Electric Vehicle Update and Question

[leitmotif]

Greetings
Here is the status of the electric vehicle project
1. Bought 1956 Chev pickup. Body in decent shape some work needed of course.

2. Intend to use Allen Bradley Powerflex 700 VFD

3. Dream of using 75 HP TEFC motor but there are some drawbacks on this weight, larger battery, cost, and just how am I going to get the big thing to fit? Would be neat though on the drag strip. So am going most likely with 50 HP maybe open drip proof to save on weight and cost.

In the Grainger catalog listing for 50 HP motors I find a listing for NEMA MG 31 that I am unfamiliar with. I will copy that here for two motors and their part numbers then will give entire listing for one motor below.

MOTOR P/N 1XTR3
Inverter NEMA MG 1 Part 31: 100:1 Variable and 20:1 Constant Torque

MOTOR P/N 1EBH9
Inverter NEMA MG 1 Part 31: 100:1 Variable and 12:1 Constant Torque


What do the 100:1 Variable and the Constant Torque ratios mean to me?
Why the difference between the two motors when in most respects they seem identical?
Where can I study more on this to ensure I know what I am doing picking these motors and get the best one for the application?

Thanks for the help
Dan Bentler



COMPLETE descriptin of motor P/N 1XTR3

ItemNEMA Premium Efficient Motor Motor Type3-Phase EnclosureTotally Enclosed Fan-Cooled DutyInverter HP50 Nameplate RPM3550 Voltage208-230/460 NEMA/IEC Frame326TS Service Factor1.25 Hz60 Nominal Efficiency94.1 MountingBase Mounting PositionHorizontal BearingsOpen Regreasable Ball Thermal ProtectionNone Full Load Amps123.0-111.0/55.5 RotationCW/CCW Insulation ClassF ******t (C)40 Efficiency GroupNEMA Premium Length Less Shaft (In.)25 7/8 Shaft Dia. (In.)1 7/8 Shaft Length (In.)3 3/4 Frame MaterialCast Iron Body Dia. (In.)15 9/16 BaseRigid Agency ComplianceUL Recognized (E104590), CSA Certified (LR38324) FinishGreen Alkyd Enamel NEMA DesignB Phase3 NEMA StandardInverter NEMA MG 1 Part 31: 100:1 Variable and 20:1 Constant Torque Rated50 Hz Operation on 190/380V at rated HP and 5/6 of 60 Hz RPM Part Wind Start CapableNo Usable on 200V @ 1.0 SFNo

COMPLETE descriptin of motor P/N 1EBH9

ItemEnergy Efficient Motor Motor Type3-Phase EnclosureTotally Enclosed Fan-Cooled DutyInverter HP50 Nameplate RPM3555 Voltage208-230/460 NEMA/IEC Frame326TS Service Factor1.25 Hz60 Nominal Efficiency92.4 MountingBase Mounting PositionHorizontal BearingsOpen Regreasable Ball Thermal ProtectionNone Full Load Amps125.0-113.0/56.5 RotationCW/CCW Insulation ClassF ******t (C)40 Efficiency GroupEPAct Length Less Shaft (In.)25 7/8 Shaft Dia. (In.)1 7/8 Shaft Length (In.)3 3/4 Frame MaterialCast Iron Body Dia. (In.)15 9/16 BaseRigid Agency ComplianceUL Recognized (E104590), CSA Certified (LR38324) FinishBlue Alkyd Enamel NEMA DesignB Phase3 NEMA StandardInverter NEMA MG 1 Part 31: 100:1 Variable and 12:1 Constant Torque Rated50 Hz Operation on 190/380V at Rated HP and 5/6 of 60 Hz RPM Part Wind Start CapableNo Usable on 200V @ 1.0 SFNo

 

[DickDV]

The MG1 P31 endorsement means that the motor has been tested to a higher standard for withstanding inverter pulses. You need a motor with that rating.

The constant torque motor speed turndown ratios give you the range of speed that is usable at full torque output. Neither 12/1 nor 20/1 is slow enough for a vehicle traction motor. You need something in the range of 1000/1 which is full torque output down to stall.

 

[leitmotif]

Dick

The application will probably do an average 30 mph which is average motor and driveshaft speed of 1800. 60 mph would have driveline speed of 3600 (slightly over baseline). We do have some fairly steep hills in Seattle which will impose tough starting but I estimate these will be in a small minority of demands (ie 3 percent ?). I don't intend to do long term very slow high torque (stump pulling etc) and would have to exercise same care and caution as would be done with gas engine and manual transmission. Most very low speed 5 mph and less would be in parking lots and for short duration. Creeping along on the freeway during rush (which I avoid like the plague) seems to average about 15 to 20 which I think will give the motor enough cooling (about 15 Hz) without booster fan. Will definitely have some way of monitoring motor temp. Guess I better start looking for one with RTDs or TC built in the windings.

I realize that very low speed would need additional cooling for motor (which is why open drip proof is also under consideration).

What confuses me is that several textbooks all show the torque as a flatline (and all say it is constant torque) from 0 RPM to baseline.

Gives me food for thought and additional study. I would much rather think my way into preventing a problem than have to think my way out of it.

Recommend additional reading please? I realize this may be conflict of interest so will understand if you have to "bow out".

Dan Bentler

 

[DickDV]

From a torque production standpoint, pretty much all induction motors are capable of constant torque from basespeed down to stall.

The limitation on using that torque at low speeds is purely thermal. As long as you can cool the motor adequately, you can use full rated torque over that whole speed range. Clearly, an ODP or TEFC motor is not going to be able to cool at very low speeds because the motor's fan is turning too slow to move any air.

