# Differences And Types Of Dc Motors



## calstar (Mar 4, 2015)

There are three basic types of dc motors: (1) Series motors, (2) shunt motors, and (3) compound motors. They differ largely in the method in which their field and armature coils are connected.

*Here's a link to what seems like a good summation of DC motors for those like myself that want to learn more about them:* http://avstop.com/ac/apgeneral/typesofdcmotors.html

Another link to Shars extolling the type their DC compound powered  feeds use(Im including this just because I saw it recently, probably not a great source for info !)
http://www.shars.com/products/view/20355/APX150_Milling_Machine_Power_Feed_X_Traverse_150_Lbs

Power and speed graphs:

from shars



from the first link, looks like shars in the above  graph kinda skewed the data in marketing




Theses motors are available on ebay from several venders, they don't say what type they are but they do have brushes




http://www.ebay.com/itm/DC-MOTOR-1-2HP-56C-90V-1750RPM-TEFC-PERMANENT-MAGNET-/251581341980

I'm interested in using a DC motor and pwm(power wave modulator for the unenlightened like myself) on my small Clausing mill(for variable speed control and greater torque than an AC motor) and I would appreciate any thoughts/ideas from those having experience/knowledge of DC motors in this application.

thanks, Brian


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## ironmonger (Mar 4, 2015)

Hi Brian
The motor that you have pictured is a Permanent magnet motor. The field winding is replace by permanent magnets, and it is close to a shunt would motor in characteristics. The PWM is pulse width modulation. This speed control applies full voltage but  only for a percentage of the time. Full power is just on where 50% power might be on for 25 milliseconds and then off for 25 milliseconds. Gives better starting torque at lower speed. The PM motors still have brushes. 

Series wound motors, like a typical automotive starter motor, have super low end torque and are also called traction motors in larger sizes. The have very poor speed regulation and will draw a lot of current to start. Larger ones require a special motor starter to limit inrush current. The permanent magnet motor would prolly work well for your application, but don't over look a VFD and a three phase motor, especially if your mill came with one in the first place.

Have fun

paul


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## calstar (Mar 4, 2015)

ironmonger said:


> Hi Brian
> ....The* PWM is pulse width modulation*. ...
> Have fun



Knew I should of checked what PWM was, just pulled that out of thin air I guess, slightly embarrassing but not the first time its happened (and not the last).  I am, after all, unenlightened!

_"The permanent magnet motor would prolly work well for your application, but don't over look a VFD and a three phase motor, especially if your mill came with one in the first place."_

I have given that some thought but I'm thinking the DC and a PWN is less $ and I can't see any advantage the 3phase has over it(please enlighten as needed).The mill came with a single phase, otherwise I would think its a toss up $ wise.

Is a permanent magnet motor one of the three types of DC listed above or an entirely different kind?

thanks,
Brian


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## ironmonger (Mar 4, 2015)

The PM motor closely resembles the shunt wound motor in performance. The only drawback to any brushed DC motor is the brushes. They do wear out, there is sparking to some degree, so one needs to be mindful of combustible atmospheres. Not a great hazard. but there it is. The brush wear in a home shop might not ever be a concern.

I kind of like VFD's and the biggest difference is the ability to run at a higher speed than the nameplate by raising the frequency. You can't do that with DC stuff without raising the voltage, and that is not going to be good for the motor in the long run. Somewhat similar problems can exist for AC motors in the form of excess heating at really high speed (read frequency). 

I don't want to seem to put down DC motors, I have a 25 horsepower GE motor that I purchased to build an electric car... so I must like them a little bit. It has a 1.75" shaft, is around 11" in diameter and is about 19" long... Now that’s a motor... And big DC series wound motors make enough torque to really break stuff. Scary big torque.

DC stuff has some what less exotic controls, but electronically the difference in complexity between a PWM power supply and a VFD is not that great. They both need to handle similar wattage loads. In a SHTF situation you could run your mill on batteries though... maybe go solar :>)

What's cheaper and at hand is a biggie.

paul


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## great white (Mar 4, 2015)

Personally, I'm going the DC motor route for my drill press and my atlas th42.

