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Re: Thirsty for Mobile Power

From: Christopher Allen <>
Date: Fri, 3 Nov 2000 08:43:00 -0800 (PST)

On Fri, 3 Nov 2000, Doug Sutherland wrote:

> Okay, the reason I want to double the voltage is because my 
> regulator has input voltage range of 9 to 26 volts. Does 
> anybody know if it would make a difference in running time 
> if it was 19.2v 4.5AH (serial) vs 9.6v 9AH (parallel) 
> assuming that the power regulator voltage range is 9-26v? 
It depends on your exact regulator. In order to determine the answer to
your question you would have to look at the efficiency plots. You'll
either have to get a hold of them somehow or make some yourself.

Maxim has plots (or they used to) online. I can't figure out how to view
PDFs in Linux or I'd give you a specific URL...but anyway, last I looked
they had over a dozen different plots just for one DC-DC converter.

http://www.maxim-ic.com/

(I'm not sure about this, but) You might want to consider your current
capacity, something which is critical with LiIons since they (unlike NiMH
for example) have high internal resistance and don't like to put out a lot
of current. When you're spinning your disk drive up, is your efficiency
going to be worse with your batteries in series (high voltage) as opposed
to parallel (high current capacity) or will the regulator take the higher
voltage of a series coinfiguration and automagically turn it into the
equivalent current? Beats me.

Steve Mann has advertized that he likes to run 12 volt as opposed to 7.2
and he claims higher efficency at this level.

-Chris

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