New toy.........

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granada203028
Posts: 38
Joined: Wed Apr 30, 2008 5:03 pm
Location: Bristol, UK

Re: New toy.........

Postby granada203028 » Fri Oct 15, 2010 7:38 pm

That monster CA120-70 looks a nice motor. Reading deeper into your thread you are making a motor form a kit? Isn't one of the reasons for using many parallel threads of thin wire to reduce skin effect losses, so if you use rectangular wire of heavy gauge the copper fill improvement will be offset by greater skin effect losses? These motor have high pole numbers so have high drive frequencies.

I like the look of your home brew controller. I’m interested to see how you get on. I guess sensored commutation is a must for slow speed performance, obviously not an issue driving a prop.

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Jeremy
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Location: Salisbury

Re: New toy.........

Postby Jeremy » Fri Oct 15, 2010 8:29 pm

I've bought one ready-built 75Kv motor and one kit of parts to wind my own. Virtually all these motors are wound very inefficiently in China, using multi-strand wire to make winding quicker. This massively reduces the amount of copper in the stator, so impacting adversely on winding resistance and efficiency.

Skin effect is a non-issue at the low frequencies these motors run at. With a maximum commutation frequency of 3kHz (and it's commutation frequency, not PWM frequency that determines the effective frequency of the current in the windings) it would be OK to use a single strand of 10g wire, which would be near impossible to wind. I will probably use rectangular wire with a CSA equivalent to around 14g round wire, which will have no skin effect losses at all. My controller will only run up to around 2Khz, so I could use much thicker wire if it was practical to wind it on to the stator.

Using sensors for position feedback certainly improves start-up and low speed, high torque, performance, but the back EMF closed loop position feedback controllers used in the RC world can be pretty good, too, at least in the more expensive controllers. It very much depends on the effectiveness of their code in being able to derive good position signals when the back EMF in the unpowered phase windings is relatively low, which is the case for low speed operation. The ability of the start-up algorithm to quickly determine motor angular position and direction, even under load, is also another key factor. The cheap RC ESCs seem to be pretty poor in this regard.

I should get some more work done on the controller soon, as soon as I've paid the penance for retiring by finishing off the new kitchen and making a start on the new bathroom...........

Jeremy

ex925
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Location: Plymouth, England

Re: New toy.........

Postby ex925 » Mon Dec 20, 2010 9:48 pm

A surprising (to me, at least...) number of die-hard petrol-heads like to deride electric traction
One of the pseudo-complaints I often hear is the lack of a "soulful EXHAUST-NOTE"............
I have also read somewhere of a possible obligation on EV drivers to generate a continuous "warning noise!"
Maybe a threatening howl from such a motor as you are building would solve both "problems"?
Just my tuppence-worth

OK, I'll get me coat
Atb

Ed

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Jeremy
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Location: Salisbury

Re: New toy.........

Postby Jeremy » Tue Dec 21, 2010 9:35 am

Glad you kick started this thread back into my consciousness, I'd forgotten about it.

Anyway, I've not done much with the motors yet but I have built a BLDC controller to drive them, The whole saga is in this thread on the ES forum, with some photos: http://endless-sphere.com/forums/viewto ... =2&t=23350

This controller has a much higher commutation speed limit than the typical modified Chinese ebike controllers I've been playing with and will allow the motor to be driven to it's mechanical speed limit, probably well over 12,000 rpm. It will most probably howl like a banshee at that rpm..................

Jeremy

rustybkts
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Joined: Sat Mar 08, 2008 12:15 am

Re: New toy.........

Postby rustybkts » Tue Dec 21, 2010 10:23 am

ex925 wrote:A surprising (to me, at least...) number of die-hard petrol-heads like to deride electric traction
One of the pseudo-complaints I often hear is the lack of a "soulful EXHAUST-NOTE"............
I have also read somewhere of a possible obligation on EV drivers to generate a continuous "warning noise!"
Maybe a threatening howl from such a motor as you are building would solve both "problems"?
Just my tuppence-worth

OK, I'll get me coat
Atb

Ed


I wonder what the modified AC sine wave feeding the 3 phase motor would sound like on my Elise?

It could be sampled and modified further using one of these cheap kiddies voice synthesizers to become a unique sound.

You could pick up the signal from a simple pick up coil on or near the motor wiring.

Boost it through a 50 watt amp and you have a Veyron beater and old lady scarer (in the interests of road safety of course!). :twisted:
EV Lotus Elise with 30/67Kw Siemens ex Ford Ranger motor
Sinclair C5 twin battery
2 x Zike bikes
Electric Ride On Mower (Lynch Power!)
Bosch beard trimmer

ex925
Posts: 331
Joined: Wed Jun 04, 2008 9:13 am
Location: Plymouth, England

Re: New toy.........

Postby ex925 » Tue Dec 21, 2010 7:50 pm

Should compulsory EV noise ever be, a friend has offered a track of the Lockheed SR71 Blackbird.............

I love the idea of light, cheap, cheerful, brush-less motors...

How powerful is their biggest motor?
More powerful than an equivalent weight ac motor?
(remember how much I don't know about ..... everything)
All the best
Ed

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Jeremy
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Re: New toy.........

