----- Original Message -----From: Andrew GilchristSent: Sunday, April 21, 2013 5:53 PMSubject: RE: [Electric Boats] How about a LOW RPM electric motor?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, it's 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: electricboats@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 probably 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 :-)
>Andrew, many thanks for taking the time to provide the information.
>As to your question, for my term "soft laminations", I should have
>said: "simple soft iron laminations". The lamination material being
>iron; rather than any type of alloy or carbon steel. By "simple" I
>mean that the core laminations are made in a simple orthogonal
>geometry without clever touches like curved or sloping flux gaps. No
>matter how much I would wish to put oddly shaped flux gaps on
>laminated cores, such gaps can make winding the coils real difficult
>& expensive.
>Please keep in mind that some or most of what I'm talking about is
>ancient history now (more than about 15 years old). So the value is
>nearly nil.... although some of the understanding of how we got to
>the motors of today might be useful to someone who is re-using older
>industrial motors.
>
>And I've got an idea to propose for low RPM efficiency that might
>be interesting. (at the end, below)
>
>I'll confess that I quit using soft iron in lamination design about
>that long ago when computer modeling became popular. Historically,
>engineers used pure soft iron for lams because the div,grad, and
>curl calculations for magnetic flux through the stack of laminations
>making up a core were so fiendishly time consuming that they started
>analysts to gibbering. And the specialty high permeability
>silicon/cobalt steels so expensive and hard to work that the bean
>counters started gibbering too......... so that in the end the more
>humanistic designers would just specify soft iron for
>laminations and call it good enough to quiet the gibbering in favor
>of beer and sailing.
>
>Now that computer modeling has made those wretched
>vector calculations trivial, my own preference is towards using a
>common 1018 mild steel for everything the flux path and doing just
>enough modeling to insure that it doesn't saturate.
>But I got to do that because the design work I used to do allowed
>that approach. Specifically because the eddy current losses in the
>laminations aren't the problem for low amperage & low frequency
>instrument and controls systems that they are in high amp and high
>RPM boat motors.
>
>Still, the idea of an electric drive with a very low rotational
>velocity and a gearbox to drive a prop tickles my imagination.
>There's that battery time lag inherent in moving from chemical
>energy to electric current and there's also all sorts of weird
>magnetic and back emf (commonly abbrev. as "Bemf") effects that we
>don't even have to worry about if only we can keep the RPM low
>or the cycle time long enough.
>
>It's sort of like the two different ways of using steam: The
>steam can either feed a cylinder/rod/valve like in a locomotive, or
>it can spin a turbine. The turbine is more efficient, but unlike
>steam, at higher RPMs the efficiency of electric motors, batteries,
>and controllers takes a triple hit. And at what price for the
>necessary technology?
>What I'm saying is there's a point where an electric motor made
>along the lines of an old steam engine where a pushrod spins a low
>rpm crankshaft might have it's own advantages. If nothing else, the
>calculations could be fun.
>
>I haven't done the math and doubt that I will, but I've done this
>sort of thing long enough to know when an idea is interesting enough
>to be worth kicking around. Yes, it's an off-the-wall idea....the
>idea of using a very LOW RPM electric motor or even a linear driver
>with a gearbox instead of a HIGH RPM electric motor. One thing that
>got me thinking this way is the availability of dirt cheap permanent
>magnets with incredibly high energy levels and low temperature
>tolerance. It was the magnets that got me to wondering about other
>ways of solving the prop/thrust problem. Someone ought to take a
>long look at a linear driver using those new magnets.
> Enjoy! Roger L.
> ....
>..................
>
>----- Original Message -----
>
>From: <mailto:andrew@fastelectrics.com>Andrew Gilchrist
>To: <mailto:electricboats@yahoogroups.com>electricboats@yahoogroups.com
>Sent: Saturday, April 20, 2013 1:42 AM
>Subject: RE: [Electric Boats] Orest have u considered AC motors
>
> Roger
>
>Advanced timing is used to increase the amperage draw and therefore
>torque. It can have a significant effect on thrust acceleration and
>speed as it acts cross the amp range and past the point of say
>92-93% rpm so the prop can maintain a higher speed. All fine if the
>power is available to use or there is a short term need for torque
>and power. It is not the most efficient way to make a motor perform
>but it is useful in competition. The controller power board need
>not be large and it can incorporate a range of functions as diverse
>as the fuel metering electronics on ICE and because of the variables
>the esc processor needs to operate the motor – it can also be easily
>tapped for a full range data including ripple voltage and current.
