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Danfoss softstarter MCD500
- Thread starter Keith1976
- Start date
Smooth stopping with a soft starter is a relative term. It depends a lot on the type of load you have and no amount of "learning" can overcome a bad application. Describe your entire application if you want more help.
One of our members was the chief design engineer for that product in a former life, he knows it intimately and if he sees this I know he will be willing to help, but he will need details.
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376
One of our members was the chief design engineer for that product in a former life, he knows it intimately and if he sees this I know he will be willing to help, but he will need details.
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376
ozmosis
Electrical
- Oct 12, 2003
- 1,794
I work for Danfoss and know the MCD500.
There is a useful booklet that explains the soft start and the feature AAC (Adaptive Acceleration Control) although this wording probably does not do it credit as it is also adaptive deceleration control too.
However, and as jraef points out, better to outline your requirements relating to the application than use this site to discuss specific functions of a product.
There is a useful booklet that explains the soft start and the feature AAC (Adaptive Acceleration Control) although this wording probably does not do it credit as it is also adaptive deceleration control too.
However, and as jraef points out, better to outline your requirements relating to the application than use this site to discuss specific functions of a product.
- Thread starter
- #4
Hi Jraef and Ozmosis;
The application is for distribution pumps with 3 pumps (@ 75kW). Each discharge line has a motorized valve and check valve.
The pumps were run by star-delta starters in the past that is why they need the motorized valves.
So this is a retrofit project.
Two pumps are driven by Danfoss FC202 and the third one is driven MCD3000.
The normal water consumption required about 2 and a 'half' pumps. So one FC202 will act as the master while the other FC202 and MCD3000 are the follower.
I use a pressure transmitter at the header pipe to give feedback to master FC202's PID controller.
In the beginning, the standard MCD3000 fail to give smooth stop. Then Danfoss recommended me the "MCD3000 advanced soft stop module". I purchased it and installed it. Here comes the headache. Sometimes it can stop nicely, but sometimes it shut slam the check valve, causing a big noise.
Initially I thought it is because of the programming.(I use modbus RTU to start/stop the MCD3000). But after I tried using a temporary external switch to control the MCD3000 terminal, the same symptom remains. It gives smooth stop once and then for the nextstop, terrible noise occurs.
I report this to Danfoss. Surprisingly they give up and I can have my money back for the "advanced soft stop module". They claim that they don't know what is the cause of the symptom.
I purchased this module with doubt actually because no one has used it before. The Asia Pacific water department manager convinced me that time that Danfoss will give full technical support and even said that the "advanced soft stop module" is the module used in the new MCD500.
I am considering MCD500 now as the solution for my customer. That is why I hope you can share your experience with me. Is it true that NOT ALL distribution pumps can have smooth stop?
PS: 3 years ago I installed MCD3000 standard at the same customer's plant, 75kW, and everything is normal.
I thank you in advanced for your valuable advice.
Keith
The application is for distribution pumps with 3 pumps (@ 75kW). Each discharge line has a motorized valve and check valve.
The pumps were run by star-delta starters in the past that is why they need the motorized valves.
So this is a retrofit project.
Two pumps are driven by Danfoss FC202 and the third one is driven MCD3000.
The normal water consumption required about 2 and a 'half' pumps. So one FC202 will act as the master while the other FC202 and MCD3000 are the follower.
I use a pressure transmitter at the header pipe to give feedback to master FC202's PID controller.
In the beginning, the standard MCD3000 fail to give smooth stop. Then Danfoss recommended me the "MCD3000 advanced soft stop module". I purchased it and installed it. Here comes the headache. Sometimes it can stop nicely, but sometimes it shut slam the check valve, causing a big noise.
Initially I thought it is because of the programming.(I use modbus RTU to start/stop the MCD3000). But after I tried using a temporary external switch to control the MCD3000 terminal, the same symptom remains. It gives smooth stop once and then for the nextstop, terrible noise occurs.
I report this to Danfoss. Surprisingly they give up and I can have my money back for the "advanced soft stop module". They claim that they don't know what is the cause of the symptom.
