# Industrial 3-phase motors, stripped weight



## coulombKid (Jan 10, 2009)

Hi,
I've torn down motors big enough to push my station wagon and was wondering what percentage of their weight could be lost with composite outside shell for the stator core and composite end bells to hold the bearings?
A pair of metal rings laid-up in the glass can hold the bearings with the added side benefit of eliminating stray shaft currents generated by the AC drive. For a given speed motor there must be a nominal magnetic circuit weight per N.M. of torque. The motor no doubt would be a little bulkier in order to accommodate generous cooling air ducting. I've cast aluminum before but for one-offing composite layup would be easier.


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## karlos (Jun 30, 2008)

Could you roll some aluminium plate to make a cylinerd, maybe two to create a water jacket for cooling? I have briefly considered what you are proposing but never took it anywhere so I will be interested to see the responses.


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## RIPPERTON (Jan 26, 2010)

composite is too hard to work with and $$$$$$$$$$

just cnc some aluminium end frames.
That what Ive got planned for my AC90


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## karlos (Jun 30, 2008)

RIPPERTON said:


> composite is too hard to work with and $$$$$$$$$$
> 
> just cnc some aluminium end frames.
> That what Ive got planned for my AC90


Sounds like a good start. Is it possible to retrospectively cool an AC motor with a rebuilt case? How effective would it be? Does a liquid cooled motor actually just use the cooling just for the casing?


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## JRoque (Mar 9, 2010)

Hi. My 25HP Marathon Electric AC motor weighs <175 lbs. That's because the only "heavy" parts of the enclosure are the two ends; face mount and the back. The body of the motor is made out of rolled steel. The base is bent steel welded to that. There are 4 bolts that run the length of the motor to pull in both ends. A typical 25 HP ACIM can be upwards of 550 lbs.

Here's a pic:
http://www.diyelectriccar.com/forums/attachment.php?attachmentid=6594&d=1272405647

JR


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## karlos (Jun 30, 2008)

JRoque said:


> Hi. My 25HP Marathon Electric AC motor weighs <175 lbs. That's because the only "heavy" parts of the enclosure are the two ends; face mount and the back. The body of the motor is made out of rolled steel. The base is bent steel welded to that. There are 4 bolts that run the length of the motor to pull in both ends. A typical 25 HP ACIM can be upwards of 550 lbs.
> 
> Here's a pic:
> http://www.diyelectriccar.com/forums/attachment.php?attachmentid=6594&d=1272405647
> ...


Thats a significant difference in weights and seems to encourage the 'lightening' of a typical industrial motor if it can be done cost effectively! Looks like some space saving there too.


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## peggus (Feb 18, 2008)

One aluminum housed motor I've been drooling over has a 120Lb stator, 80lb rotor, the cast iron end bells, encoder housing, fan etc weighs 80lbs.


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## Huub3 (Aug 16, 2009)

peggus said:


> One aluminum housed motor I've been drooling over has a 120Lb stator, 80lb rotor, the cast iron end bells, encoder housing, fan etc weighs 80lbs.


Hi, my 15.5 kW alu ABB dahlander is in total ca. 120 kg. However, I would say that the end bells of that motor (I removed one last friday) are not very heavy (maybe 1-2 kg, not sure). I think main weight is the stator package (the copper and the iron) and the rotor. Housing, fan and end bells seem to be a small part.

I would not go for a composite endbell. The airgap between rotor and stator is pretty small. A composite endcap that is both dimensionally accurate, and stable/stiff over time (think creep due to the gravity force) is not simple to make.

Aluminium is quite an OK material for this endcaps I think.

Regards,


Huub

BTW, here is a picture of my motor:


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## coulombKid (Jan 10, 2009)

RIPPERTON said:


> composite is too hard to work with and $$$$$$$$$$
> 
> just cnc some aluminium end frames.
> That what Ive got planned for my AC90


 I helped a friend build a long easy. Extremely strong and light airframe. I've handled some graphite body parts and they seem stronger and lighter than aluminum. The F-15 strike eagle had graphite composite wings. I toured the shop where they were autoclaved back in the '80s.


