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   I'm an entry level guy, don't laugh at my suggestions if it's too simp=
le.
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   1. I don't think that 24V dc rail can charge two 12V batteries. Usuall=
y when lead acid or NIMH reaches high state of charge, its voltage is lik=
e 26-28V. I would suggest some regulator circuitry first to convert the d=
c voltage to like 30V to charge the battery.
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  2. I'm not a good digital person, so what i think is: use some FET, if =
dc rail fails, it simply pull the FET low or high, thus turn on some swit=
ch for the battery. Another LED loop is turned on too to notify this swit=
ch over, note you need a regulator to limit the LED current as well.
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  3. As to maintain the battery charge and health, it's a little bit conf=
using, i guess you need to check the battery data sheet and find out what=
's the best charging sequence. I used to make two levels of charging, a h=
igher charging current when state of charge is low, and lower current whe=
n SOC is high. At this level, you might need some micros. However, it dep=
ends on how accurate you need.
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> Date: Wed, 19 Mar 2008 08:41:59 +1100> From: grant@sitedoc.com.au> To: =
piclist@mit.edu> Subject: [EE] Battery Backup IC> > Hi List> > I need som=
e sort of battery back up switch IC that can do the following > things> >=
 The back up battery will be two 12Vdc 220 AH lead acid battery's set up =
> in parallel in order to have a 24Vdc backup supply. I am open to other =
> suggestions so long a s the amp hour rating is maintained.> > The syste=
m main power source is a 24Vdc rail that supply's 20Amps.> > What I need =
is an IC or device that will do the following,> (1) Maintain the backup b=
attery voltage and health.> (2) Provide automatic switch over to the back=
up battery on main power > failure.> (3) Notify the system of the backup =
battery switch over event.> > The device can be one that uses an external=
 MOSFET for the main load > switch if required.> > Look forward to your i=
nput.> > Kind Regards> Grant Brown> -- > http://www.piclist.com PIC/SX FA=
Q & list archive> View/change your member
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