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Old 08-26-2020, 06:40 AM   #1
georgia088
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Default Sepex Motors explained for dummies (like me) by JohnnieB

JohnnieB can you explain how a sepex motor works please. Your explanations always seem to be useful and easy enough for a dummy like me to understand. If I am not mistaken both DCS and PDS carts have sepex motors and differ only slightly in how they operate (correct me if I'm wrong). I am not sure if there are other ezgo models that run sepex motors, but if there are any information you can give will be appreciated! Thanks!
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Old 08-26-2020, 12:51 PM   #2
georgia088
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Default Re: Sepex Motors explained for dummies (like me) by Johnnieb

Sorry JohnnieB. I just noticed I’ve been spelling your name wrong. I tried to go in and edit, but I can’t figure out how. (Seems to be fitting as it shows how big of a dummy I am!)
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Old 08-26-2020, 01:18 PM   #3
JohnnieB
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Default Re: Sepex Motors explained for dummies (like me) by JohnnyB

The DCS was EZGO's first attempt with a sepex motor and there were some issues, so it was soon replaced by the PDS. The DCS did not have a speed (motor RPM) sensor, while their subsequent sepex systems did.

The best way to explain a sepex system is to explain the simpler series motor first and build on it.

The difference between a high-speed series motor and a high-torque series motor is the relative strength of the electromagnetic field created by the stator (stationary) windings and the armature (moveable) windings. When the stator magnetic field is strong relative to the armature field you get a high-torque motor and if it is relatively weak, you get a high-speed motor. with series wound motors, the strength of the stationary and moveable electromagnets are determined by the number of turns of wire used as well as other factors and are more or less cast in stone at the motor manufacturer's factory.

The motors installed by the cart manufacturers are typically someplace the high-speed and high-torque extremes, but motors that have more speed or more toque are available. There is a trade-off. In the same size case, if you up the motor's speed, you lower the motor's torque and vice versa. However, there are aftermarket motors with longer cases the have the same speed as stock with more torque or same torque with more speed, but the speed/torque curve is still set in stone since exactly the same amps that pass through the stator windings also pass through the armature windings.

Attached is a series drive with F/R reduced to its simplest form. The direction the motor spins (CW or CCW) is determined by the direction the amps flow in the stator windings.

-----------------------------

There is a 5000 character limit on BGW posts, so I'll post this and go to sepex in next post.
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File Type: jpg Hi Current Circuit - Series Motor -simplified.JPG (73.6 KB, 0 views)
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Old 08-26-2020, 01:22 PM   #4
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Default Re: Sepex Motors explained for dummies (like me) by JohnnyB

SepEx stands for Separately Excited and means the stationary windings and the moveable windings are excited (powered) from separate power sources.

---------------
Ooops hit wrong button.
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Old 08-26-2020, 01:51 PM   #5
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Default Re: Sepex Motors explained for dummies (like me) by JohnnyB

Fixed the spelling for you
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Old 08-26-2020, 01:56 PM   #6
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Default Re: Sepex Motors explained for dummies (like me) by JohnnyB

SepEx stands for Separately Excited and means the stationary windings and the moveable windings are excited (powered) from separate power sources.

Remember, the difference between a speed and torque motor is the relative strength of the magnetic fields, so the speed/torque curve can be changed electrically by altering the voltage applied (which in turn alters amp flow through) to the stationary and moveable windings.

The motors themselves are wound for speed or torque or something in between at the factory, but once installed in the cart and connected to a sepex controller, the speed/torque curve can be adjusted in either direction by altering the voltage applies to the stationary winding in a process known as field mapping. (Stationary winding is typically called the field winding in sepex motors)

Basically, when the cart is in a situation that needs high torque, the voltage to the field windings is increased and the the sepex motor becomes more of a torque motor and in a situation when more speed is called for the voltage to the field winding is decreases to create more of a speed motor. This is done during operation and is more or less unnoticeable by the operator.

