# Baldor 3phase AC 1745 rpm?



## RatSoup (Aug 30, 2009)

How do you plan to generate the 3 phase AC signal with the solid state relays to run the motor?


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## few2many (Jun 23, 2009)

yeah, youll need a vfd to control the motor voltage and frequency at the same time to control the motor speed. If you intend to use the pickup to generate the frequency, youll still need three phase just to get it going. been trying to determine my own using some igbts and a commutator like device to generate the 3 phases, very the speed of the motor for freq control. I know this is pretty lowbuck and *******, but i'll try this pipe dream before i drop several grand for a vfd. Look on ebay or industrial equipment auctions sites for a vfd 3-4 times the motors rating, check the specs of any potential controllers for shared or common dc bus, as these should be able to run on batt pac voltages alone.


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## few2many (Jun 23, 2009)

I mentioned it, but wanted to elaborate a bit. anything times 0 (x0) is zero. if your motor speed is zero, youre slotted rotor wont be sending the signal to generate 3phase.


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## Green (Aug 6, 2009)

RatSoup said:


> How do you plan to generate the 3 phase AC signal with the solid state relays to run the motor?


I plan on using a plate that is half moon shaped mounted to the drive shaft and then I'll have infra red lasers with sensors mounted stationary with the motor shining through this plate. as the plate/encoder rotates with the motor it will switch on and off the infrared sensors. each sensor correlating with a pole on a winding one for + and one opposite for - for each winding. As the half moon disc mounted to the drive shaft would interrupt the lasers in sequence. the signals coming from the sensors would then in turn switch on and off the solid state relays sending 3 phase square wave current to my motor. keeping the frequency timed in relation to where my motor is at all times. And I would only have to vary the amps going from my batteries to the Solid state relays. sorry I'm not very good with describing what i've got envisioned. If this is clear as mud please let me know. My motor being a low rpm motor should make this easier for me.


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## Green (Aug 6, 2009)

few2many said:


> I mentioned it, but wanted to elaborate a bit. anything times 0 (x0) is zero. if your motor speed is zero, youre slotted rotor wont be sending the signal to generate 3phase.



It would be like a brushed motor except the brushes are sensors and SSR's.

check out the image on this site.
http://www.zeitlauf.co.uk/technology/motoren/three_phase_motor.html


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## samborambo (Aug 27, 2008)

Green said:


> I've got a Baldor motor P18G3889 5HP,1745RPM,3PH,60HZ,184TC, that I was hoping to use as a direct drive motor. It has roughly 45.5 lb-ft of torque. Which is very similar to my current metro's max torque of roughly 50lb-ft. I hope to put it in my chevy metro with a as many lithium ion batteries as I can fit in my remaining space.
> this motor weighs something around 135 lbs. I"ve found hp in gas and hp in electric are two entirely different animals!! So I've been going by torque and rpm to figure out roughly what kind of power comes out of the system.


This motor is not powerful enough even for a smaller car. Acceleration would be poor in direct drive and the motor would overheat if pushed much further than 25mph.
The ICE may have 50lb.ft of torque but its made usable through a gearbox. Have a look for a 50lb.ft 2 pole motor (3600 rpm) - should be around 15hp.



Green said:


> Here's my controller Idea.
> I want to put a slotted disk on the drive shaft with some infra red lasers and pickups to act as an encoder and generate a motor location signal that I will feed into some solid state relays that are hooked up to my batteries and capacitors. I would then vary my torque with a potentiometer on the main power supply to vary the amps. It would act as a variable speed but I wouldn't be trying to dictate motor position (aka rpm) I would just be dictating how much torque I want from the motor and I'd let the rpm govern itself.


This will not work for many reasons.

Solid state relays are not designed for high frequency switching duty.
In an induction motor the rotor lags the stator in speed, not position (as for synchronous motors). The optical encoder idea may work for a synchronous motor but not an induction motor.
A 10kW potentiometer? You sure you don't mean PWM control? Linear control of a traction motor is just insane.
You need to ramp up the phase voltage proportional to speed. Too much voltage and the motor overheats. Too little and it will stall.
Good enthusiasm on wanting to get into AC motors but there's a whole bunch of motor theory (and electronics theory!) you need to know before even attempting to design a controller.

A good place to start learning about induction machines is Microchip's application notes. There's a bunch of links on my DIYEC blog to relevant ANs.

Sam.


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## Green (Aug 6, 2009)

Thanks Sam 

For the induction vs synchronous, theoretically could I gear drive my encoder so that it would rotate to create a 60Hz signal at the rpm that the motor would normally run at if it were attached to regular 60 Hz grid?

