[PSUBS-MAILIST] air compensation

Mon Jul 31 08:52:08 EDT 2023

 Jon, from my perspective, it is true that there is more kit required for air compensation.  For the R300 the incremental parts are an additional regulator that can be set to 2-5 psi above ambient water pressure and an over pressure valve and some 1/4 SS tubing and fittings.  When I orginaly had air compensation on this boat, I combined the regulator and over pressure function in a single regulator.  I would use the existing HP air supply.  And yes, these do introduce additional leak points.  As I use Swagelok fittings, this air leakage is almost nonexistent.  Having said that all this, oil compensation has fewer components.  I am still of two minds on this compensation business for the 101s. As such, I am still researching a way forward.
"the photos appear to show a lot of sludge…do you attribute this to the brushes only?"  100% yes.   I know that part of black appearance of the WD-40 fluid was suspended particles of the brush.  Part of the blackness is probably due to arcing that is cooking the WD-40.  Gas for sure has to be coming from arcing.

"How badly were the brushes worn and are they still solid or has the oil penetrated them to the point that they are soft and decaying?"   The brushes in this motor were completely worn down so that they were no longer making contact with commutator.  At the Beaver Island expedition, after disassembly and inspection, since I did not have replacement parts i.e., lip seals, shaft bushing and brush set, I elected to just put the motor back together for the open house and trip back home.  While apart I did not test how soft the brushes were.  I am waiting on rebuilding all the thrusters until I pick a compensation oil.
"Are all four motors in the same condition with score marks on the shaft and commutator?"  Unknown.  I have not disassembled them.  When I do, I will report findings.  At the end of last year's diving season.  I was having trouble with my starboard vertical thruster.  It was not generating as much thrust as the identical port vertical thruster.  When I had the boat in the water for diving in Lake Charlevoix, when I would ascend, the boat would noticeably roll to the starboard side.  When I got back from the trip, I investigated this by temporarily wiring this problematic thruster from the opposite side.  Same symptoms so this told me the issue was the thruster itself and not the motor controller.  Upon disassembly, I did notice some brush sludge but not at the level of the aft thruster that failed this year.  Also, the brush was worn but not excessively.  I did notice the commutator looked bad.  I used Emory cloth on the commutator and replace the brush set and reassembled.  I did not notice any wear ridges on the shaft.  This brought the thruster back to 100%.  I did not experience any rolling on ascent at the Beaver Island expedition.  My take on the brush wear being less than the aft thruster that failed was the stern thrusters are used for propulsion and yaw control so get more use than vertical thrusters.

Cliff

    On Monday, July 31, 2023 at 04:34:06 AM CDT, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

  I don’t think we should lose sight of the logistical issues surrounding air comp including regulators and hoses which open potential failure points, and the potential of additional tanks and getting them filled in a location that does not have good SCUBA support.  Just the fact that oil comp reduces the number of components to achieve the intended result makes it an attractive option in my eyes. 
Cliff, the photos appear to show a lot of sludge…do you attribute this to the brushes only?  How badly were the brushes worn and are they still solid or has the oil penetrated them to the point that they are soft and decaying?   Are all four motors in the same condition with score marks on the shaft and commutator?
Jon

    On Sunday, July 30, 2023 at 03:20:17 PM EDT, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

  Hank, I did a calculation yesterday as to how much air it would take for the four Minn Kota 101s for a round trip to 300 fsw and back.  The answer was 1.5 SCF for the total (37 fluid oz internal volume in each thruster).  This was less than I expected so I am not feeling so concerned about the R300 HP air supply if I switch back to air compensation.  I have not made this decision yet, but I don't have high hopes that I am going to be able to find an oil that will not be affected by the arcing for these 101s.
Gas leak detection with soapy water works.  Can you send me the make and model of the first stage scuba regulator you are using and the part number for the pressure relief valve you are using?  If I switch back to air compensation, I cannot use the first stage I have because I have need for it at 50 psig above ambient for BIBS and MBT blowing.  I found the previous pressure regulator I used was just too small to handle four thrusters which was how it was plumbed.  It sounds like your regulator might work better.  
I will be interested in your next dive with all four thrusters under air compensation.  Hopefully it will be deeper to give the air compensation system a good test.
Cliff
    On Sunday, July 30, 2023 at 09:36:09 AM CDT, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Cliff, I am wondering if you can reduce the volume of air inside the motor to reduce air consumption?  Maybe some form fitted plastic inserts between the magnets etc. I have just discovered a nice feature while connecting my rear thrusters to the air compensation  system this morning.  You can pressure test for leaks with your soapy water sprayer. Hank_______________________________________________
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