I purchased this module with doubt actually because no one has used it before. The Asia Pacific water department manager convinced me that time that Danfoss will give full technical support and even said that the "advanced soft stop module" is the module used in the new MCD500.
I am considering MCD500 now as the solution for my customer. That is why I hope you can share your experience with me. Is it true that NOT ALL distribution pumps can have smooth stop?
PS: 3 years ago I installed MCD3000 standard at the same customer's plant, 75kW, and everything is normal.
I thank you in advanced for your valuable advice.
Keith
Where I have had the most trouble with soft stopping is when there is a low head pressure or very strong check valve springs. Soft stopping works by reducing the output torque of the pump motor which effectively reduces the pressure output. As the pump output pressure approaches the head pressure, the check valve springs (or counter weights) have less force to overcome. By keeping the pressure in that zone and passing through it slowly for a period of time, the valve can close gently. But if the head pressure is low to begin with and the output torque of the pump motor drops precipitously, it can be difficult to hit that "sweet spot" where the valve springs still have enough resistance to avoid slamming.
Your application may have an added issue with the motorized valves. Are they being closed as you are soft stopping the motor?
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376
Your application may have an added issue with the motorized valves. Are they being closed as you are soft stopping the motor?
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376
- Thread starter
- #6
Hi Jraef;
Thanks for the input.
I forgot to inform you that in my proposal, I told the customer that the motorized valve will no longer be needed. And during test-com, we let the valves open all the time.
At the moment, I still make use of the valve. I close the valve first before stopping the sstarter. But my customer does not accept this solution as it is against my proposal.
Keith
Thanks for the input.
I forgot to inform you that in my proposal, I told the customer that the motorized valve will no longer be needed. And during test-com, we let the valves open all the time.
At the moment, I still make use of the valve. I close the valve first before stopping the sstarter. But my customer does not accept this solution as it is against my proposal.
Keith
Hi Keith
If you close the valve first, and then stop the starter, you will not get a good soft stop.
The soft stop will work best when the load on the motor is highest.
If you have other pumps in the line, you will also affect the soft stop performance.
If you found that the MCD3000 soft stop performance was erratic, that suggests that the hydraulic characteristics were not consistent and under those conditions, I would not expect the MCD500 to be a significant improvement.
Soft stop operates by starving the motor of current and thereby reducing the torque produced by the motor. When the torque is too low for the motor to drive the pump at full speed, it will begin to stall. The torque required by the pump will fall as the pump slows and the speed of the pump will be determined by the intersection of the motor speed torque curve and the pump speed torque curve.
The performance of the soft stop is very dependent on the speed torque curve of the motor. If the motor has a very peaky speed torque curve, it will not give good soft stop performance. If the motor has an almost flat speed torque curve, it will soft stop very well provided that the load is high. The lower the flow driven by the pump is, the worse the soft stop performance will be.
Best regards,
Mark.
Mark Empson
L M Photonics Ltd
If you close the valve first, and then stop the starter, you will not get a good soft stop.
The soft stop will work best when the load on the motor is highest.
If you have other pumps in the line, you will also affect the soft stop performance.
If you found that the MCD3000 soft stop performance was erratic, that suggests that the hydraulic characteristics were not consistent and under those conditions, I would not expect the MCD500 to be a significant improvement.
Soft stop operates by starving the motor of current and thereby reducing the torque produced by the motor. When the torque is too low for the motor to drive the pump at full speed, it will begin to stall. The torque required by the pump will fall as the pump slows and the speed of the pump will be determined by the intersection of the motor speed torque curve and the pump speed torque curve.
The performance of the soft stop is very dependent on the speed torque curve of the motor. If the motor has a very peaky speed torque curve, it will not give good soft stop performance. If the motor has an almost flat speed torque curve, it will soft stop very well provided that the load is high. The lower the flow driven by the pump is, the worse the soft stop performance will be.
Best regards,
Mark.
Mark Empson
L M Photonics Ltd
- Thread starter
- #8
Hi Marke;
You got it wrong. I make use the motorized valve AGAIN after all the failure to get soft stop. When I test-com, all the valves are let open.
