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Re: [PSUBS-MAILIST] Oil Compensated Thursters
I hate to but in, because both of you have good points.
it will always be a trade off.
facts
1 brush less DC motors are usually 3 or 4 phase AC running lower voltage some times with magnets
2 3 phase ac motors don’t usually have starter circuits.
3 ac motors are speed controlled by phase if you are running an DC to AC converter speed controller can be built in.
4 AC and Brush less dc motors have near flat power curves
5 DC to AC power controllers are around 90% efficant
Andy J.
---- Brian Cox <ojaivalleybeefarm@dslextreme.com> wrote:
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
----- Original Message -----
From: DJACKSON99@aol.com
To: personal_submersibles@psubs.org
Sent: Monday, November 20, 2006 21:32
Subject: Re: [PSUBS-MAILIST] Oil Compensated Thursters
Brian
You mentioned that before, and I ignored it out of ignorance, so
explain it to me. I think we use to use these in the warehouse on some
of the feed mixing equipment. AC induction motors don't have brushes to
contaminate the oil and with no brushes the voltage to cross the gap is
a moot point right? And they done have electronic controllers because
they use the AC cycle to flip the juice on and off right? But don't
they do often have starter coils and centrifugal switch that kicks in
the main coils once they are up to speed? And they have lousy starting
tork too right?
The down side has got to be having high voltage AC in a boat
surrounded by salt water. ...you know, I have been shot, cut, burned,
thrown from a motorcycle and I can tolerate lots of painful stuff, but
Jesus, getting electrocuted is the thing I hate the most. Last time it
happen I twitched the rest of the day. So what is the up side, beside
no brushes? How do you control the speed? And why not use Brushless DC
motors? They are my current choice, because they now come sensorless so
there is nothing to crush, and the speed controllers are small enough to
put in a small 1ATM box, and I can control the speed with a PWM signal.
[These are the bigger hobby RC motors that I am looking at; 250 watt.
Zzzzzapped --Doug J
In a message dated 11/20/2006 7:40:49 PM Central Standard Time,
ojaivalleybeefarm@dslextreme.com writes:
Doug,
What I'm thinking of now doing is instead of using an oil
filled DC motor ( where you have the problem of the carbon from the
brushes getting into the oil) is to use a AC induction motor and use an
inverter from the DC batteries. There are water and oil filled AC
motors out there which could probably be used. The inverters that they
have now are very efficient. I just need to figure out what my battery
capacity will be and go from there.
Brian
----- Original Message -----
From: DJACKSON99@aol.com
To: personal_submersibles@psubs.org
Sent: Thursday, November 16, 2006 01:30
Subject: Re: [PSUBS-MAILIST] Oil Compensated Thursters
Brian:
My dad motivated me to stay in High School by putting me to work
on Sanitary Sewer Systems (there is an oxymoron) and I serviced some
lift station pumps. We used transformer oil in them.
The engineer in your URL says "The lower efficiency carries about
a 2% increase in overall energy costs." -- I'd like to see what that is
based on, and does it pertain to low voltage motors too?
And the water well pumps are often compensated with plain water.
They just use wire in the winding that still has the insolation and
stainless steel and plastic guts, but again these are high voltage.
I suspect the efficiency may be really bad due to low voltage
trying to cross through the oil. Perhapes I'll have to experiment on a
smal DC motor to find the answer.
The next question would then be, does 500 psi change the
resistance of the connection between the brush and commuter in and oil
compensated 24 to 36 volt DC Motor? What do you think?
--Doug J
In a message dated 11/16/2006 1:36:05 AM Central Standard Time,
ojaivalleybeefarm@dslextreme.com writes:
Doug,
Do you think something like this would work? These
are not DC however.
http://www.zoeller.com/zep/techbrief/JF8article.htm
Brian
----- Original Message -----
From: DJACKSON99@aol.com
To: personal_submersibles@psubs.org
Sent: Wednesday, November 15, 2006 19:35
Subject: [PSUBS-MAILIST] Oil Compensated Thursters
Can anyone support this statement: "Scripps has tried to fill
the DC motors with oil, but the oil gets between the brushes and the
commutator, where the insulation properties of the oil causes problems.
Although it would be possible to use high voltage to break through the
oil film, the high voltage is a safety hazard for the divers."
-- www.empiremagnetics.com/articles/deep_sea.htm
I was thinking about 24 or 36 volt oil compensated brushed
trolling motors, but after reading the above I looked and could not find
any examples of oil compensated brushed motors under 100 volts.
What are your experiences and thoughts?
Thanks
--Doug J
http://www.submarineboat.com/
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