Re: [Paddlewise] VHF battery drain when monitoring.

Saul Kinderis wrote:
> 
> My question would be not when do the batteries drain too much to keep
> monitoring, but when do they drain so much that you have compromized your
> own transmit power?
> 
> If we assume 70 hours of monitoring before we can no longer monitor, then we
> could also assume that transmit power requirements would be compromised much
> earlier. This is in part due to the larger current demands which if I
> remember correctly would produce a corresponding voltage drop. This would
> seem to indicate that on a day trip using alkaline batteries, we could all
> monitor, but that on a multi day trip we may have a battery degradation issue.

[snip]

> Has anyone in the group done any standby drain and then transmit tests at
> different temperatures?

Sort of.  See below.

> At 03:40 AM 12/3/98 -0800, Richard Mitchell wrote:
> >How long can you listen?  With a little help from ICOM and some
> >battery manufactrurers, here is the estimate.  We have little
> >excuse for not monitoring because of battery drain unless one is
> >limited to nicad (an unfortunate choice for backcountry
> >paddling).
> >
> >ICOM B3, M7, M9, and M10 and M10a handheld VHF radios all
> >discharge 19 milliamp per hour on standby, i.e. with power on and
> >squelch turned up just slightly to inhibit static.  [snip]
> >the batteries will last 70
> >hours before the threshold is reached.  At higher temperatures
> >(113 degrees F.) drain is more rapid and batteries will reach
> >threshold in 30 hours.

I have not done any controlled, quantitative studies of the sort Saul
describes.

However, I am confident that my typical use on an extended trip gives me
about 5 - 6 days of monitoring, and that I can expect good battery
performance for an hour of TX, even on that fifth (or sixth) day.  Here's
my rationale:

The radio is on, in Rich's "19 milliamp mode," when I am on the water,
which is only about 5 - 6 hours per day, with maybe another 15-20 minutes
of weather monitoring each day.  That's about 30 - 35 hours at the end of
the sixth day.  Because I only paddle in temperate places (<70 F), that
leaves me about "half" of the alkaline's capacity remaining, enough for the
30 - 60 minutes of TX I might need in an emergency.

(Calculation:  TX current is about 500 milliamps: 500 mA x 1 hr = 500 mA-hr
capacity needed;  19 mA x 35 hr = 665 mA-hr capacity available.)

To confirm that I still have live batteries with the capacity to handle 30
- 60 minutes of TX, I pull a battery from the pack at the end of each day
and hit the "PowerCheck" strip.  When the indicator falls below 70 per
cent, I would replace the batteries with fresh,  *even if I have not used
the batteries for 5 - 6 days yet.*  So far, I have never seen the indicator
go below 70 per cent with this use method.  I think this means I'm OK.

This protocol generates a pile of "half-spent" alkalines, which I cycle
through headlamps, etc., to avoid wasting their energy.  Yeah, I go home
with a handfull of alkalines.  But, I have a radio I can leave on for
monitoring, AND which can handle TX needs, on an extended trip.

During the rest of the year, when most of my trips are day trips -- and
sporadically placed -- I use the PowerCheck strip to confirm that I have
capacity, before I leave home.  Naturally, there is always at least one
complete set of fresh alkalines in my E-bag every time I launch, in case
the set in the radio pukes.

-- 
Dave Kruger
Astoria, OR
sea kayaker / chemist
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