On 4/6/11 9:00 AM, Joseph Gray wrote:

Isn't your real problem going to be that the oven on the oscillator has
cooled off?  Or does the GPS lose the whole almanac, so the time to
first fix is forever?

Yes, the Oncore looses the almanac.

Joe Gray
W5JG

This will be interesting.
I have not added a battery to my 3801. Have the same issue annoying but in
general not enough to get me to do something.

But believe it may be as simple as taking a cr3026 lithium as an example and
holder.
Slap it on the back and change the battery every so often. Doing something
with recharge-ables and super caps adds a lot of complexity. Using the
disposable battery should make this a ground and battery connection. Do not
believe a diode is required.
But this approach only works if the almanac memory and such draws very very
low current. Might guess in the 1-10 ua. If its a pig you could always use 2
AA alkalines.
Regards
Paul
WB8TSL

On Wed, Apr 6, 2011 at 12:19 PM, Joseph Gray jgray@zianet.com wrote:

On Wed, Apr 6, 2011 at 9:00 AM, Joseph Gray jgray@zianet.com wrote:

I have an Oncore too.  I added a coin size battery salvaged from an
old PC.  It is easy enough to do there is a header pin just for that
purpose.  The Motorola user manual says the battery woks better
because it lasts longer but that was written ten years ago.  If you
use a cap you will want to add a resistor in series to limit current.

The Onore looses the almanac and all settings if there is no battery.
There is zero non-volatile memory in the device.

--

Chris Albertson
Redondo Beach, California

At 12:15 PM 4/6/2011, Jim Lux wrote...

The more significant problem is that it loses its surveyed position, so
it takes even more than forever to recover.

Robert,

I completely disagree with such a simple answer !  Lets review the issue here.  Joe has not given any information as to the
equipment in question, nor has he stated his desired goals other then by assumptions based upon his questions.

First, which Oncore receiver is he using ?  If it is the older series such as a GT+ or UT+ they are designed to have a
Lithium 3 volt cell soldered onto the board.  The memory draws 5 micro amps at 3 volts and 100 micro amps at 5 volts.  There
is an external connection available to provide the battery back-up off board with a caution of NOT exceeding 5 volts.

The non rechargeable Lithium COIN battery has a discharge function that holds its voltage fairly constant right up until the
end.  They will last a very long time with just 5 micro amps of discharge.

The problem with the Super Cap is the charge circuitry could damage the GPS if not properly protected.  The Super Cap will
not last as long as the Lithium; we are talking years here under the right condition.  Unless you are skilled at changing
small foot print surface mount components, presuming the memory chip is still available, you stand the chance of destroying
the receiver.  Why subject yourself to additional unnecessary expense.  Why add all that complexity to an otherwise simple
application.  If you add up the cost of the CAP and all the parts to charge it and protect the load, I think that would
exceed the cost of the battery.

If your whole existence relies on a single back-up strategy to save your butt, then you should not be there in the first
place.  So, I think it is time for Joe to think all of this through with some proper goals stated and reasoned thought
applied.

Bill....WB6BNQ

Robert Atkinson wrote: