Chris S,
In my enthusiasm for the yet-to-be Hardy VFD, I was dreaming of a "better" battery system. A 420volt DC bank is indeed dangerous, but also very difficult or expensive to balance (that many cells in a series WILL quickly pick one after the other to destroy with over- and under-voltaging)
Most good deep cycle batteries can give 250, maybe 300, amps continuous. The internal cell connectors are designed for max amperage intermittent.
Parallel 48VDC systems is indeed advantageous (great safety and redundancy) , except for cost and maintenance.
So the practical limit for the Hardy VFD is 300A 48VDC input. Short, fat cables, cheap components, long AC cables possible, BMS optional. Still a "killer app", compelling application of electric propulsion.
Mark Stafford
dreamer
--- In electricboats@
>
> The amp draw would be no different to any other system .if youre taking a given power from your batterries it doesn't matter whether that power goes to a DC motor VFD , inverter or any other type load and you size your batteries to suit.
>
> In the higher power ranges I think you would need to work with a 300 to 450 volt battery bank which is what the proffesional electric boat and vehicle builders use, to keep the currents managable .THis allows adapted standard VFDs to be used. Though I hesitate to advise hobbyists to experiment at such high voltages in a watery environment! Though it used to be common practice in the early days of electric boats around 1900.
> One way to get round this would be to use multiple 48 volt motors and parrallel controllers. I recently saw an interesting article where 4 of 48 volt 10 Kw motors had been used . they made a neat unit by putting the motors in pairs , back to back . each pair sharing a small shaft . then belts linked from the two small shafts to the prop shaft. with four controllers which also gave the great benefit of quadrupal redundancy!!
> Chris S
>
> Chris S
> --- In electricboats@
> >
> > I'd pay $4000 for one right now. The only caveat would be you could
> > not use lead-acid with it. The Peukerts effect would cripple your amp
> > hour rating. The amp draw per cell would be astounding. But again I
> > would buy one right away! Then I could have one simple high amp hour
> > LiFePo4 48V bank instead of six lower amp hour 48v banks that I need
> > right now. Easier to charge easier to wire, less connections to fail.
> > Would all around make my life less complicated!
> >
> >
> > On Aug 3, 2009, at 11:10 AM, Mark Stafford wrote:
> >
> > > Chris S,
> > > You have a great idea and product potential: 48volt DC in, variable
> > > three phase 460 AC voltage out. 250amp DC continuous, 750amp max
> > > draw. This "Hardy VFD" (your email name) would match many batteries,
> > > many AC motors, many gensets, under 70' sailboats and under 20'
> > > runabout powerboats. Most importantly from a sales volume
> > > perspective, this imaginary VFD could crack the huge recreational
> > > fishing market (primary & trolling propulsion from the same motor/
> > > prop with genset support for distance).
> > >
> > > Any manufacturers interested?
> > >
> > > Mark Stafford
> > >
> > > --- In electricboats@
> > > wrote:
> > > >
> > > > I predict that AC motors WILL become universal in cars and
> > > boats .AC controllers are now readilly available from industry .What
> > > we really need to make it easy is a controller than takes a low
> > > voltage DC in direct from your batteries and puts out a variable
> > > three phase Ac Line voltage to power an inexpensive standard rugged
> > > induction motor.Thats to say the missing link is a variable
> > > frequency low to high voltage inverter (VFD)
> > > >
> > > > Chris S
> > > > --- In electricboats@
> > > wrote:
> > > > >
> > > > > Arby Bernt wrote:
> > > > > > Locomotives use AC drive systems due to the complexity of
> > > coupling the engine to the drive wheels. Before AC coupling was
> > > available, the slip between the drive wheels and the track was
> > > nearly impossible to control, as the friction of a non-slipping
> > > drive wheel can transmit more force than than a slipping wheel. By
> > > comparing the rotation of a drive wheel to a static wheel, the speed
> > > difference can be maintained at under 0.5%.
> > > > >
> > > > > Most of the world's railway 'diesel electrics' are DC motored. AC
> > > > > motors have only come in over the last 10 years and then only at
> > > the big
> > > > > end. Railways have been reluctant to switch from series DC motors.
> > > > > 'Switchers' would still mostly be series connected DC motors, AC
> > > > > traction motors are still working their way down the feeding
> > > chain.
> > > > >
> > > > > Even then they are not all induction motors - the French were
> > > big on
> > > > > Synchronous motors with slip rings for a while - I presume so
> > > they could
> > > > > control the current in the rotor coils.
> > > > >
> > > > > EMD apparently built their first AC motored locomotive in 1987,
> > > but the
> > > > > first big order wasn't till '93. The same source says at 2005 ,
> > > 50% of
> > > > > the market was still DC motored, EMD's split was 60% AC, 40%DC.
> > > > >
> > > > > Sounds sort of like us electric boaters - those 'new fangled AC
> > > motors'
> > > > > are still not quite trusted yet :-)
> > > > >
> > > >
> > >
> > >
> > >
> >
> >
> >
> > [Non-text portions of this message have been removed]
> >
>
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