Power consumption

[wa2crk]

I came across some nice vintage ( that means old ) Simpson meters the other day and decided to do something that I have intended to do for a long time.
I checked the amperage and voltage of the items in my shop simultaneously and got at least one surprising result. All of the items powered by induction motors drew in excess of 15 amps on initial startup which did not really surprise me. The length of time that the current was over 15 amps did surprise me.

[ATTACH]25425[/ATTACH]

A Shopsmith bandsaw on a Shopsmith power stand
Steady state running amps with a 1/4" blade was 6.5 Amps

Shopsmith Power Station with no load attached
Steady 10 amps

Delta dust collector
steady 9 amps

Jet 10/20 drum sander
steady 6 amps

Old Craftsman drill press (Circa 1960)
steady at 7.4 amps

Delta 46-460 VS lathe
Surge current was 5 amps and the steady state current with no load was less than 3 amps but rose rapidly when I loaded the lathe by grabbing the handwheel.

Jet 1 HP 8" grinder
The surge current was in excess of 15 amps and remained at that level for at least three seconds then held steady at 10 amps. (small surprise)

Craftsman 1/4 HP 6" grinder (circa 1953)
Surge current over 15 amps for 3 seconds then dropped to 3 amps (also a small surprise)

I attribute the small surprises to the fact that the grinders have to spin up the wheels and the inertia causes a lingering surge current.

Now for the final test the, Shopsmith Power Pro headstock.
The test box was inserted into the line and the headstock was turned on to let the system boot up. The current was very low and difficult to resolve because of the compression of the meter scale but was less than three amps and then fell to almost zero. I attribute most of the current to charging capacitors.

Now for the good part
A speed of 3450 RPM was selected and the headstock had a DeWalt 10" blade attached. Start and Confirm were pressed and as the blade came up to speed the current never went over 6 amps. As soon as the system achieved operating speed the current dropped to 3 amps and remained steady. That's less than 1/3 of the power consumption of the Power Station alone!!

When you read some of the current draws you will realize why good circuits are an absolute necessity.

Hope this helps someone.
Bill V

[dusty]

I can't speak to the PowerPro at all but the rest appear as I would expect except for the Power Station.

That seems high but maybe I just don't remember.

I assume that "no load" means no SPT attached and the motor running at low rpm.

[wa2crk]

Dusty
You are correct in that no SPT's were attached to the Power Station. The current remained constant throughout the speed range. I think this because the motor runs at a constant RPM but the additional losd of the reeves drive may cause a bit more current draw.
Bill V

[BuckeyeDennis]

I came across some nice vintage ( that means old ) Simpson meters the other day and decided to do something that I have intended to do for a long time.
I checked the amperage and voltage of the items in my shop simultaneously and got at least one surprising result. All of the items powered by induction motors drew in excess of 15 amps on initial startup which did not really surprise me. The length of time that the current was over 15 amps did surprise me.

[ATTACH]25425[/ATTACH]

A Shopsmith bandsaw on a Shopsmith power stand
Steady state running amps with a 1/4" blade was 6.5 Amps

Shopsmith Power Station with no load attached
Steady 10 amps

Delta dust collector
steady 9 amps

Jet 10/20 drum sander
steady 6 amps

Old Craftsman drill press (Circa 1960)
steady at 7.4 amps

Delta 46-460 VS lathe
Surge current was 5 amps and the steady state current with no load was less than 3 amps but rose rapidly when I loaded the lathe by grabbing the handwheel.

Jet 1 HP 8" grinder
The surge current was in excess of 15 amps and remained at that level for at least three seconds then held steady at 10 amps. (small surprise)

Craftsman 1/4 HP 6" grinder (circa 1953)
Surge current over 15 amps for 3 seconds then dropped to 3 amps (also a small surprise)

I attribute the small surprises to the fact that the grinders have to spin up the wheels and the inertia causes a lingering surge current.

Now for the final test the, Shopsmith Power Pro headstock.
The test box was inserted into the line and the headstock was turned on to let the system boot up. The current was very low and difficult to resolve because of the compression of the meter scale but was less than three amps and then fell to almost zero. I attribute most of the current to charging capacitors.

Now for the good part
A speed of 3450 RPM was selected and the headstock had a DeWalt 10" blade attached. Start and Confirm were pressed and as the blade came up to speed the current never went over 6 amps. As soon as the system achieved operating speed the current dropped to 3 amps and remained steady. That's less than 1/3 of the power consumption of the Power Station alone!!

