# Series DC characteristic at reversing?



## Semper Vivus (Apr 13, 2011)

Hello,

I've just read Netgain's "shop manual" to learn more about this motors. I've found the following sentence:
"In other words, if you are rolling backwards, make certain the motor is stopped before applying power to move forward."
Assuming that a car with a series DC motor rolls back (i.e. stopplight on a hill) and (forward) power is applied to accelerate, is there the possibility to damage the motor?

Kind regarads,
Tom


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## major (Apr 4, 2008)

Semper Vivus said:


> Hello,
> 
> I've just read Netgain's "shop manual" to learn more about this motors. I've found the following sentence:
> "In other words, if you are rolling backwards, make certain the motor is stopped before applying power to move forward."
> Assuming that a car with a series DC motor rolls back (i.e. stopplight on a hill) and (forward) power is applied to accelerate, is there the possibility to damage the motor?


I suppose if the speed is great enough it is possible to damage the motor. There is also a situation where a series motor rolling backwards can self excite and abruptly come to a stop. This can cause damage to the motor due to a high pulse current and possibly other components in the system from the mechanical shock.

The Curtis controllers have an A2 terminal for a plugging diode which eliminates or softens the torque. More modern controllers do not have this feature. There has been disagreement over the use of the A2 on the Curtis. For EVcars, plug reversing is definitely not recommended and I would avoid rolling backwards with the motor in a forward gear just to be safe.


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## arklan (Dec 10, 2012)

:O i didnt know about this
mines a ADC motor but i assume the same would apply
i will keep this in mind


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## Semper Vivus (Apr 13, 2011)

Hello,

thank you!
What does the term "plug reversing" exactly mean? 

Kind regards,
Tom



major said:


> I suppose if the speed is great enough it is possible to damage the motor. There is also a situation where a series motor rolling backwards can self excite and abruptly come to a stop. This can cause damage to the motor due to a high pulse current and possibly other components in the system from the mechanical shock.
> 
> The Curtis controllers have an A2 terminal for a plugging diode which eliminates or softens the torque. More modern controllers do not have this feature. There has been disagreement over the use of the A2 on the Curtis. For EVcars, plug reversing is definitely not recommended and I would avoid rolling backwards with the motor in a forward gear just to be safe.


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## major (Apr 4, 2008)

Plug reversing is the act of going from forward to reverse by simply switching the direction of rotation of the motor. No mechanical braking involved. The plug reversing method is used extensively in electric forklifts. The operator can switch the control lever to reverse while traveling at full speed froward. The electric drive will automatically slow the vehicle to a stop and seamlessly accelerate it in the reverse direction. It does this by reversing the torque on the motor. This is not regenerative braking, although newer model forklifts will do the same reversals using regenerative braking to slow the vehicle.

An uncontrolled plug reversal of a DC motor at full speed will draw a peak current of twice the normal stall current and produce twice stall torque. This tends to break most things. So a controlled plug uses a diode across the motor armature to short it and has the controller pulse the motor field weakly. The result is a lot less torque, but still enough to stop the vehicle. The kinetic energy is absorbed in the plug diode and motor armature. It is rough on the motor, but the series wound forklift motors tolerate it, most of the time


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