Electric motors

[Ian S CParticipant @iansc]

John, I think these cars are still around, there was an E car race meeting in Christchurch about a month ago, I think they were there along with a Tesla, and some(? 18) E vehicles built by secondary schools.

The only thing I'll say for now on 1PH/3PH motors, there is a problem if you want to replace a 3PH motor with a 1PH one with the same power out put, The !PH motor will be larger in diameter which can be a bit of a problem if the motor is inside the machine such as a lathe. I do know that for second hand motors, 3PH are less than half the price of 1PH.

Ian S C

[MuzzerParticipant @muzzer]

Americans traditionally tended to prefer induction (asynchronous) machines in their electric and hybrid vehicles, as they are simpler and don't require the expensive (and foreign) neodymium magnet material. They are also more rugged and larger, which often isn't such a problem with their vehicles. Europeans and Far Eastern manufacturers are happy with permanent magnet (synchronous) machines which are smaller and thus easier to package – but more challenging to design and drive – you need a rotor position sensor for a synchronous machine, whereas you only(!) need a speed sensor for an asynchronous machine. The drives are fundamentally similar to the VFDs we know and love and 4-quadrant regenerative operation comes as standard with modern digital control – it's hardly a technological breakthrough.

Modern vehicles have pretty sophisticated braking and stability systems (by law), so it's not surprising that there's a legally binding regulation (UN ECE 13h) that governs regenerative braking. The idea is to prevent the vehicle losing control due to inappropriate application of large amounts of braking torque. It's pretty complicated when you consider that the amount of braking available will be dependent on the state of charge of the battery and how much power it can accept, so the motor drive must interact with the engine, transmission and vehicle controllers. You'll be glad to know there is also a safety regulation (ISO-26262) that aims to ensure that these systems are designed and validated to meet an appropriate level of robustness and reliability.

Switching the power devices at frequencies above 10kHz helps to reduce the audible noise from the motor but requires more processing power and increases the switching losses in the IGBTs. The Toyota / Lexus vehicles make an audible noise although it's not off putting. I believe they used to operate at 5 and 10kHz.

AFAIK, the university e-racers typically use brushed motors (eg fork lift hydraulic pump motors) which allows for simplicity and pretty much prevents any regen, at least from what little I know of the US scene currently. The drive is essentially a beefy buck converter.

3-phase motors generate a pretty constant torque, unlike single phase machines, which is why they are smaller for the same power rating. The starting torque for a single phase motor is entirely dependent on the auxiliary starter winding etc, as its inherent stall torque is otherwise essentially zero, unlike a 3-phase machine which can generate full torque over the whole speed range, notwithstanding the need for cooling air flow at low speeds.

Murray

Edited By Muzzer on 31/12/2014 12:38:36

[john jennings 1Participant @johnjennings1]

OuBallie has raised the significant question of new types of electric motor that are now available, as has been pointed out it is now possible to drive flying model plane with electric motors: a step similar to the Wright brothers finding a internal combustion engine that combined power and light weight.

We need to be better informed.

I am probably not the only reader of MEW to have read recent articles with items powered by "NEW MOTORS" to have been very disappointed when the final part elapsed with a very cursory description of the motive power source, providing little guidance on how to use such devices (or even what they are!) in designing or modifying other tools.

John

[John Stevenson 1Participant @johnstevenson1]

This is a motor from one of the electric TT racer bikes.

Three phase running off an inverter that is more like the power modules off a radio control aircraft than one of the VFD's we are familiar with on lathes.

Note the temperature and the peak horsepower which for this motor has been modified to give 80 Hp.

Oh and BTW they fit two of these side by side.

Brushed motors went out the door years ago as these are far more powerful and more important, controllable.

[Michael GilliganParticipant @michaelgilligan61133]

John,

Are you at liberty to tell us any more about the TT project ?

MichaelG.

[John Stevenson 1Participant @johnstevenson1]

Can't really tell you a lot about these Michael as I don't know a lot. AFAIK nothing is secret.

My brief was to take one motor, the one in the shot and extend the shaft and make a new mounting end with slots in so that it could take a sprocket and enable a chain drive to connect the two motors together. The HTD pulley was for the final drive.

I had layout drawings to use but other than this it was a weld it where it touched sort of job. I was under the impression and because of what it was used for, that these ran at peak power all the while because they were getting speeds very close to normal racing bikes with far more horsepower. They only did one lap of the 37 and a bit mile circuit because of battery life.

