240V motor barely turning and smoke appeared...

[burrism]

Good morning. I recently purchased a used Devilbiss air compressor. I connected it to an existing 230 line that was previously used for an RV connection. I connected it up as seen in the images and it ran great for 30 seconds then acted as if it was only getting 110v then smoke appeared from the end of the motor. Checking the power, the black line is providing 120v and the white line is 110v. I have no idea and am hoping for some suggestions.

 

[Strostkovy]

Does the compressor have oil?

We tripped the overload on our compressor motor a few times due to the oil being too cold (35F) and bogging down the motor.

 

[RoundHouse M&F]

1. since it is single phase power the motor should have 1 to 2 covers on the outside of the case one will defiantly be a start capacitor and one will be a running capacitor. Check to see if they have popped

2. If its belt driven remove the belts and see how the compressor pump spins it shouldn't be to hard to spin but it should still compress but not build line pressure, it should vent thru the compression release at the pressure switch (most newer compressors do) as you do this. If its going straight into the tank, the motor was trying to dead start with a load and that's what would lead to blowing a capacitor. also free spin the motor to check for bearings and to make sure its not dragging.

3. you said smoke came from the end of the motor, your windings have probably fried as that would be the insulation smoking so the motor is probably done for if its bad enough. last motor i had that smoked was a 3phase motor for a chip conveyor on a cnc lathe, it bound up (didnt have a safety clutch to save the motor) and stalled the motor and burnt the winding insulation. it would still run but poured smoke, had to buy a new motor and move on.

 

[Strostkovy]

On that note, if your motor is fried surpluscenter.com has lots of compressor motors

 

[DDoug]

On that note, if your motor is fried surpluscenter.com has lots of compressor motors

I know a guy that has a 6 hp motor not doing anything.....

 

[BobM3]

You measured 120 V and 110 V from what to what? You should have at least 208 V across the 2 lines. White is usually a neutral used in 115/120 Volts AC.

 

[doug8cat]

Yhea what Bob said.
Before you let any more smoke out ohm or meg out the motor.
We have gotten some other DeVil products and where of lesser quality than I would purchase.

 

[J_R_Thiele]

I agree with BobM3

There are two types of RV connections. The 30 amp is supposed to be 30 amps at 120 volt. with 3 wires, hot 120 volt, neutral and ground. The 50 amp is supposed to be two 50 amp 120 volt using two 120 volt hot leads, a neutral, and a ground.

Someone could have wired the 30 amp RV with two hots and a ground with 240 between the hots. When you plug it in to a conventional outlet, you get 120 volts. The 50 amp receptacle could have been wired with both 120 volt lines off the same leg, so they are 120 volt to neutral, but would be 0 volts between each other, or wired of different legs, which would be 120 to neutral, but 240 between lines.

The only way I see you getting 120 and 110 volts and having had it run is if it is 50 amp connection, with one leg pulled down to 110 volts BEFORE you try and start the compressor. You would have 230 volts between the two lines before starting the compressor. Normally 230 volts would be fine- but if one leg is already pulled down to 110- what does it go down to with the compressor starting/running? As the volts go down, the amps go up, and the motor overheats.

 

[burrism]

Thanks for all the replies. To clarify and add more info:

I measured the 120b and 110v on the black and white lines respectively, at the line input to the pressure switch. This is a direct feed from the circuit breaker. While the compressor is running I measured them again and got the same (118v/115v) and on the motor side of the pressure switch I got 117v/2-5v, respectively. So I am thinking J_R_Thiele's comments about the RV connection might be most accurate. Additionally, I am not familiar with these specific ganged breakers in the panel. Regarding the smoke, I am not sure (and hopeful) that I smoked the motor. It still runs and both capacitors appear undamaged. The smell is more of a dust on an electric heater vice burnt plastic or rubber and there is no visible signs of burning. I guess the next step would be to open the panel and see how the breakers are installed as it seems the white line is providing 110v but when a load is applied it quickly drops to 5v.

Can't attach a video

 

[J_R_Thiele]

We still do not know how you are measuring to get the voltages you report. I assume between the wires and ground. That is not what you need to be measuring

The motor needs 240 volts measured BETWEEN the black and white wires. It does not matter which probe is on which wire, you will get the same results either way. Measure that on both sides of the pressure switch, both before running, and when running.

Let us know what you find.

Do you happen to have an IR (infra red) "gun" that you point at something to measure its temperature? If you do, after the compressor has been running a while, measure the temperature on the black wire side of the pressure switch, and the white wire side of the switch. If there is poor contact being made on one side it will run hotter.

 

[burrism]

Ahhh...

So what I thought was obvious, was not. So black to ground is 120v and white to ground is 115v. measured across black and white is 122v at power source and when running. I didn't realize that I could measure across the power sources and get a reading. I am still learning...

Guess I need my breakers/panel re-wired.

thanks for all the help!

 

[J_R_Thiele]

When you say you are measuring 122v at "power source" I assume you are measuring where the cord connects to the switch.

You earlier mentioned the RV connection, but later say it is a direct feed from the circuit breaker. I take this to mean that the cord goes directly from the circuit breaker to the pressure switch- with no outlet or plug in the line. Is this correct?

