RE: [PSUBS-MAILIST] Oil Compensated Thursters

The blind leading the bind right? :)

Low voltage AC? I was only planning on 12 to 36 volts DC, and most likely 12v which is not a problem. I knew a guy that had a scuba light made from a car battery and a head light and he didn't even insulate the poles; worked great, in fresh water mind you.

BLDC - Brushless DC do magnets. I got my education about these from the RobotROV group: http://groups.yahoo.com/group/robotrov/

Yes carbon is a problem but the oil provides a lot of area to harmlessly suspend the contaminates until the oil is changed. And our lift station pumps [think sewage] that had brushes ran for hours each day for years.

About the prop, I know, bigger and slower turning is better but it all just general advice. Do you [or anyone] know of any resources that explain sizing props, pitch, motor, rpm? I also know that higher volt motors are more efficient but they have higher rpm's which is not efficient. So where is the biggest pay off? Do I use a 36 volt motor with a gear box and a big prop, or just a 12 volt trolling motor and hope for the best?

-- Doug J

In a message dated 11/21/2006 12:41:10 AM Central Standard Time, ojaivalleybeefarm@dslextreme.com writes:

Doug,

I'm not exactly the brightest bulb in the tool shed ( however that goes) myself on electric motors. I just got done talking to the motor people here in Ventura where they rebuild motors for the oil industry. They use some DC motors and some AC as well. I think you will be able to be equally electrocuted whether you use AC or DC. In my situation my batteries and motor are going to be outside my pressure hull and I will be controlling it using low voltage. I don't know how brushless DC motors work unless maybe they are permanent magnet motors? If I'm not mistaken I believe the starter coils and centrifugal switch is an antiquated method but I could be wrong, don't they use solid state components?. These motor guys were telling me that the carbon from the brushes is THE major reason they rebuild motors. They were saying that just a tiny line of carbon will carry an electric charge to ground very easily, so in oil that could contaminate the windings and make a short very easily. So thats how I got to the AC motor scheme. I think there are a number of ways to contol the speed. The starting torque I wouldn't think would be a problem, unless you had a very large propeller. As my system stands at the moment I'm planning on having six 183 amp hour 12 volt batteries, so my next decision is how long of a time would I want at full power to determine the horsepower of the motor. I'm going back to the oil field electric guys to try and get straight on this and see what they would recomend.

Brian