Differences And Types Of Dc Motors

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

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

ironmonger said:

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

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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

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

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.

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.

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

thanks, Brian

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.

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:

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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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

Click to expand...

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.

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.

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.

Click to expand...

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

Stuart