Generator to motor

[dskira]

Do I am getting closer to understand? Ok as says Hibbo,(thank you for your input) to reverse will be no problem, just one more problem: what pice of equipment do that? Now for the speed, what pice of equipment do the voltage control or frequency control?
Thank you all for trying to make me understand in what pikkle I am with my idea of a three phase AC controlable and reversible motor! But it seams it can be done, and your infos seams going in that direction. So more idea please !! and if its without any computer the better, no elecronic is also the goal. A solution close to the bare basic will be fantastic.

[Holter]

Ok, I think the things I said have been not clear enough, I will try again with some new vocabulary an an example:

1. I have no Idea of the necessary torque and rpm of a ship's propeller. I assume, the propeller will be designed for around 2-3 kW at 600-650rpm, you talked about direct drive.
Now we take a standard Lister(oid) 6/1, 6hp@650rpm.
directly to the shaft of the motor can be connected a synchronous generator, either a special permanent magnet (How to proceed with this will depend on the generator itself and should be discussed with the possible generator).
or one with rotor windings and AVR. Perhaps a ST Generator for three phases with around 8 kW and 4 poles (1500 or 1800 RPM). Three cables will go now to a (sealed) box, that has to be made by a friendly electrician. This Box is connected to another switch where you control the boat with 5 or 7 positions (2-3x forwards, 2-3x backwards and one for stop). How many positions will depend on the asynchronous motor.
This Motor could be a multi-speed Motor where you can switch between 4, 6 or 8 poles and a maximum power of around 7-10kW.
If the AVR works at low rpm, this system should work quite well. In full speed the propeller should have something between 600 and 650 rpm, at "half speed" around 400-430 and at "low speed" 300-320. This of course in both directions.


The sealed box is a setup with a number of electromagnetic switches and a complex cable system. I would recommend to use 24V DC switches and one a little overdimensioned 3-phase transformator with rectifier. This 24V DC kan also be used on the Boat for Lamps or so.

The complete system (perhaps except the AVR on the ST gen head) is built with technology not younger than a Lister.

Physics:
The Generator will be driven with around 650 rpm. The voltage of a synchonous motor is regulated with the excitation of the rotor field, which is independent from the rpm and controlled by the avr. If the Generator is brushless, there could be a problem. The current of the Generator depends on the angle between the magnetic field of the stator and the rotor, thus is also independant from the rpm. The generator needs to be bigger for two reasons: The torque, that is needed to drive the generator to get ca. 3kW is bigger than at the rated speed of 1500 or 1880 rpm, because the Power is the product of torque and rpm. Added to this is the irregular speed of a one cylinder motor, which puts additional stress to the generator shaft. If the Shaft of a smaller generator is sufficient for this, even a 3-5kW gen head could be ok. The generator could be also much bigger, but then efficiency will drop, weight and costs will rise and you will have to cranc this when you start. On the other Hand, if these were major concerns for you, you would not even consider a Lister

After that you will have threephase Power of around 400V (US=230?) and 21 Hz(!) With this you can start the asynchronous Motor in the lowest "gear". The maximum Power of this Motor with 6 poles is around 2kW, so starting it with the Lister is no Problem and also the Load from the Water resistance will be much lower, because the rpm will be at ca. 300-320. Now you can switch between the different positions. If you switch between full speed forwards and backwards with no Time Delay too fast, either some protective fuses (that the electrician installs) will blow or the Lister will stop. The same Thing happens when the propeller gets caught or so. Which case of both happens will depend on the dimensioning of the Fuses: If they are only there to protect Motor and Generator (that both can do much more torque than the Lister), than the Motor will stop. If the fuses are smaller and awitch already at the designed Load of the Lister (around 3kW), then you will just have to switch them on.

