RE: [PSUBS-MAILIST] diesel electric

[MerlinSub@t-online.de]

To run a AC-Motor from a DC battery needs a special frequency drive 
which can handle the high difference in voltage between nearly empty 
and full DC battery. 

For example : 
DC battery empty = 344 Volt
DC battery full  = 400 volt 

Most frequency drives are programmed that way that the quit if 
voltage is 10% lower than nominal Voltage.. 400 -40 V = 360 Volt

My problem is that I have a DC-Motor/Generator which load and run 
from the DC battery - no problem - but all the secondary system like 
air compressors and bildge pumps runs on AC..  so I need a AC- Network
This required a frequency converter - and this seems is not off the shelf.  

There seems some available in the e-car market, the UPS-market 
and the solar-energy market which can handle that.. 

regards Carsten


"Stephen Pearce" <sjpearceqld@bigpond.com> schrieb:
> Frank
>  
> Without getting in to a Pissing competition I will quote my friend who
> is an electrical engineer "the motor (AC) that has been selected will
> handle full load at all speeds, yes without using braking
> resistor/dynamic braking." I am not an expert but I have consulted
> several and not one has suggested a DC system in practice will be
> practical without manufacturing a Customised purpose specific motor like
> in conventional military subs. 
>  
> If you are talking about small DC motors like on the K boats or Kara
> then DC is the way to go. The size of the sub Brian has on the drawing
> board he will need a 600+ Volts DC for the system to work. That's a lot
> of 2 volt Cells or even 12 or 24 volt cells. Ask Carsten, I believe
> several months ago he was making substantial modifications and now
> requires 600 Volts because of his choice to go DC and had not yet
> concluded the make up of his final system. 
>  
> The problems and expense of a 600Volt system and the cost of the
> switching and associated components are huge. For example a 75KW DC
> motor is in the range of 28K to 30K (USD) new. The AC equivalent is
> about 12K and Reconditioned about 6K.
>  
> I would also fell less comfortable in a vessel with a 600V DC system
> that under certain circumstances may be subject to partial flooding. You
> will need room to house all those batteries in water and air tight
> 'spark free' containers.
>  
> By all means run your hotel load off 12V DC batteries but DC setups for
> 50+ HP can be impractical and cost much more in real terms. I went
> through this process with the initial view of wanting a DC only system
> but I have modified my design as a result of being prepared to accept
> that there are experts with experience in this area that know more than
> I do. I want a successful P-sub at the end of the process even if that
> means that my initial design was impractical due to my ignorance.
>  
> Frank if you can design a better propulsion system using 50+ volts DC
> motors and Diesel Gensets that overcomes the problems and
> impracticalities I have described I would be sincerely interested in
> looking at it and if it is superior to my current design adopt it as my
> system of choice.
>  
> Respectfully (sorry Jay for borrowing your tag line :-) )
>  
> Steve P
>  
>  
>  
> -----Original Message-----
> From: owner-personal_submersibles@psubs.org
> [mailto:owner-personal_submersibles@psubs.org] On Behalf Of
> ShellyDalg@aol.com
> Sent: Wednesday, 1 November 2006 4:43 PM
> To: personal_submersibles@psubs.org
> Subject: Re: [PSUBS-MAILIST] diesel electric
>  
> Just a quick note.... D.C. motors have more torque at lower speeds,
> where the power band of an A.C. motor isn't realized until the optimum
> speed of the particular A.C. motor is achieved.
> The universal availability of A.C. components doesn't work either, when
> you consider the use of different Hertz configurations in foreign
> countries. D.C. is D.C......no matter what country you're in. Everybody
> in the world uses 12 volt chargers.....and batteries the world around
> are all compatible. My jumper cables built in Chicago, will connect to
> my Toyota, carry a charge to my wife's Volvo, which will get us to my
> broken down Harley out on Interstate 5, and getting me back home with
> time to see Monday's game on my 12 volt T.V.
> Stick to D.C. and save yourself a lot of expense and grief.
> Frank D.
> 





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