Danfoss cyclotrol 150 controllers are 30-40 bucks on eBay and offer start/stop/job/brake/emergstop/tach inpiut/speed control and I like the DC motor characteristics.

The drill press is getting a repurposed treadmill motor and the lathe will get a purpose bought motor (haven't narrowed down the specs yet).

Is it perfect? Probably not. But more than adaquate for my quiet little home shop.


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## calstar (Mar 4, 2015)

great white said:


> *Danfoss cyclotrol 150 controllers* are 30-40 bucks on eBay and offer start/stop/job/brake/emergstop/tach inpiut/speed control and I like the DC motor characteristics.



Please supply a link for these controllers, the only ones I saw on ebay are $150.

thanks,  Brian


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## atunguyd (Mar 4, 2015)

My mill came with a variable speed DC motor very similar to the one in that picture. After about a year of operation it started to spark excessively at anything over 60% speed. When I contacted the supplier (I had since moved countries) and he told me he no longer supplies this model as "they go through brushes at a rate".  This I found to be true and I was replacing brushes every 6 months. 

In January I was replacing the brushes and while testing the motor there was a sort and I ended up frying both the motor and the controller. 

After discussions with a local motor supplier I decided to go for a similarly rated AC motor with a VFD. 

From my experience I can tell you this :

1. The PM  DC motor is physically smaller than the equivalent AC one.  The supplier had to order three motors till they found one that would fit the space on my mill head. 

2. The AC motor is much quieter, I only realised now how much of the mills noise was from the motor alone. 
3. For me the AC motor seems to run smoother. There feels like I lot less vibration now. I attribute this to the fact that the PWM controller will cause the DC motor to apply power in  pulses. 

4. As stated above, the VFD has a lot more adjustability and provides superior protection to the motor. 

5. I am told that the DC motors are expensive. 

In summary I am very happy with the 3 phase motor in place of the DC one however had my DC motor not packed up I don't think I would have justified the expense of the change even knowing what I know now.


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## stupoty (Mar 5, 2015)

The issue i've always had when looking to use DC motors has always been the transformer or power supply required to knock the voltage down.

Stuart


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## great white (Mar 5, 2015)

stupoty said:


> The issue i've always had when looking to use DC motors has always been the transformer or power supply required to knock the voltage down.
> 
> Stuart



That what the cyclotrol does. They come in 110 and 220 models. I do believe the 220 models go higher in max voltage out though. The 110 does 90v, I can't recall bit I think the 220 does 110 v.



calstar said:


> Please supply a link for these controllers, the only ones I saw on ebay are $150.
> 
> thanks,  Brian


Sorry, you have to watch for them and grab em when they show up. Its eBay, lots of people still try to get too much for stuff on eBay. You have to watch for the fair deals to show up.

This is the last one I bought for 35 bucks. Auction is over and no more left: http://www.ebay.ca/itm/161288514776?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

I offered 35 and he took it.

I've seen em on offer for 40-50 bucks and auctions go 30-40 final price. But they go quick at those prices. You have to hunt for them if you want them at a good price. Same as a vfd on eBay. I've never seen them sell much under 150 bucks, but I'm sure they go cheaper than that, I've just never seen it.

I'm not looking to sell anyone on DC motors, just stating how I'm going.


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## stupoty (Mar 6, 2015)

great white said:


> That what the cyclotrol does. They come in 110 and 220 models. I do believe the 220 models go higher in max voltage out though. The 110 does 90v, I can't recall bit I think the 220 does 110 v.
> 
> 
> Sorry, you have to watch for them and grab em when they show up. Its eBay, lots of people still try to get too much for stuff on eBay. You have to watch for the fair deals to show up.
> ...



Sorry if i'm just being slow, is that a BLDC motor controller ? Or a pwm dc motor controller?

