Running a stepper motor continuously for years

Hello Arduino community, It’s been a while since I have had a project that requires the help of an arduino, but I need lots of help.

Needs:
-Need a motor that can be precisely driven (stepper)
-Motor needs to be reliable in that it has to run continuously 24/7/365
-Needs to be controllable by either a pot or buttons to speed up and slow down RPM (0-100 RPM)
-Lastly, needs a simple digital display to read RPM

The motor will have very little load on it, it will be driving a paristaltic pump head that I will make with a 3d printer(more inside my wheel house)

There’s a lot to learn about stepper motors and I am hoping someone will chime with a reliable stepper motor that doesn’t break the bank. Will this one fit my needs?

I have an uno that I will devote to this project and will also need to know what display I need to purchase to give me a simple digital read out.

Lastly, I’m hoping there’s a code already in the library that will fit my needs and all I have to do is tailor it.

It has been over 8 years since I’ve had the pleasure of working with an arduino, and I will have to relearn quite a bit. Can you guys point me in the right direction to get started?

Thanks!!!

One of your requirements is: "Motor needs to be reliable in that it has to run continuously 24/7/365. BUT you have not described how you are going to ensure the entire system will be powered so this service can be obtained.

Curious, what happens if the system suddenly stops one year form now?

Paul

For that sort of reliability you need a motor without brushes. (preferably is fully sealed and uses fully sealed bearings).

In a clean, dry environment without much dust such hermetic requirements can be relaxed. If moisture / leaks are possible, a "food-grade" hermetically sealed motor is probably a wise choice, though more expensive.

Steppers and brushless DC motors are possibilities, stepper being more power hungry but simpler to program (no encoder needed).

And clearly it needs enough torque for the pump load.

Paul_KD7HB: One of your requirements is: "Motor needs to be reliable in that it has to run continuously 24/7/365. BUT you have not described how you are going to ensure the entire system will be powered so this service can be obtained.

Curious, what happens if the system suddenly stops one year form now?

Paul

I'm not quite sure what you're asking. The system will be stand alone and based on the stepper motor that is needed will dictate the power requirements. There will be no other outside influences on what controls the system other than the poteometer or buttons to dial in the RPM.

Some more details: I'm a saltwater reef tank hobbyist and to meet the needs of calcium in the tank to grow corals, we usually employ a calcium reactor which is simply a container with calcium rich media and by lowering the pH inside the reactor (by pumping in a metered amount of CO2) the media is dissolved inside the container and then a separate pump slowly pushes tank water inside the reactor and pumps calcium rich saltwater into the tank at a very slow rate. normally this procedure is done with a small 120vac power head pump but the flow rate varies and the accuracy is far from providing stable water parameters.

People have started using paristaltic pumps to meet these needs, but these stand alone paristaltic pumps aren't cheap and I thought this would be a great project to DIY.

If the system stops after a year of operation the tanks stability will be compromised, but I will be alerted by a sudden change in pH and I will be able to take immediate action to solve the problem.

Forgive me if I did not answer your question, hopefully this will give you more insight.

MarkT: For that sort of reliability you need a motor without brushes. (preferably is fully sealed and uses fully sealed bearings).

In a clean, dry environment without much dust such hermetic requirements can be relaxed. If moisture / leaks are possible, a "food-grade" hermetically sealed motor is probably a wise choice, though more expensive.

Steppers and brushless DC motors are possibilities, stepper being more power hungry but simpler to program (no encoder needed).

And clearly it needs enough torque for the pump load.

The exact metering of the fluid by exact revolutions is why I chose a stepper motor rather than a BLDC motor. Humidity will somewhat be a factor the room in which it will be operating has a humidity control to keep the overall humidity at 20%, and the calcium reactor will be far enough away from salt water that it won't get wet or splashed on. and of course another added layer of protection will be that the entire unit will be sealed inside it's own container.

Are most stepper motors designed to run continuously or is that a special feature that I have to look for?

The nominal current rating will run the motor hot - if heat dissipation is a problem you might need to de-rate the current of the motor.

