New motor not working? Confused.
Seriously, I think I need to find a good electronics forum. I post more electrical questions here... it is getting embarrassing This is a brand new motor. No joke. I bought it months ago, but for any number of reasons I have only now hooked it up. This is meant to be driven by a VFD. Hook it up; it makes strange noises, and the VFD faults "Overcurrent" every time. Figure it is the drive, so I connect to my standard 3-phase, RPC power to make sure. Blows the 20A fuse every time. Got real discouraged. This was yesterday.
Today I decide to re-wire the motor per the connection diagram for "high voltage" (it is 230/460V). The darn thing runs fine! Trying to discern if this is a mis-labeled connection diagram, I search around and pretty much determine it isn't. Now I'm totally lost.
The question is -- there IS something wrong, right? I don't want to drive out to my motor shop and get the "dumkoff!!" response Like I said, this is a brand new motor, so I am liable to lay the fault on myself first in this instance. There is nothing wrong with the standard power line it is connected to. It runs every other 230V three phase motor in my shop---even one of equal horsepower---with no issues whatsoever.
Last edited by Arthur.Marks; 12-18-2011 at 08:50 PM.
Video of motor wired for "low voltage" connected to 230V, 3-phase, RPC power: (p.s. it stops because it blows the fuse, not because I turned it off.)
Video of motor wired for "high voltage" connected to 230V, 3-phase, RPC power:
The label shows the 'standard' wire number assignments, so providing it is hooked up as shown it SHOULD run?
When you had it connected to the vfd, what type of ramp times were you using?
When you had it connected to the rpc, the 20 amp fuse that you melted, was it a time delay fuse or fast acting?
The diagram is fine. At least it is internally consistent, as far as I can see.
Clearly has a big issue in low volts..... does not appear to get up to speed, growls and complains
WIRES might be mis-labeled..... like a backwards phase (reversed numbers) on one winding.
In high voltage, is the current identical on each wire?
if one winding is reversed, it would be messed up badly when in parallel, but not so messed up when in series but connected to low voltage.... although I would expect to see SOME change.
Run on high voltage connection , and check motor currents.
It may run on 240 when wired or 460, but that doesn't mean it's running fine. You would get very low power.
Try a long ramp - say 20 seconds, when running on the vfd when wired for 240 - just as a test. Check the motor current on each leg - some vfd's allow you to see this, others just give you an average.
Where are the fuses on the rpc. - input only, or on the output (you'd have three fuses on the output)?
Oh... a quick trip to the motor shop may be your best option. They will tell you in minutes if there is anything wrong
Last edited by lakeside53; 12-19-2011 at 01:16 AM.
Another question..... are you certain that it was wired correctly to begin with?
Sometimes the wire numbers can resemble each other as you work.
Try disconnecting ALL wires, and re-wiring it for low voltage relying only on the table and wire numbers as-labeled, with NO reliance on "memory", etc. Sometimes that allows one to see the numbers correctly and do it right. DAMHIKT
That is obvious....
Originally Posted by lakeside53
The test is just that, a test to identify if there is a problem, and try to localize it. Nobody is suggesting to run the motor like that "because that's how it works best".... it is just a test to get at the issues.
A motor shop may be an option, but it can be an expensive option, particularly when one has just laid out substantial cash on a NEW UNUSED motor which SHOULD be trouble-free and perfect.
Last edited by J Tiers; 12-19-2011 at 07:46 AM.
Trying to get to all the questions posed...
●When you had it connected to the vfd, what type of ramp times were you using?
Didn't matter. Started with 10 seconds, upped it drastically to no effect.
●When you had it connected to the rpc, the 20 amp fuse that you melted, was it a time delay fuse or fast acting?
Strangely -- the time-delay, 15A, RK5 fuses on the RPC output don't blow. It is the 20A breaker on the main single phase panel.
●In high voltage, is the current identical on each wire?
High voltage connections on the motor legs produce the following:
And just for the heck of it, I checked the rpm while it was running with a contact tachometer: 1798 RPM.
●Check the motor current on each leg
Low voltage connections on the motor legs produce the following when connected to RPC output and then the RPC turned on:
NOW -- here is the strange, ah-ha part… I forgot to connect the motor to the RPC just now when I turned it on. What I find is that if the RPC is up and running already and then the motor connected:
…and it runs fine! That still doesn't help me with the VFD, of course. Maybe it diagnoses an issue, though?
●Where are the fuses on the rpc. - input only, or on the output (you'd have three fuses on the output)?
Output. One 15A, RK5 Bussmann for each leg. A total of three.
●are you certain that it was wired correctly to begin with?
I've checked this numerous times and completely separated all the wires to go from low to high connection more than once. I am 100% confident in the wiring accuracy to the diagram.
●Does the VFD have torque boost ?
Probably? I figure it does, but I didn't turn that "on". It is the second TECO N3 drive I've wired. There's been no issue with the other one---or the motor (also a Marathon Black Max), for that matter. Seems unlikely to be the real issue here.
Last edited by Arthur.Marks; 12-19-2011 at 08:45 AM.
Does the VFD have torque boost ? If that is set too high it will cause the motor not to start.
OK, your motor "runs", but... You are supposed to have your RPC ON before applying the load. If not you have two stalled motors it's trying to start, which is why you got the currents you recorded. You can get way with it on some RPC, but usually when the RPC is a lot larger than the target motor.
BTW... Your current settings - Often an unloaded motor will show different "idle" currents, especially on an "unbalanced" RPC You'd need to load it up to get better results. You do have a wide range though and 6.3A is way too high for one leg, especially unloaded .... what are your RPC voltages? And... based on your motor plate, I would have expected numbers in the 2.5 amp range (40-50% of max at idle). What are you measuring current with? As Jerry points out, numbers can be easy to confuse -6 and 9 are a problem unless they put the bar beneath to show. Undo all winding connections and take ohm readings.
VFD : if your rpc currents are valid, that's why it's tripping.
Last edited by lakeside53; 12-19-2011 at 08:48 PM.