The AC Induction Motor Ebike Project

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The AC Induction Motor Ebike Project

After much searching for an AC Induction motor that would be suitable for an ebike I arrived at the older model Frigidaire Dishwasher motor. Apparently they made a newer one that was a little different, but looked to be bigger. I like this one because of the smaller dimensions.

This thread will track the progress of this project. (the motor arrived today)

The dimensions are more of a "pancake" than the Unite motors I've been using and the width is about 3.75" and the diameter of the shell is about 6" on the inside and 5" on the outside.

I don't know the weight exactly, but it feels about the same as a Unite motor... somewhere around 10 lbs. A 10 lbs motor is okay (in my opinion) if it can deliver the perfect flat powerband over a large rpm range.

The central goal here is to create the "ideal" LEGAL powered motor that delivers a flat 750 watts (or slightly above) across the widest possible range of rpms while the motor is under full load. It's effectively a "race motor" for an ebike racing class that I want to invent and promote someday.

This motor will be EBRR "Electric Bicycle Road Racing" Legal. (which means the power input will be strictly restricted to a maximum of 1000 watts of power with no exceptions)

The racing class will be called "Formula 1K".

And so the project begins...

 

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Disassembly

This older motor was a Single Phase and not a Three Phase motor. Unfortunately they didn't make all the grooves the same size as they used what appears to be a capacitor starting technique and some smaller starter wires to get the thing going. Not sure how I'll adapt to that... otherwise the wires came out really easily and it looks like a pretty good motor to start with. The rotor is made of pressed iron plates like the stator and there is a slight rotational skew to them in order to reduce ripple currents. (all to be expected) With the very open design the airflow looks to be very good, so cooling should happen easily.

The wire thickness is slightly thicker than 18 AWG wire and the larger grooves held 33 turns of that wire.

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The Single Phase motor is listed as 3450 rpm for 60 Hz.

Doing the math we would get:

Single Phase (2 poles, 4 grooves needed) : 3450 / 1 = 3450 rpm

Two Phase (4 poles, 8 grooves needed) : 3450 / 2 = 1725 rpm

Three Phase (6 poles, 12 grooves needed) : 3450 / 3 = 1150 rpm

Four Phase (8 poles, 16 grooves needed) : 3450 / 4 = 863 rpm

Five Phase (10 poles, 20 grooves needed) : 3450 / 5 = 690 rpm

Six Phase (12 poles, 24 grooves needed): : 3450 / 6 = 575 rpm

...and there are exactly 24 grooves available. If you wire the motor as a Three Phase then you double up on the grooves with one overlapping the other on both sides.

The advantage of a Six Phase controller is that you can eliminate the need for a geardown unit. You could take 575 rpm and a smaller sprocket like about an 11 tooth and then match that with a front chainring of about 55 teeth and you get the proper final gear relationship.

Hmmmm.... more complexity in the circuits to do Six Phase, but it might produce a really nice motor that way. Will have to research more the positives and negatives of higher phase motors. Three Phase is clearly the easier path to take.

 

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Notes About "Multi-Phase" AC Induction

http://www.gm-volt.com/forum/showthread.php?t=1306

Due to the potential benefits resulting from the use of a phase order higher than three in transmission, some interest has also grown in the area of multi-phase machine. For machine drive applications, multi-phase system could potentially meet the demand for high power electric drive systems, which are both rugged and energy-efficient. High phase number drives possess several advantages over conventional three-phase drives such as: reducing the amplitude and increasing the frequency of torque pulsation, reducing the rotor harmonic currents, reducing the current per phase without increasing the voltage per phase, lowering the dc link current harmonics, higher reliability and increased power in the same frame. The high phase order drive is likely to remain limited to specialized applications where high reliability is demanded such as electric/hybrid vehicles, aerospace applications, ship propulsion, and high power application where a combination of several solid state devices form one leg of the drive. The research has been underway for the last two decades to investigate the various issues related to the use of multi-phase machine as a potential alternative to the conventional three-phase machine. This paper, therefore, reviews the progress made in multi-phase induction machine drive research and development since its inception. Attempts are made to highlight the current and future issues involved for the development of multi-phase induction machine drive technology for future application.

...so it appears that if I could pull off Six Phase power then I would have less to worry about as far as things like heat in the motor because less current is required per wire to get the job done.

It's kind of like deciding if I want a three cylinder motor or a six cylinder. We all know that as you increase the number of pistons that the overall system becomes smoother, however, the complexity also goes up. Each piston becomes less stressed while the overall power is still higher.

This might solve the smaller groove problem because I could just wind all the grooves to the smaller size and leave extra space in the bigger ones.

 

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Fitting To The Bike

It does look like the width is good and the size can be handled within the space I've already built into the frame.

I'm planning on using this motor on the new bike (as in my avatar) and not my old bike which will still get a brushed motor for now.