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## coulombKid (Jan 10, 2009)

JRoque said:


> Hi. My 25HP Marathon Electric AC motor weighs <175 lbs. That's because the only "heavy" parts of the enclosure are the two ends; face mount and the back. The body of the motor is made out of rolled steel. The base is bent steel welded to that. There are 4 bolts that run the length of the motor to pull in both ends. A typical 25 HP ACIM can be upwards of 550 lbs.
> 
> Here's a pic:
> http://www.diyelectriccar.com/forums/attachment.php?attachmentid=6594&d=1272405647
> ...


That is about as minimal as it gets. Is that motor rated at 3,450 or 1,760 RPM. I'd think the faster motor would be better, especially if I was using one of the new power-glides I've seen on here. Looks like a C-face motor which would simplify making an adapter.


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## JRoque (Mar 9, 2010)

coulombKid said:


> Is that motor rated at 3,450 or 1,760 RPM. I'd think the faster motor would be better, especially if I was using one of the new power-glides I've seen on here. Looks like a C-face motor which would simplify making an adapter.



It's a ~3600 RPM. I thought about having a motor with it's rated speed closer to what the ICE peak power RPM was and picked this motor based on that. The downside is that it's a 2 pole motor and pound for pound (no pun intended) those have less torque than 4 pole counterparts. However, this particular motor peaks at 110 lb-ft of torque which is close to what I get from the ICE. This motor has both C-face and foot mounts and I would use both to keep the instant torque clamped down. The motor is also inverter rated (ie: handles hard switching) and a "safe" rating to 5400 RPM. Too bad the darn thing is too long to easily fit my car. I'll try though....

JR


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## coulombKid (Jan 10, 2009)

JRoque said:


> It's a ~3600 RPM. I thought about having a motor with it's rated speed closer to what the ICE peak power RPM was and picked this motor based on that. The downside is that it's a 2 pole motor and pound for pound (no pun intended) those have less torque than 4 pole counterparts. However, this particular motor peaks at 110 lb-ft of torque which is close to what I get from the ICE. This motor has both C-face and foot mounts and I would use both to keep the instant torque clamped down. The motor is also inverter rated (ie: handles hard switching) and a "safe" rating to 5400 RPM. Too bad the darn thing is too long to easily fit my car. I'll try though....
> 
> JR


Is it going in a rear wheel or front wheel drive car? The power glide transmission has a 1.86:1 low gear in it so if you are using a 2-pole motor the transmission makes up for the halving of available motor torque. If I was going with direct drive to a conventional rear axle I'd want the 4-pole motor. With a four pole one can re-wire them internally so that rated voltage is 125 VAC. Of course rated current with that mod doubles.


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## cyclops2 (Feb 12, 2011)

There is 1 really NOT SO GOOD thing about inverter drive motors. The very high switching currents cause a current to flow thru the metal of the rotors, along the motor shaft and into the bearings, thru the balls or rollers, thru the stator frame and into the system ground wire.

It is a serious problem. It actually etches the bearing surfaces away with each hour of operation. Only known cure is some copper grounding braid that is bolted to the stator and the braid rides, drags, on the shaft all the time. 
The braid shorts the etching curent away before it gets to a bearing.

2 braids are needed 1 on each end of the rotor.

Medicene kick in. Later


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## JRoque (Mar 9, 2010)

coulombKid said:


> Is it going in a rear wheel or front wheel drive car?


Front drive, unfortunately, and the motor is too long as it is to fit comfortably. I might be able to work it in if I remove the back fan cover... but then I'd need to find a solution for that. Don't know, but I'll try when the time comes since I already have the motor.




cyclops2 said:


> There is 1 really NOT SO GOOD thing about inverter drive motors.


I'm not sure this will affect motors in EV application the same way that it would a 24/7 pump or fan. But if it does, and thanks for the pointer, this device says it'll cure it for about $35: http://www.mercotac.com/

JR


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## Huub3 (Aug 16, 2009)

Hi Cyclops,

indeed, sometimes currents will flow through the bearings.

However, motor suppliers do provide info and solutions for this.

E.g. ABB has a statement that this issue is relevant for motors 100 kW and above (that is continous power). Below it seems not to affect lifetime. Even then it might still happen long after the car is rusted away?

Standard solution is isolated bearings, either through the mounting, or by using ceramic balls in the ball bearing.

