Hot-rodding the Toyota MGR

[freebeard]

Please do post.

My project involves replacing a 36hp gas engine. So it is ~twice the rating off the bat, it all comes down to the drag coefficient.

I've no intention of exposing those magnets to the ambient environment. I suspect they would be immediately covered with microscopic ferrous whiskers.

What would your method do that a boost circuit wouldn't?

[TT-Man]

Hi Freebeard,
Your are quite correct, my suggestion would do nothing that a boost circuit ( Voltage doubler) of suitable rating could not.
My rational is,
I'm not happy with 650 volts as seemingly engineered by Toyota.
If it is possible to bye-pass the Toyota CAN Bus and use (hack into their liquid cooled invertor package, then their standard voltage 300 Volts (? about) would certainly work.
I do not have access to that technical ability.
Also as an Electrical Utilities Engineer (retired) I have a health respect for the increasing risks with higher voltage.

In the commercial field it seems that there may be more controllers capable of working at the 300 Volt range.

My recollection of motor theory lets me down when it comes to the 'reluctance motor'. It seems that Toyota have employed magnets as (simplistic) synchronous machine, where torque is directly proportional to current up to the point where back-emf reaches the applied voltage with the consequent reduction in torque and acceleration.; but also a reluctance motor component, who's torque / current /voltage curves I know nothing about.

It5 seems that to try to run this motor with a reduced voltage alters the power in a on linear manner, apparently significantly lower than a linear proportion. It seems that other experimenters have been disappointed in their results.
It is my attempt to employ the KISS principle.

By separating the windings full battery voltage may be applied to each, but would need a 12 diode bridge (of full rated current) to run it.
Something that I "may" attempt.

Cheers, TT-Man

PS You are correct, it is necessary to work in a clean environment when exposing high strength magnetic fields, and watch fingers as well!! I have worked with Lynch / Agni DC motors, and they are air cooled over magnets exposed to air stream.

[TT-Man]

Sorry, a typo error: reduces power in a non-linear manner. TT-Man

[P-hack]

Originally Posted by TT-Man

By separating the windings full battery voltage may be applied to each, but would need a 12 diode bridge

if you can seperate them, you can re-join them in delta and get the same thing with a standard 6 switch inverter.

I did some brief analysis of a 12 switch, and there isn't any difference (except more complicated), with three phases in delta you can see full voltage swing across each field (sinewave assumed)

[AlexanderB]

But there was a reason delta wouldn't work?

[MPaulHolmes]

All I know is, for each epsilon, there exists an delta, such that if dist(x,a) < delta, dist(f(x),f(a)) < epsilon. So, as long as the motor isn't pushed past its "limit", delta should work. haha

[TT-Man]

Hi P-Hack and AlexanderB,
Yes, mmmmm maybe!
In simple induction motor terms it might work, but as Alexander says the delta may not work as applying volts to say one winding applies a split voltage across the other 2. With switched mode this may not work.
Anyone know?
Thanks you all for the interest.
TT-Man

[freebeard]

Also as an Electrical Utilities Engineer (retired) I have a health respect for the increasing risks with higher voltage.

Congratulations on retiring. I'm not officially retired, but 'between gigs'. Yes, gas will burn your house down but it won't instantly stop your heart.

https://www.youtube.com/watch?v=O-PaSSTA2YE

For five minutes after a post, the Edit button is penalty free. After five minutes there is a timestamp added in the lower left.

My recollection of motor theory lets me down when it comes to the 'reluctance motor'.

I can convince myself I understand it while I'm watching the Texas Instruments Youtube videos, but it starts to fade immediately. They had an analogy about determining the position of a carousel while you're standing on it vs watching from the side.

[P-hack]

Originally Posted by TT-Man

Hi P-Hack and AlexanderB,
Anyone know?

I wish I spoke paul, but all I know is a rotating magnetic field is a rotating magnetic field. I did a bit of analysis on wye delta (based on the boost discussion, only wanting to consider winding for wye in low voltage, then switching to delta when the bemf comes up), and everything seems to stay in phase during the switch. I used fixed current sources, so the resistor (pretend motor field windings) currents drop in delta, but obviously a typical inverter is voltage sourced.

[e*clipse]

Originally Posted by TT-Man

Hi e*clipse, thanks for the info posted on the Toyota MGR.
I also several years ago bought an MGR unit, thinking all the same thoughts.
I wanted to convert a small car to a local runabout.
Then started discovering the limitations.
EV's need continuous power ratings.
I thought Toyota MGs would be conservatively rated ..... seemingly not.
The 50kW rating on the MGR seems to be 18 seconds.
Logical for acceleration 0 to 60 mph so to speak.

A continuous or RMS value may not even be half at 25 kW. That might have been OK, until you find that the power available .... apparently .... is not a linear relationship to voltage. Seemingly, the motor is a combination permanent magnet and reluctance motor, all designed about the 650v applied.

I have wondered about rewinding or cutting the windings mid-point to parallel, messy.
And splitting the star point to make a delta conversion will not work.

However, I have an alternative, split the star point. bring out the 3 connections, then run a second switching inverter to effectively parallel the 2 active windings. This inveror at the star point would be slave to the main inverter.

The perceived benefit would then allow the battery voltage to be a more accepable 325 volts maintaining the original performance of the MGR.

So 18 seconds acceleration with High low end torque, and for me 25 kW continuous running power.

I may draw up my proposition and post.

The hard bit making a master and slave invertor!!

Cheers,
TT-Man

I'm curious - what do you think I'm thinking? All my statements about this motor have been based in solid engineering principles.

Just for starters: No, EV's don't need continuous power ratings. Their operating environment is extremely variable, allowing significantly different peak and continuous power ratings. Industrial motors tend to be built for continuous power ratings and are considerably larger (and heavier) than similarly rated power plants found on vehicles. Thus it's wise to select a motor based on it's ability to provide continuous power for a continuous requirement, like cruising on the highway at 65mph. This number is considerably smaller than the power required to accellerate up to 65mph in 10 seconds. This is true of all vehicles, whether powered by a diesel engine or an electric motor. The 25kW continuous power rating of the MGR is more than adequate for a small runabout like freebeard wants to build. My interest in a multi-motor system is based on dynamic requirements, not keeping up with traffic in a commute.

Also, changing from wye to delta will not change the power output capability of a motor, just the bus voltage. But you don't get something for nothing, and the current will have to be increased if the voltage is decreased. This extra current will result in more I^2R heating, demanding more heat rejection just to keep the same continuous power output.

The continuous power output ability of any motor eventually goes back to the motor's ability to reject waste heat. An example of this are the motors used in EV drag racers. If the motors are cold at the start of the 10 seconds they are used, then the thermal mass of the motor keeps temperatures within a reasonable range even though they pushed to well over 10X their continuous power rating. Again, the ability to remove waste heat is one of the most important factors affecting a motor's power output. This is true for both electric motors and internal combustion motors. This is why people bother with water cooled motors and the military is experimenting with oil spray cooling.

- E*clipse