400 Hz motor characteristics

If I have a 2 pole motor designed to operate at 400 Hz
THEN would its baseline RPM be 24,000?

IF driven by VFD then would it be constant torque below baseline and constant HP above baseline (assuming motor line voltage held constant when above baseline as is done with 60 Hz motors)

Thanks
Dan Bentler

Yes to everything, Dan. But it would not necessarily be true that this motor can operate above 24000rpm. I'd recommend a check with the manufacturer before I went overspeed.

Thanks Dick

Dan

Dan
Are you sure that it is really a 2 pole motor?
I experimented a bit using aircraft type motors because they were small. The motor supplier referred the them as 2 and 4 pole when they were obviously were not. 1800 and 3600 RPM.
I would like to hear more about that motor.

It would be fairly easy to put very low voltage at 60hz on the motors and see how fast they turn. The voltage would have to be about 1/7 of the nameplate voltage whatever that is.

You might be able to find three control transformers would 480/24 or 20/1 and set them up in a delta arrangement to create three phase power at 5% of whatever you put into them.

If you test run the motors unloaded, you shouldn't need much kva to get them to spin.

As I think more about this, you just might be able to single phase the motor and manually spin it to get it started. Even single phased, it would run up to sync speed.

You haven't said how big this motor is but this scheme would work out better if the motor were smaller rather than larger, of course!

I am asking the question bevause quite a few ask about it with respect to electric vehicles. Apparently from what LIMITED info I can get there are some motors and VFD combinations where the motor runs at 12,000 RPM. IF you assume driveline speed is 3600 RPM differential is 4:1 thus wheeel RPM at 900 then I cannot see the reason for this motor setup because
1. You need a gearbox with say 12,000 to 3600 RPM reduction.
2. From the little I know bearings for 12,000 RPM are very "twitchy"
3. Past attempts at using fuel turbines for driving vehicles did not have bearing problems as such but the gearing and pumping of lubricant caused oil deprivation to seals which led to shot seals, leakage and potential bearing loss. 12,000 RPM bearing failure is not something I would want to witness at close distance.

The argument goes that for electric vehicles the motor is much smaller and weighs less ( which is the magic manna in many EV advocates minds. There would also be less motor inertia as another "savings".

I am also not wild about these setups because these are very limited production runs in an industry where factories evaporate overnight. IN addition I do not like their insistance you MUST use THEIR matched VFD and motor.
I theorize
1 the volume reduction is lost when you have to add a gearbox.
2. the weight savings are almost lost when you go to a gearbox.

I intend to electrify a 56 Chev pickup with AC drive. I will use standard industrial "stuff" to ensure good spare parts and repair capability here in Seattle and only have to drive across town to get it.
I Will use Leeson 3600 50 HP motor and Hitachi SJ 700 drive. Motor is open drip proof - not the best I know given wet conditions - but I paid only $230 for it -will need water splash protection but will incorporate that into a separate forced ventilation for low speed operation.

Battery will tie direct to DC bus and be approx 325 VDC at open circuit. The motor is "standard industrial" at 526 pounds so I am paying a weight penalty there. However I feel that this is a standard motor
It is rugged and can tolerate abuse.
I can get bearings anywhere
and I can have any good rewind shop do rewind on it if needed.

Same thinking goes for Hitachi VFD. I can drive many motors with this provided I stay properly sized matched voltage etc.

As a comparison a Canada outfit did a 58 Chev pickup with Azure Dynamic 65 HP motor. They claim it is a hot rod - no performance data - which seems to be normal for Electric Vehicles. But sure is a pretty looking truck - nice to be able to afford all professional workmanship - owned by a brewery in Ottawa and used for marketing. As comparison I think I will do pretty well with my proposed design.

So there is the gory background behind the question.
Dan Bentler

DickDV said:

It would be fairly easy to put very low voltage at 60hz on the motors and see how fast they turn. The voltage would have to be about 1/7 of the nameplate voltage whatever that is.

