[PSUBS-MAILIST] Dive report: Snoopy at Seneca

Sun Jun 7 06:19:36 EDT 2015

Thanks people,I looked at a tuned inductor esc & it was 600- Euro.. ouch!This guy has a 15ft wire run & is using a 30,000 mfd capacitor & says it works well.That's a 2" X 3" capacitor. I am not sure what model he is refering to, but he makespeople carrying electric helicopters with 30ft span motor arrays.Alan

   - Permalink Reply by Brad Hughey on January 24, 2013 at 7:14pm

      - The problem really lies in the "coil of wire" like effects (parasitic inductance) on the battery lines and the way Metal Oxide Semiconductor Field Effect Transistor speed control circuits are designed to work.  MOSFETs in this application are used as an all-or nothing switch that turns on and off very quickly.  The unfortunate thing is that high currents develop strong magnetic fields, and when the current is interrupted suddenly by the MOSFET doing what it's supposed to do, very high transient overvoltages can be generated by the collapsing fields around the stray inductance of the power wiring. MOSFETs don't like being constantly "kicked in the ass" like this (really referred to as avalanche voltages) at levels higher than their maximum ratings.  One way to solve the problem is by giving the sudden voltage spike energy somewhere else to go, and this is what the capacitors are for.  Another method is to tie a zener diode between the drain (assuming n-channel) and gate, to literally turn the MOSFET back on for a bit to dissipate the transient (if you don't understand what I just said - you're a more and bigger capacitors person).The whole notion of a "sinusoidal" MOSFET switching circuit sets off my hogwash detector.  If an ESC doesn't need a big capacitor (you can't make it too big electrically), then the latter approach is probably what they're depending on.  Biasing MOSFETs in the active region (as in what applying a sinusoidal signal to the gate would do) and asking them to handle a high drain current usually guarantees nearly instant vaporization of the device.I have a rather large run in my, ahem, model of around 15 feet at the extreme, and found a 300,000 uf capacitor quells the effects of the inductance rather well (yes, that's .3 farads folks).  So yes, you can't go too large, and there's the added benefit of vastly increased power supply voltage stability in the opposite direction (less "sagging" due to transient battery impedance). 

      From: via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Sunday, June 7, 2015 1:32 PM
 Subject: Re: [PSUBS-MAILIST] Dive report: Snoopy at Seneca

Also tuned inductors will help disipate the spikes caused by the controlers.

Keith T

Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

>Thanks Ken,I was nearly going to ask you to comment in my post.Is there an alternative to capacitors or to the electrolitic capacitors usually used?I was looking at this option.http://www.dialelectrolux.ru/files/file/electronicon/e61-data-charts-engl-deut.pdf
>Alan
>      From: Ken Martindale via Personal_Submersibles <personal_submersibles at psubs.org>
> To: 'Personal Submersibles General Discussion' <personal_submersibles at psubs.org> 
> Sent: Sunday, June 7, 2015 12:19 PM
> Subject: Re: [PSUBS-MAILIST] Dive report: Snoopy at Seneca
>  
>#yiv9053454032 #yiv9053454032 -- _filtered #yiv9053454032 {font-family:Helvetica;panose-1:2 11 6 4 2 2 2 2 2 4;} _filtered #yiv9053454032 {panose-1:2 4 5 3 5 4 6 3 2 4;} _filtered #yiv9053454032 {font-family:Calibri;panose-1:2 15 5 2 2 2 4 3 2 4;} _filtered #yiv9053454032 {font-family:Georgia;panose-1:2 4 5 2 5 4 5 2 3 3;}#yiv9053454032 #yiv9053454032 p.yiv9053454032MsoNormal, #yiv9053454032 li.yiv9053454032MsoNormal, #yiv9053454032 div.yiv9053454032MsoNormal {margin:0in;margin-bottom:.0001pt;font-size:12.0pt;}#yiv9053454032 a:link, #yiv9053454032 span.yiv9053454032MsoHyperlink {color:blue;text-decoration:underline;}#yiv9053454032 a:visited, #yiv9053454032 span.yiv9053454032MsoHyperlinkFollowed {color:purple;text-decoration:underline;}#yiv9053454032 span.yiv9053454032link-enhancr-element {}#yiv9053454032 span.yiv9053454032link-enhancr-view-on-domain {}#yiv9053454032 span.yiv9053454032EmailStyle19 {color:#1F497D;}#yiv9053454032 .yiv9053454032MsoChpDefault {font-size:10.0pt;} _filtered #yiv9053454032 {margin:1.0in 1.0in 1.0in 1.0in;}#yiv9053454032 div.yiv9053454032WordSection1 {}#yiv9053454032 Adding extra capacitors helps reduce the magnitude of the inductive voltage spikes.  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 tomotor 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 brushedmotors would be similar. Because of the rapid switching on & off of the power to the motor, there is acurrent 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 witha "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 Alantoo long battery wires will kill ESC over time: precautions, solutions & workarounds - RC Groups
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>      From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
>To: Personal Submersibles General Discussion <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> wrote:
>
>Subject: [PSUBS-MAILIST] Dive report: Snoopy at Seneca
>To: "Personal Submersibles General Discussion" <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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