[PSUBS-MAILIST] Dive report: Snoopy at Seneca

Sat Jun 6 20:18:18 EDT 2015

Actually the long wires add inductance which can cause voltage spikes as a result of the fast switching. This can blow the devices (MOSFET) used to switch the currents.

It can overvoltage the caps also but that may not be the main problem.

I had some trouble like this when I designed my controller.

Ken Martindale

From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of Alan James via Personal_Submersibles
Sent: Saturday, June 06, 2015 6:48 PM
To: Personal Submersibles General Discussion
Subject: Re: [PSUBS-MAILIST] Dive report: Snoopy at Seneca

Thanks for the report Alec, great stuff.

re the motor controllers; I've been reading a bit about inductance in long wire runs from battery to

motor controllers, that harms the capacitors on the controllers.

This could be a problem that is unique to our submarines & not an issue with things like golf carts

& wheel chairs.

My reading has been mainly about BLDC motor controllers but asume PWM controllers for brushed

motors would be similar. Because of the rapid switching on & off of the power to the motor, there is a

current surge hitting the capacitors & the longer the wire run, the more the power in the surge.

A water analogy would be turning a valve off suddenly as washing machines do, sometimes with

a "thunk" sound & a rattle of the pipes.

Hugh mentioned he had problems with his Curtis BLDC motor controllers.

Attached is the problem & solution, which is to put capacitors in parrallel along the battery wire; 

however there must be a better way.

Regards Alan

too long battery wires will kill ESC over time: precautions, solutions  <http://www.rcgroups.com/forums/showthread.php?t=952523> & workarounds - RC Groups

 <http://www.rcgroups.com/forums/showthread.php?t=952523> 

 <http://www.rcgroups.com/forums/showthread.php?t=952523> too long battery wires will kill ESC over time: precauti...

Careful! too long battery wires will kill ESC over time: precautions, solutions & workarounds Electric Plane Talk

 <http://www.rcgroups.com/forums/showthread.php?t=952523> View on www.rcgroups.com

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From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> >
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > 
Sent: Sunday, June 7, 2015 12:20 AM
Subject: Re: [PSUBS-MAILIST] Dive report: Snoopy at Seneca

Alec,
I don't know what type of speed controller you are using, but I like and use Curtis golf cart controllers.  They are rated for huge amperage and seem bullet proof.  I have an extra 36V controller I can send you to try out.  They use a 10 OHM potentiometer for the throttle.  They also have a battery protection mode, a sort of get home conservation mode.  
I labeled the motor in Gamma for a jumper cable, so that I can get home without the controller.  As you said it is electronic and it will fail.
If you want the controller send your address of list.
Hank
--------------------------------------------
On Fri, 6/5/15, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> > wrote:

Subject: [PSUBS-MAILIST] Dive report: Snoopy at Seneca
To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org <mailto:personal_submersibles at psubs.org> >
Received: Friday, June 5, 2015, 6:16 PM

