# voltage and amperage differences for parallel and series motors



## Anaerin (Feb 4, 2009)

few2many said:


> Does placing 2 motors in series allow for higher voltages and less amps?
> Does placing 2 motors parallel allow for higher amps at less voltages?
> Trying to wrap my head around the idea of series and parallel switching, as mybe 2 or 3 smaller motors could be used as an E-trans.


AIUI:

Motors in series have full amperage, but half voltage.
Motors in parallel have full voltage, but half amperage.

So, if you had a 110V 500A system:

Each motor in series would see (a maximum of) 500A @ 55V.
Each motor in parallel would see (a maximum of) 250A @ 110V.

With DC motors, they create "Back EMF", essentially a voltage that has to be overcome, proportional to their RPM.

So, you start off in series, so you get maximum power (Amperage), and ramp up until the current you are putting in meets the back EMF.
Then you switch to parallel, so you can continue accelerating, albeit not quite so strongly (Higher voltage overcomes the back EMF, but the halved amperage means you don't accelerate so quickly).

You would thus end up with a torque curve something like this:

```
|            |                        ___________|
|            |                    ___/           |
|            |                ___/               |
|<- Series ->|            ___/                   |
|            |        ___/                       |
|            |    ___/                           |
R            |___/                               |
P          __/                                   |
M        _/  |                                   |
|      _/    |                                   |
|    _/      |<----------- Parallel ------------>|
|  _/        |                                   |
| /          |                                   |
|/           |                                   |
+----------------------TIME------------------------
```
While the power seen by the motor (This is for one motor) looks like this:


```
|----500A----,
|            |
|            |
|            |
|            |
|            |
|            |
|            '--------------AMPS-------------250A-
|
|            ,==============VOLTS============110v=
|            |
|            |
|====55v====='
|
+-------------------------------------------------
```
Without switching, the graph speed/time graph would look like this (with switching shown in dotted line):

```
|                                     ............
|                                 .../           
|                             .../               
|                         .../                   
|                     .../                       
|                 .../                           
R             ____________________________________
P          __/
M        _/
|      _/
|    _/
|  _/
| /
|/
+----------------------TIME------------------------
```


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## few2many (Jun 23, 2009)

Thats kinda what I figured, remembering back to school where we did the lights in series and parallel and how it affected brightness and amps and such.
Would this be a worthwhile endeavor? Could I run two 110v motors in series at 220v, or would it just reduce the amps?


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## Anaerin (Feb 4, 2009)

Two motors on a 220V bus, in series, would see 110V each. So yes, you could run two 110V motors that way, and both motors would see full amps.


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## jehan12413 (Feb 4, 2010)

That's what they do on electric trains for speed and acceleration control, but they use more than just two motors.


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## few2many (Jun 23, 2009)

Kinda thought so. I work with dual voltage motors alot. They are 110-220v ac motors. The only difference is the windings inside are either parallel or series.


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