I hope it is not so much an issue for EV use, but if you have some more data on this aspect, and the influence of not going 100 % duty cycle, but accellerating and decellerating (with current and voltage peaks), I would be very interested.

Regards,


Huub


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## cyclops2 (Feb 12, 2011)

JR

Love your slip rings. 
Allows use of steel bearings to take torque shocks when wheel spin stops suddenly on solid pavement. Hydroplanning, or winter, sand, leaves.

Piece of cake. Much more reliable. Also any airflow thru the motor WILL NOT LIFT it off of the shaft. The braid could be lifted off at maximum rpms.
Still need 1 at each end, as I do not know if 1 brush will draw most of the current away. Only a oscilloscope check would prove that.

Insulated bearings do or do not create a problem if the current has no low resistance path back to the controller ?
Some motors can have a holding current flowing while the motor is stopped. That also causes etching.........How much ?????


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## cyclops2 (Feb 12, 2011)

I did a web search for...... V F D bearing problems ...... Read up & make up your own mind.

Remember this.

Some drive controllers can have known " sore spots " where the drive will cause the motor to oscillate to varying intensities. That is cured by feeding the motor a small percentage of AC current to all the phases constantly. 
They are actually applying a parking brake to the motor. This subtracts from usable power. Causing a heating condition.

If there is any of this " parking brake " applied it will cause etching any time the drive is on. How bad ? Only the drive controller company knows.


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## DawidvC (Feb 14, 2010)

We run a number of large drives and motors (Class H ins. and Flux vector drives). We only had one motor with definite bearing damage in the last 15 years (running 24/7), and I believe that the details of the installation may have contributed towards the damage. BTW it was a 75kw motor (Cont rating).

If you are serious about making your own enclosure and end-plates, think about making the motor internally ventilated as per DC motor practice. You can improve your continuous rating from 50% to 100% using the right cooling. I remember reading an article a while ago from some big company (use to be Indramat - now owned by Bosch) on how to use an external watercooling circuit to cool the internal air circulating through the motor. It might be worthwhile looking at their site, since they sell frameless motor (basically just a stator and shaftless rotor, and there used to be a lot of information on doing the engineering required to make these motors work. Unfortunately I have not been around there since Bosch took over, so I do not know if the info is still available.

Regards
Dawid


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## coulombKid (Jan 10, 2009)

cyclops2 said:


> JR
> 
> Love your slip rings.
> Allows use of steel bearings to take torque shocks when wheel spin stops suddenly on solid pavement. Hydroplanning, or winter, sand, leaves.
> ...


At work we have a 100 Hp pump motor on an inverter. I has placards on the end bells indicating that the bearings are insulated. I notice that it also has a Goodyear rubber flex coupling on it. They must have had a bearing problem there in years gone by. In theory the flex coupling would not be needed if both bearings were insulated because current needs a complete path, through two bearings somewhere in this case.


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## Schmism (Aug 16, 2008)

i just replaced the water cooled brushless alternator (180 amp) on my bmw. The entire rear case of the alternator is one cast AL piece. There is a matching slightly larger cup mounted to the car that the alt fits into. it uses a simple O ring seal on a machined surface to make a water tight seal. Water is pumped into the top of the outer case and flows around the alt in the space provided and out the bottom of the case.








to give you an idea of what a water cooled version might look like


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## coulombKid (Jan 10, 2009)

Schmism said:


> i just replaced the water cooled brushless alternator (180 amp) on my bmw. The entire rear case of the alternator is one cast AL piece. There is a matching slightly larger cup mounted to the car that the alt fits into. it uses a simple O ring seal on a machined surface to make a water tight seal. Water is pumped into the top of the outer case and flows around the alt in the space provided and out the bottom of the case.
> 
> 
> 
> ...


That's pretty cool (no pun intended). I wonder if they potted the windings in an electrically insulating but thermally conducting medium. That would do a good job of conducting the heat to the water jacket. I would also eliminate some of the whine.


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## cyclops2 (Feb 12, 2011)

As I recall ?? BMW used to also water cool the transmission with a built in water passage ?


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## Schmism (Aug 16, 2008)

coulombKid said:


> I would also eliminate some of the whine.


