[Milsurplus] Re: [armyradios] BB-490U from Fair Radio

[Patricia Watkins]

George,

Thanks for the extra info.  I am using the charger that came with the
batteries, so I am assuming that the charge voltage is correct for these
cells.  I am also doing the 2nd charge cycle by the book, and will do
another load test tomorrow after an 8hr rest time.  The Kelepa web site has
some instructions on rehydrating gel cells, but I don't want to do that if
it isn't needed, and I will just do the load test to see if I can get the
correct or nearly correct amp hrs out first.  I am sort of hoping that one
is bad so that I can try out the desulfating circuit.

John  WD5ENU/A45XV
----- Original Message -----
From: "aGEnuine ham" <gl4d21@juno.com>
To: <jwatkins@omantel.net.om>
Cc: <milsurplus@mailman.qth.net>
Sent: Wednesday, January 15, 2003 7:10 PM
Subject: Re: [Milsurplus] Re: [armyradios] BB-490U from Fair Radio


> John and group:
>
> Let me share a couple of very brief comments about lead acid batteries
> (wet or gelled electrolyte) in long term applications.
>
> First, if the actual chemistry of specific cells is unknown, particularly
> the plate alloy contents, it is all guesswork anyway.  Having started
> with that caveat, for all lead-acid batteries, constant voltage charging
> is the accepted charge regimen.  For most common varieties, at room
> temperature, the charge voltage is 2.4 volts per cell.  Various books
> show the voltage vs. temperature curves for other environments.  When a
> cell which has useful capacity and useful remaining life has been on
> charge at that voltage long enough to recharge fully, the current will
> drop to a low value, milliamperes for even large cells.  (Sorry, I don't
> have my tech manuals here, or I could quote specific values.)  Anyway, if
> the charge current is never very high, the cell is probably sulfated or
> dry, either constituting failure.  If the current stays relatively high,
> the cell has developed internal physical damage resulting in internal
> current leakage, and is also failed.
>
> Now, when the full charge state of a good cell is reached, long-term
> constant voltage charging (float) at 2.4 volts will eventually damage the
> battery.  In the fully charged state, the float voltage must be dropped,
> and here is where it gets very tricky.  The exact voltage is VERY
> temperature dependent, and VERY alloy dependent.  I use 13.2 volts for 6
> cell batteries as an average, but the actual range may be from 12.8 volts
> to 14+ volts, depending.  Now, go back and reread my second sentence
> starting with: "First, if..."
>
> The only successful rehabilitation scheme I have ever seen is the pull
> out and replace the old plates and separators approach used in telephone
> central offices and switching centers back in the early part of the last
> century.  But, glass cased batteries are expensive and hard to come by
> anymore.
>
> One final comment.  Be aware of the difference between standard
> automobile batteries and deep discharge (often called marine or RV)
> batteries.  Typical auto batteries are designed to produce the highest
> peak (starting) current per unit volume, but will be ruined by one or two
> full discharges.  This also applies to many gelled electrolyte cells.
> The deep discharge batteries trade peak current and capacity for the
> ability to withstand numerous deep discharges.  Different plate alloy,
> and most importantly, stronger separators between the plates.
>
> There are a number of excellent resources in print, both from battery
> manufacturers, and in the open literature.  I recommend perusal of some
> of these if you want specific numbers or other details.  And, I might
> add, I have encountered many designs of battery chargers and battery
> operated systems which were designed by people apparently unfamiliar with
> even the most rudimentary characteristics of lead-acid batteries.  There
> is no fame or glory in being the power supply designer, so that task is
> too often shoved down to the lowest person on the team, and he or she may
> not have the background or experience to do it right.
>
> 73,
> George
> W5VPQ
>
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