I often use a shunt regulator so as to extract the maximum charge
possible from the panel.
I run 450 watts of PV panels for Ham radio at home.
Use a PNP POWER transistor with a low power zener in the base as your
shunt..
BYPASS THE ZENER as it is a great RF source.

JB wrote:

>I have a panel that delivers up to 21.5V in full sun with 3.5A short-circuit
>current. This panel is used to charge a 17Ah 12V sealed lead-acid battery that
>can be floated at 15V for cyclic usage patterns, with a maximum charge rate of
>around 1.5A. Using a LM317-T set at 15V with no ballast resistor (using
>internal battery resistance) this works fine in full sun, but anything short of
>about 17V at the panel results in zero charging. I would like to utilize the
>power available when the panel is at any point above the battery voltage so
>that I am not wasting that energy.
>
>A switching regulator with a wide input range, say 12-30V to 15V out would be
>perfect, but I have yet to find one.
>
>Should I drop the 317 and simply shunt the panel output at 15V with a Zener? I
>don't care about anything over the 15V point, as I don't want to over-charge
>the battery. This of course assumes I can find a 15V/50W zener to mount on the
>panel.
>
>Are there better alternatives? There is a 16F873 in the project with available
>A/D and TTL ports, so that may be an option with the right components, but I'm
>running out of experimentation time, so I'd rather not venture into something
>that "might" work.
>
>I can justify up to about $50 for the components.
>
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>
>

--
  *
  |  __O    Thomas C. Sefranek  tcs@cmcorp.com
  |_-\<,_   Amateur Radio Operator: WA1RHP
  (*)/ (*)  Bicycle mobile on 145.41, 448.625 MHz

ARRL Instructor, Technical Specialist, VE Contact.
http://hamradio.cmcorp.com/inventory/Inventory.html
http://www.harvardrepeater.org

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