Drill Press motor trips breaker - help troubleshooting needed

[Friendly non murdering Sword]

I seem to be getting unlucky when buying used machinery off the german equivalent of craigslist lately. I was sick and tired of my dirt cheap drill press, so I bought this used "Genko" brand drill press (was also sold by Metabo back in the 80s/90s). It is known for its good reputation in all regards a better built and sturdier machine compared to my cheap drill press.



On pickup, the drillpress was plugged in and tested - everything worked fine. When I got it home and plugged it in, it immediately trips the circuit breaker (not RCD) after switching it on. The motor doesn't move an inch before tripping, but there is also no arcing, humming, electrical noise or burnt smell noticable. Absolutely nothing.

Maybe someone can help me out troubleshooting this. It is a 4-wire 230V AC motor with 370W and a capacitor connected to one of the winding since its an AC motor. I first checked the wiring and it is correct. There is also no short to ground.

So I cannot imagine that the startup current is reaching the breakers limit - it is only a 370W AC Motor. For example my 2,1kW AC milling machine Motor is not tripping the breaker.

One of the windings has a resistance of 31 Ohm and the other one 11,5 Ohm. The second one is seemingly too low, right? At 230V this would mean a current of 230V/11,5Ohm=20A. (The breaker is rated at 16A)

One other thing I noticed is there is a resistance between the 31 Ohm winding and the motor casing of 37kOhm, while the other ones is infinite.

Other than that I don't know what to look out for anymore? I also don't have the device for measuring the capacitor.

Unfortunetely the motors casing has integral parts for the CVT transmission built into it, so I cannot replace it by a standardized one. If I can't fix it, the machine is scrap metal.

 

[Eddyde]

I don't know enough about European electrics to give advice on the immediate problem. However, I wouldn't write off the machine as scrap if the motor is shot. It appears the lower end of the motor has a fan housing. If so, usually the shaft extends enough for the fan to be attached, which means you could possibly remove the fan and attach a shaft coupling or pulley and attach a new motor. You would have to fabricate a plate or bracket to attach the new motor to the old one but it should be possible.

 

[Jim F]

What changed from pick up location to home location ?

Is your CB weak ?

 

[markba633csi]

The 37K reading to the case is troubling, and may or may not be the issue. I would start by measuring the resistance at the power plug between the prongs and see what you get. The vibration of transport may have caused a short somewhere.

It looks like the motor is a permanent split-cap design so no internal centrifugal switch to malfunction.
RCD is the European equivalent to our GFI ground fault interrupter- I looked it up
You didn't plug into one of those so there must be a low resistance to trip the breaker so quickly- and yes the 11.5 ohm reading on the one winding seems low to me also- was that with the cap disconnected?

You can do a simple test on the capacitor with your ohmmeter; it will tell you at least that the cap isn't shorted or open but only give a rough idea of the value in microfarads. You should see the resistance rise each time you swap the test leads. Check for shorts to the case also. What is the voltage rating on the cap?
-Mark

 

[matthewsx]

You may have already tried this but plug it into a different circuit to make sure it’s not a bad breaker.

John

 

[markba633csi]

The winding inductance limits the current so it will be less than the 20 amps you calculated for the one winding.
Capacitors limit voltage rise, inductors limit current rise
But the reading to the case should be higher than 37K - like a half-megohm at least (500k)
Be sure to remove the cap for any winding tests

 

[C-Bag]

Can you turn the motor and drill press by hand? Sure seems like something got bent or jammed in transit. Like maybe something in the motor fan?

 

[WobblyHand]

The winding inductance limits the current so it will be less than the 20 amps you calculated for the one winding.
Capacitors limit voltage rise, inductors limit current rise
But the reading to the case should be higher than 37K - like a half-megohm at least (500k)
Be sure to remove the cap for any winding tests

37K is worrisome. That corresponds to a leakage of almost 6 mA. (220 V / 37,000 ohms = 0.00595 A = 6mA) That's essentially a ground fault trip point. In the US, a ground fault needs to trip if the current is between 4-6mA. https://code-authorities.ul.com/abo...-ground-fault-and-leakage-current-protection/ The resistance reading to case should be at least 10 x greater, 370K - 500K or higher.

 

[den-den]

When you say your wiring is correct, are you considering that the drill press might have previously been connected to a plug that was not wired "correctly"?

I agree the winding to ground resistance is low but am not convinced that level of ground fault would trip a standard breaker instantly.

 

[WobblyHand]

When you say your wiring is correct, are you considering that the drill press might have previously been connected to a plug that was not wired "correctly"?

I agree the winding to ground resistance is low but am not convinced that level of ground fault would trip a standard breaker instantly.

I don't think it would trip a standard breaker at all, but it is a ground fault. Something else is causing the standard breaker to actuate.

Have to agree with you, we don't know how the drill press was connected to the mains in the other shop. Can't assume that the original location was wired correctly...