  Increasing the wire size allowed a bigger fuse, but also drew more amps, which I don't particularly want. 

  A simple way to make this work.

Thanks for all the help on this, Steve

_________________
Steve

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Aug 24, 2016 8:06 am Post subject: Battery charging

At 07:45 AM 8/24/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Steve Kelly" <amsk22(at)gmail.com>



 Just a followup on this thread.

   The question was how to charge an "accessory" battery off the main buss.

   I ran about 16' of #20 wire, with the schottky diode and a 7.5 amp fuse in line from the main buss to batt #2.  

   Since the airplane is not running yet , I used the charging system on my car to test.

   With the #2 battery discharged down to 10.7 volts the draw was 5.7 amps.  The initial surge was 6.8.  At 12 volts the draw was 4.2 amps.  So it looks like this will work.  

   Increasing the wire size allowed a bigger fuse, but also drew more amps, which I don't particularly want. 

   A simple way to make this work. 	


   Let's back up a bit. What accessories

   are on your "aux bus"? How big is the

   second battery?



 

 

   Bob . . .

Steve Kelly

Joined: 08 Jul 2016
Posts: 18

Posted: Wed Aug 24, 2016 10:38 am Post subject: Re: Battery charging

Bob,

  The second battery is a small 9 ah sealed lead acid batt. The kind with 2 fast-on tabs to connect to.  It's purpose is to operate a few things on the ground, like comm, efis, cabin lites, cigarette liter outlet for charging phone, i-pad. 

These and some other items are powered by the aux bus.  The other items would only be used in flight.

The aux bus is powered either by the main bus in flight or by the small battery while on the ground.  An on-off-on switch selects the source.  If needed, battery #2 could also power these items in flight.

I have been charging it with a charger and wanted a way to do it when the engine is running.

  Another question I have here is if I changed to a larger battery, say a 15ah, would it draw more amps than the current one.

Steve

_________________
Steve

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Aug 24, 2016 1:28 pm Post subject: Battery charging

At 01:38 PM 8/24/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Steve Kelly" <amsk22(at)gmail.com>



 Bob,

   The second battery is a small 9 ah sealed lead acid batt. The kind with 2 fast-on tabs to connect to.  It's purpose is to operate a few things on the ground, like comm, efis, cabin lites, cigarette liter outlet for charging phone, i-pad. 

 These and some other items are powered by the aux bus.  The other items would only be used in flight.

 The aux bus is powered either by the main bus in flight or by the small battery while on the ground. 	


   What is the power demands for all this stuff . . . and

   how long would you expect to operate all of it

   without running the engine.



   In other words, what is the predicted battery life

   for running the aux bus with the battery you have?



  	  Quote: 	
		    An on-off-on switch selects the source.  If needed, battery #2 could also power these items in flight.

 I have been charging it with a charger and wanted a way to do it when the engine is running. 	


   Okay, what size is your main battery . . .

   and what kind of engine?



  	  Quote: 	
		    Another question I have here is if I changed to a larger battery, say a 15ah, would it draw more amps than the current one. 	


   Yes . . . but that cart is WAAaayyy in front of

   the horse. I'm exercising the old "Short Circuit" ploy,

   "Input, I need input."



 

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1924
Location: Riley TWP Michigan

Posted: Wed Aug 24, 2016 2:22 pm Post subject: Re: Battery charging

Steve K,

Below is a link to an electrical drawing that I drew some time ago.  Two separate master switches could be used instead of one double pole switch as shown.  The circuit features a small brownout battery and E-Bus which are isolated during engine start.

  I would wire the aux battery with 14 AWG and a 15 amp fuse and not be concerned with charging current.

  Good going with your test using 16' of #20 wire.  That convinced me that a resistor is not needed to limit charging current.



https://drive.google.com/file/d/0B7ZTG2VpCuDRSVNVa3JwUmFuMzQ/view?usp=sharing

_________________
Joe Gores

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