>
>
>
>RC is a simple thing – it is the difference between the voltage of
>the battery at rest and under load. As batteries get stiffer in
>terms of voltage under load it improves. It is worst at acceleration
>and part throttle. The harder the battery is pushed the more the
>issue arises. The best analogy I can think of is a wave in a
>bathtub it splashes between the two ends of the battery controller
>wire until there are big drops in water level and rises which the
>bath cannot contain. The caps on the battery side of the
>controller deliver a charge to the wire to fill the drops in power
>level; hence smoothing caps. Once the wave exceeds the capacitors
>ability to discharge and recharge the caps blow and shortly after
>the fets start to leave the power board.
>
>
>
>Bigger slower motors put out more torque –however if you were
>thinking over driving it isn't the way to go as the amp draw simply
>rises again, and the motor runs less efficiently. What is possible
>is to use a small motor at higher rpm and not too extreme a load,
> water cool it and run a high reduction gearbox – these setups can
>produce relatively astounding power from light packages without
>heating
>
>
>
>I don't know what you mean by soft laminations – ultra thin silicon
>steel plate laminations are the way to go - very little interactions
>with fields in the coils, i.e. very low iron losses and ;low start
>up torque, One motor to have a look at is the CSIRO's Halbach array
>device used in the solar racers – very efficient across a very wide
>range
>
>Yours,
>
>
>
>Andrew Gilchrist
>
>fastelectrics.com
>
>Australia
>
>0419 429 201
>
>
>
>From: electricboats@yahoogroups.com
>[mailto:electricboats@yahoogroups.com] On Behalf Of Roger L
>Sent: Saturday, 20 April 2013 1:38 AM
>To: electricboats@yahoogroups.com
>Subject: Re: [Electric Boats] Orest have u considered AC motors
>
>
>
>
>
>I assume that by "advancing the timing" you are talking about the
>timing of the front of the "square wave"?Meaning to injecting the
>drive energy when the motor rotor is probably a few degrees before
>optimal coil/flux gap.?? Is that right?
>
>
>
>I can't think of any advantage to advancing the timing unless it
>might be a type of controller marketed for controlling the speed of
>(older?) motors that were originally designed to run at one RPM.
>
>
>
>Just speculating now, but my intuition is that for a single speed
>motor, a large inductive/capacitive time constant for the
>interaction of the permanent magnet and the drive coil could be
>dealt with. And maybe that's how they were made: soft iron lams
>could be used along with simple lamination geometry. At least that's
>where I would start if I was faced with such a motor design.
>
>
>
>Wow! I hadn't considered the time lag in the battery itself! That's
>a physical reaction and has to take significant time for high
>amperages. You have given me a lot to think about there.
>
>
>
>It almost seem counter-intuitive, but I wonder if there could be a
>solution found by looking at a slow turning hi-torque electric motor
>coupled with a gearbox?
>
> Roger L.
>
>
>
>
>
>----- Original Message -----
>
>From: <mailto:andrew@fastelectrics.com>Andrew Gilchrist
>
>To: <mailto:electricboats@yahoogroups.com>electricboats@yahoogroups.com
>
>Sent: Friday, April 19, 2013 8:38 AM
>
>Subject: RE: [Electric Boats] Orest have u considered AC motors
>
>
>
>Roger
>
>
>
>The solution I have seen to linear drop off in amps with rising rpm
>is a progressive timing advance – it is good if you need
>acceleration, speed and have power reserves, however efficiency
>usually falls as advance increases.
>
>
>
>Most controllers do not have wave shaping. DC PWM Brushless uses a
>half sine wave output. A square wave output. The problem is like a
>bad amplifier the square wave isn't. Some designers assume the
>interaction with current and stator will "smooth" – blunt is
>probably better the leading and trailing edge of the square wave.
> That is inefficient. At part throttle the pulse width is anything
>from some ten thousandths of a second to the full second at full
>power. The switching can result in efficiency losses. Batteries
>which cannot deliver and shut down power output at near the rate the
>fets in many controllers are switching. This can give rise to ripple
>voltage and current which requires larger smoothing caps on the
>controllers and losses within the batteries. This effect is much
>greater in multiphase DC controllers (brushless) than for brushed
>motor controllers. Brushed controllers have similar efficiencies at
>full and part throttle.
>
>
>
>At part throttle Brushless controller losses can change at rates
>inversely proportional to the degree of throttle in use i.e. 20%
>throttle 80% of the input is lost as heat at 100% they too are 98%
>efficient .
