230 / 115 v question....confused in CA

[Steve Speiser]

Well, now I'm confused. I've read numerous times that it makes not difference in h.p. whether a motor is wired 110/115 or 220/240. And yet, my Nova DVR xp lathe states something different in the owners manual. Specs as follows:
-Motor Type: Digital Variable Reluctance
-Accuracy of Speed Stabilization: <2.5%
-Motor Power: 1.75 Hp for 115v, 2.3 Hp for 230v
-Regulator Type: PID
-Efficiency: > 0.80 Speed Stabilization: Current level, pulse width
Is there something different about the type of motor they use or am I just missing something.
Knowledable comments will be most appreciated!
Thanks,
Steve

[Mike Henderson]

Note that what you have is not an induction motor but a reluctance motor. A reluctance motor is controlled by electronics but I don't know the reason for the difference in HP. You might drop Teknatool an e-mail and ask them. They've probably been asked that question a bunch of times and have a ready response.

Mike

[Robert Reece]

For a "dumb" motor, the rule you have is correct. Double the voltage, the current drops by half and you end up with the same power. However, the DVR has circuitry that determines how it runs and such so that circuitry is going to determine to some extent your effective horsepower. The internals of a DVR motor are not the typical windings that we find so it sounds like a DVR produces more horsepower at higher voltage. Maybe you should run it at 440V. Just kidding.

[Mike Lipke]

This is the exception, due to the Variable speed control.
There is no difference in hp, but a 220 volt has a little more starting torque, due to the wires will carry more current, but your electric bill will be the same (we often hear an urban legend that 220 v motors are cheaper to run, cuz they use half the current). Watts is what you pay for, and watts are volts times amps.

So, 15a times 110 v = 1650 watts
7.5a time 220 v = 1650 watts.

[Andy Bardowell]

As far as I knew it was the savings in amperage that was the big advantage, to do the same amount of work, a 110 (115 where you are) volt electric motor will use about twice the amperage as a 220 volt motor so 220 saves money obviously. I suppose though that it could be wired to give more HP, I know a 220 will start faster and come up to speed faster.

[Dan Friedrichs]

As far as I knew it was the savings in amperage that was the big advantage, to do the same amount of work.

The advantage from savings in amperage is that you can use thinner (cheaper) wire. The size of the wire determines it's ampacity, but the wire can carry any voltage (as long as the insulation is rated for said voltage).

a 110 (115 where you are)

Actually, it's often 110 where we are, too. The voltage on the line easily varries +/- 10%.

volt electric motor will use about twice the amperage as a 220 volt motor so 220 saves money obviously.

You're billed by the watts you use, not amps. Go check your power meter - it says "watt-hour meter", not "amp hour meter". Suggesting that you pay for amps is like saying the water company bills by the speed of the water going to your house, without accounting for the size (diameter) of the pipe, as well.

I suppose though that it could be wired to give more HP, .

Only in the VERY specific case the OP mentioned, a reluctance motor can change it's torque/speed characteristics at a different input voltage based on how the electronics switch the current to the windings. Chances are, though, that you'll never see a reluctance motor in your life, and re-wiring a motor to get more HP is impossible on any other kind of motor.

I know a 220 will start faster and come up to speed faster.

Not ture (universally). If you had a motor wired to 110, then you changed it to 220 and noticed it comes up to speed faster, that means your wire was undersized to run the motor at 110V, and you shouldn't have been doing that. Using appropriate sized wire (which is smaller at 220 than 110), a motor should require an equal amount of time to come up to speed, etc.

[Andy Bardowell]

Wow I stand corrected.

[Gary Click]

I think that you will find the difference is based upon the current rating of the dirve. At 115VAC the drive is current limited resulting in REDUCED horsepower at the lower voltage.

The logical assumption is that the higher voltage gives higher horsepower. I don't think this is the case, I think the motor is rated at the higher horsepower but at the lower voltage the maximum current the drive can supply limits the horsepower to the lesser amount.

Just a guess.

[Steve Speiser]

Thanks for all the responses. I went ahead and emailed the question to tecknatool. I'll post their reply in this thread. Thanks again!
Steve

[Rick Christopherson]

-Motor Power: 1.75 Hp for 115v, 2.3 Hp for 230v

The reason for this is because the motor is being artificially held back at 120 volts by the VFD. You cannot legally obtain more than 1.75 hp from a standard outlet unless you have a 30 amp circuit, which is pretty rare in a residential setting.

If you were going to install a 30 amp circuit, you may as well jump to 240 volts, so that is why they didn't bother permitting the VFD to go higher than 1.75 hp.

Summary: The motor is not more powerful at 240 volts, but instead, the electronics are preventing the motor from achieving its full capabilities when used at 120 volts.

[Steve Speiser]

Well, I got a pretty quick response from Tecknatool, from their Asian operation. The explaination was a bit difficult to decipher, but basically said about the same thing Rick Christopherson said. So it appears the motor is actually computer down rated for 115v. The tecknatool people said the more important factor was low speed torque, which is supposed to be equivalent. Hmmmm, at the end of the day, I think I'll go 230v and have available all the hp it can produce. May not use it, but can't hurt to have it. Thanks again for the comments!
Steve