dual voltage lathe motor questions

I am looking at a Powermatic 90 on my local Craigslist. It is currently set up for single phase 220Volt, but it has a Baldor motor in it with a wee wiring diagram on the motor plate.

If I take off the cover and rewire this motor to run on 110VAC until I can sell this house and buy a house with enough room in the breaker panel to add a single phase 220 circuit, what would I be giving away in the short term running this lathe and motor on 110volts?

Attachment 453627

Dang it, I rotated the image in my phone and re-saved it and it came out upside down anyway. the motor is rated 110-220 Volt, with a wiring diagram for how to setup the connections in the junction box.

Thanks

You would be giving up very little running it at 120 vac. Yeah, double the current, and twice the voltage drop. But when turning - - will you know the difference? Most likely not!

In real life, nothing. Just re-wire it as shown on the plate and you're good to go. Given the amperage you'll want it on a 15 A circuit that is not shared with anything else that runs at the same time, or on a 20A circuit where it can share with smaller stuff. I think the rule of thumb is to keep loads at 80% of the capacity of the circuit.

A couple such tools (eg lathe and a small DC or compressor) could run simultaneously on a 20A 240V circuit with the same 12 ga wire; that would be the advantage of running a 240V circuit for it. Sounds like not applicable in your case.

Actually in all but the very worst situations (like 60 amp service) make it possible to add a sub box to run more circuits.

Quote:

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Originally Posted by Scott Winners

...what would I be giving away in the short term running this lathe and motor on 110volts?
...

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If you have a long run on the circuit, running at 240 can be more efficient than running on 120 since the motor will draw more current and have more voltage drop with 120v. With a short run, the voltage drop will be no problem.

If you DO have a long enough run for a significant voltage drop, you may experience slower starting with 120v. In extreme cases, you can even damage the motor.

Two examples:
- I ran an underground cable to my shop at the previous house and initially powered it with 120 volts. When I switched the same cable over to 220 volts I was surprised at how much faster my radial arm saw came up to speed. It seemed to have more power too. (I didn't monitor the before and after voltage.)
- My brother in law had a long 120v line to pump in his spring house. He destroyed several motors due to the voltage drop. He finally switched the power to 240v and that motor never failed with decades of use.

The problem with voltage drop and electrical motors is the motor will try to deliver the same HP regardless of the voltage. With full voltage it will draw a given amperage. At reduced voltage it will draw more amps to give the same HP. The increased amperage can heat the wires causing the resistance in the wires to increase and reduce the voltage even more. This results in the motor drawing even more current. The struggling motor can overheat, destroying it.

How long a run is too long for the current? There are on-line voltage drop calculators that will give you the voltage drop for a specific wire size and length for a given amperage. (It gets more complicated with a long run in the case where the conductors on part of the run, say the power to the sub panel in the shop, are larger than the conductors from the subpanel to the tool.)

IIRC the accepted standard for the tolerated voltage drop is about 3%. When I put the power to my shop about 250' from the meter, I sized the conductors such that the maximum voltage drop was less than 1% even in the unlikely case of full amperage draw on the panel. This required larger conductors which were more expensive, but I figured the cost of the wire was a pretty small cost compared to the cost of the materials to build the shop!

JKJ

I'm going to agree with JKJ. This is one where theory and real life have nothing to do with each other. In theory, yes you will lose nothing. But in real life, unless you wired the house yourself and know that the outlet that you plug the lathe into is a short run straight to the outlet, you have NO idea how far that run of wiring is. It can and probably does run through 1 or more Junction Boxes, each with 2 wire nuts, which is voltage loss. It can and probably does run around in your attic for at least 30 feet. Each run also powers a few other things which also causes voltage droop. Unless you can plug it into a dedicated and known 20 amp outlet, you'll have some voltage losses. 20 amp outlets have heavier wire, which you do want. And most of them are dedicated.

Quote:

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Originally Posted by Kyle Iwamoto

... unless you wired the house yourself and know that the outlet that you plug the lathe into is a short run straight to the outlet, you have NO idea how far that run of wiring is....

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Or wire it up for 120v, plug it into the intended outlet, and turn it on. Measure the voltage drop with a good quality meter with a load on the motor.

Got my volt meter out. With nothing else running on my 20 amp "garage outlet" circuit I see 110VAC with my existing lathe powered off at the receptacle where the lathe plugs in, and 105 VAC with my existing 1hp lathe running with no load, not even a spindle mounted. 4.5% drop. Need to address that.

House is a +/- 1980 build with stab type connections on the receptacles. The wiring I have seen on the receptacles I have replaced has all been 12ga copper, but not executed in an orderly, workmanlike manner.

Thanks for the pointers y'all.

Not to be overlooked is the fact that often the 110V outlets are on a shared breaker and the combined load of multiple users even lamps, sander, vacuum, etc can result in a tripped circuit. One good thing is that a lathe normally is not drawing full load except when doing heavy cutting and then seldom are additional tools like sander, vacuum, etc being used in a single person shop.

Quote:

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Originally Posted by Scott Winners

Got my volt meter out. With nothing else running on my 20 amp "garage outlet" circuit I see 110VAC with my existing lathe powered off at the receptacle where the lathe plugs in, and 105 VAC with my existing 1hp lathe running with no load, not even a spindle mounted. 4.5% drop. Need to address that.

House is a +/- 1980 build with stab type connections on the receptacles. The wiring I have seen on the receptacles I have replaced has all been 12ga copper, but not executed in an orderly, workmanlike manner.

Thanks for the pointers y'all.

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Is 110 VAC typical of your supplied voltage? Can you check voltage at the panel? If you have higher voltage at the panel/breaker, and you are sure there are no other loads on that circuit, you likely have a wiring problem.

In my area the supplied voltage is 120-121 volts line to neutral, and I see that same voltage anywhere on a circuit with no load. You would have to have thousands of feet of wire before you would see any voltage drop with no load.

If you are consistently outside the normal 114-126 V service range at the service entrance you should ask your power company to check your service. Another worthwhile thing to check is the differential between each leg and neutral, if they are out of whack it can indicate a bad neutral connection. I had a 17V difference (105 on one side 122 on the other, but a solid 238 between the two hots) and it turned out there was both a bad neutral connection at the service head and one out at the street which clearly had been on fire at some point. They were very happy to fix both. The lineman was shocked (as it were) we hadn't had a lot more serious problems.