>
>This has to be offset against the efficiency losses of the brushed
>motor which generally has lower efficiency levels across the working
>range, and narrower power of high efficiency, and generally lower
>power handling, than a brushless motor.
>
>
>
>Yours,
>
>
>
>Andrew Gilchrist
>
>fastelectrics.com
>
>Australia
>
>0419 429 201
>
>
>
>From:
><mailto:electricboats@yahoogroups.com>electricboats@yahoogroups.com
>[<mailto:electricboats@yahoogroups.com>mailto:electricboats@yahoogroups.com]
>On Behalf Of Roger L
>Sent: Friday, 19 April 2013 11:12 PM
>To: <mailto:electricboats@yahoogroups.com>electricboats@yahoogroups.com
>Subject: Re: [Electric Boats] Orest have u considered AC motors
>
>
>
>
>
>Andrew wrote:
>
>
>
>"The issue of the linear drop in amps and torque as the motor revs
>rise remains"
>
>
>
>Yes, although I'm a motor guy rather than a controller guy....I've
>seen huge advances in wave-shaping by controllers.
>
>I do believe that most of the problem of torque (amps) dropping with
>RPM can be overcome by a controller that will increase the input
>voltage to compensate for the BackEMF it is seeing from the PM
>motor. It used to be difficult to find a commercial controller that
>would operate in that manner. But that was because of a flaw or
>gap in the CE, CSA, and UL underwriting approvals which hadn't been
>challenged a decade ago. Is that still the case? Are there now
>controllers that will raise the input voltage proportionately to
>overcome Bemf as RPM rises?
>
>
>
>"The issue that remains is the very poor performance of most
>brushless dc controllers at part throttle"
>
>
>
>Andrew, I do not understand that comment. I'm making the assumption
>that most controllers have near infinitely variable wave shaping
>available - either automatically or as input by the operator. So
>why would throttle setting have any effect at all on performance?
>
> thanks,
>
> Roger L. - call me a retired but still curious old engineer.
>
>.........
>
>.................
>
>----- Original Message -----
>
>From: <mailto:andrew@fastelectrics.com>Andrew Gilchrist
>
>To: <mailto:electricboats@yahoogroups.com>electricboats@yahoogroups.com
>
>Sent: Thursday, April 18, 2013 6:31 PM
>
>Subject: RE: [Electric Boats] Orest have u considered AC motors
>
>
>
>One of the big advances in recent years with brushless DCPMs has
>been in the controllers which enable the throttle curve to be
>infinitely recontoured, variable timing depending on load
>conditions, degrees of softness in the motor start up etc.
>
>
>
>The issue of the linear drop in amps and torque as the motor revs rise remains
>
>
>
>The issue that remains is the very poor performance of most
>brushless dc controllers at part throttle
>
>Yours,
>
>
>
>Andrew Gilchrist
>
>fastelectrics.com
>
>Australia
>
>0419 429 201
>
>
>
>From:
><mailto:electricboats@yahoogroups.com>electricboats@yahoogroups.com
>[<mailto:electricboats@yahoogroups.com>mailto:electricboats@yahoogroups.com]
>On Behalf Of Chris Morriss
>Sent: Friday, 19 April 2013 1:05 AM
>To: <mailto:electricboats@yahoogroups.com>electricboats@yahoogroups.com
>Subject: RE: [Electric Boats] Orest have u considered AC motors
>
>
>
>
>
>I do understand where you are coming from here, but you have
>highlighted the key problem for the application I was looking at.
>We need to operate the motor over a 10:1 speed range, (10% of
>nominal to 100%) rather than the 25% to 130% you quote. The
>problems that I have seen widely reported are with attempting to get
>power from a 3-phase motor driven in this way at low rpm. Now I
>have to admit that although I have good knowledge and some practical
>experience with BLDC motors, I have never used 50Hz 3-phase
>conventional ac motors with a variable speed drive, but thinking of
>the physics of it all, I am not surprised that there are problems
>when using the VS drive to give low, but controllable, rpm.
>
>
>From:
><mailto:electricboats@yahoogroups.com>electricboats@yahoogroups.com
>[electricboats@yahoogroups.com] on behalf of Julian Webb
>[julian.proto@gmail.com]
>Sent: 18 April 2013 15:06
>To: <mailto:electricboats@yahoogroups.com>electricboats@yahoogroups.com
>Subject: RE: [Electric Boats] Orest have u considered AC motors
>
>
>
>If you use a good TEFC squirrel cage 3 phase motor you have a unit
>90+% efficient over a wide range of speeds and coupled with a
>matched Variable Speed Drive you can hold torque at 125% from
>25%-130% of rated RPM with no loss of efficiency. They are robust,
>cheap and easily fixed if needed.
