At 02:59 PM 2/24/2004, Byron A Jeff wrote: >On Mon, Feb 23, 2004 at 03:01:52PM -0700, Dwayne Reid wrote: > > > > The simplest (and one of the most reliable) charger for charging 12V gel > > cell battery from a 12V automobile is to use a schottky diode in series > > with a current limit resistor. The 12V supply is already at the correct > > voltage. > >No it isn't. Lead Acid requires a minimum of 2.3V/cell to charge. That means >you need 13.8V. Now usually this isn't a problem because the car alternator >will produce somewhere in the ballpark of 14V. But if it's a true 12V it won't >properly charge. Hi there, Byron. I don't mean to start an argument but consider the following: the battery in the automobile also uses lead acid chemistry. The alternator output voltage is regulated so as to charge that battery properly. That's why it measures between 14.0 - 14.5V (engine running, head-lights off). I've glossed over a whole bunch of issues (mostly temperature compensation) but, in general, a 12V gel cell battery charges very nicely from that voltage. It is important to limit charge current and I'm not real happy about the ~0.18V drop of a large sized schottky diode (increases the top-off time) but it does work. dwayne PS - that's why I worded my message the way I did: "charging a 12V gel cell battery from a 12V automobile". dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 20 years of Engineering Innovation (1984 - 2004) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu