I measured the current to the 8.6a motor on my table saw while ripping some
6/4 oak with a combination blade. I figure that is about the heaviest I ever stress it. It measured 9.1a. What should I make of that? Is it normal to go over the rating on heavy loads? I haven't had any problems; I was just curious what the current would be.
small typo, the motor is rated at 8.4a, not 8.6a. 240v.
Perfectly normal. When motors wear the bearings are one of the first things to go and a quick way to find out is to measure the load. It will be higher than the rating. Left to go too long that way the motor will burn out. Same with blower motors when the bearings on that start to bind the motor overworks. Pumps, same deal.
You did not harm running that way for a few minutes, but after a few hours, you'd potentially have a problem.
According to Toller :
Well, there's always the question of how accurate the meter is - expecting high precision in amperage and voltage measurements on AC circuits is a bit of a mistake, particularly with normal "consumer grade" voltmeters.
That said, the plate rating is more-or-less the maximum amperage expected when running the motor at the rated duty cycle/loading that you could continue indefinately without overheating.
Chances are that you were loading the motor a bit beyond its ratings, and the amperage reflects that.
It's of no great import for short periods, however, if you kept at it long enough, there's a darn good chance that the motor will begin to overheat and have the thermal protector cut-in.
I would never use it like that for more than a minute at a time. So, am I okay, or are you warning me my bearings are going?
No, just a heavy load. No harm for short periods. Knowing what it takes under no load, you can always check it years from now if you suspect a problem.
Peak meter or RMS meter? Where did you measure? When was the meter last calibrated?
How big of a cord are you using and how far are you from the source? (total distance)
I have a 10 inch dewalt that I hammer occasionally. I just let the motor run for awhile after I am done pushing it so it can cool off.
It was like 3.8a no load. Reason I was looking at it so I could compare it to my "new" shaper. The shaper has a 14.4a motor (120v) and draws 11.5a no load, and 12.1a while shaving an eighth inch off the same 6/4 oak. The no load is rather high, but it hardly goes up while doing serious work. I am not sure what to make of that.
Just a $60 HD special. I don't know how accurate it is, but it is extremely consistent.
12 gauge, maybe 60'. Wouldn't be significant voltage drop.
If I am not going to cut with it again immediately, is it best to let it run afterwards anyhow?
My habit it to hit the "off" with my knee when the cut is done; but could let it run if that is important. (saw came with a 10"x12" off switch; seems like a waste of $100 to me, but it sure is easy to use.)
Hmm. Ever see the amperage given and stated as maximum. Electric motors draw more power the harder they are worked. Of course if you work it hard enough it draws a law of power (liked at locked rotor) and will burn up rather quickly. Most however are are protected.
So what does it read when the motor is just spinning and not sawing? 9.1a is not significantly higher than 8.6a, depending on the accuracy of your meter.
It was 3.8a no load. I guess I will just forget about it then, except to avoid cutting too much
6/4 oak at a shot. Thanks
Completely normal. I know of a couple motors running exhaust fans that operate 24/7. The motors were slightly undersized for the job. When we left the job the motors were pulling 1 amp over the name plate rating. That was four years ago and the motors are still running fine! Your few second venture into a slight motor overload will not hurt them at all. Greg
According to Toller :
After hard slogging, even a few seconds of freerun will make a huge difference in "bake time" - having given the blower chance to move cold air without the coils producing any heat. Whether that decreases safety otherwise, is something only you can answer.
One way to tell if the motor should be run to cool is how hot it gets, including a little after it is turned off. Motors can run pretty hot in normal use. I don't see any problem with what you are doing either.
A lot of motors also have a Service Factor, or SF, rating. Typical would be a SF of 1.15 which means you can run the motor at 1.15 times the rated current full time at a slight reduction in life.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.