>They aren't as exotic or trendy as PM units but they're not that far
>down on torque or efficiency either.
>They are considerably heavier, but for canal or slow cruising that
>isn't normally a consideration.
>If a few percent efficiency is of greater importance than the
>thousands more you'll pay for a PM unit and its controller in any
>decent KW or dual drive system over 3 phase a.c. VSD and motor then
>I guess you've probably got it decided already?
>
>On Apr 18, 2013 2:26 PM, "Chris Morriss"
><<mailto:crsm@oroboros.demon.co.uk>crsm@oroboros.demon.co.uk> wrote:>
>>
>>
>> Moderm Permanent Magnet AC (PMAC) motors and Brushless DC (BLDC)
>>motors are very similar to each other. The big difference is is
>>the shape of the current wavework flowing in the stator coils.
>>PMAC motors have the stator windings and controller drive
>>electronics giving an essentionally sine-wave current, making the
>>motor mechanically quieter.
>>
>>
>>
>> There still exist old-fashioned ac 3-phase motors, but brought
>>(slightly) up to date by using a PWM 3-phase sine-wave inverter
>>unit providing a variable output voltage and frequency to provide
>>much greater control of the motor. These can provide a lower-cost
>>solution for some applications, as you pay essentially the metal
>>scrap value for the 3-phase motor (Although usually you have to pay
>>the cost of rewinding them for operation at lower
>>voltages). Industrial electrical scrap yards have plenty of 3-phase
>>motors in them that are of little value. The problem is that the
>>3-phase motors were originally designed for optimum efficiency at
>>50 or 60Hz, and operating them over a wider frequency range gives
>>good speed control, but the efficiency suffers. I have been
>>involved with a group wishing to electrify a British canal
>>narrowboat using this sort of motor, and I'm still not convinced
>>that I have managed to show them the error of their ways!
>>
>> ________________________________
>> From:
>><mailto:electricboats@yahoogroups.com>electricboats@yahoogroups.com
>>[<mailto:electricboats@yahoogroups.com>electricboats@yahoogroups.com]
>>on behalf of Roger L
>>[<mailto:rogerlov@ix.netcom.com>rogerlov@ix.netcom.com]
>> Sent: 18 April 2013 13:36
>> To: <mailto:electricboats@yahoogroups.com>electricboats@yahoogroups.com
>> Subject: Re: [Electric Boats] Orest have u considered AC motors
>>
>>
>>
>> Uh-oh....If I may join the conversation..... it looks like I may
>>have to go back to school on electric motors. It's a Good Thing
>>that learning something new is always fun.
>>
>> The only electric motors I am familiar with are the high
>>efficiency kind made with permanent magnets and driven by a pulsed
>>DC wave. And without really thinking about it, I've been making the
>>assumption that this was the type used in electric boats.
>>
>> But if so, why is AC any different from pulsed DC? In that type
>>of motor I don't know of any reason or advantage to sinusoidally
>>reverse the polarity of the driving wave. (making it AC).
>> Am I missing something?
>> thanks,
>> Roger L.
>> .........
>> ..............
>>
>>
>>>
>>> ----- Original Message -----
>>> From: Andrew Gilchrist
>>> To: <mailto:electricboats@yahoogroups.com>electricboats@yahoogroups.com
>>> Sent: Wednesday, April 17, 2013 8:18 PM
>>> Subject: [Electric Boats] Orest have u considered AC motors
>>>
>>> Orest
>>>
>>>
>>>
>>> there is another option – others here my have tried it
>>>
>>>
>>>
>>> You may want to look at an AC motor . A DC motor's amp draw and
>>>torque level fall away at higher rpm, an AC motor has a lower
>>>start torque – but you don't really need much at low rpm, but the
>>>high end torque is better.
>>>
>>>
>>>
>>> If that isn't an option a more efficient better sized prop than
>>>the current one could achieve very significant gains either in
>>>performance or efficiency
>>>
>>>
>>>
>>> Yours,
>>>
>>>
>>>
>>> Andrew Gilchrist
>>>
>>> <http://fastelectrics.com>fastelectrics.com
>>>
>>> Australia
>>>
>>> 0419 429 201
>>
>>
>>
>>
>
>
>
>
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