 

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Actual Information

Emerson Electric Company

Part Number: S447301

Model: S62NXHMP-7198

HP: 1/3

Volts: 115

Single Phase

Frequency: 60 Hz

RPM: 3450

Amps: 6.2

Temperature Rating: 40C

Manufacture Date: 5/1988

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So this is an old Single Phase motor that seems to be about the right size as a foundation, but there's no way you could run it stock for anything. Here's another for $29:

http://cgi.ebay.com/FRIGIDAIRE-WHIR...emQQptZLH_DefaultDomain_0?hash=item3ef7e20b80

...had I to do it over again I might have taken a look at the newer version that is a true Three Phase from the start because then the stator grooves would already be the same size. (a problem I have to deal with on this one)

It's also possible that the Frigidaire Dishwasher motor was originally a Single Phase and the replacement is still Single Phase and I got my information wrong somewhere along the way. But I will say that upon taking it apart it does look like the situation is workable. I knew it was going to involve a rewind before I started.

 

[spad4me]

I found this searching google.
http://www.surpluscenter.com/item.asp?UID=2009083010481208&item=10-1225&catname=electric
For me this seems an easier way.

I will probably order the motor and three phase controller chip on monday.
When it comes I put it on a serious diet LOL
Don's waste your time searching bing you only get noise from microsoft search.

 

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It's probably a good motor, but 17 lbs is a "non-starter" in my opinion for actual ebike use. That's about double the weight of the motor I'm using. Are you going to rewind it to run better at lower voltage or are you going to step up the voltage? Rewinding is better I think because you lose some efficiency every time you step up the voltage and 240 VAC would require some serious stepping up.

However, I'm glad you are doing a parallel development effort and have a good knowledge of this stuff because we will be able to share information about our struggles.

I'm going to give the Six Phase concept a try because I want the ability to reduce the motor rpm by half so that I can eliminate any geardown unit. Being able to drive the chain directly will reduce complexity and improve efficiency because that's one less source of friction.

Since I'll be building my own controller it will make for a good winter project. I'm going to use a generic PIC and then I can program the algorithm myself. There are some techniques that you can get away with because of Six Phase power since the many phases allow more overlap. You can do what they call "Flat top" algorithms where you only open the MOSFET's when the curve is nearing the top. All the midrange (0.5 or less amplitude) is essentially wasted energy because the angle is bad so you can leave the MOSFET's closed during those areas. This would allow me to run a leaner motor which should run cooler. I've been reading a bunch of AC motor theory stuff... there's a lot out there.

When it comes to getting the motor rpm matched to human pedal power rpm your choices are geardown units (which are complex) or more sophisticated controller algorithms. I'm taking the software approach this time so that I can avoid the mechanical approach. (my home built geardown unit took six or seven rebuilds before I got it to work reliably)

With the Induction motor I can abandon multispeed gears without sacrificing anything, so that's an another reduction in complexity.

So are you going with the "custom" Three Phase chip that does the algorithm?

If I knew of a Six Phase "custom" chip I'd buy it, but I think I'm probably on my own having to program it myself. I used to be a computer programmer, so it shouldn't be too hard. I already know "C" and did assembly language programming back in college.

 

[spad4me]

I have to see where this takes me.
I have since found many different motors some better some worse on weight .
I believe that I will use a ballbearing 1 hp 3000 + rpm 48 to 60 volt three phase motor.
The final weight is expected to be around 9 pounds.

I am going for sunset tech not sunrise tech all of the surprises have been removed for me allready

 

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More Poles, Less Phases?

I was reading some more about the windings possible and came to realize that 2 poles per phase is not the only way to do it. You can actually go to 4 poles per phase in the windings and that way I could use simple Three Phase control (that custom chip) and save myself a lot of trouble.

The more poles you use the better because the formula is:

Motor Speed = 120 * Frequency / Pole Count

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It's funny when you learn this stuff over the internet because multiple solutions can be found and each one has it's plusses and minuses.

The goal is to get the lowest rpm motor with the least effort.

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http://www.uiitraining.com/b51a/100/15104ac_motor_rewind_intro1.htm

PHASES: As the name implies, three-phase motor stator windings will consist of three separate groups of coils called phases. Phases must be displaced from each other by 120 electrical degrees. Phases must be electrically balanced (contain the same number of coils) and connected for the same number of poles. Phases will always be designated as A, B, and C.

POLES: Poles refer to a coil or group of coils wound and connected to produce a unit of magnetic polarity. Poles are referred to as either north or south. The number of poles a stator is wound for will always be an even number and refers to the total number of north and south poles. For example, a four-pole motor will have two north and two south poles alternately spaced around the stator.

 

[spad4me]

Your emerson motor could be considered a two phase motor .
The single phase power is shifted by the capacitor by ninety degrees to start the motor.

See what I mean by sunset tech a motor re winder has long ago solved your problem.