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Alternators - To Fuse or not to fuse - That IS the questi

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nuckolls.bob(at)aeroelect
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Posted: Sun Sep 10, 2017 6:38 am Post subject: Alternators - To Fuse or not to fuse - That IS the questi

At 12:35 PM 9/9/2017, you wrote:

  	  Quote: 	
		  Don,

 Thanks for the West Mountain CBA info. One possible problem I see with using the carbon pile is that the algorithms used to derive capacity are probably based on lead acid batteries, not LiFePO batteries. Aren't the discharge characteristics of Li batteries radically different from lead acid batteries? 	




    Yes. You can use the load tester on LiPo but I'm

    uncertain as to the target voltage for the test.

    9v may be too low . . . but certainly 10v would

    not hurt it.



    The load test for battery performance is a COMPARATIVE

    activity that looks as changes over time staring with

    the new battery. You won't find useful data or algorithms

    that equate load number to capacity values.  This

    is like using a dip stick in the oil pan . . . you

    don't know the capacity of the pan . . . only how

    much it has dropped from full.



 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Sun Sep 10, 2017 6:52 am Post subject: Alternators - To Fuse or not to fuse - That IS the questi

At 01:21 PM 9/9/2017, you wrote:

  	  Quote: 	
		  The discharge characteristics are not dirrerent enough to cause a problem using the carbon pile. If you try the pile be careful, they get quite hot. I prefer to use the CBA, but it takes many hours to discharge to 10 volts. 	


   Yes . . . because these are entirely different

   kinds of tests. The carbon pile tester does get

   hot . . . it will stink at the end of your test.

   5-600 amps at 9v is 5400 watts . . . enough snort

   to run your house. This energy is dumped into

   that little stack of carbon disks.



  http://tinyurl.com/ybcc9v9r



 

   [img]cid:.0[/img]



   So yes, extending the test beyond 15 seconds

   is probably not a good thing to do!



   The CBA test gets you a whole different set

   of data. It counts electrons under a specified

   load (your ENDURANCE load) and measures the

   time that load will be supported.



   A much more precise measurement of the battery's

   ability to perform in alternator-out conditions.

  

   Another alternative is Z13/8. Here there is

   no plan B that calls for tapping the battery

   during main alternator out conditions. Hence,

   you replace the battery at first sign of

   sluggish cranking performance (the crudest

   form of a load test).



   This is why I've long suggested that Z13/8

   is the lowest cost of ownership, highest

   reliability system you can install on your

   a/c.  No test equipment, no preventative

   maintenance, run the battery 'til it wheezes.



   How much simpler can it get?



 

 

   Bob . . .

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nuckolls.bob(at)aeroelect
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Posted: Sun Sep 10, 2017 7:13 am Post subject: Alternators - To Fuse or not to fuse - That IS the questi

At 03:22 PM 9/9/2017, you wrote:

  	  Quote: 	
		  Well, an single SLA has very different amp-hour ratings depending on the discharge rate. And 'consumer' SLAs (PC680, etc that were originally intended for watercraft, and others that some of us use that were intended for UPSs and/or electric carts, etc) are rated differently from the certified a/c SLAs, if I've read spec sheets correctly.Â 	


    SVLA batteries have very significant internal

    resistance which wastes energy under load . . .

    a loss that increases with load. The battery's

    USEFUL capacity must be tied to the load. 



    Here's the spread sheet on a PC680



 [img]cid:.0[/img]



   Note that the LIGHTER you load it, the BETTER the

   capacity. The PC680 is speced as a 16 a.h. device

   at the 20 HOUR RATE.



   But cranking your engine at 150 amps will get

   your only  2 minutes of operation with a 65%

   drop in capacity. The rest of that engergy will

   be used up getting the battery hot.



   Lithium's very low internal resistance produces

   very flat load vs. capacity curves. Here's

   an exemplar family of LiPo discharge curves.



 [img]cid:.1[/img]



   Note that you get essentially ALL the capacity you

   paid for irrespective of load.



   Early on in the marketing of LiPo you saw the

   term "lead acid equivalent". This was a smoke-n-

   mirrors term created by the LiPo marketing that

   spoke only to cranking ability . . . fine if

   you owned a motor cycle or snowmobile. Totall

   bogus for airplane guys that had ENDURANCE

   requirements. I hammered EarthX about this and

   in years since you will see BOTH numbers.

   LAEQ and CAPAH.



   I'll have to back off on that 10v figure for

   using a load tester on LiPo batteries. The

   Significant load test for LiPo has to be

   select a number on a par with the real cranking

   current of your engine. Apply THAT load for

   15 seconds then read the voltage at the

   end of 15 seconds.



   The most telling figure of merit is still

   ENDURANCE under anticipated load. Do that

   in the hangar or get the instruments that

   will count the electrons.



 

   Bob . . .

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