Acra mill 80,ish model low speed out on motor

[Chips]

Ok , I just got here so I hope everyone is doing well. I have an older model acra mill 3 phase that I bought new several years ago. It has held up pretty well and a few days ago I lost low speed on the machine. The reverse low doesn't work at all and the forward only hums. I don't have a meger to check the windings so I rigged up a light bulb on a 9volt battery and the windings seem to be intact even though I can only check for a circuit not amperage , no broken wires going from the switch to the weather head and no loose connections that I can find. The barrel switch looks kinda cheap so I was wondering if any of you guys had an acra mill and had the low speed go out on the switch . Low is basically all I ever used on the machine . The high speed runs fine on forward and reverse. Thanks for any ideas or help on finding the problem.

 

[Chips]

I was just checking for an open circuit with the battery and wire , I understand I couldn't produce enough power to check for bad windings. Thanks for your response and I hope the switch is the problem. It is a "3 phase machine" so I am reluctant to start checking across wires with the power on. If you have any ideas --shoot them across. Thanks again.

 

[Chips]

Ok --maybe I can get this baby going again on low speed-- I will post back when I find out exactly what the problem is but it does point to a switch problem after thinking about your replies .The motor hum on the forward side would indicate a leg out on the switch side since everything checked out as far as no wires disconnected and the high speed runs fine. thanks for the help from everyone and safe machining.

 

[Tony Wells]

Kill the power to the machine. Open the switch housing. If each position, measure resistance across each set of contacts that should be closed to see that they are virtually zero ohms. If one or more sets has a few ohms or more resistance, they should be cleaned. Some contacts are made to be burnished and can be salvaged, others are not. Some are solid copper and can be dressed with fine paper to make sure they make good contact. Review with your ohmmeter. This may be easier than d/c the leads to try a straight low winding only power-up. Just remember to measure directly across the contacts that are closed.

 

[Tony Wells]

I definitely agree that the switch is the likely culprit, and eliminating it as part of the low speed circuit is a positive method of confirming that the motor windings are not at fault.

I failed to consider that the meter the average hobbyist would have at hand would probably not be the best for very low ohm measurements required to check switch contacts in circuit. The odds on the windings reading as low as a set of contacts would if they were in good shape are pretty low, but again, the meter being used is a factor, as well as the user. Of course, in extreme cases, a visual can be very revealing as to condition of contacts. Since these are (assuming it is the switch) the contacts would probably be obviously pitted and burned. Of course, not seeing examples of good and bad contacts would put a person at a distinct disadvantage.

 

[Tony Wells]

For accurate low ohm measurements (in the milliohms range) a 4 wire technique is preferred. It uses the voltage drop method you describe. But that is beyond the scope, or necessity of this discussion. In practical terms, d/c the motor from the switch would probably suffice, as would wiring the motor directly to the low speed windings. Most DMM's do not offer a low range.

Good, another 260 user. The R X 1 uses 1.5 volts, but the higher ranges employ a 9 volt power source, but it is still insufficient to develop useable current cross a good set of contacts to declare them to be "as new".

I have a battery powered hipot tester that comes in handy from time to time for measuring leakage in circuits.

 

[Chips]

I'm thinking that your getting to complicated for Chips. As he said he was using a 9V battery and light. Adding an ohm meter to the test complicates things not to mention checking the right terminals on the switch. Furthermore if the motor is still connected low resistance Might be available thru the winding of the motor. Keeping it simple is the best way for someone with a limited understanding of 2 speed motor switching. Connecting the motor directly to the power source connected for low speed as shown in the motor diagram eliminates the switch completly and errors derived from incorrect measurement. If I were doing the testing I would go directly to the switch as I think it's the probable cause of the problem.

Yep--Swarf should have been a profiler for the FBI ---the reason I was using a light wired to a 9v battery was because I didn't have an ohm meter. I wired my shop for 3 phase but basically when it comes to trouble shooting motors I am dead in the water, because I don't have the necessary tools to do the job. That switch has enclosed contacts so I am going to have to trace the wires from the low speed side back to the switch and remove them and wire up direct--put the switch in and look for smoke [grin] --I hope that doesn't happen. I will print your responses on trouble shooting and save them as an ohm meter is is my future since everything is getting some age on it. Thanks again for the help guys.