[Elecraft] K-2 Power Supply

[Kenneth Cooperstein]

 >Thom R. Lacosta wrote:
 >Can the output voltage be changed to something above that conforms 
with the voltage required to charge the internal gel cell?

I offered a tiny 12.0 VDC switcher and Thom asked the above question.  
The answer is Probably, but you would have to destroy the case to open 
it up.

I see from the K2 manual that you need to apply 14.0 VDC at the jack to 
charge the optional internal SLA battery.  Does the K2 have circuitry 
that regulates this voltage down to float level (13.4 VDC) when the 
battery has been fully charged?  If not, you will ruin the battery if 
you don't closely monitor the charging.

If the latter is true, and you want to be able to recharge your SLA 
battery with the same source as powers the radio, then you should 
consider a high-quality marine battery charger as a power supply -- one 
that can be set for SLA and one that automatically goes to "float."

I don't think this is cost-effective, though.  You would probably be 
better off with a small supply like my 12.0 VDC unit and use the $40, 
1.25V "Battery Tender" to charge the battery -- all the way to "float".

I have been trying to design a "13.8 VDC UPS" for my QRO shack and it is 
not trivial to have a system that will provide clean power at the right 
voltage, keep your batteries charged but not overcharged, and that is 
also capable of fast charging your batteries.  I think I can do13.8 VDC 
at the 30 amp level for around $250 (not counting batteries), but it 
requires a volume purchase of 100 off-the-shelf units.  It involves a 
sophisticated marine charger and  sophisticated boost converter (to keep 
the voltage at 13.8 when the grid is down).  If you are willing to rely 
on the batteries during normal TX and your duty cycle is around 30%, you 
could squeak by with a 10 amp marine charger.  The cost would come down 
to around $165, in quantity.

Ken KC2JDY



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