 Reasons i ran across(when searching for a replacement part) for the water cooled version was noise and due to its size, heat output.


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## coulombKid (Jan 10, 2009)

karlos said:


> Could you roll some aluminium plate to make a cylinerd, maybe two to create a water jacket for cooling? I have briefly considered what you are proposing but never took it anywhere so I will be interested to see the responses.


Ahh the possibilities. And aluminum double walled water jacket around the stator with windings potted in for excellent heat transfer, mechanical support, and superior electrical insulation, (water passages TIGed on). Air passages in end plates with one internal fan too cool the rotor. Fine laminations throughout to minimize iron losses at high RPM. Stiff but non-conductive end plates so vector drive induced shaft current can not take out the bearings. A ring at tip of fan blades with opto-scratches for a high resolution through the jacket encoder pick-up. Sounds kinda like a $600 Dod hammer at this point. We can dream right?


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## DawidvC (Feb 14, 2010)

coulombKid said:


> Ahh the possibilities. ....
> ... We can dream right?


It is do-able. Just need some mechanical guys doing a motor from their perspective. The main part (electrical) of an AC motor is the stator and rotor. If they are OK, the rest is pure mechanics. 

Dawid


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## coulombKid (Jan 10, 2009)

DawidvC said:


> It is do-able. Just need some mechanical guys doing a motor from their perspective. The main part (electrical) of an AC motor is the stator and rotor. If they are OK, the rest is pure mechanics.
> 
> Dawid


OK, I,ve checked the numbers of two different 25 hp c-face pump motors. The Marathon mentioned by one of our members above is very similar to the Leeson # 801057 listed in another thread. In that thread the member thought it weighed 166#. My reading indicates that it weighs 270#. Both the Marathon and the Leeson in this size/speed weight roughly 11 pounds per horspower. The Leeson is 80% efficient at FLA. ($910.86) eitsher indicated that they run hot. With 20% waste heat it would need a damned good fan and duct work to survive at high load levels, especially here in Arizona. I've noticed that the really rugged vector motors often have an accessory blower motor on them to get their reliability up. It may have been major that discussed the insulation. i.e. they aren't VFD rated. The Leeson at 230 VAC rms would see about 325 0-peak volts on a 60 herts line feed with a near pure sine wave. 325 is about the same voltage as the proper pack for these motors so it must be the high frequency component of PWM chopped DC that tends to go through the cheaper insulation. Thoughts? Also discussed was the merits of 3400 rpm, 1700, and 1100 rpm motors. To me that all depends on the gear reduction used. Lower rpm motors could allow one to skip the transmission and drive direct to the gear around the differential. In other words a 2-pole motor and transmission may very well weigh the same as a 6-pole motor. Old drag racers use to love the Ford 9" rear axle and so does the owner of White Zombie (plasma boy racing). You can buy gear- sets for it all the way up to 5.88:1. food for thought.


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## few2many (Jun 23, 2009)

Getting back to the VFD or inverter rated motors, Cant you just install a spring loaded brush with a gounding strap?
Maybe even use the energy spikes and instead of grounding them, capture them as energy from the vacuum and run the car....sorry, wrong thread.
The huge ugly motor I've been holding onto has ISR, inveter spike resistent windings. How much can you strip the core to drop weight before you have saturation issues(or whatever the issues is when you dont have enough metal surrounding the windings)?


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## DawidvC (Feb 14, 2010)

Running a brush against the shaft before the bearing on both sides, connected to the earth stud of the motor, should work in suppressing bearing damage due to circulating current in the rotor, *IF* the motor is properly earthed to the chassis. BTW, in my experience (16yrs of FOC drives) we only experienced bearing failure on one motor, which had particularly long leads - more than 30m. None of the other motors which we had to send out for repairs over the years had any serious erosion or pitting on the bearings from rotor currents - I had the rewinders send the bearings back with the motor for this express reason. 

You can also run without the brush - I have seen a commercial motor sold with flat earth strapping trailing over the shaft. If it is good enough for them ... 

Removing material from the actual rotor or stator is not a good idea - that is part of the magnetic circuit and, unless you are a motor designer, it is best to leave it alone. You can chop and change the housing of an ac motor to your hearts content, though. It is not part of any electrical or magnetic circuit. 

