[Elecraft] KX3 and solar panels

[Jim Brown]

On 11/25/2013 11:42 AM, Gene Ruff wrote:
> I am looking for  information on using folding solar panels with my KX3 . success stories or sad ones. Thanks G. R.

The best response to this is to simply read up on how solar panels are 
used to charge batteries. There's plenty of good stuff on the internet 
about it.

The key thing is to get current into the battery without overcharging 
it. There are boxes that do this -- they are called "charge 
controllers"  and they vary in cost from a little to a lot. The most 
efficient ones regulate the charging current by generating square waves 
and modifying their width. The problem with that approach is that unless 
the designer is VERY careful, the square waves generate lots of RF 
trash. Another approach is to simply use your brain and a simple 
volt-ammeter, monitor charging current and voltage, and disconnect the 
charger when the battery is fully charged.  I use a real cute little 
inline volt-ammeter called Watts Up. About $50 with power pole connectors.

One simple charge regulator that does not make square waves is the 7A 
Sun Force unit.  About $15.  It's designed to work with 12V batteries 
and panels that put out up to about 20V open circuit.  It simply senses 
battery voltage, and functions as a simple on/off switch to allow 
charging if the battery voltage is below 14.2 volts, and cuts off above 
that.

Someone turned me on to a really nice and more efficient MPPT charger 
made by Genasun. Kansas Wind and Power is selling one for $125. I bought 
one, and it's RF quiet.

Hookup is quite simple.  Solar panel feeds the battery, either through a 
controller or directly, and the battery feeds the radio.

Our FD group runs QRP battery, using a 50W solar panel and a big battery 
for each radio. We don't use charge regulators, because we're not 
charging the batteries hard enough or long enough.

73, Jim K9YC