[Elecraft] Using the KX1 on Solar Power

[Don Brown]

Hi

There may be two different types out there or you may not have them in the 
same intensity light. A Solar panel is a constant current generator. Its 
current and open circuit voltage is dependent on the amount of light falling 
on the panel. Each cell in the panel outputs about .5 volt in full sun. The 
cells are connected in series or series-parallel to get the voltage high 
enough to charge the battery plus a little overhead. The VW panels only need 
about 14 volts to charge the battery in the car so they may have a version 
of the panel wired for only 15 volts. The three panels I once had would 
output about 18 volts in full sun open circuit and about 170 mA under full 
load. You can test the output current by connecting a 10 ohm 5 watt resistor 
across the panel and measuring the output voltage. 170 mA would be 1.7 
volts. I have some commercial Solarex panels that will output up to 30 volts 
open circuit in full sun and almost 6 amps under load. This panel is about 
20x57 and rated at 80 watts. The VW panels have a blocking diode in the plug 
to prevent reverse current. This reverse current will discharge the battery 
when the panel is dark. If you remove the plug be sure to install a blocking 
diode unless your controller includes one internally. You can parallel 
several panels to increase the current but a blocking diode is a good idea 
on each panel to prevent reverse current flow when one panel is in the sun 
and another is in the shade. Even if you have two panels with different 
voltages if you parallel them through the blocking diodes once they are 
connected to a load the voltage will drop to the battery voltage and the 
current from each panel should flow into the battery.

Don Brown

KD5NDB



----- Original Message ----- 
From: "Scott" <aves-specta at comcast.net>
To: <elecraft at mailman.qth.net>
Sent: Tuesday, June 21, 2005 6:48 PM
Subject: Re: [Elecraft] Using the KX1 on Solar Power


> Don Brown mentioned the VW solar panels...
>
> After seeing them referenced on this list a few times over the years, I
> finally went to the local dealer yesterday, asked gently about solar 
> panels,
> and walked away with two of them. What a deal!
>
> ( Now I'm wondering: Why does one read 15V and the other 25V when they're
> side by side? )
>
> Scott N1AIA
> K1 00139
>
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