Stuart


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## great white (Mar 6, 2015)

stupoty said:


> The issue i've always had when looking to use DC motors has always been the transformer or power supply required to knock the voltage down.
> 
> Stuart





stupoty said:


> Sorry if i'm just being slow, is that a BLDC motor controller ? Or a pwm dc motor controller?
> 
> Stuart



Dunno for sure. Documentation doesn't spell it out in layman's terms.

Says good up to 60 CPM for cycle duty permanent magnet motors, so I'll guess pwm.



> Graham's Cycletrol® Series DC adjustable speed controls provide rapid cycling capabilities, while offering higher reliability and lower maintenance compared to clutch/brake mechanisms. The Cycletrol Series consists of two product lines, the 150 Series rated for up to 60 cycles/minute and the C2000 rated for up to 30 cycles/minute.
> COMMON FEATURES:
> All Cycletrol digital logic inputs are optically isolated
> Versatile logic allows direct interfacing with switches and push-buttons or solid state devices
> ...



I can get around with electrical work, but I'm no engineer. Perhaps one of the "electrogeeks" on the forum can shed some light on the specs.


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## hman (Mar 7, 2015)

Great White -
I just looked on eBay and, amongst the many expensive units saw several that were under $80.  All of them, however, were rated for a 1/8 to 1 horsepower motors.  So be cautious.  I've seen lots of treadmill motors that are (at least claim to be) in the 2.5 to 3 HP range.  Check yours!


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## RJSakowski (Mar 7, 2015)

One consideration in choosing a DC brush motor with PWM vs. 3 phase with VFD is electrical noise.  Because of the commutator switching at high current loads, a significant amount of RF noise is generated.   If you plan to use a DRO, it could be a headache trying to eliminate the interference.


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## RJSakowski (Mar 7, 2015)

calstar said:


> There are three basic types of dc motors: (1) Series motors, (2) shunt motors, and (3) compound motors. They differ largely in the method in which their field and armature coils are connected.


It appears that the axes are reversed in the above graph.  Torque should be on the y axis and speed on the x.  One should also understand that the graphs are normalized.  A 1 hp differential compounded motor will have a lower  low end torque than a 1 hp cumulative compounded motor.


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## timvercoe (Mar 7, 2015)

Great article.  Thanks for posting.  I've been rebuilding starters and alternators for 34 yrs now and my understanding of how they work has been greatly enhanced by reading your posting.  I've been considering the purchase of an old Heavy Duty LeBlond lathe that originally had a motor that would run at about 20 different speeds.  It could be "shifted" electronically linearly from the apron.    It has been converted to a 3 phase motor  and a 4 speed transmission added to replace the variable speed motor.  I also have a 5 hp DC motor rated 180 to 240 volts.  I had understood that the torque would be pretty close to 10 hp 3 phase.  After reading your link, I now understand how that would be.  I was considering using the 5hp on the LeBlond.  It may be a little under powered, as the lathe is a 33" by 8'.  but if worked would re-establish the way it was originally designed.   If I purchase the lathe might be worth a try.    

Thanks again for posting,     Tim


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## great white (Mar 7, 2015)

RJSakowski said:


> One consideration in choosing a DC brush motor with PWM vs. 3 phase with VFD is electrical noise.  Because of the commutator switching at high current loads, a significant amount of RF noise is generated.   If you plan to use a DRO, it could be a headache trying to eliminate the interference.



No worries. Not a factor. This is only an old th42 its going on. I don't do extensive work on a lathe, just a few things for my cars and motorcycles.



hman said:


> Great White -
> I just looked on eBay and, amongst the many expensive units saw several that were under $80.  All of them, however, were rated for a 1/8 to 1 horsepower motors.  So be cautious.  I've seen lots of treadmill motors that are (at least claim to be) in the 2.5 to 3 HP range.  Check yours!



Not too worried. Its an experiment as much as anything else.


