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AGM longevity (was: Odyssey % of charge)

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

Posted: Fri Feb 24, 2006 5:31 pm Post subject: AGM longevity (was: Odyssey % of charge)

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.

Brian Lloyd wrote:

 	  Quote: 	

Robert L. Nuckolls, III wrote:

>>Having a smart energy monitor is necessary in a system where you will

>>have irregular charge/discharge cycles and want to know how much is left

>>in the battery.

>>      

>>

>    Agreed . . . but how does this happen on an airplane and how

>    often might one expect to encounter it?  . . . and are there

>    less complicated and more positive ways to achieve the desired

>    mission/maintenance conditions?

>    

>

Oh, I agree that you don't need a complex energy monitor nor do you need

a fancy charger. OTOH, I have had experience with batteries failing due

to overcharge in hot weather and failing to charge properly in cold weather.

>>If you always recharge the battery to full every time,

>>you can have a much simpler energy monitor that isn't quite so smart.

>>      

>>

>    Yup.

>    

>

>>The biggest issue as I see it is that you need to make sure you don't

>>overcharge the battery in summer but that you do actually charge the

>>battery in winter. That implies temperature compensation.

>>      

>>

>    Agreed . . . and it's not clear that we have really practical

>    ways to achieve that. The LR-3 from B&C offers a battery temp

>    sensor option. But it's not clear to me that this option will

>    produce really meaningful differences in battery performance for

>    most of our fellow airplane drivers.

>    

>

I believe that this is one of the key reasons why current crop of

"sealed" AGM aircraft batteries have such a poor service record. Flooded

cell batteries shrug off overcharge by just boiling off excess water

which gets topped off by the owner or mechanic. AGMs build up pressure

in the case and valves open and relieve the pressure, letting the water

go to the atmosphere. The AGM battery, having no excess

electrolyte/water, quickly quits working. I have never had an AGM

battery (Concorde especially) survive longer than two years in a

standard aircraft electrical system.

Brian Lloyd

brian-yak(at)lloyd.com

brian

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

Posted: Fri Feb 24, 2006 7:50 pm Post subject: AGM longevity (was: Odyssey % of charge)

Bill Dube wrote:



 	  Quote: 	
		     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.


	


Right. This is called an equalization charge.



 	  Quote: 	
		       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.


	


Hmm. The big, expensive AGM and gel-cell batteries I used on my boat

came with warnings from the manufacturer to never do an equalization

charge, that the normal charging regimen would ensure proper charging.



So when it comes to batteries, I read and follow the manufacturer's

recommendations.



Good information by the way.



-- 

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-Exupery

_________________
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

klehman(at)albedo.net
Guest

Posted: Sat Feb 25, 2006 6:22 am Post subject: AGM longevity (was: Odyssey % of charge)

This is one I've never heard of before.



The manufacturer of my wee AGM specifies a float voltage which I've been 

using. This implies that a pulse type battery maintainer might be better 

or maybe that they should not be float charged continuously while in 

storage??  These are small but somewhat pricey Dekka batteries on a Z-14 

architecture so there is no plan to periodically replace them  - just 

flog flog them until noticeable starting performance suffers.



thanks

Ken



 	  Quote: 	
		      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.

brian

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

Posted: Sat Feb 25, 2006 9:11 am Post subject: AGM longevity (was: Odyssey % of charge)

Ken wrote:

 	  Quote: 	
		   

 

 This is one I've never heard of before.

 

 The manufacturer of my wee AGM specifies a float voltage which I've been 

 using. This implies that a pulse type battery maintainer might be better 

 or maybe that they should not be float charged continuously while in 

 storage??  These are small but somewhat pricey Dekka batteries on a Z-14 

 architecture so there is no plan to periodically replace them  - just 

 flog flog them until noticeable starting performance suffers.


	


Follow Deka's instructions for maintaining the battery. My larger 245AH

8D Deka AGMs say don't give them an equalization charge. Flooded cell

batteries benefit from a periodic equalization charge.



-- 

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-Exupery

alexpeterson(at)earthlink
Guest

Posted: Sat Feb 25, 2006 7:07 pm Post subject: AGM longevity (was: Odyssey % of charge)

 	  Quote: 	
		     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.


	




Bill, excellent post!  What would be your recommendation for a charger to

accomplish this periodic overcharging method for cleaning the negative

plate? I suspect that this is what my PC680 needs after two years.



Alex Peterson

RV6-A N66AP 719 hours

Maple Grove, MN

brian

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

Posted: Sat Feb 25, 2006 7:50 pm Post subject: AGM longevity (was: Odyssey % of charge)

Alex Peterson wrote:

 	  Quote: 	

>   Occasionally, you need to purposely overcharge the battery 

> to let the negative plate catch up with the positive plate. A 

 Bill, excellent post!  What would be your recommendation for a charger to

 accomplish this periodic overcharging method for cleaning the negative

 plate? I suspect that this is what my PC680 needs after two years.

Before you opt for an equalization charge make sure this is supported by

the manufacturer.

As for an equalization charge, you can accomplish it with any adjustable

power supply that will allow you to set the voltage to that specified by

the manufacturer for performing an equalization charge. Typically an

equalization charge takes around two hours over and above the time

required to bring the battery up to full charge.

-- 

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-Exupery

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

Posted: Mon Feb 27, 2006 5:14 pm Post subject: AGM longevity (was: Odyssey % of charge)

I know a little bit about batteries. Check out my other hobby. 

