×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

How slow can I run my DC motor?

How slow can I run my DC motor?

How slow can I run my DC motor?

(OP)
I've got a 90Vdc 1/8hp gearmotor (Dayton 4z383) that has an output speed of 30rpm.  I have an application that would require me to run it as slow as 2 rpm - so I'd be applying only about 6 volts to it.  I believe that there is a problem with running dc motors too slow and overheating them - how slow is too slow.  If I need to change ratio or speed it up, how far do I have to go to be in the "green zone" again?

Thanks.

RE: How slow can I run my DC motor?

Need to know some more info
Whats the gear ratio of the unit?
What form factor is the control?
What's the load on the gearmotor?

I've had a small 130v Bodine on the bench and it runs OK at 6 volts but thats off load

RE: How slow can I run my DC motor?

You have three things to consider when running a DC motor at low speeds:

First. Cooling. Will the air circulation be adequate at that speed? You have to test to find out. If the motor gets too hot - than external cooling is needed.

Second. At that speed, the collector can overheat locally, since the brushes will stay on each segment for a prolonged time. The time constant of these little bronze pieces is very short.

Third. The winding is usually not designed to be carrying current for a long time. If the motor runs very slowly, the commutation between different parts of the winding does not happen very often. And that can lead to overheating the coil that is carrying current. It definitely does so if you stall the motor for en extended time.

But since this is something like 6 or 7 percent of nominal speed, I think that the motor will be OK. Make sure it doesn't stall.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: How slow can I run my DC motor?

Why not just gear it down and avoid these problems?

TTFN



RE: How slow can I run my DC motor?

You say, "as low as 2RPM".

"How fast do you need it to go?", and we can tell you how much to gear it down.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: How slow can I run my DC motor?

(OP)
Thanks for the input guys.  I did get in touch with the mfg and am told that they normally are OK with a 1/20 speed reduction from nominal but that the 1/17 that this application represents could be considered "on the edge" and may cause problems.  Changing the gearmotor to a larger reduction is the easy answer but one we were trying to avoid in order to keep this drive the same as some past machines.  However, in light of the mfg's comments I think we'll do just that and go to the next size reduction which puts us back in the acceptable range.

Thanks again.

RE: How slow can I run my DC motor?

If you can afford it conservative is always good!  Good luck.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: How slow can I run my DC motor?

I do not quite get it.

Quote: normally are OK with a 1/20 speed reduction from nominal but that the 1/17 that this application represents could be considered "on the edge" Unquote.

The 1/20 is a larger speed range than the 1/17 that you need. So, according to that statement, you should be fine.

But do not expect speed to follow voltage linearly. The internal resistance in these small motors is quite high. So do not be surprised if you need about 10 V instead of 6 V to get your 2 PRM out of it. The main question is how it is loaded. If your load changes a lot, then a new gear ratio is needed. If it is more or less constant, a voltage reduction should be OK.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: How slow can I run my DC motor?

We are assuming that your motor has a permanent magnet field. If it has a shunt field the field should be held at full voltage and only the armature voltage varied.
respectfully

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources