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Will SVLA charge on a sustaining voltage?

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nuckollsr(at)cox.net
Guest

Posted: Fri Feb 16, 2007 7:20 pm Post subject: Will SVLA charge on a sustaining voltage?

After a 3.0A discharge to 11.0 volts where the battery

delivered at total of 11.2 ah of capacity, I connected

the battery to a 13.0 volt power supply and waited 18+

hours until the 're-charge' current was down to under

30 milliampers.



A subsequent 3.0A discharge produced only 8.8 AH of

useful output. The same battery is back on a Battery

Tender Jr for another charge/discharge cycle.



This experiment suggests that there's something to

the notion of carrying the battery's recharge profile

up to the point where rate-of-change for voltage takes

the upward inflection which is the battery's way of

letting the outside world know that it's getting pretty

close to full.





        Bob . . .



        ----------------------------------------

        ( IF one aspires to be "world class",  )

        ( what ever you do must be exercised   )

        ( EVERY day . . .                      )

        (                  R. L. Nuckolls III  )

        ----------------------------------------

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klehman(at)albedo.net
Guest

Posted: Sat Feb 17, 2007 9:33 am Post subject: Will SVLA charge on a sustaining voltage?

I always deal with partially discharged batteries rather than fully 

discharged ones but I have probably waited at least a couple of days to 

notice the recharge current to fall to the float current and that is 

typically under 10 ma depending on the battery.  The actual energy under 

that upward inflected curve is small but it still takes awhile to get 

the equivalent at very small charging current of course. I use 13.5 

volts for AGM batteries which probably helps. 13.5 is more in line with 

what I've seen on things like burglar alarms and small UPS batteries.



Someone will no doubt mention that there is more to this than just 

restoring a full charge though. Below is a repeat of a very good post 

out of the archives which suggests that charging with that voltage 

inflection is a good thing for storage batteries that don't get a bit of 

overcharging in a vehicle. It might also give a possible reason why 

pulse charging might have some benefit even if the desulphation theory 

is bunk. The  strong inflection that shuts off the built in charger on 

my booster battery pack is a better scheme for frequently used batteries 

and probably for VRLA batteries in general.  That $30. booster battery 

pack has a 15AH battery and it often runs a 120vac inverter and it also 

makes a handy (less than an amp) charger by just clipping it onto 

another battery and plugging it in to let them both charge in parallel.



Ken






There are four main reasons why AGMs wear out.



1) Loss of electrolyte

2) Grid corrosion

3) Sulfation

4) Paste degradation



    If you overcharge an AGM excessively, it will lose electrolyte and 

dry out. This is NOT why they wear out in airplanes and cars (typically.)



    Typically, AGMs go bad because they are not properly charged. If you 

don't over charge them a little bit on a regular basis, the negative 

plate gets further and further behind the positive plate. The negative 

plate then sulfates and you lose capacity and cranking power. (In the 

short term, you lose capacity simply because the negative plate is not 

fully charged.)



    Why you don't need to add water to an AGM is that the oxygen and 

hydrogen gas recombine in the separator to form water. This 

recombination process is not 100% efficient, and it causes the negative 

plate to take slightly less charge than the positive plate when you 

re-charge the battery. Each cycle gets the negative plate a bit more behind.



  Occasionally, you need to purposely overcharge the battery to let the 

negative plate catch up with the positive plate. A couple times per 

year, you bring the battery up to 14.8 volts and let the current taper 

off to less than an amp. You then push in a constant current of about 4% 

of the  amp-hr rating of the battery for about an hour. This cleans off 

the negative plate.



    High-end voltage regulators do something like this (like on boats 

and motor homes). Every time you start up the engine, it charges up the 

battery to normal voltage, then it gives the battery a slight overcharge 

for a few minutes. Makes the big expensive AGM batteries last much longer.



 >>>> What causes the other types of failures, just in case you wanted 

to know. <<<



    Excessive overcharging will cause the loss of electrolyte. Severe 

discharge, causing reversal of a cell or two, will also cause 

electrolyte loss.



    Grid corrosion occurs if you leave the battery on float  for a long 

time. The oxygen gas formed eats at the grids that support the paste.



    Sulfation is caused by leaving the battery discharged for extended 

periods of time. Not fully charging the battery and leaving that way 

will also cause sulfation.



    Paste degradation is caused by repeated severe and/or deep 

discharges. Cranking the battery flat over and over is a good way to 

cause paste degradation.

Robert L. Nuckolls, III wrote:



 	  Quote: 	
		   

 <nuckollsr(at)cox.net>



 After a 3.0A discharge to 11.0 volts where the battery

 delivered at total of 11.2 ah of capacity, I connected

 the battery to a 13.0 volt power supply and waited 18+

 hours until the 're-charge' current was down to under

 30 milliampers.



 A subsequent 3.0A discharge produced only 8.8 AH of

 useful output. The same battery is back on a Battery

 Tender Jr for another charge/discharge cycle.



 This experiment suggests that there's something to

 the notion of carrying the battery's recharge profile

 up to the point where rate-of-change for voltage takes

 the upward inflection which is the battery's way of

 letting the outside world know that it's getting pretty

 close to full.



        Bob . . .

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William.P.Dube(at)noaa.go
Guest

Posted: Fri Feb 23, 2007 10:13 am Post subject: Will SVLA charge on a sustaining voltage?

To charge a lead-acid battery 100%, you must go to to at least 13.8 

volts. It will take _forever_ at this voltage. To charge it more 

quickly, and to help remove any sulfation, you have to go above 14 

volts. Ideally, you would want to go to 14.7 volts (or a bit more,) let 

the current taper off, then go to 13.8 volts to maintain the charge.



Bill Dube'



Robert L. Nuckolls, III wrote:



 	  Quote: 	
		   

 <nuckollsr(at)cox.net>



 After a 3.0A discharge to 11.0 volts where the battery

 delivered at total of 11.2 ah of capacity, I connected

 the battery to a 13.0 volt power supply and waited 18+

 hours until the 're-charge' current was down to under

 30 milliampers.



 A subsequent 3.0A discharge produced only 8.8 AH of

 useful output. The same battery is back on a Battery

 Tender Jr for another charge/discharge cycle.



 This experiment suggests that there's something to

 the notion of carrying the battery's recharge profile

 up to the point where rate-of-change for voltage takes

 the upward inflection which is the battery's way of

 letting the outside world know that it's getting pretty

 close to full.





        Bob . . .



        ----------------------------------------

        ( IF one aspires to be "world class",  )

        ( what ever you do must be exercised   )

        ( EVERY day . . .                      )

        (                  R. L. Nuckolls III  )

        ----------------------------------------

- The Matronics AeroElectric-List Email Forum -

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:

http://www.matronics.com/Navigator?AeroElectric-List

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