Re: External power to eMap

From: Bill Cotton (Billcotton_at_comcast.net)
Date: 02/02/05 

Date: Wed, 2 Feb 2005 06:18:38 -0500

<miso@sushi.com> wrote in message
news:1107329271.097847.323810@c13g2000cwb.googlegroups.com...
> You might want to examine that cigarette ligher adapter for the Garmin.
> Some designs can be current hogs. You would measure the current
> entering at the 12V side, and then break into the path to the emap to
> see how much current enters the emap.
Thanks, I hadn't thought of this, I will make this measurenent on my Quest.
( In earlier portion of this thread, I mention that the Garmin power adapter
was used less power that an off the shelf 3 volt adapter and I was please
with the Garman adapter with the wire shorten, but, then the eMap backlight
failed.)
The Quest with speaker and a brighter backlight uses much more current. I am
not ready to cut the cable on the Quest yet. I do plan to make a cradle to
connect with the contacts on the back of the Quest. I will need 5 volts of
regulated power when this is finished. I assumed that the Quest accepted 12
volt direct at the external power input, like the Garmin V form factor.
>[Current not entering the emap is
> shunts to ground.] If the difference is significant, I can design a low
> drop out regulator that is reasonably efficient. This assumes you can
> build electronic gear.
I would welcome a design. I was given a design for a fast charger using a
Maxim chip that I was able to getas a protype issue from Maxim. Before I got
around to building it , I was able to buy a unit very cheap.
.
>
> If you cared about the battery weight, you could go to a lower voltage
> battery just for the emap. You won't get longer operating time, but it
> would be a smaller and lighter package.
I like the idea of a centry power supply. My LED light work best with three
cells but changing indivual cell with the kind on night bicycle riding I do
is a hassle.
> Lastly, you could go to a switching regulator which would be much more
> efficient than the low drop out regulator. For example, if the low drop
> out regulator was perfect, it would still be consuming three time the
> power of the emap. [Same current as the emap, but the emap uses 3V and
> the regulator will be dropping 9V.] With a switcher, this would not be
> the case, but switchers are noisy. It may effect the GPS performance.
I like to follow up on switcher, for touring I carry a 7 Ah battery and it
is mounted in a pannier away from the GPS. I am now look for 5 volts for the
Quest. http://www.billcotton.com/gps.htm 

-- 
www.billcotton.com

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