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Battery charging

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sam.marlow

Joined: 25 Feb 2006
Posts: 99

Posted: Thu Mar 23, 2006 11:20 am Post subject: Battery charging

I'm planning on using dual Light Speed ignition on my RV10, but I don't 

feel comfortable using just one battery for both systems. Can someone 

explain how to charge a second battery with different AMP hr rating, 

with a single alternator system?

frank.hinde(at)hp.com
Guest

Posted: Thu Mar 23, 2006 11:43 am Post subject: Battery charging

Connect both positive terminals together...Thats the short answer.



BUT if you have a major ground fault on the primary battery you'll want

to stop the second battery losing all its charge. Put a Shotkey diode

(small forward voltage drop)  in the line tying the two batteries

together...The the alt will feed the small second battery but it won't

flow the other way.



Frank



--

sam.marlow

Joined: 25 Feb 2006
Posts: 99

Posted: Thu Mar 23, 2006 12:14 pm Post subject: Battery charging

I understand if you connect hte two batteries the second, and smaller 

battery will get somewhat of a charge, but will the second battery stay 

in a charged state, and be at full capacity when you need it? Looks to 

me if you connect the two together, they act as one battery, as far as 

the voltage regulator is concerned, and if the little battery demands 

volts from the voltage regulator, the other battery gets over charged, 

or vice versa. Am I thinking right here, can they be charged separately 

with only one voltage regulator?



Hinde, Frank George (Corvallis) wrote:



[quote]



Connect both positive terminals together...Thats the short answer.



BUT if you have a major ground fault on the primary battery you'll want

to stop the second battery losing all its charge. Put a Shotkey diode

(small forward voltage drop)  in the line tying the two batteries

together...The the alt will feed the small second battery but it won't

flow the other way.



Frank



--

frank.hinde(at)hp.com
Guest

Posted: Thu Mar 23, 2006 12:41 pm Post subject: Battery charging

According people much smarter than me (electrically speaking this would

be BOB!) you can use a single charger to charge two batterries wired in

parallel.



Thus if you simply connected the batteries together they look like one

battery and they both get fully charged.



The problem with a diode is that is has a forward voltage

drop...Radioshack diodes lose about 1 volt going forward but apparently

the Shotkey loses only about 0.25volts.



My little battery says it needs about 1 volt less than what my big

battery does...so I usead a RS diode, thinking all would be well...Bob

pointed out though that because the chemsitry of the big battery and the

little one is the same, they must both have the same charging

voltage...Bit of a bummer but I guess I'll be changing to the Shotkey at

some point.



The other thing is to plug a smart charger in and that can be presumably

wired directly to both batteries, i.e bypassing the diode.



Frank



--

nuckollsr(at)cox.net
Guest

Posted: Thu Mar 23, 2006 4:53 pm Post subject: Battery charging

At 02:20 PM 3/23/2006 -0500, you wrote:



 	  Quote: 	
		  



I'm planning on using dual Light Speed ignition on my RV10, but I don't

feel comfortable using just one battery for both systems. Can someone

explain how to charge a second battery with different AMP hr rating,

with a single alternator system?


	


   You can add as many auxiliary batteries of any size

   as you like/need as illustrated in Figure Z-30 of



http://aeroelectric.com/articles/Rev11/AppZ_R11F.pdf



   If they're smaller than the main battery, don't close their

   respective contactors until after the engine is started.



   Bob . . .

nuckollsr(at)cox.net
Guest

Posted: Thu Mar 23, 2006 4:57 pm Post subject: Battery charging

At 11:41 AM 3/23/2006 -0800, you wrote:



 	  Quote: 	
		  

<frank.hinde(at)hp.com>



Connect both positive terminals together...Thats the short answer.



BUT if you have a major ground fault on the primary battery you'll want

to stop the second battery losing all its charge. Put a Shotkey diode

(small forward voltage drop)  in the line tying the two batteries

together...The the alt will feed the small second battery but it won't

flow the other way.


