VFD installation with pics

[Swede]

After my wail for VFD help, and some excellent advice, I went out to PolySpede (www.driveswarehouse.com) here in Dallas to pick up a shiny new VFD for my vertical mill.

The current mill installation consists of a 4/8 pole (0.75/1.50 HP) 3p motor, 240V, fed with a "Phase-A-Matic" rotary phase converter. The rotary converter has served me well for many years, and being rotary, it produces a true, high-quality waveform. The 2 drawbacks are the noise it creates (even in the attic rafters; it's a nasty hum), and the mill itself, being step pulley, can be a bit irritating to change speeds.

Before I went out and bought this VFD, I did some experiments with a much smaller Hitachi VFD, a 4A job. Since the motor is 2-speed, I was able to attach the small 4amp VFD to the 4-pole motor inputs and proved to myself that the concept was sound and that the motor would respond well without overheating. It generated nice torque even at slow speeds. There was some PWM carrier noise which improved when I jacked the carrier freq. up to the max of 16 KHz. Upping the PWM carrier forces one to derate the VFD 20%, but the behavior of the VFD improves.

Here is the original 2-speed switch which I have dismounted.

[Swede]

The motor cover removed... note the two sets of three phase inputs, one for 4-pole, the other for 8 pole rotation.

[Swede]

The VFD I purchased is the Hitachi L100, capable of 10 Amps output at 240V. The input may be either single phase or 3 phase power. This gives me flexibility for the final installation. Many VFD's force another derating when used with single phase input, but not this one. The list of features is very long... modern VFD's are microprocessor controlled, and you can control acceleration, deceleration, braking, discrete speed levels, all sorts of cool functionality. It will output 360Hz, so it can be used with some HF 3phase motors, or the stock motor itself can be overdriven (go FASTER) with loss of some torque.

For now, I am going to mount the entire unit next to the mill head on an aluminum bracket. Ultimately, I can create a simple remote control keyset with a rheostat, or it can be controlled with a computer.

I went with the much larger 3HP VFD rather than a 1.5HP unit just to have the safety overhead on the current rating.

The display output can be set for current, frequency, or a user-defined scale which corresponds in a linear fashion with the frequency output. I'll probably set the latter up for a tach display.

Later today I'll power it up before going to the trouble of mounting it in detail, just to verify that it'll do what I want.

Stay tuned!

[Bloy2004]

I'm rivited to this one, Swede. Your demonstration is just what I(and many others, I surmise) were hoping for. Having followed that URL posted earlier regarding the L100's, your pictorial here makes the whole picture clearer. Especially your comments about the single-phase options. This seems to be an excellent and compact way of bringing 3phase power(variable) into a single phase environment, while reducing the discomfort of noise and mass.
Thanks!

[Swede]

Thanks Bloy, I'll keep posting. I made a mistake already in the posts... the motor is in fact a 4/8 pole motor, but the more poles a motor has, the SLOWER the speed. So for this motor, when the output of the inverter is connected to the set of terminals which corresponds to 8 poles, the motor will be SLOWER. So more poles = SLOWER MOTOR SPEED. My plan initially is to connect it to the 4-pole set to get the higher speed, and set up the step pulleys to be one "notch" below top speed.

[Bloy2004]

hmmm. What is the purpose of the Slower 8pole hookup...is there more torque in this configuration? If so, it may be handy if switchable for those jobs requiring slow speed/high torque.
..just wondering...
John Bloy..(remember "the Waltons"?)

[HuFlungDung]

I don't know the details of this particular VFD, but is the number of poles of the motor just a parameter to set up in the VFD? Then of course, the motor windings will be connected Delta or Star according to your real world choice.

True, the 8 pole setup will develop full horsepower at a lower rpm (perhaps 900rpm?). However, you don't want to "lie" to the inverter setup about the number of poles (by saying it is a 4 pole hookup when it is actually 8) , or it could allow too much current to flow and burn out the motor.

So it depends on what speed range you find really the most useful. It is conceivable to use the 8 pole setup and run the motor frequency up to 240hz to get 3600 rpm. This way, you will get full motor hp at 900 rpm, and it will stay at that hp up to the maximum. Whether this high of a frequency would damage your motor insulation is something to consider, perhaps.

The motor should not normally have a big imbalance problem up to 3600 rpm. If it does, I have had good success with disassembling the motor and balancing the rotor, just by setting up parallel knife edges, and letting the heavy side roll down. Just remove a little bit of metal from the aluminum bar fins of the rotor to improve the balance.

Be cautious of the quality of the fan if you run it up to 3600. Make sure the fan is in excellent condition, and keep it shrouded.

[Swede]

VFD updates - The initial experiment is coming along nicely with one exception.

The first tests made use of a single phase 240 V input source. I randomly selected a "pole set", the right hand set of three terminals in the motor junction. After some initial programming to enable the pot and keypad, I had the motor spinning nicely at 60 Hz output, about 1800 RPM. The current draw was higher than I thought. This is a 10 Amp / 3HP VFD, and this motor is drawing 7.5 Amps. It's a good thing I bought a "bigger" VFD.