I would only need 60 Hz capability out of the SSR's usually they would be running at lower frequency. I think I can find some in that range.

If I were to drive the wheels with a 2:1 ratio it would put at the wheels torque at 91ft-lbs and a max speed of 60mph. I'll look into whether or not 91ft-lbs at the wheels is enough to get my car moving, and whether or not 30 lb-ft at the wheels is enough to maintain a decent speed. 

Thanks again man! I'll go check out your blog stuffs.


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## few2many (Jun 23, 2009)

Originally Posted by *Green*  
_Here's my controller Idea._
_I want to put a slotted disk on the drive shaft with some infra red lasers and pickups to act as an encoder and generate a motor location signal that I will feed into some solid state relays that are hooked up to my batteries and capacitors. I would then vary my torque with a potentiometer on the main power supply to vary the amps. It would act as a variable speed but I wouldn't be trying to dictate motor position (aka rpm) I would just be dictating how much torque I want from the motor and I'd let the rpm govern itself._

I understand the idea to use the shaft mount encoder to generate a 3 phase square wave, but you need 3 phase to get the motor going in the first place. if you had a small dc motor just for the encoder, you might have a chance.


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## few2many (Jun 23, 2009)

few2many said:


> Originally Posted by *Green*
> _Here's my controller Idea._
> _I want to put a slotted disk on the drive shaft with some infra red lasers and pickups to act as an encoder and generate a motor location signal that I will feed into some solid state relays that are hooked up to my batteries and capacitors. I would then vary my torque with a potentiometer on the main power supply to vary the amps. It would act as a variable speed but I wouldn't be trying to dictate motor position (aka rpm) I would just be dictating how much torque I want from the motor and I'd let the rpm govern itself._
> 
> I understand the idea to use the shaft mount encoder to generate a 3 phase square wave, but you need 3 phase to get the motor going in the first place. if you had a small dc motor just for the encoder, you might have a chance.


 bullshooey


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## Green (Aug 6, 2009)

few2many said:


> I mentioned it, but wanted to elaborate a bit. anything times 0 (x0) is zero. if your motor speed is zero, youre slotted rotor wont be sending the signal to generate 3phase.


there will be a signal it would just have a frequency at zero and would increase as the motor rpm increases There would be a signal and stator poles with current thus an induced field and according to my thoughts rotation? if the magnetic poles on the stator and the induced field in the rotor are such that they wouldn't act to create rotor movement then i would have a problem. do you think this would be the case?

Thanks much

Here's my math

60 Hz signal = 3600 cycles per minute my motor rpm at 60 Hz is roughly 1745 which is slightly less than half, the difference being the slip. if I gear the signal encoder to run at twice the speed + slip then I'd have the right ratio for good alignment on the signal? or maybe I'm missing the Boat on this one? If so please enlighten me.


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## few2many (Jun 23, 2009)

Yes, absolutely that would be a problem. For that idea to do anything, youll either need to find a way to seperately start youre motor(think starter on an ICE), or have youre encoder set up on a seperate little dc motor. control the speed of the dc motor, control frq. Sorry, I must be missing something. you need frequency just to start the motor. sending amps to an induction motor will only create and mag field with high amps, you need a rotating frequency to actually start the motor turning. To say a frequency of zero? Zero has no value, its not a freq. A dc motor does this(kinda) with the brushes and so it needs no freq..


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## samborambo (Aug 27, 2008)

Green said:


> there will be a signal it would just have a frequency at zero and would increase as the motor rpm increases There would be a signal and stator poles with current thus an induced field and according to my thoughts rotation? if the magnetic poles on the stator and the induced field in the rotor are such that they wouldn't act to create rotor movement then i would have a problem. do you think this would be the case?
> 
> Thanks much
> 
> ...


Still way off base. Slip is proportional to torque in an induction motor. 

Are you trying to design a mechanical commutator because you don't understand how electronic commutation works? 

Are you trying to design an AC motor controller without knowing the characteristics of an AC induction motor?

Please, go back to the books. Learn everything there is to know about induction motors (and other types of motors for that matter) before going any further. Otherwise, you'll just keep going round in circles.

Sam.


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## major (Apr 4, 2008)

Green said:


> 60 Hz signal = 3600 cycles per minute. my motor rpm at 60 Hz is roughly 1745 which is slightly less than half, the difference being the slip.


No. The difference is a 4 pole motor.

You really do need to go back to the books, as Sam said.