Postby Jeremy » Tue Dec 21, 2010 10:29 pm

These motors are pretty light. The 7kW ones I have are around 1.6kg, so compare very well with the heavy industrial motors that have been adapted for EV use. I'm planning to use two of these on a common shaft to drive my motorcycle conversion. This'll give me around 14kW peak for a motor weight of around 3.2kg, which compares very well to the PM motor I have in it at the moment that weighs around 13kg and delivers maybe 7kW peak.

The 12kW CA120-70 is just over 2.5kg. My guess is that a typical 12kW AC motor will weigh maybe ten times that weight.

Jeremy

andylaurence
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Location: Bristol
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Re: New toy.........

Postby andylaurence » Wed Dec 22, 2010 8:48 am

ex925 wrote:A surprising (to me, at least...) number of die-hard petrol-heads like to deride electric traction
One of the pseudo-complaints I often hear is the lack of a "soulful EXHAUST-NOTE"............
I have also read somewhere of a possible obligation on EV drivers to generate a continuous "warning noise!"
Maybe a threatening howl from such a motor as you are building would solve both "problems"?
Just my tuppence-worth

OK, I'll get me coat
Atb

Ed

It's not just petrolheads. My mum said she spotted an EV in a car park this week because it nearly ran her over. She didn't hear it and walked behind it as it reversed out of a space. As a petrolhead myself, I know that noise is important to how a car feels to drive. However, I think it's the tone of the noise, not the volume, that's important. I don't want to lose what's left of my hearing just to appreciate driving.

At the Race of Champions, they used some Tesla Roadsters and the crowd were noticeably quiet as all you could hear was tyre squeal. They soon got used to it though. I think some noise is essential for exciting people, both in and out of the cars. Bristol Motor Club recently ran an AutoSolo at Castle Combe Circuit. We ran two course cars - my Smart Roadster and a Mitsubishi Lancer. My car made very little noise but the Mitsubishi was much louder. The crowd got much bigger when the Lancer was on track compared to my little Smart. Of course, I ran the whole day on about £10 of fuel, but the Lancer did a whole tank...
Image
Above figures include track days and the odd competition.

Deker
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Location: Borehamwood

Re: New toy.........

Postby Deker » Thu Jan 20, 2011 4:44 am

ChrisB wrote:Ooooo yeah, more data please, that looks very interesting.

Any chance of the source of these ? I'm thinking this would be a nice electric bike upgrade for me :shock: although 7kw might be a tadge too much ....... I can see broken spokes coming up :lol: :lol: :lol:

ChrisB

Not really Chris, youv'e seen my E-bike with the Lynch motor,
rotate the twistgrip smartly, up comes the front wheel :)
rotate the twistgrip sharply and you'll be on your back with the bike on top of you :shock: :(

At the most I guess the Lynch motor at 24v pulls about 4 hp to 4Kw.
And you know how torquey they are.

The 60 tooth rear sprocket does come a wee bit loose sometimes, havn't tightened it for about 3 years -
must check that :wink:

No problems with spokes, although, when I rebuilt the wheel I did put a bit of extra tension on the spokes,
to prevent the wheel warping under full power.

I do like the idea of Jeremy's lightweight motor, I cannot imagine it would have the torque of a Lynch motor at, say 0 - 10 RPM.
Properly geared to to give 20 mph on the flat a max RPM Jeremy' motor should give good uphill performance,
you don't have that problem on Happy Hayling :!:
I do in Hilly Hertfordshire. Up hills = battery killer :(

Talking of batteries, I bought two used Sonneschein 12v 30ah SVLA A500s from Neil B about 8-9 years back, for the E-bike,
they're still going, admittedly not as strong.
And Iv flattened them to the point the bike won't go,
they must have had a few thousand cycles since Iv had them :)
(No low volt lockout, been disabled) on my Curtis controller.

Brings the Q, are SVLAs more long lived than some of the modern lightweight equivelants :?:

I have similar batteries (bought from Neil of course) on my home made traversing elevator they are still strong, fitted 2003.

Deker

granada203028
Posts: 38
Joined: Wed Apr 30, 2008 5:03 pm
Location: Bristol, UK

Re: New toy.........

Postby granada203028 » Sun Nov 27, 2011 12:29 pm

Hi Jeremy

Could you update the thread on where you are with the project.

I have bought one of these large motors, a turnigy C80100-180, and am wondering about doing my own drive electronics.

I was wondering about using a relatively old fashioned circuit of a current fed inverter, i.e. a chopper stage driving the 3 phase bridge. So the bridge would only switch at the commutation frequency driven by hall sensors. The chopper would run at 25KHz and control on current. The chopper would be a "buck" type circuit with no output cap, the inductor connecting to the common + of the bridge. So the phases are truly driven by a current source, the inductor smoothing the current.

A snag though is how exactly to switch the phases as three simple square waves shifted at 120 deg would cause shoot through currents. So these would have to switch on for 120 deg with 30 deg dead time.

Do you have any circuits or links to designs?

Thanks

Paul


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