Also if the motor is idle for periods, using a driver that can drop the idle current to about 1/2 the normal value will reduce power dissipation and heating substantially - this is usually fine as stationary torque is a lot higher than dynamic.

What you have not described is your UPS system to make your design run 24/7/365 when there is a fire in your neighborhood and the power company cuts the power to the area.

Paul

Paul_KD7HB: What you have not described is your UPS system to make your design run 24/7/365 when there is a fire in your neighborhood and the power company cuts the power to the area.

Paul

The point I was making is that I need a motor that can run continuously without it breaking down after 3 months on the job.

The fish room is equipped with a generator backup that kicks on automatically when power is disrupted.

Based on that information, do you have a stepper motor that you would recommend?

Can the tube in a peristaltic pump tolerate being pinched a relaxed over and over for an extended period of time?

BTW I just realized you will be in a salt-rich atmosphere. This is your main longevity issue I think - salt laden air can corrode almost anything (even stainless steel), so good ventilation to keep the humidity down may be important, and conformal coating all the electronics may be wise. At least its not a real marine environment with salty spray to contend with...

outsider: Can the tube in a peristaltic pump tolerate being pinched a relaxed over and over for an extended period of time?

I get it.... but Yes.

MarkT: BTW I just realized you will be in a salt-rich atmosphere. This is your main longevity issue I think - salt laden air can corrode almost anything (even stainless steel), so good ventilation to keep the humidity down may be important, and conformal coating all the electronics may be wise. At least its not a real marine environment with salty spray to contend with...

Salt may play a role, however with the steps that I have taken to lower humidity with a humidity controlled exhaust fan as well as a dedicated air conditioner for the room, that's not necessarily the chief concern as much as getting a stepper motor that will handle constant operation. OR perhaps that's not a major issue and any motor will do... I don't know because this isn't my line of expertise. With that in mind, where do I start my search?

Interesting and very expensive project. BUT, with the proposed components, you really have NO feedback from the motor/pump to tell you if it is actually moving the pump or not. You ask for display of RPM, but you are only looking for the program that controls the stepper to tell you what it thinks is the RPM. You need something from the pump itself to indicate the solution is actually moving at the rate you desire. IF not, then send an alarm condition.

Paul

Very good, point but requiring feedback to ensure the motor is rotating is not a need. An easy way to determine operation is to monitor pH.

What made you conclude “very expensive”?

I don’t want to over complicate things, and wish to work within the parameters laid out by my needs, environment aside, bells and whistles aside, I want to purchase a stepper motor, driver (if necessary) that can be set with a potentiometer and run continuously. Although a sensor to report back proper RPM would be great, it’s not a need. I was simply thinking that this could be coded to calculate steps to determine 1 revolution and display that as RPM.

Do I have to be concerned with continuous motor operation? or will any stepper do?

sisterlimonpot:
Very good, point but requiring feedback to ensure the motor is rotating is not a need. An easy way to determine operation is to monitor pH.

What made you conclude “very expensive”?

I don’t want to over complicate things, and wish to work within the parameters laid out by my needs, environment aside, bells and whistles aside, I want to purchase a stepper motor, driver (if necessary) that can be set with a potentiometer and run continuously. Although a sensor to report back proper RPM would be great, it’s not a need. I was simply thinking that this could be coded to calculate steps to determine 1 revolution and display that as RPM.

Do I have to be concerned with continuous motor operation? or will any stepper do?

Your description of your installation with a backup power generator led my to believe what you have must have cost a lot and the on-going operation rather costly. I was partner in a company that installed a backup generator system that started automatically when commercial power went away and switched between the two automatically. Rather expensive.

To me, you seem to not understand that anything rated to run 24/7/365 is only based on statistics. Such a device could fail a day after installation. All systems need maintenance, even the space station.

Sure a program to run and control the speed of a stepper motor could compute the motor RPM, but that gives no assurance that the motor is actually turning. I suspect the system power could be turned off, the wires to the stepper disconnected, power returned and the program would still give you the RPM you want.

Paul

I have to be honest with you, I feel like this is all on purpose. Are you guys having a laugh at my expense? Are you seeing how long you can string me along until I wise up and simply give up and leave?

