Running 230 v. Compressor on 208 volts

Cannonmn · May 26, 2018

I’m looking to buy a new compressor with tag pictured. I think 208 volts (2 wires of our 208 v. 3 phase) is closest we have to the 230 volts single phase the compressor specifies. I’m thinking if I wire it up to 208 volts it’ll draw more current, but I don’t know if there will be any problems or not. Opinion?

dalmatiangirl61 · May 26, 2018

Should work fine, but I'm no sparky, doing the same did not kill my old office AC.

Bobw · May 27, 2018

Yeah, its single phase, so just grab any 2 wires (which should be 110-120V each) and you'll
end up somewhere between 220v and 240v... Just like plugging in your dryer or electric oven
at home.

Strostkovy · May 27, 2018

Measure the current draw from the motor when the tank is at the highest pressure. If it is within the motor's FLA you're fine.

TDegenhart · May 27, 2018

The hp requirements of the compressor are constant for a given pressure. At the lower voltage the current must increase to produce the same output hp. Check the current as mentioned and the temperature and they are within spec you are ok.

Tom

m-lud · May 27, 2018

http://www.practicalmachinist.com/vb/transformers-phase-converters-and-vfd/wild-leg-149745/

This old thread would be good to read
As said just check voltage

Modelman · May 27, 2018

I think the OP should start a new thread in the Transformer and VFD forum, because nobody here seems to know what they are talking about. Has it occured to any of you that since he said he has 208V, he most likely has a 120 / 208 Y service, and DOES NOT have 240V. Nothing a boost trabnsformer wouldn't fix, but ask the electricians.

Dennis

dalmatiangirl61 · May 27, 2018

Or he could just hire an electrician......my old shop had 3 ph, I know there was a high leg and you did not want to use it for single ph, thats all I remember.

Cannonmn · May 27, 2018

. Thanks, our service comes in at 480/3, and 30 kva transformers step it down for other uses. I really need to put a voltmeter on the outlet I’m planning to use, which I’m guessing was installed by a previous tenant for some similar machine. I’ll post a pic of that outlet I took but didn’t have a voltmeter at the time. Outlet is an L6-30 with blue circle near center, rated for 30 amps, 250 volts.

Strostkovy · May 28, 2018

Modelman said:
I think the OP should start a new thread in the Transformer and VFD forum, because nobody here seems to know what they are talking about. Has it occured to any of you that since he said he has 208V, he most likely has a 120 / 208 Y service, and DOES NOT have 240V. Nothing a boost trabnsformer wouldn't fix, but ask the electricians.

Dennis

You typically don't need a boost transformer to run 240V stuff on 208V. It's worth a shot to check current draw and see if you are safe.

A lot of equipment is even dual rated, or has a service factor of 1.15, which is conveniently how much higher current a motor will draw on 208.

Bondo · May 28, 2018

2 things when deciding to do this...

Will the equipment run non stop and hard?

Will the equipment be subject to heavy loads? Such as a shear, brake, Ironworkers, large chop saws

If you answer both of these with no, then 99.9% of the time, it will be fine. A compressor itself is subject to a hard start. This is not a heavy load, it's a startup load which is a surge load. This type of load disappears in a second. Now if the compressor has to start up every 30 seconds, now a surge load is turned into a constant surge which can be bad.

Sent from my 2PS64 using Tapatalk

guest · May 28, 2018

Cannonmn said:
I’m looking to buy a new compressor with tag pictured.

...

Opinion?

If you're buying a new compressor, and you already have 3-phase power, why do you want a single-phase compressor?

EPAIII · May 28, 2018

"The hp requirements of the compressor are constant for a given pressure." OK, that may be true, but does the motor actually work at that HP level on a lower Voltage? Or does it just "wimp out" at a lower level. And does this limit the pressure that you can get or does it just take longer to get there. Most compressors will not be running at the maximum pressure that they are rated for so there will be some margin there. AND even at the max rated pressure, the designer would have been very negligent if he did not build in at least a small margin to take care of unpredictable factors.

I ran a 230 V, single phase mill on 208 V for years with no adverse consequences. It was installed by a licensed electrician and he said it was done all the time. I never even noticed any performance problems. The Voltage difference was almost completely invisible.

But to be completely safe, do check the current and the temperature as Tom suggests. I think you will be fine.

TDegenhart said:
The hp requirements of the compressor are constant for a given pressure. At the lower voltage the current must increase to produce the same output hp. Check the current as mentioned and the temperature and they are within spec you are ok.

Tom

Larry Dickman · May 28, 2018

I had a speedaire compressor years back, and in the manual it stated that to run it on 208v, you just needed to change the pully on the compressor side to a slightly smaller one.

9100 · May 28, 2018

The basic effect of running at the lower voltage is that the motor will run slightly slower, more slip, and hence will draw more current and run at a higher temperature. You can often get away with it, but you are "getting away" not being happy. I worked for a company that had a number of 240 V 3 phase injection molding machines running on a 208 service. Motors on 30 hp hydraulic pumps ran so hot you couldn't touch them but managed to survive.

Bill

CarlBoyd · May 28, 2018

guest said:
If you're buying a new compressor, and you already have 3-phase power, why do you want a single-phase compressor?

Good question.

CarlBoyd

Strostkovy · May 29, 2018

guest said:
If you're buying a new compressor, and you already have 3-phase power, why do you want a single-phase compressor?

He doesn't necessarily have all of the legs.

The high school I went to was all 208V single phase in every building except for the metal shop. It would be impractical to run three phase to any of the other buildings.

Modelman · May 29, 2018

Strostkovy said:
You typically don't need a boost transformer to run 240V stuff on 208V. It's worth a shot to check current draw and see if you are safe.

A lot of equipment is even dual rated, or has a service factor of 1.15, which is conveniently how much higher current a motor will draw on 208.

All very true, for 3 ph. equipment rated for 208V on the plate. But this is a single phase consumer grade compressor, which means the motor is underrated to begin with. The plate says 15A at 230V which isn't even a standard NEMA rating, would equate to about 2-1/2 HP by the NEMA chart. And air compressors are by definition NOT easy starting loads. Plus, duty cycle will kill it. My commercial grade Quincy is rated for ten starts per hour, IIRC, more often than that and the extra heat generated by the starting current won't dissipate during the off time, and Quincy recommends a continuous run set-up with an unloader.

With all these strikes against him, it's foolish not to just provide a common buck-boost transformer from the get-go, but since I never have to deal with this problem, I'm not the one to specify the transformer. The OP should go where the people who can do this off the top of their head reside.

Dennis

Lakeside53 · May 29, 2018

That motor is only rated for a 50% duty cycle anyhow... So it's already "consumer-grade over-rated". On 208 it may wimp out or overheat. The later depends on how often you use/start it.

Running 230 v. Compressor on 208 volts

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