[PSUBS-MAILIST] DC Systems Primer

Wed Oct 16 15:26:03 EDT 2013

Joe,

I have to plead ignorance on the BLDC motor.  I'm guessing it's some kind of permanent magnet field DC motor... Correct?   Typically they are smaller in diameter then a wound field type.  

For my rear thruster I got the last of the three horsepower motors George had.  So my rear thruster in pretty much as the plans show.  

My side thrusters are even a bit larger then the plans since I found two 3/4 HP brush type, 36 volt motors for very cheep in a surplus close out.  I built around them but similar to the plans.  

To get props for them I called Michigan Wheel and gave them my HP and RPMs and a description of my sub.  They recommended the props and sold them to me.  

When I was doing my wet testing, I put a amp meter in the motor power line and found the side thrusters were fine but the rear thruster was drawing a little to many amps.  A little hand grinding to reduce the area of the prop blades brought the amperage down to the max rating for the motor.  I don't know if that the best way, but it worked for me.  

Now if your thinking of building a true Kort nozzle your definitely going to have to do some experimenting.  Even the prop guards as called out on the plans effect the prop efficiency and so also the motor load.  

You may be better off to find your motors then figure out what you can attach to them, open prop, shrouded prop or Kort nozzle.  Anything will move the sub.  I have a total of 4.5 HP and I don't know if I could control any more power as the sub gets squirrelly when trying to travel fast.  When submerged, the side thruster are almost all that's needed.

Dan H.
  ----- Original Message ----- 
  From: Joe Perkel 
  To: personal_submersibles at psubs.org 
  Sent: Wednesday, October 16, 2013 2:08 PM
  Subject: Re: [PSUBS-MAILIST] DC Systems Primer

        Dan,

        What I was hoping to find was BLDC motors matching 36v 1800 - 3600 rpm, 1/2 to 2 hp range. They don't seem to be out there.

        I have matched up brushed motors with those specs at both Baldor and Leeson with the appropriate face plates. But, then we are back to the same large / heavy motors at least there in the $500 range.

        You have the standard motors on Persistence, what are the size and pitch of the respective props?

        I'm going to just have to suck it up and draw these up with new Kort nozzles.

        Thanks!

        Joe

        Sent from Yahoo! Mail for iPad 

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  From: Dan H. <jumachine at comcast.net>; 
  To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>; 
  Subject: Re: [PSUBS-MAILIST] DC Systems Primer 
  Sent: Wed, Oct 16, 2013 1:48:13 PM 

        Those high voltage DC motors are designed for variable speed drives where the power is first line voltage AC then converted to DC through a motor controller for accurate motor speeds and torque.  They aren't practical for a battery powered system.

        For battery powered systems your probably better off to stick to the lower voltage motors.  With an inverter I guess you could convert the battery power to high voltage AC then convert it to DC, but I'm pretty sure you'd find it impractical with the extra equipment.  

        It's hard to beat golf cart controllers for speed regulation and there's tons of them out there.  Battery powered floor scrubbers use a variety of DC motors too. 

        Dan H.

          ----- Original Message ----- 
          From: Joe Perkel 
          To: Psubbers Mailist 
          Sent: Tuesday, October 15, 2013 11:02 PM
          Subject: [PSUBS-MAILIST] DC Systems Primer

          Since my Navy "A" school is some 30+ years ago, I need a little help in trying to understand and match up something close to Georges motors. What I dont understand is why is there such an array of DC motors in the 1 - 3 hp range with wildly varing input voltages?

          If you notice those Tecnadyne thrusters have stupendous input voltages up to 330vdc. I dont understand why and need a primer on DC systems for this application. Can anyone point me to one?

          What I'm trying to do is to slim down the housing, get more bollard thrust from the prop by adding a real kort nozzle, and use a mag coupling instead of a shaft seal, all else remaining essentially the same.

          I want to slim down Georges T-Rex cans with similar power specs, but new and improved components, keeping the items conducive to homebuilding, like the housings and mountings, electrical penetrators, shaft seals if I cant do mag couplings. 

          What I've found so far http://www.baldor.com/support/literature_load.asp?LitNumber=FL1210  fractional hp and up to 3 hp @ 1800 rpm but, here again @ 320vdc !?

          Whats attractive about this one is the dimensions, 6.5" on the mounting flange would fit quite nicely in the 6 nom SCH40 pipe which is 6.625"

          But I dont know what im doing with regard to the input voltage / output power / torque relationship and how to match this all up correctly.  All Ive confirmed so far is that Georges motors were TENV (totally enclosed non-ventilated), 36vdc @ 1800 to 3600 rpm for 1/2 and 3 hp respectively.

          Joe

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