Dual OEM AC EV motors, one drive?

[thingstodo]

Originally Posted by freebeard

If you're talking about a Ford Fusion/Tesla type throttle, they report over two different voltage ranges, and use the difference as a sanity check.

Agreed. But if your 2 controllers only use one each, and they can be calibrated for min/max throttle ... one throttle *COULD* do it. SHOULD it - another question.

[thingstodo]

Originally Posted by oil pan 4

To get full torque on a 3 phase motor rotor inductance and reactance have to be equal, this usually happens at 20% to 30% rotor to stator magnetic slip speed.

Perhaps I mis-spoke. Should that have been maximum torque instead of full torque?

Somewhere around to top of the curve where the motor runs out of torque and stalls... somewhere 2X - 4X rated torque, way over rated slip, way over rated current ... stuff that you do for short periods of time

[oil pan 4]

My statement covers both.

If the motor is operating below 70% slip it is not developing full torque.

When the motor slips too much the internal cross bars in the rotor start to operate on higher and higher inducted frequency. The problem is the stator is almost always designed to run at peak efficiency well under 10Hz.
Increased slip just creates more heat, not more torque.

[cajunfj40]

freebeard:

Linky, please?

http://www.diyelectriccar.com/forums/showthread.php?t=151458

oil pan 4:

To get full torque on a 3 phase motor rotor inductance and reactance have to be equal, this usually happens at 20% to 30% rotor to stator magnetic slip speed.

Does this mean I have to get the *stators* aligned in such a way that both *rotors* have equal inductance and reactance? Or is it something I have to do to the rotors themselves to make them equal? How equal, in either case, to minimize excess heating due to mismatch when running two 3-phase induction machines in parallel on a single shaft and single drive?

thingstodo:

I like the "sanity check" feature of the two different voltage ranges on the throttle. If I am "twinning" the throttle output to two separate drives, so long as both drives can handle those two voltage ranges, then there should be no issue. IE, use the throttle assembly that goes with the donor drive(s). If using a non-OEM drive, I've got to figure out whether I want to put in that sort of fail-safe, and how to handle it. Possibly with the GEVCU? Haven't read up on it at all yet.

Hmm. I wonder whether eldis' UMC drive

http://www.diyelectriccar.com/forums/showthread.php/any-ac-motor-any-inverter-umc-152234.html

will end up being a contender here. The basic idea, as I understand it, is to rip the brain out of any given OEM EV inverter and hook up his board to drive the power stage instead. One stays limited by the capability of the OEM inverter power stage, but get to skip reverse-engineering the appropriate CANbus commands and either spoofing the parts you don't want to use from the donor or having to put them all in.

Thanks, all!

EDIT: links are not links yet, guess I have too low a post count, or didit worng. Seems legible, at least.

[thingstodo]

Originally Posted by cajunfj40

Hmm. I wonder whether eldis' UMC drive

http://www.diyelectriccar.com/forums/showthread.php/any-ac-motor-any-inverter-umc-152234.html

will end up being a contender here. The basic idea, as I understand it, is to rip the brain out of any given OEM EV inverter and hook up his board to drive the power stage instead. One stays limited by the capability of the OEM inverter power stage, but get to skip reverse-engineering the appropriate CANbus commands and either spoofing the parts you don't want to use from the donor or having to put them all in

Hmm. I have not read up on the UMC drive. It sounds pretty good! Open source is quite important to me - maybe eldis will get there.

I plan to do a similar thing with Paul Holmes' AC controller board. I have *SEVERAL* old industrial Variable Frequency Drives (AC in, variable speed or variable torque AC out) - Allen-Bradley, Siemens, Mitsubishi, Toshiba ... all air-cooled so they are heavy .. and with one thing or another not working. I would like to do a brain transplant on them and use them (since they are designed with 600VAC parts and tolerances, touch-safe enclosures) for battery chargers, DC/DC converters, and perhaps even single-phase 120/240V to power my shed.

None of them are suitable for a car - the heat sink being double the weight of everything else in the drives, huge inductors .. etc. But I might be able to help Paul make his control board easier to use when driving 'foreign' controller structures.

We have discussed that it would be nice to add another CPU, on a different board, to Paul's AC controller (and come to think of it, his DC controller as well) to do the CANbus interface, making the data pretty for a bluetooth link to android .. and a host of other things that the Motor Controller *DOES NOT* need to spend time on. IMHO reliably controlling motors is enough of a task!