Regards,

major


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## Green (Aug 6, 2009)

major said:


> No. The difference is a 4 pole motor.
> 
> You really do need to go back to the books, as Sam said.
> 
> ...


Thanks for the insight. 

I'll go hit the books a do a bit more studying....heres where I went page 378 
http://books.google.com/books?id=3Y...resnum=7#v=onepage&q=4 pole induction&f=false 

I didn't know what it was called but yeah I figured it had six windings and after reading a bit... 4 poles induced on the squirrel cage rotor and my motor has a slip factor of 1.15%. 1800 rpm with no load and 1745 at full load. 

I'm not convinced that my idea won't work though. from a stop I would start applying current to the windings inducing the 4 poles in the rotor and although there wouldn't be a frequency until the rotor had moved enough to switch some sensors, the relationship between the windings magnetic poles and the rotors magnetic poles should cause rotation...Right? 
and if so then I'd just run a direct 2 rotations on my encoder per 1 rotor rotation. I'd rather vary the current per what I want for torque and let the rpm float. 

Thanks again.
Green


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## major (Apr 4, 2008)

Green said:


> I'll go hit the books a do a bit more studying....heres where I went page 378
> http://books.google.com/books?id=3Y...resnum=7#v=onepage&q=4 pole induction&f=false


Hi Green,

Good start.



> 4 poles induced on the squirrel cage rotor and my motor has a slip factor of 1.15%. 1800 rpm with no load and 1745 at full load.


You want to show me your math on that?

Regards,

major


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## samborambo (Aug 27, 2008)

Green, the show-stopper for your mechanical commutator (apart from the slip issue) will be current regulation. In modern electronic motor controllers, voltage is regulated using pulse width modulation (PWM), a square wave signal with varying duty cycle (on vs. off time). The inductance of the motor windings acts as a low-pass filter, smoothing the square wave into an average voltage. Since the impedance and back-EMF voltage of the motor is known, this regulation of voltage also regulates current.

Prior to the viability of transistors to make PWM possible, Triacs were used on the incoming AC line voltage. These devices can turn on just like a transistor but can't turn off until current stops flowing through the switch. This is fine for AC input because the current returns to zero twice on each cycle of the AC waveform. To regulate the average voltage (an therefore current) through these devices, they would simply delay a certain time after the last AC zero crossing before turning on. It was crude, but effective, voltage control.

Another form of current regulation is used in old ARC/MIG welders by means of a gapped transformer. The gap limited the field intensity in the transformer core, effectively saturating the transformer and limiting the output current. An iron lug was able to move in and out of the core air gap to vary the reluctance of the magnetic circuit and therefore vary the current output.

Triacs and gapped transformers will not work for you because you have a DC source - the battery. You could have three gapped transformers after your commutation stage but these would be huge, heavy, expensive and fairly inefficient.

Your idea of using a potentiometer to limit current is not practical for high power systems. The losses (and therefore inefficiency) of the potentiometer will be huge. Consider a low voltage DC example: one 12V 20W DC motor on a fixed 12V voltage source and a potentiometer in series to regulate current. Lets assume the DC motor has a linear power response to voltage. Power consumed by a motor is load and speed dependent but linear response simplifies this example. The worst case power dissipation of the potentiometer is when the voltage across both devices is at 50%. At 50%, the total circuit resistance has doubled so the total power dissipation is 10W, 5W in the motor and 5W in the potentiometer. So the worst case efficiency (50%) is when the motor is outputting 25% power.

That's fine. 5W potentiometers are common and at such a low power level of a few Watts, we're not too worried about heat or efficiency. Now scale that up to a 20kW motor. You need a 5kW potentiometer and the overall system is at best 50% efficient at 25% power. You also need some way of getting rid of that 5kW of heat.

Sam.


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## few2many (Jun 23, 2009)

frq*120/#of poles=rpm?
60*120/4=1800 rpm


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## few2many (Jun 23, 2009)

without a starting frequency, the mag fields wont fight each other to force rotation.


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## Green (Aug 6, 2009)

major said:


> Hi Green,
> 
> Good start.
> 
> ...


Here's the .pdf of the motor I've got.
https://www.baldorvip.com/VIP/productInformation/P18G3889.pdf

I got these particular numbers off page 9. 

Thanks for taking the time to find the holes in my idea 

Green


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## Green (Aug 6, 2009)

few2many said:


> without a starting frequency, the mag fields wont fight each other to force rotation.


I plan on hooking this motor to the back wheels and having my oem drivetrain up front. If I got the system spinning first and then increased current to the three phase? sort of a starter like mentioned before. Would that work?

