# How to tell series or shunt wound motor apart



## Arlo (Dec 27, 2009)

Ok so I got a ALtrax dcx controller and a couple I can try to fix for a good price. The Altrax DCX is for a shunt wound motor... Meening the feild coil is powered sepratly from the brushes. But I am now second guessing my self thinking the motor might be a series wound motor.... Not sure but Gordo (guy who gave me the motor) said the motor reversed to make the golf kart go backwards. The only two ways a seires motor can do this are to change brush timing 90 electrical deg. Or to disconect the feild coils from the brushess and hook them in series the other direction. Here is some pics. The inductance of the feild coil post mesured 25uH and the brush posts mesured 280uH


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## major (Apr 4, 2008)

Hi Arlo,

All DC motors can be reversed the same way by reversing the polarity of the armature relative to the field.

The best method to determine if it is series wound is by turns count on the field coils. Those are wrapped, so hard to tell. Next best is by resistance. Resistance of the field coil set (all coils, S1 to S2) will be on the same order of magnitude as the armature. For this size and type of motor, that would be likely 0.005 to 0.02 Ω. Which would require a bridge to measure. It will show essentially zero Ohms on a DVM. 

A SepEx motor of this size and type would have a field resistance in the range from 1 to 20 Ω. A shunt motor likely in the hundreds of Ohms.

I think yours is series wound from looking at the photos. It uses heavy gauge round wire and has 4 connects to the terminal posts meaning the 4 field coils are in parallel with each other. This is consistent with a series motor.

Regards,

major


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## Arlo (Dec 27, 2009)

OK thanks major. I was told you are a good guy to ask about this stuff.
I thought sepex and shunt wound meant the same thing? Now does anyone know it the DCX controller can run it with out powering the field coil should not be a problem as far as I can tell. For me it its a controller to get the go-kart / buggy running until I find, or build a bigger controller.


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## major (Apr 4, 2008)

Arlo said:


> I thought sepex and shunt wound meant the same thing?



To some it does. The classical terms:

Shunt motor has the field voltage equal to the armature voltage.
Series motor has the same current in the field and armature.
Separately Excited (SepEx) motor has a field excitation not necessarily equal to the armature in terms of either current or voltage.
Now it gets fuzzy when one starts altering the field excitation on a series motor with a diverter resistor or on a shunt motor with a series resistor for purpose of field weakening. Here I think you fall back to the unaltered state for the definition of shunt or series motor type.

In practical terms, the SepEx field is designed for a "full field" excitation level requiring a voltage well below the full armature voltage whereas the shunt motor is designed for the "full field" to be at armature voltage. Full field here means the normal field strength typically used for running at the one hour rated load. A shunt motor therefore can easily be field weakened, but not easily over excited. The SepEx motor can easily be field weakened and easily over excited.

For traction motor applications, over excitation of the field of the SepEx motor provides excellent overload performance useful for acceleration of the vehicle or hill climbing. The controller often uses a field map to mimic a series motor. Such control would be excessively difficult for a true shunt wound motor due to the absence of a high voltage supply for the field.


Typical field current examples:

Series: 50 to 500A.
Shunt: 0.4A.
SepEx: 4 to 40A.
Regards,

major


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## Arlo (Dec 27, 2009)

So will i be ok to use the dcx controller on a series motor and just leave the feild connectors open on the controller?


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## major (Apr 4, 2008)

Arlo said:


> So will i be ok to use the dcx controller on a series motor and just leave the feild connectors open on the controller?


Won't hurt the motor but I have no idea if the controller will tolerate it


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## Arlo (Dec 27, 2009)

Ok thanks major. So to tell if its series i will hook a volt meter up to the brushe posts and a volt meter up to the field posts and run 12v in seires through the motor and i should see close to the same voltage drop on each volt meter ~6v. And if i need I will use a resistor and inductor on the feild on the dcx controller because this is just a temp controller for this motor and it will be handy to keep.


