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Jason,
I am very disappointed in you and in much the same way as George, I am
particularly offended by your mention of WKPP scooters in your
dissertation on reed switch electrical engineering. Like a shadetree
inventor who has rediscovered telephony, following the connection of two
tin cans with a string, you trumpet these revelations like an excited
Chicken Little. Since you have published these uniformed ruminations
you no force me to waste my time in responding to several of your
nonsensical conclusions.
Hermetically sealed, magnetically actuated switches (reed switches) are
a very common and highly reliable method of commutating low current
loads. Like any electrical component these switches must be
properly designed into a system, with attention being paid to both the
mechanical disposition of the switch as well as the maximum rated
current which will flow through the switch when the circuit is closed.
Your treatise on reed switches is really an interesting anecdote on the
multiple failure modes experienced by the thin walled plastic pressure
vessel otherwise known as a Tekna DV3x or Tekna 100 (Mako). You have
described to us how both the motor compartment and the battery
compartment can suddenly and catastrophically flood due in part either
to improper assembly of the scooter or mechanical flexion of the plastic
parts. The compression of the internal support pylon in the Tekna
intermediate bulkhead often was responsible for crushing the improperly
mounted reed switch. The same rocket scientists at Tekna soldered to
the terminal leads on the end of the reed switch and in the process of
doing so damaged them. The WKPP scooter uses a containerized proximity
switch which is not subjected to extreme mechanical pressure, short of
battery off gassing, nor the soldering of terminal contacts. If a reed
switch is properly installed the typical failure mode is the "ON" state
as a result of crushing the two metal contact strips together. This is
what you want so that you can "drive" your scooter back out of the cave
as averse to leaving it. The subject of extended range DPV operations
underground is another whole subject for discussion which I will not
address.
After complete immersion of the motor compartment in water I was very
surprised that you did not perform an even more obvious inspection. The
sealed automotive relay on Teknas poorly designed relay circuit board,
also will leak under pressures considerably less than those necessary to
crush a reed switch. Those sealed relays are designed to tolerate only
atmospheric solvent washing such as what is done after pc boards are
wave soldered. Are you now admitting to us that you did not perform
the most basic and rudimentary step of replacing the relay or
validating the operation of this device after you had opened everything
up. Tekna also places a free-wheeling diode across the relay coil to
protect the (vestigial and useless) battery level circuit from the
reverse emf of the relay coil. If this diode is crushed or fails, it
will generally fail as a short thereby shunting the relay coil and
rendering the reed switch useless. Did you make this obvious test?
While you were performing electrical measurement feats with your
ohmmeter on the flimsy and slipshod wiring harness, typical of Teknas,
did you bother to manually energize the relay and check the continuity
across the contacts? Did you bother to check the series resistance of
the relay coil and verify that it was in the range of 700 ohms? Did you
bother to burn test your batteries, which BTW had been subjected to the
ambient water pressure following the prior flooding(s) and are not
designed to be pressurized (recall DiveRites compressible batteries in
their late great square light)? Did you dismantle the motor and verify
that the brush board had not shorted or that the armature fields had not
dropped out of the commutator? Did you replace the motor o-ring and
intermediate bulkhead o-rings?
After not having performed these other obvious inspections and not
consulting WKPP project members, George and myself included, in a
position to advise you on the issues surrounding the reconstruction of
these flawed DPV systems you put this scooter back together and admit
to doing a 3000 penetration cave dive. As you are well aware, we
consider scooters to be critical life support systems right up there
with lights, gas and regulators. Jason, this is beyond reckless and is
exactly why George Irvine so strictly controls all aspects of WKPP dive
equipment technology, dive planning and dive executions. Just to
reiterate, in a easy to understand checklist format, what you did:
1. Made homebrew repairs on leaky scooter.
2. Failed to replace cheap relay or check critical relay board function
and associated components before
reassembling.
3. Soldered connection to reed switch and replaced switch back into
known failure position.
4. Failed to dismantle motor to inspect for brush board or commutator
damage.
5. Failed to burn test batteries, especially after flooding and as a
general practice.
6. Admitted to doing 3000 cave dive on above described
"borrowed"scooter.
Conclusion: You be the judge.
For all of you folks out there who have taken the time to read this
consider the following:
As more people become involved in so called "technical" diving they will
soon learn that DPVs are a necessity in order to get anything meaningful
accomplished and enjoy the experience as well. Before betting your like
on a "borrowed" scooter please take the time to ask about "Doing it
Right" from someone in a position and with a track record to give you
worthy advice. Do not assume that you know better about these things if
you value your life.
Regards,
Bill Mee
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