<http://www.KillaCycle.com>

   and my daily driver <http://www.haritech.com/wabbit.html>



    Bill Dube'



Brian Lloyd wrote:



 	  Quote: 	
		  



Bill Dube wrote:



  



>  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.

>    

>



Right. This is called an equalization charge.



  



>    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.

>    

>



Hmm. The big, expensive AGM and gel-cell batteries I used on my boat

came with warnings from the manufacturer to never do an equalization

charge, that the normal charging regimen would ensure proper charging.



So when it comes to batteries, I read and follow the manufacturer's

recommendations.



Good information by the way.

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

Posted: Mon Feb 27, 2006 5:18 pm Post subject: AGM longevity (was: Odyssey % of charge)

You are correct. They should not be continuously float charged for 

longest life.

AGMs typically have very small self-discharge. If your airplane doesn't 

have some continuous drain (like the clock or avionics memory) then the 

AGM should stay quite well charged for 6 months or so. If you put on the 

float (or pulse) charger for a couple of days every few months, that 

should keep up the AGM just fine.

Bill Dube'

Ken wrote:

 	  Quote: 	

This is one I've never heard of before.

The manufacturer of my wee AGM specifies a float voltage which I've been 

using. This implies that a pulse type battery maintainer might be better 

or maybe that they should not be float charged continuously while in 

storage??  These are small but somewhat pricey Dekka batteries on a Z-14 

architecture so there is no plan to periodically replace them  - just 

flog flog them until noticeable starting performance suffers.

thanks

Ken

>   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.

> 

>

>    

>

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

Posted: Mon Feb 27, 2006 5:54 pm Post subject: AGM longevity (was: Odyssey % of charge)

Here is an example of a high-end battery charger. Zivan sets these up to 

giver precisely the correct charge algorithm for the specific brand and 

type of battery.

http://www.zivanusa.com/BC1BatteryCharger.htm

    They use this sort of high-end charger on fork lifts, golf carts, 

etc where they care about battery life. Take a look at the charge curves 

on some of these chargers and you will get an idea of the right way to 

charge a battery.

I own a Zivan NG3 that I used for my electric car when I had Optima AGM 

lead-acid batteries in it. It ran the curves that I spoke of in the 

previous post. In an EV, you typically have over $1000 in batteries that 

you want to last as long as possible. Thus, you buy a charger that will 

run the "perfect" charge cycle. These high-wattage chargers typically 

cost more than $1000, so adding the brains to do the proper charge 

doesn't change the final cost of the charger very much and saves you a 

bunch in batteries.

    If you have an AGM that is a little tired, you can try the 

overcharge that I outlined in the previous post. If it has sulfation or 

a undercharged negative plates, it will perk up a bit. Crank the plane 

up, let it charge normally (like on a flight) and then give it another 

overcharge. It should crank even better.

    If it is running out of water because your voltage regulator is set 

too high, the overcharge will not help. You will not notice a difference 

in cranking voltage. Thus, there is no point in doing a second go at it. 

You should probably just get a new battery.

    To do the overcharge, I use a bench power supply and set the voltage 

and current exactly, but you won't have one probably. A good substitute 

is a 15 volt, 2 or 3 amp Toshiba laptop AC adapter. You can pick one up 

on Ebay for about $10.

http://cgi.ebay.com/Toshiba-Laptop-Power-Adapter-DC15V-2A_W0QQitemZ6853456587QQcategoryZ31517QQrdZ1QQcmdZViewItem

      or   

http://cgi.ebay.com/Toshiba-Laptop-Power-Adapter-PA2426U-for-T-Series-NIB_W0QQitemZ6852048387QQcategoryZ31517QQrdZ1QQcmdZViewItem

   or  

http://cgi.ebay.com/GENUINE-TOSHIBA-LAPTOP-AC-ADAPTER-PA2450U-POWER-CORD_W0QQitemZ6852574714QQcategoryZ116318QQrdZ1QQcmdZViewItem

Cut off the computer connector and attach a pair of clip leads. (The 

shield is negative.) Disconnect one of the battery leads and connect up 

the Toshiba laptop supply. Leave it on for a 3 or 4 hours. Should do the 

trick. Don't leave it connected for more than a few hours or it will dry 

out your battery. When the Toshiba power supply is no longer warm to the 

touch, disconnect it.

    Bill Dube'

Alex Peterson wrote:

 	  Quote: 	

>  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.

>    

>

Bill, excellent post!  What would be your recommendation for a charger to

accomplish this periodic overcharging method for cleaning the negative

plate? I suspect that this is what my PC680 needs after two years.

Alex Peterson

RV6-A N66AP 719 hours

Maple Grove, MN

hdwysong(at)gmail.com
Guest

Posted: Mon Feb 27, 2006 6:14 pm Post subject: AGM longevity (was: Odyssey % of charge)

Cool bike, Bill!  I must admit that I bookmarked your web page 

(alongside www.deadmike.com) to use when "she" starts telling me that 

flying airplanes upside-down is too dangerous.  



D



do not archive



Bill Dube wrote:

 	  Quote: 	
		   

 

 I know a little bit about batteries. Check out my other hobby. 

 <http://www.KillaCycle.com>

    and my daily driver <http://www.haritech.com/wabbit.html>

 

     Bill Dube'

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