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## major (Apr 4, 2008)

Arlo said:


> So to tell if its series i will hook a volt meter up to the brushe posts and a volt meter up to the field posts and run 12v in seires through the motor and i should see close to the same voltage drop on each volt meter ~6v.


That is only somewhat valid at stall. Any rotation gives you generated voltage on the armature.


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## Arlo (Dec 27, 2009)

major said:


> That is only somewhat valid at stall. Any rotation gives you generated voltage on the armature.


Any sugestions on how to test it to see what kind of motor it is then?


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## major (Apr 4, 2008)

Arlo said:


> Any sugestions on how to test it to see what kind of motor it is then?


It's a series motor, 99.748% confident


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## Arlo (Dec 27, 2009)

major said:


> It's a series motor, 99.748% confident


 I hooked it up in series tonight and it runs realy realy nice. I love that number. Im sure it is series as well looking at it one more time... So now once I get one more bearing installed (had a inner race crack) I will try the altax DCX with out the feild hooked up.


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## Arlo (Dec 27, 2009)

OK major how do I determine gearing for a series motor? I spun it up with some advance on the brushes. and 44v to the posts and it spins 5800 rpm. So do I use a volt per rpm calculation to figure out the max speed or does it change a lot under load?


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## Arlo (Dec 27, 2009)

I havent figure out the youtube link thing for this forum yet so here you go. http://www.youtube.com/watch?v=gvlYo6OsRQI


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## major (Apr 4, 2008)

Arlo said:


> OK major how do I determine gearing for a series motor? I spun it up with some advance on the brushes. and 44v to the posts and it spins 5800 rpm. So do I use a volt per rpm calculation to figure out the max speed or does it change a lot under load?


Hi Arlo,

Unless you run a dyno test and plot the speed/torque characteristic and calculate the load curve, you're not going to know. So the best approach is to use a reduction system which can be easily altered. Put a 5 to 1 belt or chain drive on it and see what you get. Go from there.

As far as motor RPM, you would do well to keep maximum running RPM to below 5000 IMO. And "normal" operation below 4000 maybe at 3000. But you saw that it held together over 7000 so WTF. But don't expect brushes, bearings and drive train components to last long. And stuff failing at higher speed presents increased hazard. 

major


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## Arlo (Dec 27, 2009)

major said:


> Hi Arlo,
> 
> Unless you run a dyno test and plot the speed/torque characteristic and calculate the load curve, you're not going to know. So the best approach is to use a reduction system which can be easily altered. Put a 5 to 1 belt or chain drive on it and see what you get. Go from there.
> 
> ...


 Thanks major. I understand the unloaded rpm vs loaded thing but if the motor can be fed enough power we have found the max loaded speed to be ~20-23% less with brushless motors. This motor is a temp install until I sort out hi power to run one of my awesome brushless motors.
SO the 5000 rpm max is that what we go by for a 6.7 inch dia housing or is it just a rule for all these brushed motors? I thought I saw 9 inch motors liked 5000 rpm as a max so I was thinking with a smaller dia armature I can spin it faster. Gabriel's kart runs a 6.7 inch motor with 130 volts successfully (140v blew the motor) but from their videos it sounds a lot faster then mine at 7200 rpm.


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## Tesseract (Sep 27, 2008)

Arlo said:


> ...SO the 5000 rpm max is that what we go by for a 6.7 inch dia housing or is it just a rule for all these brushed motors?....


Brushes care about the surface speed, so a smaller diameter commutator can spin at a higher RPM for the same rate of wear as a larger diameter motor. Until the commutator flies apart from "centrifugal force" or zorches from excessive voltage, that is.


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## Arlo (Dec 27, 2009)

Tesseract said:


> Brushes care about the surface speed, so a smaller diameter commutator can spin at a higher RPM for the same rate of wear as a larger diameter motor. Until the commutator flies apart from "centrifugal force" or zorches from excessive voltage, that is.


 Yeh thats what I thouht so Im just trying to find numbers to look at as rough rules of thumb for limits.


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