>Looking specifically for a 4AH Gel Cell battery charger, with
>automatic switching from full charge to float charge.
>72 es 73
>Marty, KM7W
No need for a special charger for a Gel Cell. Just get an adjustable
voltage regulator such as a LM317, and use a 25K pot and a 2K resistor to
set the output voltage for 13.8v. Feed the regulator with something more
than 16v and you are set.
12v lead acid batteries such as Gel Cells will float charge forever at
13.8v. Heck unlike Nicads, lead acid batteries *like* to stay fully
charged like this. The service life for lead acid batteries left on
"float" is something greater than 5 years.
Using a float charge to charge a Gel Cell takes a little longer. I would
expect a battery such as your 4AH to draw about 2A for a few minutes,
then quickly taper off to about half an amp. The charging current will
then gradually tail off to almost nothing as it becomes more and more
charged.
Somewhere, I have the text from the web of some Gel Cell battery
manufacturer that recommends the float charge method for intermittent
duty use (like QRP?). I think it takes about three days to fully charge
a battery this way, but the battery is *mostly* charged after the first
day.
The automatic charger you are referring to charges at a higher voltage
initially, then switches to a lower float voltage when done. All this
really does is get the battery to a final charge a lot more quickly. If
you can tolerate about 70% charge in one day, and a full charge in three
days, the float charge method is quite satisfactory.
- Dan Tayloe, N7VE, Phoenix, Az, QRPL # 696, Az ScQRPions
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