Shopsmith Forums

Tell me where I am wrong!

I'm sure Bill V. could say it better. But, I think the answer the answer is the PP isn't delivering its full potential hp unless it's called for. Spinning an unloaded blade, it's putting out a fraction of the hp it's capable of. Think of it as a super-fast acting dimmer switch.

dusty wrote:

wa2crk wrote:Dusty
Yes you are correct, but the system only draws extra current when it is put under load. That is the beauty of the whole system.
Teknatool used to have a video on their website of a side to side comparison of a conventional lathe and one of their DVR lathes. At the end of the test the watthour meter showed a savings of 50% in the power consumption. A conventional induction motor that powers my bandsaw draws 12 amps under no load and more under load. It is the "no load" power consumption where the savings are realized. The microprocessor and the RPM monitoring senses the load and makes the proper adjustments to speed and torque constant.
JPG; I think that the power dissipation limits of the power supply components have a little bit to do with the voltage ratings vs power. ( more likely an engineering decision).
Bill V

The operative word being "extra"; this is true of all electrical circuits. When the load increases, the current increases. Actually, in this discussion I consider "load" and "current" to be synonymous.

The bottom line: The PowerPro (DVR) is more efficient than other similarly sized motors of conventional design. I buy all of that. I just don't understand the apparent contradictions when one applies the mathematical formulas to the PowerPro characteristics.

If the definition of horse power remains applicable to the dvr, then it consumes 745.699872 watts of power whenever it is delivering 1 horse power. If delivering 1hp of energy, it is drawing 6.2 amperes of current if operating on 120vac. I don't care which motor technology is at play.

745.699872hp/120 vac = 6.212989 amperes.

Tell me where I am wrong!

For a resistive load, you are correct: Input Power = Voltage x Current.
However, the mechanical output power of a motor will always be somewhat less than the electrical input power. The loss energy (that makes the motor hot) has to come from somewhere.

But here's the main problem. For an inductive load (such as a conventional induction motor), the above formula is incomplete.

The complete formula is: Input Power = Voltage x Current x Cos(Theta), where Theta is the phase angle between the current and the voltage.

For a hypothetical pure inductive load, Theta = 90 degrees, and zero power is consumed, regardless of the current. What happens is that energy is stored in the inductor for part of the AC cycle, and then returned to the grid during the remainder of the AC cycle. This is why conventional Shopsmith motors draw significant current even when not under mechanical load.

By the way, the electric company doesn't charge residential customers for current, it charges them for power. So that out-of-phase, no-load current increases your electric bill by only a tiny amount, for the resistive power (heat) losses in the wiring.

OK Dusty, What power consumption results from the 'calculation' at no load? Only a small(3A?) amount of 'standby' power.

I do not understand where the inconsistency is. More likely the PP draws more than 6.2A at 1 hp.

Realize the input power is dependent upon the mains waveform(sinusoidal) which will result in power consumption only near the peak voltage values(assuming typical full wave bridge or switching power supply), but the output is pulsed at a frequency/duration independent from the mains voltage values.(sorry to use the 'mains' terminology, but 'supply' would have created confusion)

Also mains input current is determined by immediate past output power(the power supply storage is depleted).

The 'math'(745w/hp) applies to steady state conversion. The relationship of amperes to power assumes the current is sinusoidal with no current phase shift(power factor of 1). It also assumes 100% efficiency.

That precludes use on an induction motor as well, but they deviate less.

O.K. - ALRIGHT-ALRIGHT-ALRIGHT!!!!! Enough of the theory of motor/DVR theory

Did Jerry (opus 139lsb) ever get his PowerPro fixed? Will we now ever find out????

Seems you guys should start a new thread is you want to publicly discuss this stuff. Another alternative is - - Buy your own PowerPro and you can experiment on it.

opus139lsb wrote:Went to use the lathe today 5/27/15 , turned on the main power at the head and all I got was a flickering of light on the little screen the unit is dead. Has any one had this problem ? Will try to call customer service 5/28/15. Last used the lathe about a week ago without any issues.
Purchased the unit 12/13/13. Thank you Jerry

charlese wrote:Did Jerry (opus 139lsb) ever get his PowerPro fixed? Will we now ever find out????

Only if he bothers to post. Not like we have huge numbers of posts per day on this site, I kinda like the side discussions. Better than nothing!

Some members only want to discuss only what directly relates to themselves while others will participate in discussions about 'anything'. Some are even experts in everything. But I got the message. I'll go away now.

rcplaneguy wrote:

charles :D :D e wrote:Did Jerry (opus 139lsb) ever get his PowerPro fixed? Will we now ever find out????

Only if he bothers to post. Not like we have huge numbers of posts per day on this site, I kinda like the side discussions. Better than nothing!

Hopefully he has not responded because of lack of opportunity to do so.

Then again perhaps once the needed info is gotten, the source of that is 'forgotten'.

The second is all too prevalent in this day and age, but we can hope for the first.

Consider these 'side trips' as brain storming(not a bad thing). Misplaced perhaps, but not bad.

See I can be a curmudgeon as well.

dusty wrote:Some members only want to discuss only what directly relates to themselves while others will participate in discussions about 'anything'. Some are even experts in everything. But I got the message. I'll go away now.

Before you go away, I can explain it. It's magic!

My Powerpro occasionally gives me an error message if I leave it on and unattended for period of time (several hours). Of/on and it resets. I blame possible power surges...

Good evening, I have been watching the posts on this topic, really pleased on the response and the added information on power usage.
I will not be able to take the head apart until next week, my part time job runs from Thursday to Sunday and I'm too tired to drive to the shop and spend hours working on the machine. Will keep everyone up to date on what happens. I called Shopsmith also and they recommend to first make sure the 10 pin female connection is tight to the control panel and then will see what happens. The unit is covered under warranty so there's no problem. Will give a try first before sending in on warranty . Jerry

To Chris Neilan
Try tying a few overhand knots in the power cord. Sounds goofy but it adds a small amount of inductance which acts like a high resistance at the frequency of "glitches". It just might help.
Bill V