Hi Paul,
Yes, that is similar to what I have been thinking. But I can't find it
in the manual where it says the external low voltage threshold is 11V.
What I see on page 41 is it can be powered "10-18VDC (2 amp minimum)"
and also that the switch over point is 9V. If what we are suggesting
is true, that switch over voltage (actually a bit lower than 9V) is
very important, especially if using lower capacity battery packs.
Another thing to consider is that draining a NiMH battery to low may
damage the battery itself.
I have tried a few different configurations of AA NiMH (2500mAh)
rechargeables.
Original problematic configuration: Twelve AA in series (14.4V)
Ten AA in series (12V): same problems as with twelve.
Eight AA in series (9.6V): Works Sporadically. It worked once: seemed
to switch over to the attached battery when the display showed around
Message: 8.
Subject: 5V. Another time it did not switch over and just shut down.
However, when turned back on, the attached battery did come on line
even with the external battery still plugged in.
Two parallel packs of eight AA in series (9.6V). Seems to work as
normal. Switches over to attached battery and continues recording when
external pack gets low. Will have test this some more though to be
sure it's reliable.
John Hartog
--- In Paul Jacobson <> wrote:
>
> Hi John,
>
> Your NiMH pack would have a discharged voltage of around 12V.
> According to the 702 manual the external battery low voltage
> threshold is 11V, so I suspect that the external pack reaches a point
> where it cannot supply sufficient current to run the 702 before the
> power management circuit detects low voltage and switches to the
> internal battery.
>
> The solution would be to either get the factory to change the low
> threshold point to something like 12.5 or 13V for use with the 12
> cell pack, or to use a 10 cell instead.
>
> cheers
> Paul
>
>
>
> On 30/11/2007, at 3:39 PM, John Hartog wrote:
>
> > Hi group,
> >
> > I ran into a perplexing problem using an external battery pack with my
> > SD 702. Tech support at Sound Devices are perplexed also, but they
> > are trying to figure out what might be happening. In the meantime, I
> > thought I would post this to the group as a word of caution for those
> > considering external powering schemes and also by chance anyone here
> > can provide some insight.
> >
> > Using 14.4 V external battery pack made up of twelve 1.2 V AA NiMH
> > (2500mah) rechargeable batteries, the recorder does not switch over to
> > the attached battery when the external battery runs low, but rather
> > the recorder shuts down prematurely leaving a corrupted file.
> >
> > I have done a bit of troubleshooting; though I have not tested with
> > another recorder yet. I do have some thoughts on this myself, but none
> > that answer why the recorder does not switch over with some battery
> > packs. It's almost as if the 702 gets confused when both voltage and
> > power from the external pack drop too low too quickly.
> >
> > John Hartog
> >
>
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