[Elecraft] Charger for K2 internal battery?

Mon Jul 1 08:13:01 2002

Jeff,

Check out the section in Mouser catalog on SLA batteries.  There are some 
automatic chargers for the Power Sonic batteries.  Order a PSC-12500A.  You 
will have to connect it directly to the battery with a fuse Right on the 
battery, I use the XVERTER OUT hole in rear of the K2 for a power jack 
similar to the one for the K2 power.  So I can plug the charger into the K2 
power jack or the jack connected to the battery by a fuse.  The charger 
does not charge automatically unless connected directly to the battery if 
the K2 is in operation because of the diode and resistor in parallel 
between the K2 and the battery.  Also, if you plug the charger into the K2 
power jack there is a hum when receiving.  There is absolutely no hum when 
the charger is connected directly to the battery.  If you look at the wave 
form on a scope, it's a DC square wave with a big spike.  However the 
battery is a great filter capacitor, and the square wave and spike are gone 
when connected directly to the battery.  If you are receiving for a long 
period of time, the current drawn by the receiver fools the charger into 
thinking the battery needs more charging, so it keeps charging instead of 
automatically reverting to the float mode when the charging current drops 
to a few ma.  This is not a problem if you are transmitting, as the 
transmitter takes more out of the battery than the charger puts in, so it 
is quickly below full charge.

The way I am currently operating my K2 is with a miniature 3 amp switching 
power supply connected to the K2 power input, the battery switch open, and 
the automatic charger connected the battery jack which is connected to the 
battery through a fuse.  That keeps the K2 battery on float and ready for 
use if I want to use it.

So GL

At 11:44 AM 6/30/2002 -0400, [email protected] wrote:
>Gang,
>
>Where can I find a high quality charger for my K2's internal battery?  I am
>looking for one that will provide exactly 14.0V, as required by the
>battery, and that will maximize the battery's life by not overcharging,
>etc.
>
>I would be willing to venture into homebrewing a charger, if someone could
>point me to a DETAILED construction article, as I am not an experienced
>homebrewer!
>
>Thanks very much & 72,
>Jeff
>[email protected]
>"Ask me about the Long Island QRP Club!"

73, Chas, W1CG