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## John Hasler (Mar 7, 2015)

RJSakowski said:


> It appears that the axes are reversed in the above graph.  Torque should be on the y axis and speed on the x.


The graphs are often presented that way.  However, the horizontal axis should be labeled torque, not power.  Power is the product of speed and torque.


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## RJSakowski (Mar 7, 2015)

John Hasler said:


> The graphs are often presented that way.  However, the horizontal axis should be labeled torque, not power.  Power is the product of speed and torque.


Got it!  It seemed strange at first, but if you think that torque is proportional to applied current, then speed would be the dependent variable.  It also makes sense in that any d.c. motor has a maximum speed and that is where the applied torque equals the frictional losses, etc.  Otherwise, the motor would keep on reving until it self destructed.


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## John Hasler (Mar 7, 2015)

RJSakowski said:


> Got it!  It seemed strange at first, but if you think that torque is proportional to applied current, then speed would be the dependent variable.  It also makes sense in that any d.c. motor has a maximum speed and that is where the applied torque equals the frictional losses, etc.  Otherwise, the motor would keep on reving until it self destructed.


That is exactly what large series motors will do if  operated at full voltage with no load and no current limiting.  Large shunt motors will also overspeed to destruction if you interrupt their fields when they are running at full speed with no load.  However, with its field properly excited a shunt motor has a fixed no-load speed where the back emf due to generator action equals the applied voltage.


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## ironmonger (Mar 7, 2015)

As I understand it, the runaway situation only presents itself with series wound motors, especially larger ones. The shunt motors are self limiting, as are the compound motors AFAIK.

My motor theory is in the distant past, it's something to do with back emf induced in the armature I think. And while I have no experience with DRO's (but I would like to ) but do have experience with RF interference, the brush noise is a definite consideration.

Most of the things that we do in our home shops that are not for profit ventures depend on the material on hand. So in that light, using a motor that you have is superior to not using a tool because you don't have the BEST motor. 

I have found that large 3 phase motors are much easier to find than large single phase motors. And both of those are easier to find than large DC motors. A lot of the larger surplus DC motors were rated for fork lift service. In that use they drive a pump, which presents no radial load on the armature. Transferring 5 HP though anything that present a radial load would likely be a problem for long term survival of the motors bearings. I hate to build something around a part that will fail and then cause an major redesign...

paul


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## John Hasler (Mar 7, 2015)

ironmonger said:


> As I understand it, the runaway situation only presents itself with series wound motors, especially larger ones. The shunt motors are self limiting, as are the compound motors AFAIK.
> 
> My motor theory is in the distant past, it's something to do with back emf induced in the armature I think. And while I have no experience with DRO's (but I would like to ) but do have experience with RF interference, the brush noise is a definite consideration.
> 
> ...


Large shunt motors can overspeed when their fields are interrupted under full speed no load conditions because all of the energy stored in the magnetic fields gets converted to kinetic energy of the spinning armature.  You don't see this with small motors because they have large losses relative to the amount of stored energy as well as a large margin between rated speed and destruct speed.


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## f350ca (Mar 7, 2015)

On the subject of DC motors. My Hardinge lathe uses Im assuming a shunt wound motor on the carrage. But they separated the field and armature windings, feeding full dc power to the fields while varying the voltage to the armature for speed control. Why? Better low speed torque? Its the first time in my limited experience I've seen this done.

Greg


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## John Hasler (Mar 7, 2015)

f350ca said:


> On the subject of DC motors. My Hardinge lathe uses Im assuming a shunt wound motor on the carrage. But they separated the field and armature windings, feeding full dc power to the fields while varying the voltage to the armature for speed control. Why? Better low speed torque? Its the first time in my limited experience I've seen this done.
> 
> Greg


You want full field excitation for maximum torque and good speed regulation.  Note that most small DC motors these days are PM and so have no field windings.


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## RJSakowski (Mar 7, 2015)

Out of curiosity, how do 3 phase 60 hz motors fare when when controlling with a VFD at frequencies much lower or higher than 60 hz?


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