The reason I shut the valve first is to rest the check valve so that there will be no shut slam noise. To customer, no noise means no water hammer.
Quote: "If you found that the MCD3000 soft stop performance was erratic, that suggests that the hydraulic characteristics were not consistent and under those conditions, I would not expect the MCD500 to be a significant improvement."
I personally agree that the stop condition varies from time to time. The flow rate and pressure vary. So the module keeps learning and needs a trial stop (with shut slam) before getting a smooth stop in the next stop.
Keith
You got it wrong. I make use the motorized valve AGAIN after all the failure to get soft stop. When I test-com, all the valves are let open.
The reason I shut the valve first is to rest the check valve so that there will be no shut slam noise. To customer, no noise means no water hammer.
Quote: "If you found that the MCD3000 soft stop performance was erratic, that suggests that the hydraulic characteristics were not consistent and under those conditions, I would not expect the MCD500 to be a significant improvement."
I personally agree that the stop condition varies from time to time. The flow rate and pressure vary. So the module keeps learning and needs a trial stop (with shut slam) before getting a smooth stop in the next stop.
Keith
- Moderator
- #9
- Thread starter
- #10
Hi Bill
A soft starter does not change the frequency applied to the motor, so the motor will always try to run at full speed. The only way to slow the motor, is to reduce the torque and increase the slip.
To "ramp the speed down nicely" would require a VFD rather than a soft starter.
Best regards,
Mark.
Mark Empson
L M Photonics Ltd
A soft starter does not change the frequency applied to the motor, so the motor will always try to run at full speed. The only way to slow the motor, is to reduce the torque and increase the slip.
To "ramp the speed down nicely" would require a VFD rather than a soft starter.
Best regards,
Mark.
Mark Empson
L M Photonics Ltd
- Thread starter
- #12
- Moderator
- #13
I have direct experience with the product from which the MCD500 was derived.
AAC is suitable for applications that are consistent in their behaviour. That is to say it is a function that learns the application, and if the application is changing it cannot learn.
AAC is suitable for applications that are consistent in their behaviour. That is to say it is a function that learns the application, and if the application is changing it cannot learn.
- Thread starter
- #15
Sorry for the late response, I don't get on here as often as i use to.
AAC learns the characteristics of the motor and load through feedback received during the first few start and stop cycles. Each subsequent start and stop brings the acceleration and deceleration of the motor and load closer to that which has been programmed by the user. usually by the forth attempt, near linear acceleration and decelrations is achieved and the actual accel and decel times achieved are per those programmed by the user.
AAC is about achieving the best possible reduction in mechanical stress and currents during start and stop may be higher than that achieved through constant current starting.
But as mentioned above and in my previous post, it takes three or four goes for AAC to learn the application and if the application is variable in its characteristics, the desired start performance will not be achieved.
Please do not ask how AAC achieves what it does because i will not answer that on a public forum.
AAC learns the characteristics of the motor and load through feedback received during the first few start and stop cycles. Each subsequent start and stop brings the acceleration and deceleration of the motor and load closer to that which has been programmed by the user. usually by the forth attempt, near linear acceleration and decelrations is achieved and the actual accel and decel times achieved are per those programmed by the user.
AAC is about achieving the best possible reduction in mechanical stress and currents during start and stop may be higher than that achieved through constant current starting.
But as mentioned above and in my previous post, it takes three or four goes for AAC to learn the application and if the application is variable in its characteristics, the desired start performance will not be achieved.
Please do not ask how AAC achieves what it does because i will not answer that on a public forum.
- Thread starter
- #19
GGOSS;
Thanks for sharing. To be precise, does it mean that the pump should stop under the same flowrate, suction pressure, and discharge pressure? (of course with 'certain' amount of tolerance).
I hope you don't have to shoot me for answering this one.....
Keith
Thanks for sharing. To be precise, does it mean that the pump should stop under the same flowrate, suction pressure, and discharge pressure? (of course with 'certain' amount of tolerance).
I hope you don't have to shoot me for answering this one.....
Keith
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