Re: [IDEA] Poor man's UPS

From: Christian Trefzer
Date: Mon May 22 2006 - 15:33:53 EST

On Mon, May 22, 2006 at 11:54:56AM -0400, linux-os (Dick Johnson) wrote:

> Telco used watt-meters and clocks to directly monitor the batteries.
> In the event that the batteries had been floating for a month (not used
> and trickle-charging), the timer would send them an equalizing charge
> of about 10 amperes for 10 minutes. That would blast away any surface
> corruption and bring the individual cells up to an equal terminal
> voltage.

Nice : )

> Modern chargers just don't bother unless the batteries are used for
> medical equipment. In our portable CAT Scanners, we monitor current,
> voltage, and time using a uP. This guarantees that once you start
> a scan, the scan will complete (as required by regulatory agencies).
> We also charge at a constant current until getting to the correct
> terminal voltage. In other words, the charger is current-limited
> until the voltage is correct, then it becomes voltage regulated.

Constant-current / constant-voltage - just like Li-Ion batteries are
supposed to be charged. Talk about complexity ; )

IMHO battery "care" even in modern laptops sucks, so I'd rather have two
battery packs, one in use and the other one being charged. External
chargers don't seem to exist, AFAICS, so I'd very much like to build
one. Welcome to utopia...

> The regulated voltage depends upon temperature and you can get
> the numbers off from battery vendor's specifications. We don't
> set an "equalizing charge" as telco did. We found with our specific
> batteries it wasn't necessary.

Yup, the chemical processes inside the cells depend on temperature - do
your chargers monitor that as well?

Thanks a bunch,


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