Overloading a DC motor

[chet jamio]

Has anyone actually burnt up a motor on their DC? If so, what type of usage did it receive before it died (hours/day, duct sizing, number of machines on at one time...)? I have read several comments stating that increasing the diameter of your inlet size and duct diamter will overload your motor. I can see how running a motor with no filter or ducting may cause problems. However, I am skeptical about the dangers once a filter, ducting, and machine hoods are used, even if the duct size has been increased.

[Rod Sheridan]

Hi Chet, it is possible to overload a dust collector motor by running it without ducting, although of course it depends upon the dust collector design.

My cyclone does run at greater than full load with no ducting attached.

The only way to tell is to measure the motor current.

I doubt if the bag type collectors have this problem, I haven't seen one that actually meets spec's yet, let alone exceed them.

regards, Rod.

[Sonny Edmonds]

Chet, they have resistance from the ducting, and also from the filtering beyond the fan.
It would be interesting to find one of these Pollyanna's who did actually burn out a dust collector motor.
But don't hold your breath, Chet.

[Tom Veatch]

... However, I am skeptical about the dangers once a filter, ducting, and machine hoods are used, even if the duct size has been increased.

As am I!

According to my clamp-on ammeter, my motor (20.8 FLA) draws appx 44 amps spinning the impeller in free air. If the 30 amp circuit breaker didn't trip, the internal thermal protection in the motor would soon open the circuit and shut the motor down. Simply placing the impeller inside the housing and mounting it on the cyclone lowers the amperage to about 20 amps. So, regardless of the size of the the ductwork in my system, I have no worries about overloading the motor. I suspect that's somewhat typical of other cyclone systems.

YMMV, but as mentioned, the only way to know for sure with any specific system is to measure the amperage draw of the motor in the particular configuration of interest. However, you can measure the amperage with the system assembled with no ductwork connected. If the amperage in that configuration is at or below FLA, you'll know there's no problem since the motor won't draw more than that no matter what size ducts are used.

[Sonny Edmonds]

As am I!

According to my clamp-on ammeter, my motor (20.8 FLA) draws appx 44 amps spinning the impeller in free air. If the 30 amp circuit breaker didn't trip, the internal thermal protection in the motor would soon open the circuit and shut the motor down. Simply placing the impeller inside the housing and mounting it on the cyclone lowers the amperage to about 20 amps. So, regardless of the size of the the ductwork in my system, I have no worries about overloading the motor. I suspect that's somewhat typical of other cyclone systems.

YMMV, but as mentioned, the only way to know for sure with any specific system is to measure the amperage draw of the motor in the particular configuration of interest. However, you can measure the amperage with the system assembled with no ductwork connected. If the amperage in that configuration is at or below FLA, you'll know there's no problem since the motor won't draw more than that no matter what size ducts are used.

Now that, is ridiculous, Tom.
If I take my car and put heavy pressure on the brakes while driving, I can overload my engine, too.
What good would a fan, outside of a housing be as a dust collector? NONE.
That is a ridiculous comparison. Totally out of the realm of the manufacturers design.

[Tom Veatch]

What part was ridiculous, Sonny?

Was it the part where I showed that running the impeller in free air would overload the motor? That simply shows that it is possible for a motor driving a fan to be overloaded.

Was it the part where I showed that my system assembled without any ductwork doesn't overload the motor? That simply shows that it isn't necessarily true that a motor will be overloaded with "infinitely large" ductwork.

Was it the part where I advised that if the motor wasn't overloaded without any ductwork then it couldn't be overloaded with any sized ductwork that might be installed? That is a simple deduction based on the principles of aerodynamics, work and energy.

Maybe it was the part where I concurred that to really know for any specific system, testing of that particular system would be required? That's simply based on the fact that there are too many variables in the universe of dust collector systems to reliably predict the characteristics of a general system based on testing of one specific system.

Please enlighten me.

[chet jamio]

Tom - thank's for that data. I am doing similar amp readings to mine and am finding similar results. I'm starting to think all these claims of overloading the motor are on par with dust explosion claims if you don't ground your PVC. Lot's of fear, but no actual occurances. However, it is possible that a manufacturer has produced a machine which draws dangerous amps if ran without ductwork. That would be another good question: "Has anyone exceeded FLA with no ductwork attached?" I know Pentz has big worries about this. I'll check his site again to see if he has relevant data.

I completely understand what you're trying to say by comparing the 44 amp free-state to the 20 amp installed-but-no-ductwork (the cyclone body itself is enough to keep significantly reduce amps and keep them below FLA, no ductwork needed). I'm sure most readers understand too. Just wanted you to get some positive feedback for you sharing.

Sonny - you need to relax and be nice. Agressive posting causes people to be reluctant to share their ideas. Remember, we're sharing ideas, not publishing in scientific journals.

[Rod Sheridan]

Yes Chet, as I stated in my post, my cyclone does draw greater than rated motor current without ducting.

However I only ran for about 1 minute to check the motor operation before continuing with the installation.

regards, Rod.