Path: utzoo!attcan!uunet!mailrus!tut.cis.ohio-state.edu!gem.mps.ohio-state.edu!apple!mips!vaso
From: vaso@mips.COM (Vaso Bovan)
Newsgroups: sci.electronics
Subject: Re: Photovoltaic charger for NiCads
Summary: Germanium diode
Message-ID: <31730@buckaroo.mips.COM>
Date: 20 Nov 89 01:10:40 GMT
References: <1749@lafcol.UUCP> <7200043@silver>
Reply-To: vaso@mips.COM (Vaso Bovan)
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 16

In article <7200043@silver> commgrp@silver.bacs.indiana.edu writes:
>
>>I am looking for a solar-energy driven battery charger, either as
>>a commercial product or as a schematic.  For NiCad batteries.
>
>Rule of thumb for charging NiCd cells is to use constant current at 
>10% of cells' ampere-hour capacity, for 16 hours, e.g., charge 1-Ah 
>cells at 100 mA. Remember to put a silicon diode in series to block reverse 
>leakage through the solar array when it's dark, and remember that 
>about 0.6 volt is lost in the diode's forward conduction.
>

Germanium diodes (0.3V) and some schottky diodes are more efficient than
silicon diodes in low voltage charging circuits. For very low current 
applications, "signal" rather than "rectifier" germanium diodes work just
fine. Check the specs though; germanium diodes have temperature limitations.