[aprssig] Re: SLA Chargers - Battery Question

Stephen H. Smith wa8lmf2 at aol.com
Tue May 3 18:48:03 EDT 2005


>Also, since we're talking about batteries, I bought some Yuasa MP2.3-12 12V
>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 unused
>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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