Replacing Battery in Polar T61 HRM strap
martygoodman
Replacing the batery in a Polar T61 Coded HRM strap ---marty goodman
martyg...@sbcglobal.net
I today had the pleasure of dissecting an old Polar T61 coded HRM strap.
This is one that has a NON USER REPLACEABLE battery. Some old-timers here
may remember I posted here years ago info on how to open up the Polar
non-coded HRM strap and remove its battery. This proceedure for the coded
strap is similar, and has similar considerations, but is overall EASIER.
NOTE that Polar now DOES SELL a version of their HRM strap that user
replaceable batteries, and in MOST cases it makes sense to just buy one of
these. Note, too, that you can return a dead T61 to Polar, and they will
(for a fee that may or may not be similar to the price of a new strap).
However, if you were given (as I was) such a strap free, or if you picked
one up for pennies on the dollar at some used and damaged goods sale (like
an REI used and damaged goods sale), and if you love tinkering, here's some
advice that may assist you in making your own user-replacable (or at least
TINKERER-replaceable) Polar T61 coded HRM strap:
Look down on the strap, with the word "Polar" right side up (and just below
"Polar" is "T61 CODED" in small letters).
VERY CAREFULLY, taking extreme care to NOT let your cutting tool (dremel
cutting wheel, hacksaw blade, jewlers saw blade, hot tip of a fine point
soldering iron, etc.) descend more than a millimeter (preferably LESS!)
below the inside extent of the plastic, cut out a trapezoidal piece of the
front of the strap. The bottom, and longest side, of the trapezoid should
run THRU the MIDDLE of the words "T61 CODED". The top of the trapezoid
should be pretty much at the top edge of the front of the strap. And the
two sides of the trapezoid, slanting inward toward the top, are defined
loosely by the shape of the front area of the coded HRM strap.
NOTE that the first half inch of space from the bottom of the front of the
strap to a place about a third of the way (1/2 in, as I said) up from the
bottom is over a delicate COIL, that runs across the bottom of the strap.
You DO NOT want to be cutting there, lest you risk cutting into that coil,
and doing irreparable damage to the strap.
Note that removing the trapezoidal piece of plastic may prove tricky because
it's integral with a circular plastic guide area where the battery sits.
You may have to judiciously clip and cut to free the top plastic piece from
that circular / cylindrical guide / well area for the battery.
When you remove the trapezoidal piece of plastic you've cut out, you'll find
the CR2354 battery just can be teased out. It's NOT soldered in, but rather
held in by contacts and a PRESSURE FIT provided by the plastic case itself
(which you've now disrupted by opening the case). Note that in the old
Polar non coded and sealed HRM straps, the battery was soldered in, and it
even tended to be desireable to cut out a window on the BACK of the strap to
get access to the back side of the solder points, to be able to remove the
old battery without damaging the circuit board.
At this point, different tinkerers may elect to arrange for battery
replacement in different ways. ONE approach would be to just get another CR
2354 battery, drop it in, then seal the thing up using the cut-out plastic
piece and, say, duct tape. Maybe with a bit of something to force the
contacts tightly against the battery, if that turns out to be needed.
Replacement would then consist of removing the duct tape, removing the old
battery, popping in a new CR2354, and re-applying duct tape. Perhaps 2 or 3
minutes of effort.
Alternatively, you can solder flexible, stranded black and red insulation
wires to the battery contacts, then securely weather seal up the front of
the strap in a fashion of your own choice (plastic weld the cut out piece
back in, epoxy cement, silicon seal, duct tape, heat shrink tubing... some
combination of these) with the wires dangling out. You can then solder on
to the wires any similar battery of your choice (I have good stock of CR
2477's with solder tabs) and then put the battery on the front or to the
side of the very front of the strap, and cover all with heat shrink tubing.
After that, battery replacement will consist of removal of the heat shrink,
desolderng the battery, soldering on a new battery, and replacing the heat
shrink tubing. Again, perhaps 2 or 3 minutes.
Here is some comparative information on this
(to me, oddball) CR 2354 LiMn coin cell,
from "The Battery Store"
http://www.batterystore.com/Charts/CoinCell.htm
ma ma
typ max
cell mah drain drain price
------ --- ----- ----- -----
CR2354 560 0.2 3.0 $5.00
CR2016 80 0.2 3.5 $3.00
CR2025 170 0.3 3.0 $3.00
CR2032 234 0.4 3.0 $3.00
CR2450 540 0.8 3.0 $4.00
CR2477 950 1.0 2.5 $4.00
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