Thanks much
Green


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## Green (Aug 6, 2009)

samborambo said:


> Green, the show-stopper for your mechanical commutator (apart from the slip issue) will be current regulation. In modern electronic motor controllers, voltage is regulated using pulse width modulation (PWM), a square wave signal with varying duty cycle (on vs. off time). The inductance of the motor windings acts as a low-pass filter, smoothing the square wave into an average voltage. Since the impedance and back-EMF voltage of the motor is known, this regulation of voltage also regulates current.
> 
> Prior to the viability of transistors to make PWM possible, Triacs were used on the incoming AC line voltage. These devices can turn on just like a transistor but can't turn off until current stops flowing through the switch. This is fine for AC input because the current returns to zero twice on each cycle of the AC waveform. To regulate the average voltage (an therefore current) through these devices, they would simply delay a certain time after the last AC zero crossing before turning on. It was crude, but effective, voltage control.
> 
> ...


If my encoder spun at double the motor rpm. would the slip issue be a show stopper? would I have to start the system spining before turning on the current? or would the magnetic fields from the windings induce some sort of initial rotation to get things moving?
I had planned on having my batteries in series adding up to roughly 460 volts using a maximum constant amperage of 6.5 and a maximum amperage of roughly 30 - 35 amps for a very short period of time. And with losses like you illustrated above obviously a potentiometer would be very inefficient and wasteful of my precious battery power. 

As for the pulse width modulation It sounds like a nice and efficient way to go. And probably the only real way to go. Obviously I hadn't given enough thought as to how I would vary the amperage to my motor. I'll read up on PWM and learn a bit more about how I could implement it. 

Thanks again for you're insight. 

Green


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## major (Apr 4, 2008)

Green said:


> Here's the .pdf of the motor I've got.
> https://www.baldorvip.com/VIP/productInformation/P18G3889.pdf
> 
> I got these particular numbers off page 9.


Hi Green,

From your previous post


> slip factor of 1.15%


S.F. in the motor spec means *service factor*, not slip. At least you're looking at some good educational stuff.

Regards,

major


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## samborambo (Aug 27, 2008)

Green said:


> If my encoder spun at double the motor rpm. would the slip issue be a show stopper? would I have to start the system spining before turning on the current? or would the magnetic fields from the windings induce some sort of initial rotation to get things moving?
> I had planned on having my batteries in series adding up to roughly 460 volts using a maximum constant amperage of 6.5 and a maximum amperage of roughly 30 - 35 amps for a very short period of time. And with losses like you illustrated above obviously a potentiometer would be very inefficient and wasteful of my precious battery power.
> 
> As for the pulse width modulation It sounds like a nice and efficient way to go. And probably the only real way to go. Obviously I hadn't given enough thought as to how I would vary the amperage to my motor. I'll read up on PWM and learn a bit more about how I could implement it.
> ...


Green, I like your creative brainstorming and don't want to discourage it. I think thre's still lots of things that haven't yet been done with electric vehicles which is very encouraging. ICE technology has been flogged like a dead horse.

Sam.


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## Dennis (Feb 25, 2008)

> Your idea of using a potentiometer to limit current is not practical for high power systems. The losses (and therefore inefficiency) of the potentiometer will be huge. Consider a low voltage DC example: one 12V 20W DC motor on a fixed 12V voltage source and a potentiometer in series to regulate current.
> 
> 
> Lets assume the DC motor has a linear power response to voltage. Power consumed by a motor is load and speed dependent but linear response simplifies this example. The worst case power dissipation of the potentiometer is when the voltage across both devices is at 50%. At 50%, the total circuit resistance has doubled so the total power dissipation is 10W, 5W in the motor and 5W in the potentiometer. So the worst case efficiency (50%) is when the motor is outputting 25% power.


I want to make sure I am comprehending here what you telling Green here is that a motor at 50% efficiency is 25% output power? You do know don't you of the maximum power transfer theory that stats maximum power is delivered to a load when the thevenin equivalent resistance is equal to the load resistance or also it can be stated when the load is 50% efficient? So output power would be 100% (aka the MAX) not 25%.


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## samborambo (Aug 27, 2008)

Dennis said:


> I want to make sure I am comprehending here what you telling Green here is that a motor at 50% efficiency is 25% output power? You do know don't you of the maximum power transfer theory that stats maximum power is delivered to a load when the thevenin equivalent resistance is equal to the load resistance or also it can be stated when the load is 50% efficient? So output power would be 100% (aka the MAX) not 25%.