The field windings in a sepex motor are composed of a high number of turns on relatively thin wire so the actual amp flow through the field is only about 1/10th the amp flow through the armature and a sepex controller has two outputs, a high power one passing amps to the armature and a low power (bi-directional) one passing amps to the field windings.

The attached drawing showing the outputs of a generic sepex controller.

Q1 represents a number of MOSFETs in parallel capable of passing up to 500A (depending on controller) to the armature and Q2 thru Q5 form an H-bridge that pass up to about 50A to the field windings.

When Q2 and Q5 are used, field amps flow from left to right and when Q3 and Q4 are used, it flows from right to left, reversing the direction the motor rotates.
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Old 08-26-2020, 01:58 PM   #7
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Default Re: Sepex Motors explained for dummies (like me) by JohnnyB

Quote:
Originally Posted by rib33024 View Post
Fixed the spelling for you
Spelled wrong the the thread title also.

But don't worry about it, I've been called worse.
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Old 08-26-2020, 02:01 PM   #8
rib33024
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Default Re: Sepex Motors explained for dummies (like me) by JohnnyB

Quote:
Originally Posted by JohnnieB View Post
Spelled wrong the the thread title also.

But don't worry about it, I've been called worse.
I fixed the title
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Old 08-26-2020, 02:05 PM   #9
JohnnieB
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Default Re: Sepex Motors explained for dummies (like me) by JohnnyB

Quote:
Originally Posted by rib33024 View Post
I fixed the title
Didn't see the title change when I posted, had to close out BGW and re-open for it to update.
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Old 08-27-2020, 07:02 AM   #10
georgia088
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Default Re: Sepex Motors explained for dummies (like me) by JohnnyB

Quote:
Originally Posted by JohnnieB View Post
SepEx stands for Separately Excited and means the stationary windings and the moveable windings are excited (powered) from separate power sources.

Remember, the difference between a speed and torque motor is the relative strength of the magnetic fields, so the speed/torque curve can be changed electrically by altering the voltage applied (which in turn alters amp flow through) to the stationary and moveable windings.

The motors themselves are wound for speed or torque or something in between at the factory, but once installed in the cart and connected to a sepex controller, the speed/torque curve can be adjusted in either direction by altering the voltage applies to the stationary winding in a process known as field mapping. (Stationary winding is typically called the field winding in sepex motors)

Basically, when the cart is in a situation that needs high torque, the voltage to the field windings is increased and the the sepex motor becomes more of a torque motor and in a situation when more speed is called for the voltage to the field winding is decreases to create more of a speed motor. This is done during operation and is more or less unnoticeable by the operator.
So this process is done within the the controller? How does the controller recognize the need for speed or torque? Is it a drop in amps (for torque) and volts (for speed) within the controller?


The field windings in a sepex motor are composed of a high number of turns on relatively thin wire so the actual amp flow through the field is only about 1/10th the amp flow through the armature and a sepex controller has two outputs, a high power one passing amps to the armature and a low power (bi-directional) one passing amps to the field windings. I'm a little confused here. I thought the field windings were the "stationary windings" in a sepex motor. But, the sepex controller has two field outputs and one passes amps to the armature. Does this mean passes controller sends to the field windings which passes them through the armature (turning the armature)? If this is the case how are the amps passed from the field output on the controller to the field windings to change the direction?
These questions don't make sense I am sure. I just don't understand how the field outputs on the controller can pass amps to the field windings and cause two things to happen? Do the two field outputs happen simultaneously? or separately?


The attached drawing showing the outputs of a generic sepex controller.

Q1 represents a number of MOSFETs in parallel capable of passing up to 500A (depending on controller) to the armature and Q2 thru Q5 form an H-bridge that pass up to about 50A to the field windings. So an H-Bridge switches the polarity to change the direction of the motors rotation.
I assume the H-Bridge is "chosen" (Q2 and Q5 for forward and Q3 and Q4 for reverse) based on the f/r selection switch?


When Q2 and Q5 are used, field amps flow from left to right and when Q3 and Q4 are used, it flows from right to left, reversing the direction the motor rotates.
Thanks JB!
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