	


    "Major ground faults" that take down the main battery

    are interesting to hypothesize but exceedingly rare. In

    fact, I've never heard of one in any of our aircraft. I'll

    check with the folks in customer service . . . especially

    the old gray-beards on the prop airplanes. The only reason

    we ever use diodes in power distribution is to power one

    load from multiple sources (like those shown in Z-19). This

    is necessary when a double or triple-feed bus needs to power

    up and not back-feed an alternative source, like the e-bus

    normal feedpath diode on Z-11.



    Bob . . .

nuckollsr(at)cox.net
Guest

Posted: Thu Mar 23, 2006 5:03 pm Post subject: Battery charging

At 03:09 PM 3/23/2006 -0500, you wrote:



 	  Quote: 	
		  



I understand if you connect hte two batteries the second, and smaller

battery will get somewhat of a charge, but will the second battery stay

in a charged state, and be at full capacity when you need it? Looks to

me if you connect the two together, they act as one battery, as far as

the voltage regulator is concerned, and if the little battery demands

volts from the voltage regulator, the other battery gets over charged,

or vice versa. Am I thinking right here, can they be charged separately

with only one voltage regulator?


	


   Batteries charge based on voltage presented at their terminals.

   They have no way to know how or why the applied voltage got to

   be where it is right now. It might be that your alternator is

   overloaded or your voltage regulator setting is wrong but a battery

   no way to know (or react to) any number of additional batteries on

   line.



   There's a lot of myth and misunderstanding about the performance one

   can expect both in the charging and discharging of paralleled batteries.

   If your alternator and voltage regulator are doing their job, ALL batteries

   of ANY size will be serviced to their individual needs. When discharging

   paralleled batteries, you will have access to 100% of energy available

   from the sum total of energy stored irrespective of size or condition

   of the individual batteries.



   Bob . . .

jmfpublic(at)comcast.net
Guest

Posted: Fri Mar 24, 2006 11:39 am Post subject: Battery charging

Bob said:



   "There's a lot of myth and misunderstanding about the performance one

   can expect both in the charging and discharging of paralleled batteries.

   If your alternator and voltage regulator are doing their job, ALL batteries

   of ANY size will be serviced to their individual needs. When discharging

   paralleled batteries, you will have access to 100% of energy available

   from the sum total of energy stored irrespective of size or condition

   of the individual batteries."



This presumes identical battery chemistry.  It would be uncertain that charge requirements would be identical for an adsorbed glass mat (AGM) and a gel cell, for example.  The flooded battery type would be yet another voltage point.  Some battery chargers have a switch to choose the battery type.  Recall that the specific gravity of the battery acid used to activate aircraft flooded cells in higher than that used for cars, and that the specific gravity of sufuric acid in a sealed AGM battery is dependent on the choice of the manufacturer.  I suspect that the biggest difference in charge voltage is between those handy-available-in-smaller-size gel cells, and the AGM and flooded cell batteries, which are more similar.  The gel cell is a nice, low current drain type of cell, but it may not parallel well with the other types.



Jim Foerster, J400, still building

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

Posted: Fri Mar 24, 2006 12:50 pm Post subject: Battery charging

Typically, your alternator will be set at about 13.8 to 14.2 volts. All 

the variations in lead-acid battery chemistry will "fully" charge at 

that voltage. Some may take longer than others to charge up completely, 

but the difference will not be that great. This is because 13.8 volts is 

above the "float" voltage of all of the various flavors of lead-acid 

batteries.



    You can parallel lead-acid batteries with no worries.



    The only possible downside to paralleling batteries is if one of 

them develops a shorted cell. This bad battery will discharge the good 

one if you don't have some sort of battery isolator to prevent that.



Bill Dube' <http://www.KillaCycle.com>



James Foerster wrote:



 	  Quote: 	
		  



Bob said:



   "There's a lot of myth and misunderstanding about the performance one

   can expect both in the charging and discharging of paralleled batteries.

   If your alternator and voltage regulator are doing their job, ALL batteries

   of ANY size will be serviced to their individual needs. When discharging

   paralleled batteries, you will have access to 100% of energy available

   from the sum total of energy stored irrespective of size or condition

   of the individual batteries."



