V G wrote:
> However, a threshold voltage of 1.15 volts/cell would not allow the
> pack to drop below 4.6 volts. At that voltage, the pack would be
> still be drained above 90% (if not 95%?) according to the chart here:
>
> http://www.eneloop.info/home/performance-details/discharge-current.html
>
> I think that's a reasonable voltage to cut off at.

That graph shows voltages rather higher than what I've seen in other NiMH
spec sheets and have measured myself.  If that graph is to be believed, the=
n
Eneloops are a bit different from other NiMH, and they will indeed work dow=
n
to 1.2V/cell, or 4.8V/pack nicely, and you'll get most of the capacity from
them.  Keep in mind that graph shows no min/max range, so is probably
typical and at room temperature.  There will be some temperature dependence
that would be visible at the level of detail that graph shows.

Look at that graph closely, and you'll see something else you have to
consider.  Even at 1A it shows about 1.4V initial level per cell, with it
dropping to 1.3V after 200mAh, which is 12 minutes at 1A.  That's again a
bit higher than other NiMH batteries I've looked at.  USB power can be up t=
o
5.5V if I remember right, so your phone must certainly be designed to at
least that.  4 cells at 1.4V make 5.6V, which in theory is overvoltaging
your phone.

However, I think it's very very unlikely that anything below 6V is going to
hurt the phone, especially since it has to be able to take 5.5V.  If there
is a linear regulator in there as Martin's phone appears to have and Russel=
l
thinks your phone has, then it will just get a little warmer during the
first few minutes of charge.  If your phone has a switcher in there, then i=
t
won't even get warmer.

Either way, I don't think is in fact a real problem.  But you were unwillin=
g
to risk your "$900 phone" to measure its current draw with a bench supply i=
n
the totally valid range of 4.0-5.5V.  I'm just pointing out that seeing wha=
t
will happen at 5.7V is a lot riskier.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.