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Author Topic: Electric DC motors  (Read 1499 times)

Angus64

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Electric DC motors
« on: March 06, 2012, 11:36:51 AM »

Hi Boys. I am back with another question, can anyone tell me how to tell how many poles there is in a 12V DC  electric motor. I guess it is pretty obvious if you know what to look for, Make it simple I'm no electrician. Thanks.
   
  Angus. 
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Re: Electric DC motors
« Reply #1 on: March 06, 2012, 11:40:47 AM »

They have to have at least three to be self starting. After that it varies from motor to motor. Generally motors wound for torque and low speed have more poles, so the windings don't get too hot. High quality motors tend to have 7 poles or more, and are very smooth running.

essex2visuvesi

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Re: Electric DC motors
« Reply #2 on: March 06, 2012, 01:15:37 PM »

3 or 5 poles is the norm for brushed DC motors in the "Hobby" range
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Re: Electric DC motors
« Reply #3 on: March 06, 2012, 01:42:06 PM »

Anything over 5 poles can cause problems with some esc's
Action does a multipole esc I believe.

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malcolmfrary

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Re: Electric DC motors
« Reply #4 on: March 06, 2012, 01:47:37 PM »

Easiest way to find out how many your motor has is to hold the shaft in a pair of pliers withe the terminals uppermost, note the position of the tag with the red dot, and slowly rotate the motor, counting the number of times the motor resists, until you get to where you started, then divide by 2.  Normally an odd number.
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Re: Electric DC motors
« Reply #5 on: March 06, 2012, 01:55:24 PM »

Anything over 5 poles can cause problems with some esc's

That's a new one on me- how and why?

ACTion

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Re: Electric DC motors
« Reply #6 on: March 06, 2012, 03:43:32 PM »

That's a new one on me- how and why?
The more poles then the more efficient a generator the motor becomes when "coasting" between signal pulses, so the back-EMF increases drastically. This can damage some MOSFET devices (e.g. the NDP6060L type fitted to our standard Condors), so we fit SmartFETs to the P79S and P80S. These, as their name suggests, are pretty much bomb-proof, but they are hellish expensive.  The P93 and P98 are totally different, more up-to-date designs and have efficient 'flywheel' circuitry, so they will run multipole motors without those problems.
Dave M
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Re: Electric DC motors
« Reply #7 on: March 06, 2012, 03:50:36 PM »

Thanks for that Dave
I knew it was to do with the back EMF produced by multipole motors
but I did not want to give the wrong info out on here.

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Re: Electric DC motors
« Reply #8 on: March 06, 2012, 05:26:59 PM »

Okay. I'm aware of back EMF, I thought this was dealt with effectively using the free-wheeling diodes built into the Mosfets. Certainly never blown a controller to date.

Angus64

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Re: Electric DC motors
« Reply #9 on: March 08, 2012, 12:29:35 AM »

Ok, I'm starting to get the picture (I told you I'm no electrician,) Can you tell with a striped down motor on the work bench by counting the number of windings on the armature.& if your not thoroughly confused by now you should be, I know it has to do with the magnetic fields & I know pretty well how the PM DC motor works, If I could see the poles it would be great but it's a bit like electricity you can't see that either. Dave at Action knows the motors. I am still trying to find a ESC that will run these motors because I have three of them & would like to be able to use them.

     Angus.
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Re: Electric DC motors
« Reply #10 on: March 08, 2012, 07:14:46 AM »

Well that looks like a thirteen pole motor to me. You can see the poles- the prongs on the armature stator indicate that, or just count the segments on the commutator. It's got nothing to do with the winding of your motor.

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Re: Electric DC motors
« Reply #11 on: March 08, 2012, 10:02:46 AM »

Power from a motor is determined, among other things, by the amps that can be passed through the windings, and by the number of turns in those windings.  Usually expressed as ampere-turns.  Generally, bigger, thicker wires mean more current, therefore more power, but you can only get so much wire into the space available.  You can only dissipate so much power into a given space as well, before things start to melt.
The number of poles is equal to the number of segments on the commutator, thick wire indicates a high current (probably at a low voltage), thinner wire probably a higher voltage motor at a lower current.
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Angus64

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Re: Electric DC motors
« Reply #12 on: March 08, 2012, 10:06:52 PM »

Thanks boys, you explaining how that works I can understand that now. I have had a lot of people from electronics stores telling me these motors wouldn't have 13 poles, I knew Dave from Action wouldn't get that one wrong. There is a place here in Australia that sells Action electronics P98 ESC but I have forgotten who it is so I will have to do a bit of searching & locate them, If I can't find them I will send a email to Action he may be able to help. Thanks to all who replied to my post.

   Angus
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