When you read some of the current draws you will realize why good circuits are an absolute necessity.

Hope this helps someone.
Bill V

Whoa there, Bill. Unless the load is resistive, you can't just multiply voltage and current to determine power consumption. For reactive loads such as an induction motor, the complete formula for single-phase power is
P = V * I * Cos(Theta), where Theta is the phase angle between the voltage and the current.

Your Simpson meter cannot measure the phase angle, and thus it cannot be used to determine the power draw. Special instruments are necessary to measure true power.

Under no-load conditions, the phase angle for an induction motor may approach 90 degrees. And thus the actual power consumption is much smaller than it would seem from your measurements.

I do believe you that the PowerPro draws much less startup current. But even here, you can't trust the Simpson meter to be accurate. They are calibrated to give a true-RMS current reading if, and only if, the waveform is sinusoidal. But the PowerPro input is almost certainly a full-wave bridge rectifier feeding a bank of DC bus capacitors. The resulting current waveform is a series of high-current pulses at the peaks of the AC waveform, when the instantaneous line voltage is higher than the DC bus voltage. And it is approximately zero amps in between those peaks. The Simpson readout will be proportional to the true-RMS current, but will have a scaling error.

All that said, your current measurements are indeed a good measurement regarding the current-capacity of the house wiring and fuses/breakers. Those are resistive, and your Simpson meter's RMS current readings can be used to accurately predict the voltage drop (and the power loss) in a given wiring run.

[JPG]

Whoa there, Bill. Unless the load is resistive, you can't just multiply voltage and current to determine power consumption. For reactive loads such as an induction motor, the complete formula for single-phase power is
P = V * I * Cos(Theta), where Theta is the phase angle between the voltage and the current.

Your Simpson meter cannot measure the phase angle, and thus it cannot be used to determine the power draw. Special instruments are necessary to measure true power.

Under no-load conditions, the phase angle for an induction motor may approach 90 degrees. And thus the actual power consumption is much smaller than it would seem from your measurements.

I do believe you that the PowerPro draws much less startup current. But even here, you can't trust the Simpson meter to be accurate. They are calibrated to give a true-RMS current reading if, and only if, the waveform is sinusoidal. But the PowerPro input is almost certainly a full-wave bridge rectifier feeding a bank of DC bus capacitors. The resulting current waveform is a series of high-current pulses at the peaks of the AC waveform, when the instantaneous line voltage is higher than the DC bus voltage. And it is approximately zero amps in between those peaks. The Simpson readout will be proportional to the true-RMS current, but will have a scaling error.

All that said, your current measurements are indeed a good measurement regarding the current-capacity of the house wiring and fuses/breakers. Those are resistive, and your Simpson meter's RMS current readings can be used to accurately predict the voltage drop (and the power loss) in a given wiring run.

Kudos for realizing that! Those meters are 'average' responding which is why waveform is crucial for proper calibration.

[wa2crk]

I know that but I just wanted to determine what the current was and if there was any voltage variation.
Bill V

[JPG]

I know that but I just wanted to determine what the current was and if there was any voltage variation.
Bill V

Was there?

I assume you were measuring at the power plug of each machine.

[wa2crk]

Voltage held at 124 volts but dropped to about 120 volts at initial start up of each machine The photo shows the box, and the wire on the left plugs into the wall and the one on the right gets the machine plugged into it, There was no attempt to make any power factor corrections it was just a check of voltage and current to determine what machines could be run at the same time. As an example, if the bandsaw and the dust collector are run together on a 15 amp circuit for more than a few minutes the breaker will trip.
From the results, I may abandon the use of the power stand and station and return to the PP headstock to power the SPT's.
Bill V

[dusty]

Voltage held at 124 volts but dropped to about 120 volts at initial start up of each machine The photo shows the box, and the wire on the left plugs into the wall and the one on the right gets the machine plugged into it, There was no attempt to make any power factor corrections it was just a check of voltage and current to determine what machines could be run at the same time. As an example, if the bandsaw and the dust collector are run together on a 15 amp circuit for more than a few minutes the breaker will trip.
From the results, I may abandon the use of the power stand and station and return to the PP headstock to power the SPT's.
Bill V

Is that a statement of fact or are you drawing that conclusion from the amperage numbers that you have collected.

[wa2crk]

Dusty
Your highlighted statement is a fact. One of the reasons why I wanted to investigate. The rest, maybe.
Bill