Perhaps you guys are getting hung up on semantics, maybe I brought this all on because of how I portrayed one of the needs. The purpose of that need was based on my limited knowledge that most tasks I see steppers used for are short term back and forth applications, I don't see them used continuously. From that I thought that it might be important to state that as one of the needs. If stepper motors can be used continuously then it's a non issue. I think we got hung up on interpretation of what I was requesting.

I was simply trying to get information from the subject matter experts so that I can make an informed decision and complete this project. I was hoping that someone would've already chimed in and offered a few options, instead, I am spinning my wheels getting nowhere fast. I thought the motor selection was supposed to be the easy part.

Did I not follow protocol? Was I supposed to get right to the point? Did I muddy the thread up with too much detail too quickly?

Don't get me wrong, I appreciate the concern. There are many components that are sold and used in the hobby that employ DC motors, and all of them are simply your bargain bin dc motor. The environment that they are used in probably shorten their life expectancy, but I have a set of paristaltic dosing pumps that run off those 5vdc hobby motors that you can buy for $2 and they have been running perfectly for over 8 years.

I've concluded that I should refine that need based on the answer to this question:

Are stepper motors designed to run continuously?

Don't get so upset. We are just trying to get you to understand that nothing is designed to run forever. Everything that moves is designed to run for x number of hours. That does not mean it will run for that long.

Years ago we were asked to bid on some type of kitchen appliance with an electric motor. The engineering spec called for a motor with a life of 15 minutes continuous run. I was shocked at the spec, but the motor might run 2-3 seconds a day.

You can use Google as well as we can, so what motors did you find that would give you that life time? Sure, you have a motor that has run for a long time, but was it designed to do that?

Paul

To be honest, I would expect your 3D printed pump to self destruct long before a quality brushless motor would.

Did you consider just using a air lift pump. You could have the arduino monitor the ph and flow rate of the water that gets lifted and then the arduino simply controls a air solenoid to pump more or less out.

You likely already have an abundance of air pumps to tap off of.

sisterlimonpot: Salt may play a role, however with the steps that I have taken to lower humidity with a humidity controlled exhaust fan as well as a dedicated air conditioner for the room, that's not necessarily the chief concern as much as getting a stepper motor that will handle constant operation. OR perhaps that's not a major issue and any motor will do... I don't know because this isn't my line of expertise. With that in mind, where do I start my search?

Any stepper motor with good sealed bearings in a reasonable amenable environment is likely to last as long as its bearings as nothing else can wear out. You will have to check that the heat build up isn't a problem (it could be an issue for other parts of the pump) - steppers are usually rated to run well above ambient temperature (you can derate the current to reduce this, you get less torque though)

Paul_KD7HB: Don't get so upset. We are just trying to get you to understand that nothing is designed to run forever. Everything that moves is designed to run for x number of hours. That does not mean it will run for that long.

Years ago we were asked to bid on some type of kitchen appliance with an electric motor. The engineering spec called for a motor with a life of 15 minutes continuous run. I was shocked at the spec, but the motor might run 2-3 seconds a day.

You can use Google as well as we can, so what motors did you find that would give you that life time? Sure, you have a motor that has run for a long time, but was it designed to do that?

Paul

I understood your concern the first time you posted it. You're dissecting my request for 24/7/365 as needing a motor with a long life expectancy, and my reasoning for the "24/7/365" is that it will never have a break, so the motor will have to sustain the heat of continuous use. I didn't want to get a motor and after a week of running it nonstop the insulation of the windings melted and shorted out. If that's not a concern, then it's a moot point.

Here's what I was looking at for the motor and driver, I'm going to couple that with a 24v dc power supply. I would imagine that all I would need from the arduino is a PWM signal. Thoughts???

I can't see any temperature ratings for the 17HS4401 motor in the datasheet I found - but its 1.7A at 1.5ohm which is only 4.3W of dissipation. I've seen other NEMA17 motors rated for twice that power dissipation (and 80 degC temperature rise), so I think that motor's going to be about 40 to 50 degC above ambient in use.