# 8 pole series dc motor alternating polarities to coils

Joined May 27, 2018
12
Hello All. I'm new to forums and only have basic electronics knowledge. I have searched for months all over the Web for an answer to how to electronically control a dc motor/generator I have built. I can run the motor with no problems of a mechanical commutator with four copper bars to alternate polarity to coils which are set up in series. The rotor consists of 8 permanent magnets that are north and south. My question is hopefully someone can help me with a circuit design I can use along with a hall effect vane sensor with a vane that is timed the same as the mechanical commutator. I'm hoping to use the output signal to trigger a transistor, mosfet or relay type circuit. I would greatly appreciate any help.
Regards
Ben

#### ericgibbs

Joined Jan 29, 2010
19,003
hi Ben,
Welcome to AAC.
Could you post details of the motor/gen voltage, current and running rpm etc.?
Any additional electromechanical info will help.
E

#### Alec_t

Joined Sep 17, 2013
14,379
How many coils and how are they arranged?

Joined May 27, 2018
12
hi Ben,
Welcome to AAC.
Could you post details of the motor/gen voltage, current and running rpm etc.?
Any additional electromechanical info will help.
E
Hi E. The voltage I'm hoping to run at 12 or 24 volts it wI'll run on aNY voltage between 9-240vdc. Rpm obviously varies with voltage input aprox 80 rpm @ 12 volts.. I havent actually measured it but I can do... sorry for some of the wording my selective text won't let me correct it

#### ericgibbs

Joined Jan 29, 2010
19,003
hi B,
Ref the Hall device, do you want a pulse every motor pole, say 8 per rev or just once a rev of the shaft.
Are you planning to control the motor to gen voltage by varying the current coil of the Gen Field winding.?
A simple diagram would help us to suggest solutions.
There are many MOSFET's that could handle the voltage you have mentioned, what about load currents etc.
E

Joined May 27, 2018
12
How many coils and how are they arranged?
It has 8 coils wired in series.
hi B,
Ref the Hall device, do you want a pulse every motor pole, say 8 per rev or just once a rev of the shaft.
Are you planning to control the motor to gen voltage by varying the current coil of the Gen Field winding.?
A simple diagram would help us to suggest solutions.
There are many MOSFET's that could handle the voltage you have mentioned, what about load currents etc.
E
Hi Eric
Sorry I thought you had "e" as your user name. So what has to happen is 4 pulses every rotation... I think (I'm still trying to grasp exactly how it works) My mechanical commutator has 4 copper segments on it at 90 deg each piece of copper. It has two brushes that contact the copper segments as the shaft rotates. This is where the polarites are alternated. Ill send a wiring diagram. How do I upload a picture?

#### ericgibbs

Joined Jan 29, 2010
19,003
Hi,

E

Joined May 27, 2018
12
How many coils and how are they arranged?
It has 8 coils wired in series.
hi B,
Ref the Hall device, do you want a pulse every motor pole, say 8 per rev or just once a rev of the shaft.
Are you planning to control the motor to gen voltage by varying the current coil of the Gen Field winding.?
A simple diagram would help us to suggest solutions.
There are many MOSFET's that could handle the voltage you have mentioned, what about load currents etc.
E
Hi Eric
Sorry I thought you had "e" as your user name. So what has to happen is 4 pulses every rotation... I think (I'm still trying to grasp exactly how it works) My mechanical commutator has 4 copper segments on it at 90 deg each piece of copper. It has two brushes that contact the copper segments as the shaft rotates. This is where the polarites are alternated.

Joined May 27, 2018
12
The Hall vane sensor is a honeywell sr17

Joined Jul 18, 2013
28,769
The Hall vane sensor is a honeywell sr17
Wouldn't a Slot Opto been much cheaper?
About a 10th of the price!.
Max.

Joined May 27, 2018
12
The Hall vane sensor is a honeywell sr17
H
It has 8 coils wired in series.

Hi Eric
Sorry I thought you had "e" as your user name. So what has to happen is 4 pulses every rotation... I think (I'm still trying to grasp exactly how it works) My mechanical commutator has 4 copper segments on it at 90 deg each piece of copper. It has two brushes that contact the copper segments as the shaft rotates. This is where the polarites are alternated.
Hi again Eric. I cant seem to upload the electrical diagram. I've tried a couple of times now. I assume the file will show up in our conversation time line??

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#### Alec_t

Joined Sep 17, 2013
14,379
That's an unusual coil arrangement.
If the commutator is just pulsing all 8 coils simultaneously, won't the rotor spin direction (if the rotor ever starts moving) be random, independent of the supply voltage polarity?

Joined May 27, 2018
12
That's an unusual coil arrangement.
If the commutator is just pulsing all 8 coils simultaneously, won't the rotor spin direction (if the rotor ever starts moving) be random, independent of the supply voltage polarity?
No. It will run either direction smoothly depending of course with polarity. Its a difficult one to understand..

#### Alec_t

Joined Sep 17, 2013
14,379
a mechanical commutator with four copper bars to alternate polarity to coils which are set up in series
How can the commutator shown alternate the polarity when it is simply in series in the +ve wire?

Joined May 27, 2018
12
How can the commutator shown alternate the polarity when it is simply in series in the +ve wire?
I'm not sure. As I said I'm a novice when it comes to fully understanding current and voltage and electromagnets. Doesn't dc power change its direction when it is switched somehow? Like ac power would/does alternate..? Im very likley to be asking the wrong questions within this thread but I'm trying my best with the limited understanding I have. I understand how 3 phase motors etc work... but this even though it's single phase it's harder for me to understand.

Joined May 27, 2018
12
Wouldn't a Slot Opto been much cheaper?
About a 10th of the price!.
Max.
Hi Max, they are about the same in price from where i bought them. Im thinking of going over to an optical version which is a straight swap as i believe they are a little more accurate in switching, but ill wait and see how they magnetic version goes first.

Joined Jul 18, 2013
28,769
Hi Max, they are about the same in price from where i bought them. .
At DigiKey the SR17 is ~$20.00 , the slot opto ~$1.50.
Max.

Joined May 27, 2018
12
At DigiKey the SR17 is ~$20.00 , the slot opto ~$1.50.
Max.
Wow. Rs components here in Aus are priced the same for each. Ill get onto an opto..

Joined May 27, 2018
12
How can the commutator shown alternate the polarity when it is simply in series in the +ve wire?
Hi Alec.
After reading more to get a proper understanding you're absolutely correct about it being in series through the commutator. I will get there... so now my understanding is I don't need to alternate polarities at all, and what I need to do is just provide the dc power to the series coil set at the correct time on and then time off... or it could be pulsed I reckon. Either way... do you know of a circuit that I can use and trigger or switch the power to the series coils via my 3 wire vane sensor I have? Sorry for all the confusion...
Cheers. Ben.

#### Alec_t

Joined Sep 17, 2013
14,379
I can't see how your arrangement can work, except perhaps in a way analagous to an electrically maintained pendulum. I suggest you google circuits for that.