One other limitation to torque development under about 5 Hz is the drive technology. The simplest, least sophisticated drives cannot manage the motor well enough to produce full torque under that frequency. If you choose a flux vector, sensorless vector, or DTC drive, you will be ok. The AB PF700 is in that category.

 

[OkiePC]

Dan, have you thought about using a transfer case (Hi/Lo as in 4wd) to give you a little better speed range? Then you could pull stumps or creep along in traffic and simply shift into low range to keep the RPMs up.

Just a thought...
Paul

 

[leitmotif]

Dan, have you thought about using a transfer case (Hi/Lo as in 4wd) to give you a little better speed range? Then you could pull stumps or creep along in traffic and simply shift into low range to keep the RPMs up. Just a thought...
Paul

Yes I have thought about keeping the transmissions. I am going to try to eliminate transmissions and get as close as possible to direct drive (as in inhub motor) by direct connecting to driveshaft. Gain by saving space for batteries etc. This would be done for "on pavement" ie normal driving vehicles.

IF it is off pavement or a dedicated heavy haul or stump puller I would definitely have a gearbox and would maybe go to a lower RPM rated motor ie 1800 or 900 to get a beefier "torquier" motor.

BTW there is an outfit in England that is doing 4WD using in hub motors
- supposedly they are able to rely on the 4 motors alone for all braking needs
- I am little skeptical on this idea
- I am waiting to see if they actually get this into production and what their results are.

SO in the future I may have something for your Jeep.

Dan

 

[leitmotif]

From a torque production standpoint, pretty much all induction motors are capable of constant torque from basespeed down to stall.

The limitation on using that torque at low speeds is purely thermal. As long as you can cool the motor adequately, you can use full rated torque over that whole speed range. Clearly, an ODP or TEFC motor is not going to be able to cool at very low speeds because the motor's fan is turning too slow to move any air.

One other limitation to torque development under about 5 Hz is the drive technology. The simplest, least sophisticated drives cannot manage the motor well enough to produce full torque under that frequency. If you choose a flux vector, sensorless vector, or DTC drive, you will be ok. The AB PF700 is in that category.

Thanks Dick.
I will (hopefully automatically) have a booster blower running at the lower frequencies and still want RTDs in the windings.

I chose Allen Bradley because local rep is willing to support this project.

Dan Bentler

 

[Lancie1]

Dan,

I would avoid the gearbox because this is an electric vehicle. The more non-essential weight, the less range you will have. The essentials: electric motor, batteries, variable speed controller, frame, wheels, seat, controls!

An idea to make it match the latest technology: Eliminate that heavy 1956 rear differential and couple two smaller electric motors, one to each rear wheel. The electronic controller would then have to control how fast each wheel needs to turn to get around curves in the road. A lightweight electronic controller weighing 8 or 10 pounds can replace that 150 pound rear differential. Think power efficiency, which means maximizing the torque per pound of vehicle weight, which means reducing the weight everywhere possible, while increasing the battery amps/pound and the motor hp/pound.

If you can find a regenerative controller, the motors can be used to recharge the batteries while coasting downhill, and also for braking.

 

[OkiePC]

The diff might be slightly less heavy than two 25HP motors, and provides a great deal of structure to the leaf sprung suspension that would also have to be updated if you eliminated it.

A tranny is probably a waste of weight but a transfer case and driveshaft may not be.

I would, minimally, couple the motor to the driveshaft, and keep the differential. Eliminating the driveshaft might be easy enough in a truck too, since you can do whatever you want to the bed and adapt the motor directly to the input of the differential.

Keeping the driveshaft would keep the motor up front and allow a more rigid mount, and probably be simpler to adapt.

I hope Dan will post some pics of the truck! I am a Chevy and Jeep fan.

My first thought at hearing '56 Chevy' was "isn't that kinda heavy?", but it will be so much cooler looking than a Nissan or Isuzu...

JMHOO
Paul

 

[milldrone]

Eliminating the driveshaft might be easy enough in a truck too, since you can do whatever you want to the bed and sdapt the motor directly to the input of the differential.

Adding to the unsprung weight can affect handling in a bad way. I think I can remember Dan speaking about snow and ice a long time ago.

 

[OkiePC]

Adding to the unsprung weight can affect handling in a bad way. I think I can remember Dan speaking about snow and ice a long time ago.

Good point. All the more reason to keep the driveshaft too.

 

[leitmotif]

I agree a 56 Chev pickup is gonna be a little heavy which is a big downside. I am willing to accept this because as Paul said it is cooler than an everyday truck. Look at it this way:
Electric drive is unique
56 Chev is unique
THUS Electric 56 Chev is unique squared.

IF it were off road or other severe slow duty would definitely have gearbox. Will use 3600 RPM motor to get close match to driveline speed at 60 mph. Have thought about throwing out driveshaft and couple direct to differential but think it would take too much reinforcing and there is the question of unsprung weight. Opinions vary widely on this some say OK provided I beef up the shocks others say I am crazy.

The next stage after I get this running is to modify another truck (Izuzu because I have it) and do the dual motor probably 20 to 25 HP and direct drive the wheels with them at around 900 RPM. I do not think that different tire speeds at low speeds in tight turn will be a large problem with squirrel cage motors.

Different road conditions will be dealt with using different switch selected acceleration ramps.

I would like to have water cooled motor to simplify the cooling controls and to use the heat in the cab. Siemens I know has a few but their USA electric vehicle related dealer is not cooperative. Any ideas on who builds water cooled motors.

Pictures are being arranged for.

Thanks for the input

Dan Bentler