Hello friends,
I just got back from a dive trip to Seneca with
Dan Lance and thought I'd share how it went. This was
supposed to be a two sub trip with Scott Waters, but
unfortunately a business emergency intervened and it ended
up being just Snoopy.
On the way up the weather was terrible, with
driving rain so heavy I could barely see the lines on the
road. It had been raining heavily for several days
previously. Three times there were emergency announcements
about floods, large hail, and damaging winds, and the closer
I got the harder it rained. The problem with all that rain
is that in your typical lake, the runoff ruins visibility
for weeks. That is what happened last year when Trustworthy
and Snoopy rendezvoused at Summersville Lake, and it looked
very much like this would be a repeat. I'm happy to say
Seneca must be rain-proof, because the deluge only reduced
the visibility in the top fifty feet or so, and even those
were clearer than most lakes.
Here's a few things we learned:
1) Of props and shroudsThe stern
thruster speed control was dead on arrival, although I had
tested it successfully before leaving. I opened up the
enclosure, pressed down all the spade connectors, and found
it now worked - so attributed the issue to road bumps.
However, it died within a minute on the first dive. I had a
spare speed controller, so switched it out. 
The replacement died within five minutes on the
second dive. This time at least the cause was obvious, the
prop was jammed by weeds. The current Minnkota props have a
little twist at the end of the blades, and Snoopy's
shroud is made with almost no clearance. The little twist to
the blade tip causes any object coming between prop and
shroud to jam tight, and had already smoked one controller
during the convention in the Keys. I'm going to put the
prop on the lathe and take off the tips to eliminate the
pinching effect and to reduce the amperage draw a little so
the motor goes lighter on the speed controller. By the way,
the speed controller was protected by a fuse rated a little
below the controller spec current draw, so perhaps those
specs are optimistic. Anyway, as a result of the double
failure all of our dives were done on just the side
thrusters because I was out of spare speed controllers.
Lesson for next sub: Design the electrical system with a
controller bypass, so I can operate thrusters with simple
on/off switches if a speed controller fails. They're
electronic, they will fail.
2) Of air bubbles in compensation oil
Snoopy is now routinely diving deep (250 ft) and
this has showed up a puzzling issue with the thrusters. They
were feeble during dives, one died altogether on one dive,
and they kept coming up leaking oil. At first we thought the
seals were failing, perhaps due to some chemical
incompatibility. We found suitable seals at an Amish farm
supply store that sold things like tractor spares (viva
trolling motor simplicity!) When I disconnected the bladder
hose I got quite well sprayed with oil. The motor turned out
to be pressurized. 
Previously, I thought if one had a small quantity
of air left in the system it would not be an issue so long
as the compression volume of that air could be handled by
the flexibility of the hose (aka compensation bladder.)
Wrong. I now think what happens is that if the dive exceeds
the pressure rating of the shaft seal and there is a bubble
of any size, you will get water added to the oil and the
bubble stores the pressure. Upon surfacing, the bubble
squeezes oil and water back out until the pressure in the
motor falls to the "cracking pressure" of the
seal. Thus, you get an oil leak even though the seals are
fine. Lesson: Zero tolerance with oil bubbles, even a small
bubble is unacceptable if you are diving deep. I'm going
to put set screws on the motor caps so I can get rid of the
bubbles more easily.
3) An easy way to add
buoyancySnoopy's buoyancy is adjusted by
placing trawl floats in PVC tubes. On one occasion, the
oncoming passenger's weight required the addition of
just one float (i.e. the new guy weighed seven pounds more
than the one getting off). The support diver wasn't
suited up and the water was 42 degrees, so I just pushed a
float under the lip of the forward MBT. It worked like a
charm, and the float even stayed in place throughout the tow
back to the ramp. Lesson: You can easily add a few floats
for buoyancy on a standard K sub, no special tubes
required.
Most of our dives were along a very steep
incline, not quite a wall but more like a series of ledges
and very steep slopes. Between the steep terrain and the
good visibility, the K250 dome for once offered a really
good view. We typically made our way down the slopes using
very slightly negative buoyancy, trailing the back corner of
a skid on the slope. Looking aft, you could see a zigzagging
trail of silt hanging motionless in the water and tracing
our path. The sub compresses with depth, so slightly
positive buoyancy at the surface turned into slightly
negative at depth, but we're speaking of just a couple
of pounds and not anything that caused difficulty. In fact
at one point we stopped dead in the water four or five feet
above a flat bottom for about five minutes, just waiting for
a pre-arranged touch-point call on comms. The sub didn't
rise or sink an inch, she just hung there completely
immobile for five minutes. At about 140 feet the visibility
would improve significantly, and the water changed from
green to blue. It looked like ocean instead of lake water.
I'll post a video, but that'll take a few days to
put together. The only "incidents" we had were a
cold bath we took when we closed the hatch over a corner of
the crew's shirt, and when we got hooked on a log at 220
feet - fortunately reversing got us right off
it.

Best,
Alec 

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