Regards,
Dawid


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## DawidvC (Feb 14, 2010)

coulombKid said:


> OK, I,ve checked the numbers of two different 25 hp c-face pump motors. The Marathon mentioned by one of our members above is very similar to the Leeson # 801057 listed in another thread. In that thread the member thought it weighed 166#. My reading indicates that it weighs 270#. Both the Marathon and the Leeson in this size/speed weight roughly 11 pounds per horspower. The Leeson is 80% efficient at FLA. ($910.86) eitsher indicated that they run hot. With 20% waste heat it would need a damned good fan and duct work to survive at high load levels, especially here in Arizona. I've noticed that the really rugged vector motors often have an accessory blower motor on them to get their reliability up. It may have been major that discussed the insulation. i.e. they aren't VFD rated. The Leeson at 230 VAC rms would see about 325 0-peak volts on a 60 herts line feed with a near pure sine wave. 325 is about the same voltage as the proper pack for these motors so it must be the high frequency component of PWM chopped DC that tends to go through the cheaper insulation. Thoughts? Also discussed was the merits of 3400 rpm, 1700, and 1100 rpm motors. To me that all depends on the gear reduction used. Lower rpm motors could allow one to skip the transmission and drive direct to the gear around the differential. In other words a 2-pole motor and transmission may very well weigh the same as a 6-pole motor. Old drag racers use to love the Ford 9" rear axle and so does the owner of White Zombie (plasma boy racing). You can buy gear- sets for it all the way up to 5.88:1. food for thought.


Motors rated for VFD duty normally has thinner laminations, as well as insulation typically rated for 2 500Vdc. This is needed due to the high voltage spikes created by the cable inductance - the cables tend to act as antennas, and you can use antenna calculations to work out the reflected wave power and amplitude. This is also why drive manufacturers insist on a choke after the drive on longer cable runs (exceeding 100 feet). These spike can damage either the drive or the motor - we had both occured on various installations.

Regarding pole count in motors - generally, the higher the pole count, the more torque a motor can deliver for the same input power. Conversely, the lower pole count will have a higher speed than a motor with more poles. Take your pick - japanese screamer or american grunt.

I would recommend that, in any motor that will be used in VFD applications where it will run slower than its nominal speed, a forced cooling fan be used. If you are happy to absorb the extra power needed for the normal colling fan, it will provide more than enough cooling for the motor when running faster than its nominal speed rating.

As to the difference between the two motors you mention, they are right at the size where cast iron tends to be used predominantly for the construction of the motor casings. If you can, look for aluminium cased motors, they tend to be somewhat lighter. The other option is to build your own (watercooled) steel enclosure for the motor. We have a local company who builds traction motors for mines - all steel watercooled units, and they are lighter than aluminium motors, so it is possible.

Regards
Dawid


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## JRoque (Mar 9, 2010)

DawidvC said:


> the cables tend to act as antennas, and you can use antenna calculations to work out the reflected wave power and amplitude. This is also why drive manufacturers insist on a choke after the drive on longer cable runs (exceeding 100 feet).


Hello Dawid, that's an excellent piece of information. I had no idea it would do that but it makes total sense. From another hat I wear, I understand the SWR relationship. I typically "choke" the feedline by giving it a few turns, depending on the carrier frequency. But a 2/0 cable - three of them in this case - is not easy to bend. Any hints on low-cost/simple alternatives to the commercial choke solutions? How much do these chokes heat up with typical use?

JR


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## DawidvC (Feb 14, 2010)

These thicker cables are difficult to twist. This is mainly due to the minimum bend radius. Anything sharper bend than this normally damages the cables. If you want to make your own chokes you will need a former and thin strips (laminate) of busbar, which you then will have to twist in shape over the former. I do not know if something like a graphite core will work, but I recall reading of experiments using iron filings suspended in a insulating matrix, which might be worthwhile following up. As we do not actually use chokes, I have no idea how hot they might get. You would need to run an analysis on that, because much will depend on the actual design. Open core will not work - we have actually damaged cables with induced heat in a panel after the electrician gave the ends a couple of turns to make it look nice before terminating it.

I hope that helps.
Regards
Dawid


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