Extending brushed DC motor lifespan in vacuum pump

Thread Starter

Dhaya777

Joined Oct 20, 2014
4
Hi guys,

I have a brushed DC motor vacuum pump that needs to hit a target vacuum and maintain that level with a constant minimal leak. Meaning the vacuum will never be stable. I have 2 options for motor control

1. PID system which keeps the motor running constantly

2. An algorithm that runs the motor to achieve a vacuum +15% above target, stops the motor and comes on again after the vacuum reaches -15% below target vacuum and repeats the process indefinitely.

Which one will lead to longer motor life?
 

Marley

Joined Apr 4, 2016
502
It's a brushed motor. The brushes have a finite life (many thousands of hours - hopefully - but still finite).
I would have the motor doing maximum amount of work while running.
So I would go for the ON-OFF above and below target approach. Could be closer than the ±15% limits though. Also means that the controller is cheaper.
Check the brushes regularly.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
2. An algorithm that runs the motor to achieve a vacuum +15% above target, stops the motor and comes on again after the vacuum reaches -15% below target vacuum and repeats the process indefinitely.
Which one will lead to longer motor life?
What will the expected or typical duty cycle be?
 

MisterBill2

Joined Jan 23, 2018
18,176
Brused generators and motors were found to have much shorter brush life when used in aviation applications, way back in the early days of military aircraft. So there were special brushes created for vacuum (high altitude) applications. So some brush research will be useful. Otherwise, stop/start can provide the longest run time. But duty cycle of the vacuum requirement will matter.
 

Reloadron

Joined Jan 15, 2015
7,501
Normally you would with a constant gas flow-rate let the vaccum pump run constantly and use an auto or manual throttle valve to control the vacuum line conductance out of the chamber to control to a vacuum set-point.
That's how we did it. Pulled vacuum on a manifold, the pump including a turbine pump ran constantly. From there we throttled a vacuum isolation valve. This was all handled by a vacuum gauge controller or process controller.

Ron
 

MisterBill2

Joined Jan 23, 2018
18,176
Actually, it should work to speed control the motor to hold the required vacuum. With a brush type of motor running in a vacuum brush life will be shorter, unless something special is done.
And unfortunately I didnot read about what the research found as the reason for the shorter brush life.
 

nsaspook

Joined Aug 27, 2009
13,085
Actually, it should work to speed control the motor to hold the required vacuum. With a brush type of motor running in a vacuum brush life will be shorter, unless something special is done.
And unfortunately I didnot read about what the research found as the reason for the shorter brush life.
A possible problem with variable speed motor pumped vacuum systems is that most industrial long run duration vacuum systems are designed to run in a specific flow region of vacuum pumping at each type of pump. The type of seals, and pump methods is dictated by the vacuum physics of each flow region. If the pumping vacuum range is low vacuum viscous flow then motor speed control of vacuum levels is usually possible.
https://www.pfeiffer-vacuum.com/en/...vacuum-technology/fundamentals/types-of-flow/
 

MisterBill2

Joined Jan 23, 2018
18,176
OK, here is a change: Reading the question again I see that it was an error to think that the motor was in the vacuum. So brush life reduction because of the vacuum is not an issue. But still, brush wear is due to speed and current, and the current will probably be lower at the lower speed keeping a flow just equal to the leak.
But what type of vacuum pump uses a brush type motor, currently?
So now two choices exist: If brush consumption is based only on run time, then the cycling scheme is better, while if it is based on speed plus load, holding the vacuum with the servo arrangement is the better choice. So the answer is to ask the motor manufacturer.
EXCEPT that it must be a servo motor because no other use brushes these days.
 

MisterBill2

Joined Jan 23, 2018
18,176
I asked that question in my last post. And the answer is because using a servo is one method of control of pump delivery. The fact of a brush type motor points toward the use of existing resources instead of purchasing new. And it is now common, although not entirely, considered more energy efficient to vary pump speed and blower speed, rather than throttle or waste-gate volume delivery. One organization that I am quite familiar with does a great deal of business repairing brush-motor servo systems. Not all organizations have the luxury of being able to discard existing working hardware and always replace it with the latest technology.
 

nsaspook

Joined Aug 27, 2009
13,085
"I have a brushed DC motor vacuum pump that needs to hit a target vacuum and maintain that level with a constant minimal leak"

These guys sell variable speed drive vacuum pumps but most of their systems use standard industrial motor systems.
https://www.buschvacuum.com/us/en/products/vacuum-pumps/frequency-controlled-vacuum-pumps/

OPERATING MODES
In scenarios with changing process parameters, we recommend vacuum pumps that can be controlled on a demand-driven basis and that either guarantee a consistent pumping speed or constantly maintain the required vacuum level.

Speed control
For processes with constant vacuum demand, it is recommended to leave the vacuum pump running at constant speed.


Pressure control
For processes with changing vacuum demand over time, the pressure control mode is the ideal choice. In this case, the vacuum pump adjusts the rotational speed according to the required vacuum level. Once this vacuum level has been achieved, the vacuum pump continues to run at minimum speed, enabling it to respond to a sudden need for increased vacuum demand and leading to further energy savings.
 

nsaspook

Joined Aug 27, 2009
13,085
I asked that question in my last post. And the answer is because using a servo is one method of control of pump delivery. The fact of a brush type motor points toward the use of existing resources instead of purchasing new. And it is now common, although not entirely, considered more energy efficient to vary pump speed and blower speed, rather than throttle or waste-gate volume delivery. One organization that I am quite familiar with does a great deal of business repairing brush-motor servo systems. Not all organizations have the luxury of being able to discard existing working hardware and always replace it with the latest technology.
The ability to use pump speed depends on how critical (applications like setting cow milking machine vacuum levels is not critical) the vacuum control points are. Most large industrial sites have the pumps remoted with sizable lengths on vacuum pumping. For precise vacuum control you need the control functions (measurements and adjustments ) at the point of use, not at the point of vaccum creation. The long sections vacuum pipe have flow conductance much like reactance in a power supply circuit. Removing that conductance from the vacuum flow control equations makes precise, fast control at the point of use much more stable when vacuum is a critical process control point.

Remote dual blower vacuum system with piping.
 

Reloadron

Joined Jan 15, 2015
7,501
The ability to use pump speed depends on how critical (applications like setting cow milking machine vacuum levels is not critical) the vacuum control points are.
Well go figure. Seriously I never had a clue how an automatic milking machine worked or what was involved. See, hang around this place a person learns all sorts of stuff. :)

Ron
 

MisterBill2

Joined Jan 23, 2018
18,176
One place that I worked at made carburetor test stands, including fully automated ones. Many of those used a LARGE turbine vacuum blower spun really fast by a motor that drew almost 75 amps, 3-phase, 480 volts. The vacuum was controlled by a stepper driven servo-valve. It would not have worked to do speed control because the tests were so short that a blower like that could not keep up. But we also made small testers that used small motors.
 
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