You might be able to find three control transformers would 480/24 or 20/1 and set them up in a delta arrangement to create three phase power at 5% of whatever you put into them.

If you test run the motors unloaded, you shouldn't need much kva to get them to spin.

Click to expand...

Dick this takes me into another question I was asked
"can I use a VFD rated at 10 HP to test run a 50HP motor?
even assuming motor is bare shaft ie unloaded my answer was

"Rule of thumb is 20 to 25% power is needed for magnetizing etc just to get motor to spin. SO a 10 HP VFD will MAYBE just barely do it". I may be too conservative but I really hate it when people come up to me with this pile of cinders and say
"but you said I could do it"

Dan

leitmotif said:

Dick this takes me into another question I was asked
"can I use a VFD rated at 10 HP to test run a 50HP motor?
even assuming motor is bare shaft ie unloaded my answer was

"Rule of thumb is 20 to 25% power is needed for magnetizing etc just to get motor to spin. SO a 10 HP VFD will MAYBE just barely do it". I may be too conservative but I really hate it when people come up to me with this pile of cinders and say
"but you said I could do it"

Dan

Click to expand...

Set the drive to pure V/Hz mode, nothing fancy, and you shouldn't have a problem. There is no magnetizing current generated in V/Hz modes on any drive I know of currently.

I would like to hear about this project as it progresses.
I just finished helping a friend convert an older Chevy S10 to an all battery drive from a 48 volt forklift. Even with the battery weight acceleration is impressive. It is more than adequate for commuting to work and around town errands. Winter time here in Erie PA may be a problem. The electric heat and low temps may shorten the range considerably.
I had a 400 Hz motor installed into a pipe threader used in construction and maintenance. Performance was impressive, more power and speed than the series motor, used less current and ultimately cheaper to produce. The manufacturer was not interested in investing in that new product.

gas said:

I would like to hear about this project as it progresses.
Winter time here in Erie PA may be a problem. The electric heat and low temps may shorten the range considerably.

Click to expand...

Will update when make significant progress.

Yes cab heat will subtract from range without doubt. I think the "easiest" is to use factory installed hot water and heat it with electric heater. May be good for Seattle but Pa (??) I think diesel or propane fired water heater better option. These are made for trucks to stop idling at truck stop.
I intend to go with electric seats for heat - still have the windshield defrost to contend with I know.
Still no free lunch however you do it.

Battery of any kind is chemical process and affected by temperature. Cold weather will decrease range. Supposedly lead acid is most affected. Insulate battery box. If you time the end of charge to just before go to work the battery will be warmest. Store in warm garage ie 60 or so 70 better but there is the fuel bill for that. Install electric battery heaters.

Good quote - electric vehicles will satisfy the needs of only 70% of American population. As we have seen time and time again with almost any kind of equipment you care to pick they can be a good option but have their own set of trade offs - there just aint no free lunch and for sure no magic solution that will make everyone happy.

Dan Bentler

You can get electric windscreen defrosters that operate on 12vdc, they a a little bit like hairdryers, I have seen them listed on ebay.

Alan

Originally posted by rdrast:

There is no magnetizing current generated in V/Hz modes on any drive I know of currently.

Click to expand...

This is just a clarification.

Magnetizing current is always generated. It's a requiement of an AC motor; it won't run without it. However, in V/Hz mode the drive doesn't try to control it. The torque producing and magnetizing current components are just used as necessary by the motor based on the amount of electrical slip is present. And the magnetizing current is not held at the full flux level like it is with an SV of FV controlled drive. So in V/Hz mode the current requirement to spin an unloaded motor is much less than in SV or FV modes.

Keith

Keith Thanks I was scratching my head over this wondering if no mag current where does field come from?

Dan Bentler

I thought of doing the same thing but never got started. There are enough industrial parts out there to make an EV with off the shelf parts.
Will appreciate it if you can post your progress