[freebeard]

If using a non-OEM drive, I've got to figure out whether I want to put in that sort of fail-safe, and how to handle it. Possibly with the GEVCU? Haven't read up on it at all yet.

Take a look here:
EVTV Motor Verks Store:

They have the GEVCU, SavvyCAN that can read and inject CAN messages at high speed, the older CAN KIT with Arduino Due, the 1000 or 300 Amp shunts that are on the CAN bus; even (I see) a CAN-GPS that put geo-location on the CAN bus.

[oil pan 4]

The motors will be set up from the factory.
I just figured you would run 2 of the same motors.

The resistance of the windings is fixed, the reactance is varied by the current in the rotor and stator. Varying the voltage and frequency to the motors will be your torque regulation.
There are other tricks to get higher torque such as putting series winding in parallel for starting. But this is a special class of industrial motors, I don't think traction motors use it.

[cRiPpLe_rOoStEr]

Originally Posted by cajunfj40

If axle-mounted motors get a sufficient torque/speed spread without having to change gears by the time my budget is available, I could go 1 motor per end or per wheel, but at this time it is far simpler to run everything through the transfercase and driveshafts to the existing front/rear live axle setup.

With 1 motor driving each axle directly, the setup would have fewer friction losses and possibly the weight penalty would also be lower.

[cajunfj40]

thingstodo:

Sounds like a great idea to have a "universal brain" one could plug in like that, for all the reasons you list. I like the idea of re-using already "safety rated" enclosures!

The motors will be set up from the factory.
I just figured you would run 2 of the same motors.

oil pan 4:

Well, yes, 2 of the same motor. I was wondering how similar they had to be, or whether "factory tolerances" are good enough as-is. Sounds like I should reasonably carefully set up the main cables running to each motor so the per-motor phase resistances are basically equal.

With 1 motor driving each axle directly, the setup would have fewer friction losses and possibly the weight penalty would also be lower.

cRiPpLe_rOoStEr:

True, but my target application (dreamland, I know, lots of built in assumptions in terms of arranging recharging, etc.) is off-road. Getting sufficient torque to the one wheel that has decent traction to get over that rock while still retaining a sufficient speed spread in the same motor seems quite a tall order. Linking two motors across one axle with a "locker" of some kind (basically a normally open clutch between the two) halves the per-motor torque requirement, but it's still pretty difficult to get it.

Were I building a vehicle that would never go off-road, 1 Leaf setup per end or 4 geared motors, 1 per corner would work fine. If I build what I want - an FJ-40 - it must retain at a minimum the off-road ability of a stock driveline, so 6500 ft-lbs at the axle in low-range-first-gear. That got me pretty much everywhere I wanted to go off-road before, the limit was traction and ground clearance (no lockers at the time, and no lift). Freeway specs are modest, so not difficult to achieve.

Take a look here:

freebeard:

Yes, it looks like EVTV has a lot of the bits I'd need to splice some OEM goodies together. One of these days I'll have to watch some of the videos there, too.

General question to all, sort of off my original topic: What are the safety implications of using two complete Leaf battery packs, connected in series, to give ~800V to MPaulHolmes' 200kw inverter? If the + and - from each pack is fed directly to the box the inverter lives in, then aside from touching the wrong two battery posts, or chafing through both the + on one pack feed wire and - on the other there should be no voltages exposed that are higher than a stock Leaf. There'd be contactors within the inverter box to split/combine the packs based on whether the car is in "charge" or "drive" modes, and the packs would likely be charged "in parallel" (either two packs and two chargers run separately, or two packs paralleled on one charger).

I'm basing that query on the idea that doubling the voltage *roughly* doubles the RPM at which peak torque can be maintained from a given motor. Other than the additional losses from running the motor outside its' design envelope, that should give roughly double the power at stock current levels. Extrapolating from the existing ratings, and using stock current levels, that's still ~207 ft-lbs 0-2200RPM, ~192 ft-lbs 2200-6000 rpm, ~215hp 6,000rpm to 10,300rpm (keeping stock redline). If we take 200kW input to the drive, and take a 90% drive/motor efficiency, we can get ~241hp at 6000rpm on up, so ~211 ft-lbs 0-6000rpm calculating backwards. The motor would still happily run at 107hp/7,000rpm constant rating, which is "enough" for long-haul and hill-climb needs. (battery capacity limited unless fancy range extensions are figured out. Probably a pickup truck and a trailer...) Higher if cooling can be improved - and one motor is easier to cool than 2.

Thoughts?

[freebeard]

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