"Bob La Londe" fired this volley in news:L7QNq.76597$ snipped-for-privacy@newsfe15.iad:
Bob, this is just a guess, but I'm thinking it WON'T be the 20-ohm windings.
That's the DCR. With AC (even at low frequencies) the inductance of the windings will usually make them conduct somewhat less current than the DCR would allow with DC applied.
With a 20-ohm DCR, the maximum any winding could draw would be 12 amps at
240 volts DC -- Even at inrush... even when stalling.
That doesn't sound like any 5HP motor I've used before. Mine had LOW winding resistances.
A DMM will read low resistances quite accurately if you supply an external current and use the meter to read the voltage drop. I just checked the filament current of a taillight bulb, an old 1034 because it was handy. The Tail filament draws about 0.55A at 12.0V, the Brake one draws 1.7A. Since filament resistance increases with temperature a drop in the voltage caused about half as much change in the current, so you shouldn't have to compensate for the additional drop in the motor winding. If you want good absolute instead of relative measurements, add a $3 HF meter on the 10A range in series.
Attach insulated alligator clips to a trailer light socket to use the bulb as a convenient tester. When I travelled on a motorcycle that was all the electrical test equipment I carried and ever needed. It was perfect for setting ignition timing, mostly for other people.
96 RPM/3 Hz = (approx) 3680/3 In light of that, I'll withdraw my 2 speed motor guess and jump on the motor + fan bandwagon. A less likely possibility is that the second winding is some sort of resolver-like feedback device.
Ok... I got it figured out. Mostly... Its got an independent fan motor. Doh! Had I been a bit more observant I would have seen that myself, but a couple guys in this group pointed out the possibility, and commented on the probability because a motor turning only 96 RPM at 3 Hz can't possibly be turning a fan fast enough to cool itself.
It was easy enough to check. I spun the fan and held the brake disc on the motor with my other hand. Wheeeeeeee!!!
It has six primary leads because there are two motors.
I suspect the 2 smallish brown wires are a thermal sensor. Not sure I can test it except maybe... to wire up the motor and not the fan motor. LOL.
What is the resistance between the two spare wires? If it is close to zero Ohms, I would suggest that it is an overtemperature sensor.
I like the suggestion that the second set of three leads (the higher resistance set) is a built-in fan, intended to be run by the three phase from before the VFD. Since you don't have straight three phase, you would have to add a capacitor to the 240 single phase to run the fan.
As an experiment, I would suggest that you connect the higher resistance leads alone to the VFD, with it set up to produce the normal
60 Hz output, and see if you hear a fan spinning inside the motor. (It might be spinning backwards. I've got no way to tell which direction is forwards, with all six wires black. Is there a vent at each end of the motor, so you could feel air flowing through? If so, see which direction (switch two of the three wires to reverse) feels like it is producing more airflow. But it may be a sealed motor, with the fan just circulating air between the center and heat sink fins at the outside. (You have not put up a photo of the motor (use the dropbox if you don't have a web site), and that might give some clues.
But if that gives fan operation sounds (and perhaps airflow out the ends), then the lower resistance leads should be the motor itself. (At 5HP, I would expect low resistance.) So, connect those wires to the output of the VFD and see what the motor shaft does.
If both of those work, then comes the trick of finding a reasonable value of run capacitor to keep the fan working. At a guess, try something half-way between the lowest value which gives fan sounds and the highest value.
Have you tried contacting the maker? With a motor designed and rated for VFD operation, the company is probably not that old, and is likely to still be around. Let them tell you what it really is.
Given the number of places where you appear to have posted this same question, certainly you should contact the maker to ask about what you have.
That is exactly how it should behave. You pick an order, note the direction of the spindle (relative to how you want it to turn), and either mark the three leads with the designation of the terminals which they connect to (whatever the VFD maker picked), or interchange two, verify that it now turns the direction you want, and *then* label the wires. :-)
Based on the other suggestions, I believe that it is likely an internal fan, designed to keep it cool when running at low speeds, where a fan on the motor's rotor and shaft would not turn fast enough to cool things properly.
I just got through posting (elsewhere in this thread) a way to test this with your VFD, and some starting suggestions on how to run it from the single phase if it is a fan. Remember -- the fan likely wants three phase at 60 Hz to run properly, and you will have to fake that, since your VFD will be producing much lower frequencies part of the time.
Then you try the low resistance set, and expect the motor shaft to turn.
I agree. The VFD will draw a sharp spike of current when it is first connected -- to charge it's big DC capacitors.
I would suggest not expecting anything reasonable from the frequency meter. A VFD does not produce clean three phase sine waves, but instead takes the full voltage from the internal capacitors (usually
1.414 times the input voltage, unless it is playing at being a voltage doubler too, like those for operation from 120 VAC.) It then uses the output MOSFETs or IGFETs to switch that on and off to the output. It will start a phase by turning on the full voltage for a tiny amount of time and then back off (to produce the effect of a very low voltage, though it will in reality be quite high. Then it will turn it on again, a bit longer, to pretend to be a voltage a little more along the curve, and keep doing that until it keeps it on almost full time to pretend to be the sine wave at it's peak, and then start getting narrower. It will, once it reaches zero, start switching back on the same way to a negative voltage, and go through the same sequence until the other half cycle is completed. This is for one phase. The next phase goes through the same pattern, a little later in the cycle, and the third does the same again, still a little later, so they three are equally spaced.
