[Elecraft] KX3 and Solar Panel

[Dave B]

On 28 May 2013 at 12:00, elecraft-request at mailman.qth.net wrote:

> From: Greg Troxel <gdt at work.lexort.com>
> To: Elecraft at mailman.qth.net
> Subject: Re: [Elecraft] KX3 and Solar Panel
> 
> A 20W panel that is labeled as for a "12V" system will typically have
> a Voc (open circuit) of 22ish V, and a Vmp (maximum power voltage) of
> 18V.
> 
> Generally, one should not hook up a bare panel to a load, and the
> usual recommendation is charge controller and battery.   I wonder
> about a large cap instead of a battery, enough to make the controller
> stable.
> 
> I have a 20W (HQRP) panel and use a Genasun GV-5 MPPT charge
> controller and then charge about 100Ah of batteries.  I have not tried
> the controller with no batteries.
> 
> The anyvolt3 is an interesting concept for this application.  MPPT
> controllers try different voltage/current combinations to find the one
> that's in-range for the DC-DC converter and results in maximal power.
> I have found that to be around 17.5-18V whenever I get more than 200
> mA >From the system (sometimes I see 1.6A).  The anyvolt3 is expecting
> a voltage source, it seems, and the datasheet seems to imply that.  A
> panel is not a voltage source.  So I really wonder what would happen.
> Has anyone put a high-speed scope on the input when hooked up to a
> panel?

MPPT controllers are usually switch-mode regulators with special control 
algorithms, and are notorious HF noise generators!  Take care, you may 
need lots of filtering, on both the "regulated" DC out, *AND* the Solar 
DC input.

They are also designed (as you rightly say) to work with a battery bank, 
and would almost certainly be "unhappy" with a light to non existent 
load, especially one that varies a lot over a short time scale, as a SSB 
or CW transmitter does.

For portable HF radio battery-less use, a linear series regulator, or 
more likely a parallel shunt regulator would be best.  Inefficient true, 
but quiet!.

73.

Dave G0WBX.