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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 -----
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 -----
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.
Brian
----- Original Message -----
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."
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
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