Thanks Byron

What I'm using it for is a 3 wheel robot that I'm building. Right now the
battery is powering a pic16f874 and just a few circuits including a sn754410
hbridge and 2 small swiss motors that free running at 12v draw less than
100ma each ( I haven't checked them under load) but I will be powering a ccd
camera on the bot later
and some sensors and oh yeah 2 small pan & tilt motors for the camera.
I have to admit I'm a fly by the seat of my pants engineer but the battery
that I'm using seems large enough
to power all that and more for a few days but 12 hour min would be fine. I
thought I understood ah ratings this battery says (5ah/20h) that's a little
confusing.

Jim

-----Original Message-----
From: Byron A Jeff <byron@CC.GATECH.EDU>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Saturday, July 20, 2002 8:38 PM
Subject: Re: [EE]:speaking of gellcell's ?


>On Sat, Jul 20, 2002 at 06:57:05AM -0700, Jim wrote:
>> Hi
>
>> Pardon my ignorance
>
>No need. You have very cogent questions.
>
>> I'm working on a home project using a 12v gellcell.
>
>One piece of information that's missing here is how are you using the
>battery. What type of charging you need depends on how it's being cycled.
>
>> It has charging info printed on it but I'm kinda new to charging these.
>> It say's cycle use 14.5 ` 14.9v (25deg c) initial current less than 2
amps
>> stand by use 13.6 ` 13.8v (25deg c)
>
>Typical...
>
>>
>> I have been looking at charging info on the web
>> I would like to use an lm317 for the charging and have already
breadboarded
>> a cicuit that will switch between the 2 voltages
>> How important is the temp compensation?
>
>It's important if there's a wide variation of temperature from 25C.
>
>> Can I charge it at around 1 amp without any ill effect?
>
>Not at 14.6V. This voltage will guarantee an overcharge if left
indefinitely.
>
>>if the charger is working properly should I be able to measure aprox 14.6v
>>when I first connect it to the battery or does it have to climb to this
>> voltage as it charges?
>
>The latter. The battery will drag the voltage down to its level as it takes
>on charge, slowly rising to the target voltage.
>
>Battery charging is serious and complicated business. Essentially charging
>under any conditions other than ideal will eventually result in battery
>failure:
>
>* No charge will result in a dead battery.
>* Undercharging will cause sulfation resulting in lowered capacities and
>  premature failure.
>* Overcharging will result in gassing causing premature battery failure.
>
>I would advise not charging your battery from 14.5V source unless you have
>a an automatic cutoff mechanism (or two) in place. I finally decided that
>float charging was the safest dumb charging course of action.
>
>A good reliable gell cell charger is high on my list of things to build. I
>really want a 3 stage charger with autodetion of stages (bulk, absorption,
and
>float) and decent indicators. What I really haven't figured out is how to
get
>really high current for fast charging. My 33Ahr 12V gel cell will accept up
>to 10A current. But finding a 10A transformer is a tough proposition.
>
>Hope this gives you some help,
>
>BAJ
>
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>
>
>

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