Duty Cycle of Motor
Duty Cycle of Motor
(OP)
Hi, I'm an engineering student working a summer internship, and my current project has completely stumped me. I'm trying to take regular conveyor belt and automate it, however, it won't be in continuous operation; it will only be moving one 250lb cylinder about 6 feet every 60 seconds or so. So the motor needs to be in operation for about 6-8 seconds every minute.
So far, I haven't found that motor suppliers post their specs for how often you can start and stop a motor, so the next best option I was looking at was getting a motor that runs all the time, and throwing an electromagnetic clutch on it to engage and disengage when needed. The only problem with this idea was that all the electromagnetic clutches I found were in the $900+ price range.
So I guess my two questions are: do motors exist with that kind of duty cycle and where might I look for them?
Or alternatively, is there a better/cheaper option than an electromagnetic clutch to solve the problem?
Thanks,
P. Thiessen
So far, I haven't found that motor suppliers post their specs for how often you can start and stop a motor, so the next best option I was looking at was getting a motor that runs all the time, and throwing an electromagnetic clutch on it to engage and disengage when needed. The only problem with this idea was that all the electromagnetic clutches I found were in the $900+ price range.
So I guess my two questions are: do motors exist with that kind of duty cycle and where might I look for them?
Or alternatively, is there a better/cheaper option than an electromagnetic clutch to solve the problem?
Thanks,
P. Thiessen





RE: Duty Cycle of Motor
http://www.brithinee.com/knowledge/Allowable_Start...
looks like a good place to start.
$900 in the context of a line stopper sounds like peanuts to me. If you look at production machinery you'll notice that it often appears to be overdesigned, which incidentally is why we are using 60 year old stamping presses to build bodies for modern cars, but I don't think that is an accident.
Cheers
Greg Locock
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RE: Duty Cycle of Motor
RE: Duty Cycle of Motor
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Duty Cycle of Motor
1.33 here for instance. Click on the + to see NEMA's reply.
https://www.nema.org/Products/Pages/FAQ.aspx
So also should someone in the motor manufacturer's engineering department or technical (probably not sales) support.
60 starts per hour (SPH) is a bunch. Some stuff will heat up from the inrush current, and there won't be much time for the heat to dissipate.
A more appropriate question for the motor mfr is minutes between starts (sometimes called MBS).
RE: Duty Cycle of Motor
Why don't you replace the enclosed fan on the motor with a separate electrically driven fan which is on all the time?
I think you'll find a fan able to deliver the same air flow for less than $900.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Duty Cycle of Motor
You'd be better off using a VSD to control the motor as this will put far less heat into the rotor, or use a PM motor with an AC drive. The latter solution will likely cost you more than $900 though.
RE: Duty Cycle of Motor
TMoose, the article you posted lists mainly for larger motors, but there is a tendency towards smaller motors having shorter MBS. The motor I plan on using only needs about .3 HP, which is much smaller than any of the motors listed.
Do you think that the heat created by such a small motor could safely be ignored?
Alternatively, this article:
http://www.dartcontrols.com/2013/09/ac-and-dc-moto...
seems to suggest that a DC motor is better for applications with quick starts and stops, but doesn't mention if a high start/stop cycle would be damaging to the DC motor.
In the context of this project, would a DC motor possibly be more practical?
Thanks,
P. Thiessen
RE: Duty Cycle of Motor
............. In the context of this project, would a DC motor possibly be more practical? "
I would settle for nothing less than a written approval from the motor manufacturer.
RE: Duty Cycle of Motor
A booklet that I have referred to for several years on motors - the Cowern Papers is a good reference on AC (and DC) motors.