# 24 volt DCS and 12 volt motors



## machiningfool (Nov 15, 2008)

I am powering a locomotive diesel with the electronics from MTH that supplies 24 volts battery power via a TIU to the motors, but having to use NWSL three axle trucks, the motors are 12 volts. Usually the motors, one motor in each truck are wired in parallel, but what if I wired the two motors in series, would I then have the equivalent of one 24 volt motor. I don't know, that is why I would like one of the members to answer this as while I am no dummy to electric power, I do not know the answer to this one. I know if I run the 24 volts to a 12 volt motor, I suppose I could run around a half power and it would not hurt the motor, but if they were wired in series, could I then go to full power as if they were one 24 volt motor? I would appreciate any help, thank you.


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## Michael Glavin (Jan 2, 2009)

Two 12V DC motors connected in series with 24V potential is best IMO. Like current will be adsorbed by both motors netting equal/MAX torque values offering greater efficiency while operating within the motors performance/RPM/efficiency curve. 

Connected in parallel, the motor(s) unequal internal resistances (IR) will generate waste and heat. The motor that operates with less resistance will run faster and more efficiently, while the motor with higher resistance operating at lower RPM will act as a brake! And 24V will more likely than not prematurely wear out 12V motors, albeit at the luxury of greater speeds.

Utilizing for discussion a [email protected] DC power supply:

Hypothetically speaking, two 12V motors powered with 24VDC; wired in series can and will *each* consume the motors Full-Load-Amperage rating of lets say (5A) @ 12V or 10A net. 10Ax12V=120 Watts.

Same two 12V motors wired in parallel supplied 24v will *each* operate @ half the rated amperage (2.5A) @ 24V or 5.0A net. Resulting in slower acceleration (less torque), BUT greater speeds. 5.0Ax24V=120 Watts. 

In addition to IR mentioned above, BEMF (back Electromotive Force) of DC motors plays a role herein too. *Back electromotive force* refers to the voltage that occurs in DC motors where there is relative motion between the motors armature and the presence of an external magnetic field. The aforementioned BEMF voltage is directly proportional to the RPM/speed of the motor, magnetic field generated and length of wire in the armature. Once the BEMF voltage is matched/equaled/overcome by the externally supplied voltage/power its a moot consideration.

Michael


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## machiningfool (Nov 15, 2008)

Thank you very much. I asked the question, and boy did I get an answer. The next thing to do is to hook up two test motors, which I will do today, and see the results. Again, thank you.


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## machiningfool (Nov 15, 2008)

OK sir, not that I doubted your solution, but there is nothing like a test. With an 18volt transformer, I hooked up one dc motor and went to full power, (18volts), and noted the rpms. I then hooked two identical motors in series and applied 18 volts, and in fact, the rpms were cut in half and both ran smoothly, I thank you again and this will solve my problem, I can now run the MTH loco without worrying about overspeeding the motors or burning them up prematurely. Thank you, Robert Brown.


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## grsman (Apr 24, 2012)

*Motors in series*



Michael Glavin said:


> Two 12V DC motors connected in series with 24V potential is best IMO. Like current will be adsorbed by both motors netting equal/MAX torque values offering greater efficiency while operating within the motors performance/RPM/efficiency curve.
> 
> Connected in parallel, the motor(s) unequal internal resistances (IR) will generate waste and heat. The motor that operates with less resistance will run faster and more efficiently, while the motor with higher resistance operating at lower RPM will act as a brake! And 24V will more likely than not prematurely wear out 12V motors, albeit at the luxury of greater speeds.
> 
> ...




Tom


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## Michael Glavin (Jan 2, 2009)

Tom

Did I miss something, seems you simply validated my assertions?

Michael


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## machiningfool (Nov 15, 2008)

*In series motors did not work*

I tried the series wiring of two 12 volt motors powered by the MTH 24 volt system and it did not work. The motors ran erratically, one would start and the other would not. Must be an imbalance of resistance of the wiring, maybe needs a variable resistor, I don't know, so I wired them in parallel and they work fine, I will just have to watch the speed I guess. I thought I would give you an update as to the fact my idea did not work as executed, Robert Brown.


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## Greg Elmassian (Jan 3, 2008)

Actually Michael, I'm surprised at your description of the motors in parallel, besides providing over the rated voltage to each motor, your example is correct GIVEN that he was using a 5 amp supply.

