Twin AC engine

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Hebbe
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Twin AC engine

Post by Hebbe » Mon, 12 Jan 2009, 16:02

I have two Yaskawa E7 240V 18,5kW drives that i like to use with a 11-18,5kW AC engine.
I have not found a donor vehicle, but I would like a pick-up or a van. I have looked at a VW Transporter with rear engine.
This vehicle has rear wheel drive or four wheel drive.
Are there any advantages/disadvantages for a twin drive? One engine for each rear wheel direct on the wheels or a solution like this http://www.youtube.com/watch?v=Bd4EIU4QC5k trought a gear box.

Does anybody have thoughts about my options?


antiscab
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Twin AC engine

Post by antiscab » Mon, 12 Jan 2009, 20:59

are those two motors single phase 240v or 3-phase 240v?
single phase controllers are rare as hens teeth.

if both motors are mechanically locked together (as they are in the video) then driving them shouldnt be an issue. the controller will just see two big motors.

if they aren't mechanically locked together, then torque control may not work correctly. so you would need two contorllers (one for each motor).

a 240vac motor requires a 340v dc bus to run at rated spec.
ideally you want 3x that much so you can run full torque at 3x base speed.

Matt
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Hebbe
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Twin AC engine

Post by Hebbe » Tue, 13 Jan 2009, 05:30

The motors are 3-phase 240V

I was planning on running the dc-bus on 350VDC.

Is it possible to use capasitor to boost the voltage for a little moment? Just as a NOS button on the gear leaver?

antiscab
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Twin AC engine

Post by antiscab » Tue, 13 Jan 2009, 09:17

Hi Hebbe,

could you wire these motors in delta for a lower voltgae? or is the 240v already in delta?

you could put a capacitor in series with the traction pack for a higher DC bus voltage.
it would have to be one large cap though.
how much of an increase in power were you thinking?

Matt
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woody
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Twin AC engine

Post by woody » Tue, 13 Jan 2009, 18:51

Hebbe,

AC drives are usually rated at their continuous rating, i.e. what they can do 24x7. They can normally do 10%-60% over that for a short time (1 minute). E.g. a Danfoss 5042 is a 30kW drive which can do 48kW for 60 seconds. Or it can be configured as a 37kW drive which can do 40kW for 60 seconds.

Motors are also rated at their continuous rating, an 11kW motor can do 11kW 24x7. However, motors can do much more power quite happily for a short time.

Induction motors have a max torque of approx 2.5-3.5 times the rated torque (this is variously called the pullout torque, breakdown torque and sometimes expressed as a breakdown ratio). This is normally available up to the nominal speed.

Also if you use a 415 volt controller on a 240V motor you extend this speed by the ratio of the voltage, so your 11kW motor could probably do 50 kW.

To get 50kW into it, you need a controller capable of 50 kW. So with 2 18.5kW drives, I'd look for 11kW motors maximum, possibly smaller.

Back to your questions:

direct driving the wheel is the wrong speed for industrial motors - 60kph is about 500rpm.   4 pole industrial motors do 1400-1800 rpm. The other side of this coin is that you need a huge amount of torque for wheel drive, about 1000Nm total is about right. That's a huge motor or 2 very large ones.

There are a few ways around this:

* some cars (old Kombis, Unimogs, and Hummers I think) and michelin's new wheel motor system have offset drive - a gear at the end of the axle drives a gear on the inside of the hub, to give a gear reduction in the wheel.

* use the existing diff from the car

* use a diff from another car.

Most people use the diff already in the car.

The pluses and minuses of twin motors, that I can see:
+ can drive front wheels with one, rear wheels with other for tricky torque split and/or weight saving
- 2 small motors are generally less efficient than 1 large motor
+ 2 small motors coupled may fit better in the vehicle / spread weight better
- 2 small motors means 2 couplings rather than one.
+ 2 motors with one controller can be switched series/parallel
+ redundancy - limp home with one motor/controller

For coupling the motors, joining the shafts is probably the most efficient way (e.g. white zombie), but a gear / belt drive like the video has been successful elsewhere, as has one motor front diff, one motor rear diff (there is a subaru imprezza around with this setup).

For a vehicle, one of the tiny vans (Daihatsu Hi-Jet etc.) or utes (Datsun 1200) would be great for the controllers you have.

Can I ask where you got the controllers? Are you in Australia?

cheers,
Woody
Planned EV: '63 Cortina using AC and LiFePO4 Battery Pack

Hebbe
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Twin AC engine

Post by Hebbe » Wed, 14 Jan 2009, 12:34

antiscab wrote: Hi Hebbe,

could you wire these motors in delta for a lower voltgae? or is the 240v already in delta?

you could put a capacitor in series with the traction pack for a higher DC bus voltage.
it would have to be one large cap though.
how much of an increase in power were you thinking?

Matt



I have't chosen any engine yet.

Hebbe
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Twin AC engine

Post by Hebbe » Wed, 14 Jan 2009, 12:41

Thank you for a fast reply..

I live in Norway and i got the controllers from work. Someone connected them to 400AC and they are ment for 240VAC. So the input are damaged. I belive it is possible to replace the varistors and they will be fine, but I will use the DC bus and the engine output, maybe it is not nessesary to fix the mains connection.

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