How long can machines be left on?

[Gabriel Billings]

This seems like a pretty basic question. Someone has probably asked it before, but I didn't have any luck digging up an answer using the search function, so here goes.

I was sanding some plywood pieces for a closet organizer I'm making, and a look at all the dust covering everything made me think that maybe a downdraft table would be a good idea.

If I were to build one, is there any limit to how long I can leave my dust collector running without giving it a break? Are they designed to run indefinitely, or do they need a smoke break every 15 minutes? How about a shop vac? For that matter, how about the sander itself? If it hasn't burst into flames in my hand, is it doing ok? I can spend 30-40 minutes churning through one sanding pass on all the pieces.

Most of my other machines don't get used for long periods of time, but I could see putting in marathon sessions on a sander and downdraft table.

Do I actually need to worry about this, or am I just being paranoid?

[Joe Jensen]

In general, starting a motor repeatedly is harder on it than running. All the machines I have have continous duty motors. My DC only wants me to start a max of 6 times per hour..joe

[Jason Whelehon]

That's a question with about 30 variables.

What type of motor?
What brand of motor?
What voltage?
What amperage?
What wattage of work?
What kind of heat dissipation?

The list can go on and on.

The short answer? Make sure the motor has an overload switch if it's overworked or overheated. If not, I'd venture a guess that a few hours wouldn't be ridiculous.

I use a squirrel cage (http://www.willowridgestudio.com/images/SquirrelCageTight.JPG) for an air cleaner and the motor get's to about 140° in about an hour or so.

[Larry Fox]

I agree with Joe that the greater risk is probably start / stop cycling them too much as opposed to letting them run too long. I would expect that commercial shops run some pieces of gear all day every day without issue. I am definitely not an expert though.

[Rod Sheridan]

Hi Gabriel, you can indeed leave your dust collector running continuously without worry.

Your dust collector will have an induction motor, induction motors cannot be started more than a certain number of times per hour based upon the inertia of the load, and the motor design.

When starting a high inertia load, the rotor will be rotating much slower than rated speed, this difference induces heavy currents into the aluminum bars in the rotor (that's what is in between the two aluminum ends of the iron rotor). The heavy currents cause heating of the bars, and of course the stator windings have heavy current which causes heating.

The motor can only reject so much heat to the atmosphere, so startings have to limited to a certain number per hour.

Note that an electric motor at full load will have a substantial temperature rise, the motor will be too hot for you to touch, yet be well within it's operating range. The motor of course needs overcurrent protection, or built in thermal protection to protect it from overloads.

At work we often run motors continuously for 5 years, then take them out of service for bearing replacement, cleaning and testing. We haven't had one yet that needed bearings unless it had experienced an accident of some sort.

Regards, Rod.

[John Thompson]

Good advice on continous duty motors as I run my DC for two hours straight sometimes as an amateur that logs 6-10 hours a day in a shop. But.. he also ask about a Shop Vac and smaller electrice motors.

I don't have a electrical engineers answer but I don't run them for very long periods as they get very hot doing so. I prefer to turn them off and on as I need them and have not had problems doing so.

So.. any of you electrical guru's might comment on that end to avoid the OP carrying the continous duty practices over to Shop Vacs...etc.

Sarge..

[Cliff Rohrabacher]

is there any limit to how long I can leave my dust collector running without giving it a break? Are they designed to run indefinitely,


They should be continuous duty motors. Check the manuf' specs.


or do they need a smoke break every 15 minutes?

That'll cost you more electricity. Starting a motor burns lots more than running it.


How about a shop vac?

While sucking the wasps buried in the walls out one at a time I leave my Rigid from the BORG on for days at a time. No harm.


For that matter, how about the sander itself? If it hasn't burst into flames in my hand, is it doing ok? I can spend 30-40 minutes churning through one sanding pass on all the pieces.

I use my PC speed bloc for whole days at a stretch (sander sleeps when I do) no problem. Where I used to work making hand made furniture we had the same PC Speed Bloc sanders and they ran all day every day.




Do I actually need to worry about this, or am I just being paranoid?

Paranoid.

Take copious quantities of beer.

[Peter Quinn]

If your motor is continuous duty you can turn it on in the morning, shut it off in the evening, no problem. If not continuous duty, I don't know. I have forgot mine on and left the shop for hours, not a problem. At work we turn them on at 8AM, shut them off at 5PM every day for 20 years, never a problem yet.