I don't know what team this bike was for, I was never told that but then again I do work for quite a few very famous companies who don't even know I exist and would have a heart attack if they could see where things were being made.

You have to love the sub contract clause in ISO 9000 don't you.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Stevenson on 31/12/2014 16:23:58:

Can't really tell you a lot about these Michael as I don't know a lot. AFAIK nothing is secret.

…

I don't know what team this bike was for, I was never told that but then again I do work for quite a few very famous companies who don't even know I exist and would have a heart attack if they could see where things were being made.

You have to love the sub contract clause in ISO 9000 don't you.

.

Thanks, John

MichaelG.

[Phil WhitleyParticipant @philwhitley94135]

Hi All,

John Stevenson, looked at the videos………………it is a bit slack compared to a fully automated factory isn't it! When were these videos shot, any idea?

John Haine, "a stationary motor doesn't have zero slip,it has 100% slip" that is not what I said, what I said was that a motor (with the power on) with zero slip, will be stationary, not quite the same thing, but you end with my point exactly,

"Of course with 3 phase drive all this goes away and you get constant torque"

Thank you!

Phil.

[MuzzerParticipant @muzzer]

The electric TT racers were called TTXGP and are now apparently called eGrandprix or eRoad Racing. Many of the early TTXGP bikes used twin Lynch (axial flux "pancake&quot motors, named after their developer who was also active in the sport. Although they only manage one lap of the IOM TT, they are pretty nippy.

The MGU-K motors used in the F1 cars are limited(!) to 160HP and are tiny. That's partly due to the high speed of rotation but also (as ever) the state of the art design and materials used. And the almost limitless budget.

Murray

[John HaineParticipant @johnhaine32865]

"John Haine, "a stationary motor doesn't have zero slip,it has 100% slip" that is not what I said, what I said was that a motor (with the power on) with zero slip, will be stationary, not quite the same thing, but you end with my point exactly,"

Sorry Phil, but as slip is defined as the difference between the actual speed and synchronous speed expressed as a fraction of the latter, if the slip is zero then the motor will be running at synchronous speed, not stationary. See

**LINK**

for example.

[Russell EberhardtParticipant @russelleberhardt48058]

Perhaps what Phil was thinking was that with zero slip there would be zero torque but this doesn't imply that the motor is stationary it just shows that this condition is not possible in steady state with no external influence.

Of course, if the input frequency is varied the slip can be zero or negative and give a braking effect.

Russell.

[John OlsenParticipant @johnolsen79199]

Expanding on that last point, when the slip is negative, eg the frequency is reduced below the synchronous frequency, not only will there be a braking effect but the motor will start to act as a generator. This can sometimes be hard to get your head around, since an induction motor will not generate when it is just turned by mechanical force. It has to have the AC applied to the windings at a suitable frequency as well, which provides the excitation. Just to make things even trickier, a motor in this condition, eg connected to the line and being driven faster than synchronous speed, will appear to the line as a capacitive load. (Leading power factor.)

To implement a practical regeneration system with an induction motor and a VFD, all that is required is that the inverter should have diodes in it capable of passing the generated current back to the DC bus, and that the DC bus should be able to cope with the power it receives. With SCR inverters, the main switching SCRs have to have inverse diodes across them anyway, and with power MOSFETS such a diode is inherent in the construction of the device. I think this is also true of the IGBTs. If the DC bus is a rechargeable battery, as in a car, it can inherently accept charge, although some control may be needed to avoid excess current. With a vfd, external resistors may be needed to dispose of the energy.

I wonder how many other people have a vfd and three phase motor on a Unimat 3? Might seem like overkill but it is really nice to have.

John

[Anonymous]

Posted by John Olsen on 04/01/2015 20:59:38:

…………. and with power MOSFETS such a diode is inherent in the construction of the device. I think this is also true of the IGBTs. If the DC bus is a rechargeable battery, as in a car, it can inherently accept charge, although some control may be needed to avoid excess current.

Not so on any of the IGBTs I've used, and it is not inherent in the structure of the device. We have always used external diodes. For lead acid batteries managing the SOC at about 40-50% allows the battery to accept as much charge as the external system can supply. The problem at higher SOCs is not so much charge acceptance as the rise in voltage caused by said current, which then upsets the internal chemistry.

Andrew

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