[OT] Charging UPS batteries outside the UPS

Karl 33karl at verizon.net
Thu Aug 9 17:48:05 EDT 2007


Drew Van Zandt wrote:
>
> I would expect an automotive charger to exceed the 2.88A charge current
> by possibly quite a bit; it depends very much on the charger.  (I suppose
> I'm saying you should RTFM for the charger, if you have one.)  I know some
> chargers I've seen have 8A or even higher current ratings.  I would expect
> the voltage of a car charger to be in the right ballpark, at least, 
> but again
> that may be in the manual.
>
> Exceeding the 2.88A charge current by a large amount would be a Bad 
> Thing (TM);
> battery damage or even explosions could result.  Do not dispose of in 
> fire, do
> not bend, fold, spindle or mutilate, no user servicable parts inside.  
> Do not eat.
> Do not hit towards human or animal.  Not a toy, keep out of reach of 
> children.
> Not for use in medical or lifesaving equipment, may contain small 
> parts.  Contains
> energy equal to the mass multiplied by the speed of light squared.
>
> --DTVZ
> ------------------------------------------------------------------------
>
> _______________________________________________
>
>   
I have not been following this thread closely, so somebody may have 
already made this suggestion.  If so sorry.  For you techies,
    E=IR, or more to the point, I=E/R.
Since the automotive charger voltage is about 15 volts open circuit, and 
the battery voltage is unknown but near 0, an R=10 ohms will limit the 
charging current to 1.5 amps.  In truth E=E(charger) - E(battery), so as 
the battery charges, I tapers off.  This is an ideal situation, a 
tapered charge.  Go to Radio Shack and buy a $1, 10 watt, 10 ohm 
resistor and hook up in series between the charger and the battery.

Karl


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