# Speed Controller



## 8V71 (Dec 23, 2011)

It's a DC feedback voltage from a tacho generator mounted on/in the motor or somewhere in the drive system. It tells the controller that the motor has achieved the correct speed and also varies the voltage/current to keep the motor at a constant speed.

If you aren't getting the signal on those terminals the drive will act like you are describing.


----------



## JRaef (Mar 23, 2009)

"Tacho generator" = tachometer.



Not to be confused with this...










... which is a taco generator.


----------



## GEORGE D (Apr 2, 2009)

Haha! Thanks guys, so even though the pot is demanding higher/lower speeds the tachometer won't allow it? Apparently. What should I be looking for on the tach Gen terminals?


----------



## Big John (May 23, 2010)

GEORGE D said:


> ..So even though the pot is demanding higher/lower speeds the tachometer won't allow it...?


 The tachometer is just closed loop control, the potentiometer sets the reference speed, the tachometer proves to the controller that it is at that speed. If you're changing the pot and the motor speed doesn't change, there's something wrong.


> ...What should I be looking for on the tach Gen terminals?


 It's gonna be a DC voltage that varies with motor RPM, might be pretty high: Seen them at 200V at full speed.


----------



## sparkywannabee (Jan 29, 2013)

Most of the time i have had tach issues, it shows up as motor speed surging. Like John said, you should have a pretty good DC voltage when the motor is running. Is the motor AC or DC. If the the tach is motor mounted there is usually a little Thomas coupling, make sure the shim pack isn't broken. On our big DC motors we can change a parameter on the drive and run in CEMF instead of tach and this helps you eliminate tach issues and narrow down the problem.


----------



## Peewee0413 (Oct 18, 2012)

JRaef said:


> "Tacho generator" = tachometer.
> 
> Not to be confused with this...
> 
> ... which is a taco generator.


Funny


----------



## Safari (Jul 9, 2013)

. On our big DC motors we can change a parameter on the drive and run in CEMF instead of tach and this helps you eliminate tach issues and narrow down the problem.[/QUOTE

please elaborate about this 

Sent from my HUAWEI Y210-0100 using Tapatalk 2


----------



## 8V71 (Dec 23, 2011)

nickson said:


> . On our big DC motors we can change a parameter on the drive and run in CEMF instead of tach and this helps you eliminate tach issues and narrow down the problem.[/quote
> 
> please elaborate about this
> 
> Sent from my HUAWEI Y210-0100 using Tapatalk 2


I'm going to guess counter EMF which I know as armature feedback mode. BTW George, your controller might have a jumper inside to put it in this mode as well. It would help you determine that your speed pot circuit is OK but I think you have already checked that out.


----------



## lefleuron (May 22, 2010)

Most tacho-gens will put out a certain voltage for a given rpm of the motor.

This is normally stated on the tach gen, like a motor name plate.

Most of the ones I deal with are either 50 volts at 1000 rpm, or 33 volts per 1000 rpm.

So get the motor running, use a hand wheel to see how many rpms its actually turning, do the math for the voltage you should see on those terminals, and do not doubt the math.

If the math is correct, the tach gen is fine. What you are missing is a "go faster" voltage. Find the speed reference (might be a 0-10 VDC, but thats just an example), and see if you cannot make that go up and down.

If that speed reference voltage does not hit the max, the motor will not run wide open.

Let us know what you find.


----------



## ampman (Apr 2, 2009)

JRaef said:


> "Tacho generator" = tachometer.
> 
> 
> 
> ...


i almost spit my sprite out when i read this


----------



## just the cowboy (Sep 4, 2013)

*Is it running at full speed*

If you lose the tach it will generaly run at full speed, because it is looking for a feedback voltage


----------

