deep battery discharge [RE-wrenches]

[Aaron Wellendorf]

Ron,

 

The battery should be fine. It is obviously not great to discharge a
battery like that, but the heavy industrial battery is built to take it
better than your car battery can (and does from time to time). I had
this happen on my own system, which is still working fine a year later.
If a cheap car battery can handle leaving the lights on a couple of
times until it's dead, then the industrial battery can too, right? No
one should do this on purpose, but it does happen. The battery will have
a somewhat reduced life, but 15 years reduced to maybe14 years would be
hard to quantify due to the many other things that will happen in the
battery's life.

 

Because discharging the battery removes sulphuric acid from solution
the electrolyte level goes down (Basically, it is like compressing a
liquid into a solid.). Because of the very deep discharge, the
electrolyte level has gone way down. Don't be alarmed about this. Add
distilled water to raise the electrolyte level just barely to cover the
plates. If you can see the electrolyte, STOP adding water! When the
battery recharges, the level will return to normal. If you overfill when
the battery is discharged you will probably end up with an overflowing
mess.

 

When any lead-acid battery is overly discharged (<20% SOC) the internal
resistance goes up. The farther down it goes, the higher the resistance.
This is normal. Do not try to equalize the battery to get a normal
charge rate. You will have to be patient and let the battery charge
slowly. Once the battery gets to about 20% SOC, the current and voltages
will return to what you normally see. 

 

When the battery is more than ~50% full, you can initiate a full
equalization charge to 2.5V/cell and hold it there for about 3-4 hours.
You can take temperature adjusted specific gravity measurements as you
would before. Monitor the battery temperature (electrolyte temperature)
during the charging process and do not let it get above 115F. Reduce the
charge rate if necessary to keep the battery temperature less than 115F.

 

Try to have patience. This whole process may take several days. You are
like a doctor treating an injured patient, so give it some time to heal.
Once you finish the equalization process, the battery is back to normal
and should see many more years of life.

 

If this deep discharge happens to old batteries, it could cause failure
of some of the cells. But shooting an old horse tends to kill it, too.

 

Good luck!

 

Aaron Wellendorf

DC Power Systems

 

 

 

-----Original Message-----
From: Ron Young [mailto:solareagle at solareagle.com] 
Sent: Friday, July 28, 2006 2:59 AM
To: RE-wrenches at topica.com
Subject: deep battery discharge [RE-wrenches]

 

 

Hi all,

I've got a client who inadvertently discharged his relatively new set 

of 1900 a/h lead acid batteries (left a light on that was directly 

wired for about three weeks). The voltage reading is 10.5v, I can't 

even get a reading on a hydrometer so it looks like the electrolyte is 

pretty much water. The 750 watt 12v array is only registering .4 amp in 

bright sun -through an SB50L -is this because the batteries can't 

accept a charge now? Are they toast or can they be recovered?

 

Ron Young

 

earthRight - Solareagle.com

(250) 392-7119

79f North Third Ave

Williams Lake, BC

V2G 2A3

Canada

 


[Non-text portions of this message have been removed]


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