Possible Problems, that have to be considered in this Setup:
- I do not know, if a differential works at 21Hz, also the Transformator will have less Power, because of the
- The coupling of two Shafts has to be carefully done
- The Motor is not easy to find (used). Perhaps a Motor with two speeds will be sufficient
- The AVR and the rotor winding of the generator will be more demanded, because to keep the tension high at low rpm the magnetic field needs to be stronger.

These Problems could be avoided, if you use a belt drive for the generator, but then the propeller also needs to be designed for higler rpm (~1500)

The Problem of Efficiency cannotg be solved so easy: The total efficiency of this drive system is the product of the efficincies of (Belt drive), Generator, (electric system) and Motor. I suppose this will be at around 60-75% Compared to a Direct Drive that means the same loss regarding available Power and also fuel consumption.
Nevertheless I think a System of this Type could be very comfortable, maintenance-free (except the motor of course), more quiet and (if the electric Setup is well done) very durable.

Christian

[dskira]

Thank you so much Christian, I appreciated your very detailled explanaison.
I think I am finding the light thanks to all of you.
Daniel

[Doug]

dskira, this all getting a lot more complicated than it may be worth.

But...
If you can find a wound rotor motor off an old electric crane  bridge or troley  you can wire up a simple speed control thats not efficient at low speed but is easy to wire and use.  Combine this increasing and decreaing the prime Listers speed and this might be a viable choice. Changing direction is easy just a pair of contactors to reverse phase.

Realy I think this is a lot more troubel than its worth.

Doug

[adhall]

Doug:

What do you think of this scenario:
  -- Rectify the output of the ST head and use this to power a permanent magnet DC motor
  -- Vary the speed of the DC motor by varying the field current of the ST head while leaving the Listeroid running at constant speed
  -- Generate the field current using a seperate DC generator driven off the Listeroid
  -- Change direction of the DC motor by using a reversing switch (or contactor).

This looks fairly simple to me and I don't see why it wouldn't work.

Best regards,
Andy Hall

[Doug]

Probably the smartest sugestion yet.

I think you have the easiest way pinned there!

Doug

[ronmar]

That is pretty much how the USCG's Polar Class icebreakers do it, except we use a field winding on the motor as well.  Kinda hard to get 6000HP permenant magnet motors...  Motor field was adjustable for certain circumstances, but we typically left the motor field fixed.  The generator field was automatically controlled to maintain shaft RPM(motors direct coupled to the 30" dia shafts).  We used hydrauically controllable pitch on the 3 props for direction control as the motors were fixed in their rotation direction. Prop pitch would automatically lessen if we overloaded a shaft and RPM began to fall. 

For icebreaking we lifted the brushes on the motors and coupled the forward end of the shafts to reduction gears with Pratt and Whitney FT-4A gas turbines on the other end.  25,000 Shaft HP peak(20K sustained) per shaft.  Probably the coolest job I will ever have had, getting to crack the throttles on 75,000 Shaft HP:) 

Ron   

[dskira]

Adhall, that the point: no dc motor, only a ac motor. And this is the reason why which I didn't explain before and I should have:
The genset will be in the front part of the vessel and the motor to keep the shaft short, at the aft end of the vessel, therefore the dc cable will be gigantic, and realy dangerous due to the great distance. The all point of this system was to position the main engine(generator) and the propulsion motor far appart without recouring to a very long shaft. And the middle part of the boat will use for light cargo and accommodation (the best real-estate in a boat!)
I am sure your solution is very good, but dc will be not appropriate for this distribution I think.
Ronmar that will be quite out of the budget and quite out of reach, but I apreciate your input. Controlable pitch prop are quite expensive, if they where more  afordable I will put the following system:
-generator ac
-motor ac constant speed (600 rpm)
-controlable pitch prop.(take care of the velocity and the reverse of the vessel)
That will be a deam, not for the bank account of my dear customer.

[Holter]

You could also go with the AC Cable across the boat and rectify it near the DC Motor.

Christian

[Andre Blanchard]

The genset will be in the front part of the vessel and the motor to keep the shaft short, at the aft end of the vessel, therefore the dc cable will be gigantic, and realy dangerous due to the great distance.