Dennis, go and find out what a resistive divider network is. Specifically, the relevant power equation.

Sam.


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## Dennis (Feb 25, 2008)

> Dennis, go and find out what a resistive divider network is. Specifically, the relevant power equation.
> 
> Sam.


The power dissipation in a series divider network has the largest resistor having the most power dissipation. This is something all EE's and EET's have learned about in their first electronics course...

However, what you are telling Green about power delivered to the motor has nothing to do with unbalanced divider networks. You said 50% efficiency for the motor which clearly means the voltage divider has both ohm values the same value (the thevenin equivalent and load) and also means voltage is half and the efficiency is 50%. So that changes things a bit. Have you ever dealt with audio circuits? Specifically maximum power transfer to the speaker which can achieved by having the source impedance match the load impedance. The same concept can be applied to any load whether it be a motor or resistor. 


So I shall help you see what I mean. Let's take a hypothetical motor that has one ohm of total internal impedance and lets set a rheostat to a value that when summed to the total battery impedance and wiring impedance that the value becomes one ohm as well. The power supply will be 12 volts and the motor will be loaded at various levels to meet a specific back EMF voltage. 




Here is the circuit:



















Now lets apply some load to the motor such that the following back EMF of the motor occurs:




10 volts
9 volts
8 volts
7 volts
6 volts
5 volts
4 volts




The currents are ((Vs-VEMF)/Rm):


1 amps
1.5 amps
2 amps
2.5 amps
3 amps
3.5 amps
4 amps

Now to the fun part, mechanical power (I*back EMF):

10 watts 
13.5 watts
16 watts
17.5 watts
18 watts <----MAX
17.5 watts
16 watts

Efficiency (Pout/Pin*100):



83.3%
75%
66.6%
58.3%
50% <---- at MAX power output
41.6%
33.3%

What is clearly evident is that a DC motor at 50% efficiency is developing maximum horsepower which will be 100% power (ie the peak HP) not 25%...If your post to Green, meant something different then let me know.


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## samborambo (Aug 27, 2008)

Dennis said:


> The power dissipation in a series divider network has the largest resistor having the most power dissipation. This is something all EE's and EET's have learned about in their first electronics course...
> 
> 
> What is clearly evident is that a DC motor at 50% efficiency is developing maximum horsepower which will be 100% power (ie the peak HP) not 25%...If your post to Green, meant something different then let me know.


Dennis, the simplified example I gave was to show Green the effects of a voltage divider / potentiometer circuit. The assumption was that the motor is a fixed DC resistance (which, of course, it isn't).

If the potentiometer resistance is equal to the motor, the total resistance will be double and the motor will be at half the system voltage and half the current, therefore 25% power. The potentiometer will be dissipating the same power as the motor, therefore the motor/potentiometer is at 50% efficiency.

Sorry if it wasn't that clear.

Sam.


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## abudabit (Sep 18, 2008)

If you're gonna do a 3 phase motor induction motor I highly recommend at the very least a V-F controller (a basic open loop control technique) using modern power electronics and pwm generated sine waves.

I'm building my first 3 phase ACIM controller and I decided to jump right into Field Oriented Control... I wouldn't have the balls to do it normally but Microchip has some amazing documentation and example source code on the subject:

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en019806

That's just one example. But if you look at the page for one of their motor control DSP's you will find tons of application notes. Here is one for example (scroll down):

http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en537165

With FOC you will get (although I could be wrong):  Greater efficiency, greater bang for buck on the motor, greater power to weight, better control

It takes longer to implement the source code but I figure if my FOC attempts fail I can still use the exact same PCB for V-F control - which is simple with a DSP. 

Also there is a dedicated V-F chip if you don't want to mess with source code at all: MC3PHACVDWE (look it up on digikey for example). Use mosfets or IGBT's with that. It is still more efficient than using some old school tech and just as simple to implement.


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## Green (Aug 6, 2009)

Thanks Guys for the all the informative input. 

Most of the VFD's that I've run across the driver selects a frequency with a dial etc. and the controller sends whatever amps it takes to get there. Are there VFD's that go the other way around one selects and amperage and the frequency ends up wherever due to load? 
I think that's what I'm looking for. I'd also love to have some sort of regenerative braking and I'm sure that there are some EV AC controllers out there that do all of the above. Does anybody know of a nice one? or where to look?

Thanks again.


Also I have a few of these motors. 
If anybody thought it was what they were looking for I'd be happy to work something out with them.
They're in great shape never used etc.


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