From: Bruce Fortnam <bfortnam@br...> - 2007-09-26 17:17:27
3.7V is the nominal voltage for a single-cell lithium-ion battery.
The actual voltage varies between 4.2 and 3.0 volts as the battery is
A fully-charged battery starts out at 4.2V. As it's discharged, it
quickly drops below 4V, then decreases gradually to about 3.6V (at room
temperature), then drops rapidly to below 3V. If you have a cutoff
voltage of 3.5V, you will obtain about 95% of the battery's capacity.
At low temperatures, the voltage drops more quickly, and you get less
capacity. That's a fact of life for batteries.
Conclusion: use a direct connection to a 3.7V pack - that's what gumstix
was designed for.
> Does anyone have any experience powering the Gumstix with Li-Ion or
Li-Polymer battery packs?
> Common voltages for such packs seem to be 3.7v or 7.4v.
> The Gumstix power FAQ says the input voltage is needs to be between
3.5v and 6v.
> Given that, there are > basically two options as I understand it.
> 1. Use a 3.7v pack
> 2. Use a 7.4v pack with a switching voltage converter to output 5v
> Does anyone have any experience on which one of these is a better
> The concern I have with option 1 is that it seems very close to the
minimum which the wiki also states could be unreliable.
> On the other hand I've read that switching voltage regulators have the
draw back of adding noise to the power
> (will this be a problem for the gumstix?) and some data sheets mention
that you need to mount them at a distance
> from any RF components (is true with all voltage regulators or do just
some that have this problem?)
> which could be a problem since I need to use wireless.
> Thoughts? Is there a better third option?
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