If all you do is rectify the AC and feed it to a DC motor.
Why would the DC wire be any bigger then an AC wire, or any more dangerous?

[Hibbo]

Don't get caught up thinking that all DC motors are low voltage high current - thus needing huge cables.

I think a DC motor is the way to go, controlling the speed of it by varying the field current in the generator.

Speed controlling a 3ph AC motor is going to be way too complicated (read expensive!)

Get a single or 3 phase gen head, feed the field by a variac (this will be your speed control) rectify the output and feed it to a big DC motor. K.I.S.S.!

[bitsnpieces1]

Adhall, that the point: no dc motor, only a ac motor. And this is the reason why which I didn't explain before and I should have:
The genset will be in the front part of the vessel and the motor to keep the shaft short, at the aft end of the vessel, therefore the dc cable will be gigantic, and realy dangerous due to the great distance. The all point of this system was to position the main engine(generator) and the propulsion motor far appart without recouring to a very long shaft. And the middle part of the boat will use for light cargo and accommodation (the best real-estate in a boat!)
I am sure your solution is very good, but dc will be not appropriate for this distribution I think.
Ronmar that will be quite out of the budget and quite out of reach, but I apreciate your input. Controlable pitch prop are quite expensive, if they where more  afordable I will put the following system:
-generator ac
-motor ac constant speed (600 rpm)
-controlable pitch prop.(take care of the velocity and the reverse of the vessel)
That will be a deam, not for the bank account of my dear customer.

  It seems like you already have the 3ph motor, SO: what you need is a VFD (Variable Frequency Drive).  These are electronic systems in a box: feed power cables in, feed power cables out, and turn knob on front panel (or remote) to change speed or direction.  They can take 1ph or 3ph input and give 3ph output.  I have a couple that take 115v 1ph ac in and 115v 3ph out OR 230v 1ph in and 230v 3ph out and are fused at 20amp.  ( Ithink that's either 5hp or 1.5hp.) 
  Basically what a VFD does is 1) take AC power; 2) rectify it to DC; 3) store it in capacitors; 4) pull from capacitors thorugh electronics to give a 5) variable voltage AND variable frequency output.  This gives you a variable speed / reversible 3ph motor for your drive.  Now:  In order to control the speed of the motor the VFD does the following:  to go slower you reduce the voltage, HOWEVER you MUST reduce the frequency to prevent burning out the motor.  To go faster: increase the voltage, HOWEVER you MUST increase the frequency to obtain rated power. 

http://www.danahermotion.com/products/product_detail.php?parent_id=132
for VFDs.
  You can select: North America,  Europe  or Asia for your location. 
These are the ones that I have.  Quite a few people make them.  VFDs ARE expensive, but, give you really good control.  The prices have come down making them more competitive with DC drives. 

http://www.danahermotion.com/file_broker.php?document_id=2366
 I have an earlier version of one of these I got off eBay. 

[dskira]

I like your system Bitsnpieces1. It looks as KISS as it can get.
Also it make a lot of economical sense, the VFD being around $1000 or a little more. I hope it take care also of the frequency since, as you point out, is a key feature of the good fonctionement.
In short it sound great, make me understand the big picture, and make the system worth to continue to investigate.
Thanks for the links

[bitsnpieces1]

dskira:  The controller handles the voltage and frequency automatically.  As you position the speed knob the electronics vary the voltage AND the frequency according to a built in profile.  We had units controlling 3ph motors up to 100hp and down to 5hp.  It used to be recommended that you go with DC lower than 5hp simply because the controllers were fairly expensive (compared to hp) at the point.  However, things have improved since then  and prices have gone down. 

[dskira]

Many thanks Bitsnpieces. Your last post make me understand that it's practical, and feasable and with almost of the shelf components.
Whao!, you all of you know a lot about that stuff, its great to be around persons who are willing to share and help with there knoweldge.
I realy apreciated