This presumes identical battery chemistry.  It would be uncertain that charge requirements would be identical for an adsorbed glass mat (AGM) and a gel cell, for example.  The flooded battery type would be yet another voltage point.  Some battery chargers have a switch to choose the battery type.  Recall that the specific gravity of the battery acid used to activate aircraft flooded cells in higher than that used for cars, and that the specific gravity of sufuric acid in a sealed AGM battery is dependent on the choice of the manufacturer.  I suspect that the biggest difference in charge voltage is between those handy-available-in-smaller-size gel cells, and the AGM and flooded cell batteries, which are more similar.  The gel cell is a nice, low current drain type of cell, but it may not parallel well with the other types.



Jim Foerster, J400, still building

nuckollsr(at)cox.net
Guest

Posted: Tue Mar 28, 2006 6:03 am Post subject: Battery charging

At 11:35 AM 3/24/2006 -0800, you wrote:



 	  Quote: 	
		  

<jmfpublic(at)comcast.net>



Bob said:



    "There's a lot of myth and misunderstanding about the performance one

    can expect both in the charging and discharging of paralleled batteries.

    If your alternator and voltage regulator are doing their job, ALL 

 batteries

    of ANY size will be serviced to their individual needs. When discharging

    paralleled batteries, you will have access to 100% of energy available

    from the sum total of energy stored irrespective of size or condition

    of the individual batteries."



This presumes identical battery chemistry.  It would be uncertain that 

charge requirements would be identical for an adsorbed glass mat (AGM) and 

a gel cell, for example.  The flooded battery type would be yet another 

voltage point.  Some battery chargers have a switch to choose the battery 

type.  Recall that the specific gravity of the battery acid used to 

activate aircraft flooded cells in higher than that used for cars, and 

that the specific gravity of sufuric acid in a sealed AGM battery is 

dependent on the choice of the manufacturer.  I suspect that the biggest 

difference in charge voltage is between those 

handy-available-in-smaller-size gel cells, and the AGM and flooded cell 

batteries, which are more similar.  The gel cell is a nice, low current 

drain type of cell, but it may not parallel well with the other types.


	


   Why would one put a gel cell in an airplane? When we certified

   the Gates Genesis series RG batteries into TC aircraft the

   cold cranking test results were profound. After cold soaking

   new gel, flooded, and RG batteries in the deep freeze overnight

   (about -10F), each battery was subjected to a 300A constant current

   load for 15 seconds and terminal voltage plotted. The RG battery

   had higher terminal voltage AFTER 15 seconds than the flooded battery

   STARTED with. The gel wouldn't deliver 300A at any useful voltage.



   All three batteries would crank an engine nicely at room temp

   but the cold weather performance differences made it a hands-down

   decision as to the superior technology for service in aircraft.



   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       >

roadmaps

Joined: 08 Nov 2007
Posts: 49

Posted: Thu Nov 08, 2007 7:57 am Post subject: Re: Battery charging

In using a diode to charge the second battery what current rating should the diode have? How do you calculate the current going through the diode?



John T

nuckolls.bob(at)cox.net
Guest

Posted: Thu Nov 08, 2007 4:52 pm Post subject: Battery charging

At 07:57 AM 11/8/2007 -0800, you wrote:



 	  Quote: 	
		  



In using a diode to charge the second battery what current rating should 

the diode have? How do you calculate the current going through the diode?


	


   Why a diode? You can hook the second battery

   right up to the system through a switch or relay

   and make sure it gets the full benefit of a

   charge from full bus voltage.



   Dual batteries have been discussed for many

   purposes and illustrated in the z-figures.

   Assuming you have active notification of alternator

   failure (low bus volts warning light) then there's

   little to be gained and something to be lost

   in using a diode for battery isolation. A switch

   works better.



   But if you have to have a diode, get one of

   these things from Radio Shack



http://tinyurl.com/ytcdr7



   and use one of the four diodes it contains.

   It's rated at 25A and will probably handle

   the task just fine . . . assuming that the

   "second battery" is a relatively small one.

   Like 10 a.h. or less.



   Bob . . .

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