I set the accel and decel rates... it's nice to push a STOP button and have the spindle braked to a halt rather than having to apply a manual brake. 4.0 seconds is a nice accel, while 1.5 seconds for decel is perfect.

Thinking I was hooked to the slow set of motor junctions, I swapped the 'gator clips to the other... and found that the motor output was identical.

Hmmm. Maybe the function of the original switch was to route power to ALL SIX motor junction screws. I'll have to sit down with an ohmmeter and map that switch. It may be as simple as putting a shorting bar between the corresponding motor junctions to activate the high-speed.

The only bad part so far was that when I tried to feed the VFD input 3-phase power from my Phase-A-Matic, the VFD tripped (error), and the error code indicated "DC bus overvoltage". I'll need to do some research there. The VFD manual is almost 200 pages! There's plenty of protective logic built into the VFD, so short of a horribly incorrect wirng job, it looks like it will take care of itself.

Hu, thanks for the advise. I'm going to get a 115V AC fan and mount it on top of the motor. It'll run all the time to augment the internal motor fan, which will have little airflow at slow speeds.

I'll keep plugging and get some more data and pictures up. So far so good! The whole idea behind this VFD was to get rid of the rotary converter, and obtain variable speed to boot.

Swede

[Al_The_Man]

Swede, If you have a true 2 speed motor, typically the lower speed will have approx half the current and half the HP rating. (The name plate should tell you). I would make sure you have the right 4 pole connections as that current appears to be a little high if that is off load, I would expect that current fully loaded at 60hz.
The switch usually connects the windings in either a series or parallel mode.
Also if you have the display set for rpm, and you are running at 60hz for a 4 pole motor it will show the speed/freq out i.e. 1800 but with a VFD with no feedback, this display is usually not the true speed but the frequency output, as a 4 pole motor cannot run at 1800 rpm (unless its a synchronous motor) due to natural slip action .
In some cases the overvoltage fault can be if you try to decelerate too fast, the regenerative action of the motor causes the bus voltage to climb above the recommended and the VFD will shut down.
There is usually an internal braking resistor to take care of some braking, for really fast braking, sometimes an external braking option is offered.
Al

[HuFlungDung]

Swede,

There most likely is a parameter setting to reduce the hp rating of that VFD to match your motor 1.5 hp. Check that it is not defaulted to a 3hp motor rating, or it will allow a larger current than is safe for that motor.

[trubleshtr]

Good point Al,
I have seen $10,000 power supplys and drives blow up due to regenerative current not being handled correctly when it came back down the line. I would hate to see that happen here to the nice new VFD.

[Swede]

Since you guys know a lot more about 3phase motors than I certainly do, let me describe exactly what is happening, and I'd appreciate any feedback.

The VFD continues to operate perectly with single phase input, except at an apparently reduced RPM. 3ph input still produces a bus overvoltage error. This doesn't bother me too much, as I ideally wanted to feed this VFD single phase anyway.

Here's the motor plate:

0.5 / 1.0 KW
60Hz
220V
3.7/4.2A
780/3350 RPM

Remember from the picture above, there are 6 motor connection points, postulated as being 4/8 pole tie points. I mapped the original 4 position switch and how it distributes 3p to the windings. It is very simple. In FORWARD LOW speed, the right three posts are energized. In REVERSE LOW, the same three posts are energized, except 2 legs are swapped.

FORWARD HIGH and REVERSE HIGH does the same thing except to the left three posts.

The VFD manual specifies that it can handle 2,4,6,8 poles, but there is no input parameter to set the actual number.

When the three right posts are energized with the VFD (the LOW SPEED posts), the VFD is delivering 5.3A. When the left three posts are powered, the motor does not seem to be spinning faster, but the VFD is delivering 7.5 A. This is with the motor turning the spindle at its fastest pulley speed, a cutter installed, but no cutting taking place. No apparent excessive motor heating with either.

My plan right now is to set it up using the LOW speed posts. The spindle RPM is about 2200. I am going to increase the frequency of the VFD to bring the spindle up to 2500 or so, which is as fast as I've ever used it in many years.

I can program the VFD to limit current, as well as execute CONST TORQUE / CONST SPEED profiles. There are a lot of parameters to mess with.

Since the VFD has no ON/OFF switch, I am going to create a heavy relay box. The picture below shows the concept... a light toggle switch will energize the relays, one for each input line. These relays can handle 25A. Further, I have tied the DPDT contacts together to distribute the current within each relay. Energizing the VFD will also turn on a big 115V AC muffin fan which I will mount to the top of the motor to improve airflow.

All your suggestions are great! I am absorbing the information as I proceed. Really the only thing that is puzzling me is the reduction in top speed. The VFD is not limiting current at this point, as the most I have seen is 8A peak during acceleration.

Again thanks everyone.