This high frequency series of high voltage pulses are what the frequency meter will most likely see -- if the voltages don't burn it out immediately.
If you want to see the frequency, configure the VFD to display it for you. :-)
Likely fan for the high resistance, and motor for the low. (Pending you getting in contact with the maker and finding out what is
*really* there.
Someone else suggested that you take it apart to see. Maybe or maybe not. Depends on how difficult it is to take apart.
And if the two small gauge wires measure near 0 Ohms, it is likely a thermal switch, and you want to wire it into the VFD in such a way that it says *STOP* when it opens, to keep the magic smoke from getting out of the motor. Put it in series with the Stop button, if that is how you wind up configuring the VFD.
Highly unlikely -- with that wide a range of resistances.
Disconnect first, fire extinguisher *soon* after there is no power. :-)
The same 2K pot should work with voltage control too. The VFD should have a 10V output to drive the pot.
Yes -- but having the rotor rotating at some semi-reasonable speed will carry induced magnetic poles around with the rotor, so the behavior will be a bit closer to what you would see with a full three phase applied, so it may make identifying things easier.
But since there turn out to be two isolated groups of connections (either Delta or Wye -- who cares if all you have is two wires to work with), the suggestion of someone that the higher resistance ones are likely to be a built-in cooling fan makes a *lot* of sense for a motor rated to cover that wide a range of speeds. That fan really wants to be fed its own three phase -- from *before* the VFD, but he does not have that AFIK.
But a little more information when spinning it.
Absolutely. Ideally, some short lengths of a copper tubing which will just slip over the wire's insulation, with numbers stamped in, and then glued in place with tar so it *stays* with the wire. :-) For diagnostic work, colored tapes will do -- and a notepad. :-)
Yes -- but that will likely need someone to hold the drill motor steady. With the lathe (assuming one big enough for the motor), the motor is supported by its bearings and the chuck. And perhaps a couple of boards to keep the foot of the motor from bashing the bed. :-)
Opening the case could show a separately powered internal fan, intended to keep the air flowing while the motor is running at 3 RPM. :-)
It could also allow the two thin wires to be traced back to something -- I suspect a thermal switch buried in the windings so it knows when the windings are getting hot. But it could be a thermistor. A NC switch would make more sense to switch off the command voltage source at the VFD, and stop the motor when it is showing signs of overheating. It should reset when it cools off, so be sure to wire things so that one set of contacts re-closing won't start the motor in the middle of the night. :-)
Wire a capacitors across the suspect windings in or c2c configuration and spin the fan with a blast of compressed air while checking the leads voltage with a voltmeter to see if voltage is generated.
Wow! I have never had a meter zero that far off. Digital or analog. I've had cheap meters and good meters over the years, and some of the cheap digital ones did not zero, but it was usually in fractions of an ohm. 7 ohms would be a heck of a lot to have to remember to account for all of them time.
What annoys me is I pulled the back cover (it was dented) to check the condition of the fan, and it was sitting right there in front of me the whole time. Its just not what I was expecting to see.... so I didn't see it. I looked in the housing afterwards and I could see three wires going to the fan and three going down to the lower windings. GACK!
This particular VFD has an output specifically labeled for a frequency meter. I bought a panel mount so when I get it operational I can keep an eye on it. I'll probably also setup an independent panel mount tach for the motor along with a few other independent diagnostic displays. I can remote mount the display/keypad on the VFD, but I have not located the appropriate cable as of yet. Might have to make/cobble one.
Is it for a frequency counter, or an analog meter which reads a voltage proportional to the frequency? If the latter, your frequency meter will probably do nothing. You just need an analog meter (probably
0-10VDC), pop off the front cover, and hand label the scale to match the frequency. (Maybe it could be a 0-12VDC signal and meter, so you would only have to add a zero after each value (e.g. multiply by 10).
Again -- a panel mount analog DC meter, or something designed to measure frequency?
Perhaps if we knew the model of the VFD, we could download a copy of the manual and see that is what.
Simpler VFDs will at least display the output frequency in Hz on a digital readout which is part of the keypad. Fancier ones can be told how many poles the motor is, and will give a direct readout in RPM based on the frequency you are feeding to the motor.
But all of this probably does not matter if you have multiple pulley settings for different speeds (e.g. 16 of them in my drill press which I just converted to three phase, or five of them, plus five more in back gear in the lathe) and five steps in the Nichols Horizontal mill's spindle. So something as simple as an analog meter reading percent of full RPM of the motor, and a chart saying what that translates to on the spindle makes sense. Ideally, if you set the meter to read 100% at 60 Hz, your full scale could be up to 200%, and the normal spindle speeds for given belting.
In the case of the drill press, the original motor was a 1750 RPM, and the replacement was a 1140 RPM, so I put a mark labeled "Norm" at the pot setting which gives me 86 Hz -- at which point the drill press spindle is running at the speed that the original motor would have given.
What kind of connector? IIRC, the connector on the Mitsubishi which I have is an uncommon one.
But I would use the keypad only for configuration, and wire to pushbuttons and a pot on the remote control, which would have to be custom wiring, as the wires all terminate on a terminal strip. To see what my drill press control looks like, visit this URL:
This only really needs seven wires -- three for the pot and four for the FWD, REV and STOP buttons in the momentary contact wiring configuration.
After all, we are all metalworkers -- do metal work to make a box and wire up the controls to something which fits reasonably on your machine. :-)
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.