On Feb 21, 6:25 pm, AK wrote:
On Feb 21, 9:06 pm, Darryl Ramm wrote:



On Feb 21, 4:00 pm, AK wrote:

Can anyone tell me what a typical power consumption for a PDA is? I
got ipaq 3950, but I guess they all must all be close.

Typically it is greater than zero amps and less than 1 amp :-) I bet
that did not help much.

It depends significantly whether you are charging the battery, whether
the screen backlight is on, and total power drawn will of course
depend on whether you have an extended battery pack or not. Worse case
the power consumed can be even greater than those pesky transponders
everybody worries about. And a PDA can draw current even when turned
off. For a iPAQ 4700/4705 you can see numbers ranging from 9 mA (PDA
of and fully charged), 440 mA (*OFF* and charging) to 610 mA worse
case. These are @ 12 volts equivalent, i.e. roughly the actual current
you should see drawn from your glider battery. How long the PDA draws
the maximum current will depend on how discharged its batteries are.
I'm too lazy to try to reproduce it here but there is a full table of
power draw for the iPAQ 4700 in my battery presentation athttp://www.darrylramm.com/glider-batteries.

If you are trying to work out how long your glider battery can power a
PDA for, don't forget the capacity of the battery can depend
significantly on the total simultaneous current drawn from it, and the
temperature, see the discharge curves in the battery presentation
above.

If you are working out how large a fuse or breaker to put in the
charging circuit, several amps will do. It does not really matter as
you are mostly protecting the wiring. Avoid small (1A) breakers as
they waste power. You may not need a breaker or fuse if the 12 volt
powered charging circuit has its own protection.

Cheers

Darryl

I am trying to figure out what else I can have on the same battery as
PDA. Other equipment draws 600 mA with spikes to 1.7 A when
transmitting.

Typical sealed lead acid batteries will easilly be able to provide
power during these current spikes, and you would have awfully thin
wiring for this to be an issue for wiring. So if this is on a common
circuit breaker or fuse for this load make sure it is at least 3A,
maybe more and you are set. If there is only one fuse or breaker make
sure it is right at the battery, preferably mounted on the battery in
a way the leads to the breaker cannot ever short circuit even with
significant force applied. I'd make that breaker 5A usually.

Is the spike caused by radio transmission? For calculating power
consumption and battery life for things like radios typically assume a
transmition/reception ratio of a few percent unless you something more
accurate and just cheat by fudging battery capacity at this number
based on this percent between the battery capacity at the receive and
transmit current draws. This is only an issue with small batteries,
and not usually significant in gliders. But might be nice to have an
idea how long you battery runs with a stuck on microphone, or a
ballpark worst case battery life if you land out and are trying to
transmit a lot.

Darryl