But in practice he would most likely damage the motors, and possibly draw too much current and damage some wiring.

I think Tom was trying to gently point that out. I'm not so gentle ha ha! In a beginners forum, I'm very careful to give ANY example that can cause damage, not everyone understands or reads the "caveats" given.

Yes, the only safe solution for him is the motors in series. The motors should likewise be "erratic" in parallel, actually even more so, since there is nothing forcing them to use the same current. The results are strange. I would double check the series wiring, perhaps one was backwards? You wire the 2 motors plus to minus between them.

Regards, Greg


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## Jerry Barnes (Jan 2, 2008)

Does the MTH system apply that high of voltage to the motors? I would think the control system is feeding only the voltage to the motors to make them run, not the full 24 volts.


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## JPCaputo (Jul 26, 2009)

Putting 24Volts onto a 12V motor will release the internal smoke fairly soon, even with PWM such as DCS and other DCC controls. I smoked a nice motor from doing that.

2 12V motors in series should be OK. But if one motor has a problem, it can put up to the 24 volts across the good motor, killing it.


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## blazersport (Apr 10, 2008)

Is there an issue with the decoder not reading the back EMF correctly when they are in series?


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## chuck n (Jan 2, 2008)

Andrew,

I think that this is the original thread. We can only, hope the later thread is deleated.

Chuck

Multiple threads on the same topic always lead to confusion, FOR EVERYONE!

OK Semper. For most mortals. I should have made some exceptions.


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## Semper Vaporo (Jan 2, 2008)

I guess a nobody like me is not everyone... I didn't have any confusion.


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## Garratt (Sep 15, 2012)

Thanks Chuck, I'm on the right track now. The other one was leading to nowhere.

Andrew


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## Greg Elmassian (Jan 3, 2008)

Jerry all the current control systems are PWM, and all PWM systems ALWAYS put out full voltage.

Analog motor control needs big transistors, big heat sinks, and make heat, like a Bridgeworks power supply.

You might want to read up on how PWM works where there's a nice article with pictures and diagrams.

Greg



Jerry Barnes said:


> Does the MTH system apply that high of voltage to the motors? I would think the control system is feeding only the voltage to the motors to make them run, not the full 24 volts.


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## Michael Glavin (Jan 2, 2009)

Robert,

I noted you suggested the motors ran erratically in series configuration, can you offer more specific information on what was realized. I suspect your erratic behavior is a function of the power source (TIU) more so than the theory thereof. 

About ten years ago I experimented with running two motors in series and parallel for propeller drive systems, my thoughts shared previously were the direct results of said efforts. I used a large 60A HP power supply for bench work at the time.

All that said if your 12V NWSL drives work favorably with the MTH/TIU system its all good for now... 

Michael


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## machiningfool (Nov 15, 2008)

*12 volt motors in series did not work*

You are right. When I hooked the motors in series, they operated erratically. so I went back to parallel hookup with 24 volts applied to the 12 volt motors. I have a speed control in the system, maybe that will save me.


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## Torby (Jan 2, 2008)

I don't think motors will work well in series because they don't draw a steady current.


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## machiningfool (Nov 15, 2008)

OK, sorry, but I am still confused. When TIU power is applied and the motors are not moving, is there 24 volts applied. If that is true, than what makes the motor react? Amperage is increased? Or, is there just 24 volts applied to the electronic board and the board supplies voltage? Remember the motor has a speed control. I supplied the stripes on the flywheel and remounted the sensor. So, where am I now?


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## Torby (Jan 2, 2008)

I think there are 2 complicating factors with motors:

1. They're inductive, so current doesn't follow voltage.
2. They switch the windings on and off, so they don't draw a steady current.

What makes the motor move is the magnetic field created by the current through the winding. If you don't understand current, take a look at http://barefootelectronics.com/led001.aspx which is actually about LEDs but explains the relationship between current and voltage, except that in a motor, inductors are involved so you have currents changing with time adding extra complexity.


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## Greg Elmassian (Jan 3, 2008)

Do not forget the added complication of DCS, it relies on a tachometer on the motor to read the motor speed as feedback. I don't know if each truck has it's own tach.

Greg


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## machiningfool (Nov 15, 2008)

Thanks Torby, I read the article, very interesting, I will be referring to it regularly.


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