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Discussion Starter · #1 · (Edited)
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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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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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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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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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
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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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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Discussion Starter · #9 · (Edited)
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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Discussion Starter · #10 · (Edited)
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
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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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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Discussion Starter · #12 ·
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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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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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.


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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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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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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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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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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Discussion Starter · #19 · (Edited)
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 ?????
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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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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