Re: Any ideas for large motor, and electronics


John Stevenson wrote in message
<5e5qm1d7rs3lenr9qdott33a0djmsffkme@xxxxxxx>...
>On Sat, 05 Nov 2005 16:30:57 GMT, "Bob Minchin"
><bob.minchin@xxxxxxxxxxxxxxxx> wrote:
>
>>
>>Michael wrote in message ...
>>>Hi,
>>>
>>>As some of you may know, I'm building a model submarine.
>>>
>>>It will be huge with a displacement of around 500kg and a length of 4m.
>>>Having worked out a rough idea as to the size of the motor required, 3hp.
>>>I'm now looking for suggestions. Sites like technobots don't stock ones
>>>large enough and so I'm struggling to find an answer.
>>>Then there is the matter of how to control the speed. Ideally I'd like
>>>proportional control.
>>>
>>>So, does anyone know where I can find a motor, ideally with the
electronics
>>>to control it? The onboard power will be provided for by two 12V
batteries,
>>>of which the AH is still undecided.
>>>
>>>Thanks
>>>
>>>Michael
>>>
>>>
>>Hi Michael,
>>
>>You might find it interesting to consider a mains 3 phase motor.
>>
>>Before you delete this reply as a bit wacky, please read on.
>>
>>Motor inverters are quite cheap now especially secondhand on ebay. All of
>>these rectify the mains to form a DC source from which variable frequency
3
>>phase AC is synthesised by electronic switches.
>>I would think it possible to have a high voltage battery ( much more
>>efficient at these powers than low voltages and huge current draw) and
feed
>>this in the AC inputs to the rectifiers in the inverter.
>>Most of the inverters can be controlled by buttons on the module, remoted
>>switches and knobs or by RS232/485 digital commands from a microprocessor.
>>This may be a bit exotic for your project and maybe a skills mismatch but
>>I'll throw it in as an idea.
>>
>>It is *just *possible that I can get hold of programming info for Siemens
>>Micromaster inverters as someone I work with used to work for Siemens
>>Automation and Drives.
>>
>>Good Luck
>>
>>Bob
>>
>Bob,
>Not being an EE but I was under the impression that yes invertors did
>change AC to DC , work the magic bits on it and then output 3~ but on
>a single phase one they took 240v AC and converted it to around 350v
>Dc then did the ear of bat, tongue of newt routine.
>
>As I said I'm no EE but after picking a large board type invertor up
>after being switched off but before the caps had bled out I feel, nay
>insist, I'm right <bg>
>
>Whilst trying to stuff both arms under my armpits, not drop the
>invertor and do the three shoe shuffle across a cluttered
>workshop..................................
>
>--
>Regards,
>
>John Stevenson
>Nottingham, England.
>
>Visit the new Model Engineering adverts page at:-
>http://www.homeworkshop.org.uk/

John, you paint a wonderful word picture!!

Yes inverters do normally take in AC but the first thing that happens is
rectification to DC. Yes, peak dc volts will be root 2 x the AC voltage.
240Vac equates to 340Vdc but there is usually some tolerance before the
inverter shuts down having sensed low voltage.
I'd guess at 300v worth of batteries would possibly be acceptable. Yes these
voltages bite the hand that touches them ( Thinks - Are high voltages
female?) but the big advantage should be much lower operating currents (say
8 amps for 3 horses) as well as universally available motors. We all know
the superb degree of control that 3 phase inverters bring to the party.

I'm off to the workshop to play and see what degree of variability a
micromaster inverter will tolerate.

Will report back later.

Bob


.

Relevant Pages

  • Re: Motor Star / Delta question
    ... motor having three windings which are strapped to operate in star mode. ... Looking at the specs on inverters, they all seem to output three phase ... Are they rated to handle either voltage or am I ...
    (uk.rec.models.engineering)
  • Re: Any ideas for large motor, and electronics
    ... Michael wrote in message ... ... >Having worked out a rough idea as to the size of the motor required, ... >Then there is the matter of how to control the speed. ... Motor inverters are quite cheap now especially secondhand on ebay. ...
    (uk.rec.models.engineering)
  • Re: Any ideas for large motor, and electronics
    ... Michael wrote in message ... ... >Having worked out a rough idea as to the size of the motor required, ... >Then there is the matter of how to control the speed. ... Motor inverters are quite cheap now especially secondhand on ebay. ...
    (uk.rec.models.engineering)
  • Re: Motor Star / Delta question
    ... motor having three windings which are strapped to operate in star mode. ... Looking at the specs on inverters, they all seem to output three phase ... Are they rated to handle either voltage or am I ...
    (uk.rec.models.engineering)
  • Re: Any ideas for large motor, and electronics
    ... >Michael wrote in message ... ... >>Having worked out a rough idea as to the size of the motor required, ... >>Then there is the matter of how to control the speed. ... >Motor inverters are quite cheap now especially secondhand on ebay. ...
    (uk.rec.models.engineering)