Garmin GPS - Re: Caution: Watch Out for Batteries Too Long for Garmin Battery

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Re: Caution: Watch Out for Batteries Too Long for Garmin Battery

Jack Erbes

2006-01-11, 5:48 pm

MikeSoja wrote:

<snip>
> Now I know why most battery compartments have such big springs in
> them, but I'm still surprised there is that much variance in what I
> thought would be rigorously standardized, mass produced item.
>

Battery length is only part of the problem. A bigger issue is the
flawed design on the Garmin battery cases. The flat springs used are
too closely spaced and/or don't have an inadequate working and holding
range to them. They make poor contact and are doomed to failure because
they get overstressed during battery insertion.

I'd be very surprised to find that there is not some internationally
recognized range that the battery sizes do not have to fall into. The
designers were either unaware of the range of battery sizes or that they
did not work out an intelligent solution to accommodating it.

The Magellans use coiled springs on both ends of the battery. The (+)
end is a nearly flat wound coil with a short travel range, the (-) end
has about 5/16ths of an inch (8mm) of travel.

The long springs are at opposite ends of the battery case and are easily
compressed as the batteries snap down and into the case. I like the
fact that I can use my finger to find the spring and the flat end of the
battery to get the batteries in right on the first try when I am
replacing them in the darkness.

Maybe Garmin is saving a few pennies on each unit by using the flat springs?

Jack

--
Jack Erbes in Ellsworth, Maine, USA - jackerbes at adelphia dot net
(also receiving email at jacker at midmaine.com)

Jack Erbes

2006-01-11, 11:48 pm

David Lee wrote:
<snip>
> No - the Garmin design is a good idea badly engineered.

A good idea badly engineered? That sounds like a bad design.

> The problem with
> coiled springs is that they can be damaged if you try to extract a cell by
> prising out the end in contact with the coil.

That is not a problem with the spring, that is a problem with the person
replacing the battery not paying attention to what is happening. My
coil springs have survived thousands of cycles on four different GPS
receivers without a failure. If you pick up the wrong end and it jams,
you push it back down and pick up the other end. I know which end to
pick up and usually get it right on the first try. But given two tries
I can get it right every time. :> )

> Garmin get around this by
> using only flat springs at the bottom end of the unit so you can safely lift
> out either cell from this end and insert them the same way. Additionally,
> because the lower contact assembly comprises a single piece of spring metal
> there are no electrical joints at this end to fail - other than contact to
> the batteries themselves - as ther would be if a coil spring had to be
> joined to a flat one where the cells are connected in series.

On the Magellan one spring has the two coils, one long (-) and one short
(+), made from a single piece of spring wire. That one piece spring
puts the two cells in series, there are no electrical joints. The two
springs on the other ends, again one long and one short, disappear into
the case and attach to the PCB in some reliable, trouble free, manner.

> Problem seems
> to be that the size of the battery enclosure appears to have been designed
> for the coil spring solution and there is a lot less tolerance on the other
> side of the battery compartment.

> There also appears to be a significant difference between the casing of a
> yellow etrex and a Vista, in the battery compartment. In each case the
> spring strip at the positive end of the compartment is mounted in a slot in
> the plastic casing. In the my basic etrex the button of each cell can slide
> into this slot giving more play and a greater amount of spring travel. This
> reduces the insertion force and ensures that all the spring pressure is
> being borne by the electrical terminals. In the Vista, on the other hand,
> this does not occur and it appears that most of the contact force on the
> cell buttons may be bearing on the plastic rather than the spring terminals.
> Additionally the cells require a much greater insertion force, which is
> likely to cause more flattening of the springs, particularlythe flat one at
> the negative end of the right hand cell.
>
> However, I can't help wondering whether this really is always the source of
> the bad connection problem. Maybe there may also be corrosion problems
> leading to intermittently poor contact at the wire-wrap terminals at the top
> end of the battery compartment or the crimp between the top +ve terminal
> spring and the connecting wire. Just a thought.
>

Opinions will vary but I don't think anyone is in line for any
engineering awards for those battery boxes.

In summary, we have one model with flat springs that have shown problems
with power losses due to intermittent contact and with springs breaking
with some batteries. And we have another make with coiled springs that
have none of those problems with any batteries. And you think the first
one is the better design? We're just talking about the battery case
here, not the whole damn unit.

Jack

--
Jack Erbes in Ellsworth, Maine, USA (jackerbes at adelphia dot net)
(also receiving email at jacker at midmaine dot com)

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