[aprssig] Re: SLA Chargers - Battery Question

Bruce Gordon bgordon at ltronics.com
Tue May 3 21:01:18 EDT 2005

Hello all,

You may be interested in a simple solution we use in our comm van.  The van,
which is parked outside,  has a current limited, temperature compensated
charging system set to give 12 hour recovery for the main 400 AH battery
bank.  We use these same 2.3 AH Yuasa batteries for 8 portable trackers we
keep in the van.  We found that their float charging characteristic closely
matched that of the main bank.  Directly connecting the trackers could be
damaging under some conditions so we put a 500 mA resettable fuse inside
each tracker.  This type of fuse will pass its rated current but will heat
up and change to a higher resistance (trip) at about 150 to 250 % of rated
current. If either a dead tracker is connected for charging or a heavy load
is demanded from the main bank, the fuse will limit charge or discharge
current.  When the tracker comes near full charge, the fuse resets so the
tracker gets the full benefit of the precision charging system.  Simple,
cheap and working well for several years.

Bruce Gordon N6OLT

----- Original Message -----
From: "Stephen H. Smith" <wa8lmf2 at aol.com>
To: "TAPR APRS Mailing List" <aprssig at lists.tapr.org>; <jason at creager.com>
Sent: Tuesday, May 03, 2005 3:48 PM
Subject: [aprssig] Re: SLA Chargers - Battery Question

> j
> >Also, since we're talking about batteries, I bought some Yuasa MP2.3-12
> >2.3Ah SLA batteries for tracker use. Their rated "Stand By Use" charging
> >stats are 13.5-13.8V and "no limit" on current. (You may see where I'm
> >going with this.)  Is there anything wrong with hooking it up to an
> >port on my RigRunner? (Fused, of course, but for what amperage?)
> >
> >I'm perplexed by the "no limit" current. I assume that means that the
> >battery can't be damaged by too much current when charging at that level.
> >(The Cyclic Use stats are 14.4-15.0V @ .58A max.)
> >
> >
> >
> The charge current will be self-limiting.   When charging from a
> constant voltage source in this range (13.5-13.8), the battery terminal
> voltage will rise to the power supply's voltage at full charge.  When
> the voltages are equal, there will be no current flow into the battery
> at all since it takes a voltage difference between the supply and the
> battery to make current flow.
> Actually, I suspect the spec intended to say "no limit on charging TIME"
> if you use a stiffly-regulated voltage source as mentioned above. (You
> can leave a power supply connected across the batteries indefinitely as
> long as you don't try to force the terminal voltage above 13.8 which
> would cause a large current to flow though the battery indefinitely
> causing it's interior to heat up. )
>  If the batteries are discharged and have a terminal voltage well below
> 13.5, a very heavy current WILL flow until the terminal voltage rises.
> In this case you would want to limit the inrush current to something
> approximately equivalent to the AH capacity; i.e. in this case 2-3
> amps.  This implies a constant-voltage (regulated) supply with
> adjustable current limiting (or a small supply that simply can't put out
> much current -- which is probably what you would use anyway for standby
> float charging).
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