aidandj

iTrader: (5)

Going to break this out of my thread so it gets more views.

I have this motor on my air compressor:



And this plug:



NEMA 6-20.

I need my air compressor to plug into this outlet.

Options:

1. Rewire (landlord might be up for it, I'll ask, would require new breaker)
2. New Motor
3. **** it and run with it (could be bad)
4. Your suggestion here

Halp please.

Joe Perez

iTrader: (8)

Disclaimer: I am not a licensed electrician. I have no formal training in residential or commercial electrical work. Following my advice will result in your house burning down, killing your cat and destroying your whole laserdisc collection of 80s-vintage Japanese ****.


Assuming the circuit breaker is up to par (which is usually a safe assumption), the worst-case scenario is that it'll trip. Induction motors don't draw maximum current all the time, and most breakers are sufficiently slow-acting to tolerate the startup inrush.

When I lived in Carlsbad, I had a Harbor Freight compressor (120v, 15A) plugged into a 15 amp outlet in the garage. If I had the pressure switch set high enough, the motor would trip the breaker when it started. The solution was to dial down the pressure switch. This caused the tank pressure to drop lower than I'd have preferred between cycles, but it worked.

aidandj

iTrader: (5)

My **** collection is actually VHS. I'm a little young for laser disc.

My pressure switch is like 140 or 160psi. Something high. And I don't think its adjustable.

But its leaking. So I should get a new one anyways.

Erat

iTrader: (5)

You have enough voltage running to the plug right? 120v to ground on each lead? Two hots and a ground, no neutral.

If so, run it. Check rotation too.

aidandj

iTrader: (5)

Stupid question. But how do I check the voltage. When I put my multimeter between a hot and the ground then I see like 600v, then flashes to like 100ish. Then drops to 0.

How do I check rotation?

patsmx5

iTrader: (16)

Buy the right plug, connect it, and you're done. What's the problem?

aidandj

iTrader: (5)

Motor specs are above the plug rating. Hence the question.

patsmx5

iTrader: (16)

Set meter to AC volts, probe whatever two wires you want and it will tell you the voltage between those two wires. GND to HOT should show ~120V. HOT to HOT should show ~240V. Both single phase, 60Hz.

aidandj

iTrader: (5)

I'm a ******* idiot. I had it set to DC volts last night.

Erat

iTrader: (5)

Stick red probe in one opening, then black probe in ground. Should read a constant ~120v. Same with the other.
You should first figure out what is going on in the plug.

Check rotation by starting motor without it connected to the compressor... Or **** it. I honestly do not know what happens if you spin the compressor backwards. I'm guessing this is a piston type compressor. You certainly do not want to spin a rotary screw compressor backwards.

Also, forget about finding a new motor. A k184t framed 120v motor just seems impossible to find.

What kind of crazy *** compressor is this?


Edit* yeah, what P@ said!

aidandj

iTrader: (5)

You tell me. I got it for $50 after a local machine shop bought a new one.







I'll take more pics when I get home

Erat

iTrader: (5)

Yeah, Don't run it backwards:
https://www.engineersedge.com/wwwboard/posts/13561.html

At least, for no substantial amount of time.

aidandj

iTrader: (5)

How do I tell which way is backwards though?

deezums

iTrader: (3)

It's not a three phase. Inverting the hots won't make it spin backwards.

Internally rewiring the start circuit will, though, so don't do that.

Erat

iTrader: (5)

I was under the impression he was going to put a new plug on it, so that it will work with the one he has in his house.*
Which is why i was suggesting following the wiring diagram and double checking to see if it is spinning the right way. (you'll know by building pressure and if it doesn't sound like ****).

If we're doing this the right way, i would totally suggest using a 6-30 plug(which i hope is already installed on the machine) since FLA is 23. Which means talking to the landlord and replacing that 6-20 garbage.

*maybe the plug on the compressor is one of the removable types, so it's easy to swap out and no need to get into the pecker head.

patsmx5

iTrader: (16)

This. It's single phase 240V, there is no "backwards". Both phases are 180* opposite of the other. A starting cap decides which way the motor starts.

Erat

iTrader: (5)

There is no cap.
Wiring the leads different decides which way the motor spins.

patsmx5

iTrader: (16)

No starting capacitor? You sure about that?

deezums

iTrader: (3)

Simple single phase 180 out from itself will not start a motor, it does nothing without a capacitor to start the motor turning in a certain direction.

Only three phase can be inverted by swapping any two phases.

Regardless, you can see the caps on top of the motor.

Erat

iTrader: (5)

It could be split phase.

Either way, it could have a cap. It still doesn't matter, if you change the leads on the motorthen it will run the opposite way.
And you're absolutely right, if he doesn't touch it, no matter what hot gets what it will run the proper way. Since a shop already had it setup and running at one time.