Speed Control v Current Control

kootni · Apr 7, 2020

Hi

Trying to wire a DC drive controller Eurotherm 508 to run a DC Drive.

On manual it gives two options for wiring, one is Speed Control and second is Current Control. I will not be using Tacho with this motor.

Whats the difference between the two ie speed control and current control as i tried both but motor runs and controller goes to stall position with light on straightaway.

Any help appreciated.

Manaul: https://www.parker.com/Literature/SSD Drives/DC Drives/HA389427.pdf

GaryS · Apr 7, 2020

With speed control the drive uses the armature voltage feedback to regulate the speed
this is the normal way DC drives are controlled.
with current control the Dc drive supplies the voltage necessary to meet the current setpoint if the set point is low the arm voltage will be low as well
with no load on the motor the motor will tend to run at much higher speed then wen loaded the load and current limit the speed
on some drive the current limit indicator will be on when you are in current control
you can use that to know when you are actually in current control

kootni · Apr 7, 2020

Tacho option...

thanks Gary

So if a tacho is attached then do i use speed control or current control option for wiring the drive.

GaryS · Apr 7, 2020

Yes if you want to use a tach then you need to use speed control
Tach is speed feedback
us keep in mind that most DC systems use an analog tach depending on what the drive requires on some older dc drive I have seen the tach feedback voltage at 0-90 VDC
you need to make sure they match

kootni · Apr 7, 2020

Thanks

Thanks man
One more quick Q.
Why wount the drive run my motor
The controller goes to stall. Pls see attached
Pic of wiring. No tacho

jraef · Apr 7, 2020

Current control is torque control; meaning keeping control of the torque is more important than the speed, speed is secondary to torque. So an example would be a winder application where speed is constantly changing because the roll diameter changes, but applying too little or too much torque risks a tear / break in the material. If you don't need torque control, then you are using speed control the the torque / current is allowed to go to whatever is necessary to maintain the commanded speed (within the limits of the motor / drive of course).

GaryS · Apr 7, 2020

Why do you have the shield connected to term 6
term 6 in the I Limit it should be connected to the +10 pot source
the drive is in I Limit when using it as current control you would use that input for the current control input

kootni · Apr 7, 2020

The shield is the wiper from the pot.does the wiper not wiper not go there?

GaryS · Apr 7, 2020

That is correct it should go to the speed reference input
when the I Limit is used then the drive is in current control
check the manual for the correct wiring
see page 14 of the manual
there should also be a switch to change from current control to speed control

Peter Nachtwey · Apr 7, 2020

Torque or current control provides the best performance if your controller is capable of it. However, there is a safety issue with current control. There should be mechanical brakes if the system has a chance of going past a stop and damaging something. If the power goes off on the controller then its output will go to zero. This means there will be no braking current and the DC motor in torque mode will coast until it hits something. In velocity mode the motor is stopped by bleeding off energy into resistors.

Velocity mode is easiest to setup.

jimtech67 · Apr 8, 2020

Do not use the shield from the pot as a conductor...
you need to run a 3 wire cable to your pots

kootni · Apr 8, 2020

Is that so? does it have to be 3 wires

jimtech67 · Apr 8, 2020

yes
the bare wire is a shield not a conductor

the pot should have 3 terminals
Follow the drawing on page 4-1

https://www.build-electronic-circuits.com/potentiometer/

kootni · Apr 8, 2020

I am using it as a wiper as third wire
Got lost by previous man when running through
Wire through complex conduit

Speed Control v Current Control

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