T-Pain Is On A Boat: RE: [Electric Boats] How about a LOW RPM electric motor?

Monday, April 22, 2013

RE: [Electric Boats] How about a LOW RPM electric motor?

Craig.
When you first suggested the use of iron-powder toroids as cores for the stator windings I realised it was a good idea.
Here in the UK it used to be possible to buy at very low cost, reels of insulated soft iron wire for garden tie purposes. You could cut short lengths of this and bundle it up like drinking straws in a tube to make a good core material with low losses. Sadly, although the labels still call it 'iron wire'. it is now all steel wire instead which has much higher hysteresis losses.

Another advantage of your dust-iron toroids might be that the holes in the middle allow for a motor construction where a cooling airflow could be sucked through the centre holes to cool the windings, using a simple computer-style cooling fan mounted on on of the motor endplates.

________________________________________
From: electricboats@yahoogroups.com [electricboats@yahoogroups.com] on behalf of Craig Carmichael [craig@saers.com]
Sent: 22 April 2013 08:39
To: electricboats@yahoogroups.com
Subject: RE: [Electric Boats] How about a LOW RPM electric motor?

My BLDC motor designs are unconventional. In a sense I re-thought
what goes into making a motor from theoretical basics - and from
axial flux windplant designs. The Electric Hubcap motors get up to
somewhere around 95% peak efficiency. I admit they haven't been
definitively tested for this, owing to lack of time and equipment. Of
course one wouldn't expect lower efficiency from a bigger version
using more of the identical electromagnetic components each with the
same relative linear speeds, voltages, currents and switching
frequencies.

It's the axial flux, low switching frequencies, NIB supermagnets,
plastic composite bodies, and the individual unit coils. The iron
powder particles in the cores are insulated from each other and so
they have very low iron losses compared to laminates. almost trivial
losses period. (and you don't need a custom shaped die cutter.)
Because it's a toroid, it's 40% lighter than solid and the nearly
useless center area has no iron losses at all - which also
concentrates the flux at the outsides where it's more useful. The
round donut windings make maximum flux with the minimum of copper &
copper losses. The nanocrystalline ilmenite in sodium silicate
painted-on coating bends flux from going out into the air around into
the core.

Each thing made a difference. On my early primitive versions, peak
efficiency was very low - not much over 50%. The composite body was a
big help compared to steel, which interacted with the rotor
supermagnets even from a considerable distance, making heat. The iron
powder cores worked much better than my somewhat crude laminates of
the same dimensions. Then when I first painted on the ilmenite in
sodium silicate, idle currents dropped 25-40% on two different motors
at various RPMs. (Rutile worked too, but not as well as ilmenite.)
Now a few tens of watts spins up an unloaded 4.5KW motor.

There's still lots of room for various mechanical improvements I'm
sure (I've made a few), but not much more for efficiency.

The Electric Hubcap (36V, 125A, 11.25" O.D., 4+" long) is just 30
pounds or so, and the Electric Caik (24V, 125A, 9" O.D., 4+" long) is
16 pounds. When and if I make the "Electric Weel" it'll be well over
100 pounds. The body will have some steel for strength, but not near
the rim & magnets.

Craig

=====

>Very respectfully ideas are great but check the Agni vs. the other
>dc motors on the sites I sent; both are similar mass but the Agni
>due to design and materials is miles ahead. Unless you want
>relatively poor efficiency for ever sort through motors and find
>efficient ones, it¹s a cheap time saving endeavour and one which
>shows what is possible with current design and cost envelopes . The
>science in getting most of these things to their current state is
>significant and unlikely to be matched by a single individual.
>
>
>
>Check LRK motors too not big enough for these boats but the
>principles are the same or going to a motor maker to get the
>laminations cut and stacked at least
>
>
>
>Yours,
>
>
>
>Andrew Gilchrist
>
>fastelectrics.com
>
>Australia
>
>0419 429 201
>
>
>
>From: electricboa ts@yahoogroups.com
>[mailto:electricboats@yahoogroups.com] On Behalf Of Craig Carmichael
>Sent: Monday, 22 April 2013 3:38 AM
>To: electricboats@yahoogroups.com
>Subject: Re: [Electric Boats] How about a LOW RPM electric motor?
>
>
>
>
>
>Since the subject of "high-efficiency, low-rpm motors" has come up...
>I have two such large diameter, low RPM motors in mind.
>
>One is the "Electric Weel", which I've had planned for a couple of
>years but haven't built. Essentially, it's the active parts of 3 of
>my "Electric Hubcap" motors - 27 coils and 36 supermagnets - all
>arranged around the rim with a 26" rotor. Nothing in the center, just
>around the rim. It would be about 28" diameter and 5" long (except
>I'll pr obably cast the stator as 8 octagon sections, so the outside
>won't be round).
>
>This would give it about 9 times the torque of a single 11.25" O.D.
>"Electric Hubcap", with a 0 to about 600 RPM speed, but still only
>14KW of power. Maybe around 135 foot-pounds at 300 amps. It could run
>as 3 separate sections of nine coils with 3 of my (12-36V, 125 amp)
>motor controllers fed with the same sensor and control signals, or
>perhaps from some commercial controller good for 400 amps or so at 36
>volts. It would run 1/9 the RPM of the commutation.
>
>The second one is a bicycle rim motor. The magnets are to be on a
>large ring attached to the spokes or rim of the wheel. The stator
>would be an arc of 6 coils on the bike frame near the top of the
>wheel (3 KW of power, 24V 125A or 36V 82A). The diameter is a little
>less than the above motor (for 27 x 1.25" bike wheel), but it'll have
>no real 'body' of its own other than the arc shaped shell for the
>coils. It'll take quite a few magnets, only a few of which will be
>engaged by the coils at any one time, but it avoids many other extra
>parts like gears. It's low RPM. Whatever the theoretical top speed,
>it's faster than anyone will want to ride.
>
>I'll continue to use polypropylene-epoxy housings (tough,
>non-magnetic, non-conducting), holding toroidal iron powder cores, 2"
>O.D. x 1" tall from micrometals.com, wound as a donut coil, and with
>the ilmenite in sodium silicate coatings that make each coil a
>complete magnetic circuit by itself. ($10 per coil if anyone wants
>finished ones from me. They're wound with 21 turns of #11 wire,
>nominally for 12V for each one in series in a 3 phase machine, eg,
>the 6 coil "Electric Caik" uses 2 in series for each phase, so it's
>24 volts.)
>
>Craig
>http://www.TurquoiseEnergy.com/
>http://www.saers.com/recorder/craig/TENewsV2/ - Electric Caik Motor
>development
>
>Victoria BC
>
>=====
>
>At 18:06 +0100 13/04/20, Chris Morriss wrote:
>>
>>It is actually easy (*) to make a high-efficiency, low-rpm motor in
>>a DIY way if you use a large diameter, axial-flux BLDC construction
>>with a large number of the 3-phase stator triples. In this way you
>>can have the motor shaft rpm in the order of 1/8th or 1/12th (or
>>even more) of the electrical commutation rpm. The resulting motor
>>will be of large diameter but very thin front-to-back, so it will
>>not be as easy to position as a conventional high-speed motor with a
>>reduction gearbox, but it will be very quiet!
>>
> >* If you well understand the principles involved that is :-)

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