[PSUBS-MAILIST] OTS and motor controller noise

Sun May 4 17:19:37 EDT 2025

Hi Jon, I've run some preliminary tests and the results are interesting.
I'm going to rerun and try to document in better detail and frequencies.
Here's my observations. To save me typing Topside unit =TS and Diver unit=
DU. Ran the tests with the TU both sitting on my external fiberglass deck
with the Transducer from the TU placed adjacent to my builtin transducer
located externally at the rear of the hatch. Both Transducer cables are mfg
full 25' cables with no cuts. Both TU and DU are on their own battery
power. The DU is located on the starboard side, held with magnets onto the
original VBT tank. Both Port and Starboard VBT have been cut open with a
16"x14" opening. Inside each of the VBT are located one PWM from MinnKota
wired to the cutoff selector switch and then to the LiPo4 36v battery bank.
Currently I have both the Minnkota speed selector switches adjacent to each
other so they can lay over my knee to run the test. The DU is attached to
my headset with channel set to 1, transmit: PUT, squelch on.  The TU was
sitting on my feet inside the sub, speaker on, and I set the TU to the same
settings except the squelch was set to off on the rotation dial. The TU is
about 30" from either PWM.  With this setup I can hear my DU headset and
the TU speaker at the same time.
Test 1 with my DU only. Run each of the 4 channels through a series of
starting out with one thruster and slowly running the speed scale in
forward and then in reverse.
Test 2 same test with both thrusters on and running the speed scale.
Test 3 and 4 same test with the TU only
Test 5 run both thrusters and both TU and DU.
Note the DU is sitting closer to the PWM than the TU. TU is in its TU ABS
case, with no additional shielding The thruster control cables are the mfg
cables and I believe there is no shielding.
Before I ran tests 1-5, I did a 6th test with  the transducer of the TU
into the sub and placed it near the PWM units, and then again adjacent to
the thruster speed control wires.

In Test 6,I found  considerable frequency oscillation adjacent to the speed
cable and less at the PWM units ( the PW units are incased in the mfg
aluminum finned sealed case) all for channels (squelch off) I used this as
a comparative baseline against the DU to see if Transducer proximity to the
PWM made a difference and Initially I believe it does.

So here are my observations:
Test 1 & 2 DU: sometimes on start-up of a thruster I might get a short
squelch burst and then no thruster noise for the rest of the speed scale. I
believe that the DU which only has squelch on or off, is automatically
compensating on all 4 channels, hence the reason I'm not getting any speed
controller noise. No difference between test 1 & 2

Test 3 &4 TU: on all four channels with squelch off, there is a high
frequency tone,  each different on the 4 channels and when on test 4 with
both thrusters double the db of the frequency tone. No difference if I ran
one thruster forwards and one in reverse at the same time.

Here is the interesting part: on each of the 4 channels there is a point on
the squelch dial where you can eliminate the tone. approximately 25% on
channel 1, 50 % on channel 2, 75% channel 3 and 100% on channel 4.  So if I
am using channel 1, preset the squelch to 25% +/- and you're good to go,
same with the other channels. The other interesting thing is the proximity
of the TU  to the PWM. Outside the hull and about 3ft away from the PWM the
intensity of the Tonal variation is substantially less, which might imply
that additional shielding around the electronics of the TU could improve
the reduction of the tonal frequencies.
As I am planning to place the TU in the sub into one of the VBT with 1/2"
thick steel on three sides, I'm hoping that will be enough shielding, only
time will tell. Also I'm going to add some additional shielding on the
thruster speed control wires  based upon the test results of test 6.
When I rerun the test, I will data log the frequency of each channel and
try to calibrate the squelch position for the TU.
Any thoughts on how best to filter out frequency noise besides the
squelch?  Anyway these are my current observations and I hope they give
some insight into how to solve your problem.

Best Regards,
David Colombo

804 College Ave
Santa Rosa, CA. 95404
(707) 536-1424
www.SeaQuestor.com

On Wed, Apr 30, 2025 at 12:43 AM Alan James via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

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