No Load Amps for planer

[Bill Orbine]

Hi guys, love this website and I'm new here. I just aquired a new Powermatic Shaper (PM2700 5 hp 230 volts single phase) and Powermatic 20" planer (209-HH, also 5 hp 230 volts single phase). I hooked up the juice and tested the amps @ no load. Shaper is fine at 5 amps no load. Planer, I'm not so sure and have a cause for concern. The planer's no load amp is 14. Seems quite high. Took off the v-belts and it still read the same (eliminated the mechanical). Even moved the planer to the shaper's plug-in and it's still the same. I'm getting 25-28 amps planing about 1/16 off a 10 inch wide board. Motor rated for 28 amps. Seems like something is amiss. Wiring is sufficient and properly hooked up. Any suggestions before I mince words with the manufacture? I'd appreciate some comments. Thanks.

[Mike Henderson]

This is somewhat difficult to explain, but often an induction motor will have approximately the same amperage under no load conditions as under a modest load (not full load, but a modest load). The motor looks like an inductor to the power system. Under no load, current flows through the motor, but the current is not in phase with the voltage. And because of that, the real power used by the motor is fairly low. As you load the motor, the current becomes more in phase with the voltage and more power is consumed by the motor.

If you had a watt meter and hooked it to your motor, you'd see a fairly low power draw at no load, becoming higher as the motor is loaded. If you also hooked an ammeter to one of the lines, you'd see a fairly constant current draw. 14 amps no-load on a 28 amp rated motor is about right.

This is one of those non-intuitive things about electricity.

I can't say for sure that your motor is fine, but if it's not getting excessively hot, I'd just use it.

Mike

[Rick Christopherson]

Actually, the number that surprises me is the 5 amps from your 5 hp shaper. This number should be closer to the 12-15 amps you are seeing on the planer.

A general rule of thumb is that an induction motor will draw about 50% of its rated amperage when it is running idle. As Mike stated, this large current is out of phase with the voltage, so not only is it not performing any actual work, but it is also not costing you very much money--for the same reason.

[Dan Friedrichs]

Mike is absolutely right. It's drawing out-of-phase current, which makes it look like it's drawing a lot on an ammeter, but the real power consumed is low. As you increase the loading, the power factor goes up, and more real power is consumed.

If it's not getting hot, then you're not burning much power.

[Bill Orbine]

OK Guys! Thanks for your input. I did notice the motor on the planer barely got warm and the wiring was cool to the touch. Still a little skeptical but I'll take your words for it and use the machine and I will keep an eye on the temps and current draw. The planer has it's own power trip built within the machine and if the loads get heavy enough, that trip should be the first to kill the machine before the breaker in the electrical panel does. I'm sure the shaper is fine too, with the low amps it draws under no load just like all my other machines do except this planer.