We are all learning. No one is born knowing this stuff. Most will use electricity and have no idea how it all works. That is fine- as long as it works. You are now in a situation where you have a reason to learn more. This used to be through books. Now you can earn it on line.

I doubt you need the panel rewired. You may need to make some changes in how things are connected within the panel. It might be helpful to know which panel you have.

 

[burrism]

Clarity...

Power source: where the lines from the breaker connect to the pressure switch. Originally this was a 220v RV connection with an RV outlet but i removed the connection and hardwired the compressor. So I measured 122v at the pressure switch, both at the input across the black and white lines as well as the motor feed from the pressure switch.

I looked at the breaker and think that only the breaker needs rewiring. The other half of the breaker is for the outlets, which is also wired like an RV 220v.

Still not really sure about it all and will have to do some reading to fully understand the RV vs compressor 220v circuitry.

 

[HappyWyo]

It is against the electrical code to have a hot white wire. If a white wire is used it has to be marked with tape or paint red or black. White is normally neutral which is tied to the ground bus. If the white isn't properly grounded it can hold residual electricity. That is why a ground rod near your breaker box is mandatory. If your ground rod is missing the nearest ground may be the poles ground, which is often old and corroded. The voltage on your legs should always be identical. When you have different pressures on your lines none of your 240 volt motors will be balanced. Remember voltage is pressure.

 

[HappyWyo]

Clarit

I looked at the breaker and think that only the breaker needs rewiring. The other half of the breaker is for the outlets, which is also wired like an RV 220v.

Still not really sure about it all and will have to do some reading to fully understand the RV vs compressor 220v circuitry.

View attachment 340310

It isn't legal to have 120v outlets wired to one side of a two pole breaker. The outlets won't be protected. You have 120 volts on each leg of the breaker, each one out of phase with the other so when checking across the two you have 240 volts. No need of a neutral wire because the phases use each other up. The required ground wire on 240 is for safety, incase of an accidental short. That is why the legs have to be balanced. Otherwise the weaker leg wouldn't use up all the pressure in the stronger leg.

 

[Strostkovy]

It isn't legal to have 120v outlets wired to one side of a two pole breaker. The outlets won't be protected. You have 120 volts on each leg of the breaker, each one out of phase with the other so when checking across the two you have 240 volts. No need of a neutral wire because the phases use each other up. The required ground wire on 240 is for safety, incase of an accidental short. That is why the legs have to be balanced. Otherwise the weaker leg wouldn't use up all the pressure in the stronger leg.

Are you sure about that? Last I checked multiwire branch circuits (separate circuits sharing a neutral) are required to have breakers with tied handles. That's a fairly recent change and often ignored, but it's not illegal. IIRC you can tie breaker handles together all you want. If you have equipment that requires a safety system (such as an exhaust fan) to be on when it is on, you can tie the breakers together so both systems trip and are reset together.

The ground wire in a branch circuit is to make sure a short to the chassis of electrical equipment does not make the chassis an electric shock hazard, and instead trips the breaker. In this sort of scenario only one pole of the breaker trips, and the handle tie is supposed to shut the other one off. The amperage draw does not need to be balanced on the legs, and if the load requires a neutral it usually isn't, because appliances and machinery often run lights and controls off just one pole, and RVs are about the least balanced loads out there.

 

[burrism]

I have never seen a breaker wired like this either. the 20A service is for the garage 120 outlets and the 30A service is/was for the the 120v service to the RV. So none of it is really 240v service as it notes on the breaker(s).

Thanks again for everyone's input and suggestions. I have an electrician coming this week to fix it and to hopefully explain the reasoning behind the unique wiring.

 

[Gumbydammit]

Why not just install a proper 240 circuit breaker. Looking at it, and seeing the pigtail, it looks like you are using arc fault breakers. I usually don't use those unless I have a special reason to.

I know I'm not an expert, but seeing 4 switches for a single load made my skin crawl. Just seems like a lot of possible heartache.

Thanks,
Gumby

 

[burrism]

Gumby,
I will get it sorted out this week. We recently bought the house and this is the wiring as we received it. I thought the RV connection line was actually a 240v line, not a 120v line. As this breaker setup is unfamiliar to me, i will let a professional fix it. My thoughts though, are to remove the top most line (garage outlets) and put it on a separate 120v, 20A breaker and install a proper 240v, 30A breaker for the compressor line, using the existing neutral as L2 (properly labelled and colored).

 

[jim rozen]

Gumby,
I will get it sorted out this week. We recently bought the house and this is the wiring as we received it. I thought the RV connection line was actually a 240v line, not a 120v line. As this breaker setup is unfamiliar to me, i will let a professional fix it. My thoughts though, are to remove the top most line (garage outlets) and put it on a separate 120v, 20A breaker and install a proper 240v, 30A breaker for the compressor line, using the existing neutral as L2 (properly labelled and colored).

That sounds like a good plan. The common expediant is simply putting a wrap of black, or red tape on each end of the white wire to indicate 'not a neutral' and is probably what your electrician will do. The remaining worry about the situation is the motor might have been damaged by running for a short time at reduced voltage. You might ask the electrician to test the insulation resistance to ground for that motor, while he's there.