Vfd for an old 3hp lathe

[Eddyde]

My experience: I have a Huanyang VFD on my 5hp air compressor, for about 6-7 years now. It looks almost identical to the one in the picture except it's 7.5kw, which in theory, makes it rated at double the needed hp. For the most part it works fine, However, it sometimes faults for "Over Current" when run continuously, particularly in the summer or hot weather. The problem appears heat related, as once it cools down it resets and works fine. I've tried everything as far as adjusting parameters, checking connections, and wire gauge, etc. Since I rarely need continuous air, I simply put up with the problem.

For evaluating the lathe, you might try a static phase converter, yes it will only give you ⅔ of the rated hp but for a lathe it probably won't be noticed (I had a static on my Heavy 10 for years, I never stalled the motor). They are cheap to buy and you can even make one for under $20, as it's essentially, just a couple of capacitors. Schematics are available on line.

 

[Flyinfool]

One thing to consider is that most old motors are not designed for inverter duty. Most if not all modern motors are.

I am not sure about modern VFDs but when I was last using one if the motor was not rated for inverter duty it might not have a long lifespan on a VFD.

THE reason for this is that the VFD, which is an inverter, does not out put a smooth AC sine wave like the power company does. In the chart above it mentions Carrier Frequency Range. What the VFD is doing is internal converting the input power to 325V DC. It then is switching the full 325V DC on and off at the carrier frequency. In the case of a 230VAC that means that the pulses on the motor are actually coming at 325V DC and pulsed at the Carrier frequency by varying the time it is on vs off so the average voltage is correct for the point in the AC sine wave. This is also called PWM. Some old motors do not have adequate insulation on the windings to handle the 325V DC pulsing.

If your motor is not rated for inverter It may or may or may not be fine. If it happens to be a dual voltage motor that is 220 / 440 rated that means it has insulation that can handle 440V so will have no problem with the 325V of the inverter. If it is not dual rated they may still have used adequate insulation but there is no guaranty. If the insulation is not adequate it is something that will break down over time. In a hobby level of use it may still live a long useful life even though it life is being shortened. Being old and not rated only means that inverters were not invented yet so they never tested to see if they could handle it.

 

[Batmanacw]

One thing to consider is that most old motors are not designed for inverter duty. Most if not all modern motors are.

I am not sure about modern VFDs but when I was last using one if the motor was not rated for inverter duty it might not have a long lifespan on a VFD.

THE reason for this is that the VFD, which is an inverter, does not out put a smooth AC sine wave like the power company does. In the chart above it mentions Carrier Frequency Range. What the VFD is doing is internal converting the input power to 325V DC. It then is switching the full 325V DC on and off at the carrier frequency. In the case of a 230VAC that means that the pulses on the motor are actually coming at 325V DC and pulsed at the Carrier frequency by varying the time it is on vs off so the average voltage is correct for the point in the AC sine wave. This is also called PWM. Some old motors do not have adequate insulation on the windings to handle the 325V DC pulsing.

If your motor is not rated for inverter It may or may or may not be fine. If it happens to be a dual voltage motor that is 220 / 440 rated that means it has insulation that can handle 440V so will have no problem with the 325V of the inverter. If it is not dual rated they may still have used adequate insulation but there is no guaranty. If the insulation is not adequate it is something that will break down over time. In a hobby level of use it may still live a long useful life even though it life is being shortened. Being old and not rated only means that inverters were not invented yet so they never tested to see if they could handle it.

I'm fortunate because the lathe was running off a VFD already. It is set up for 220/440. I'm not out much if I have to switch the motor.

 

[B2]

Hi @Batmanacw

Mark, @mksj , used to recommend the Hitachi WJ-200-022SF. So I tried it in my VFD conversion on my PM1440GT installation and found it to be a nice VFD. I have no problems with it and the documentation and programing software is over the top! I tried to do a complete documentation of my conversion. If it helps you the link is below and the URL for the main document is: https://www.hobby-machinist.com/att...-vfddescript-links-dnl-l910_1440b-pdf.378083/ I have recently designed a pcb for the solid state control as well has have made some minor layout improvements..... which anyone who wants them are welcome to them.

VFD conversion using solid state electronic components.

Good luck.

Dave L.

 

[B2]

It then is switching the full 325V DC on and off at the carrier frequency. In the case of a 230VAC that means that the pulses on the motor are actually coming at 325V DC and pulsed at the Carrier frequency by varying the time it is on vs off so the average voltage is correct for the point in the AC sine wave. This is also called PWM. Some old motors do not have adequate insulation on the windings to handle the 325V DC pulsing.

I don't think this statement is a "fair" representation of what most decent VFD do. Inductive motors are just that, inductive. Hence, this means that they have a lot of inductance. Also, a good VFD stores the line rectified energy on high voltage capacitors. The circuit combination of the capacitors and the motor inductance, means that a step function of voltage does not produce a step function of current nor voltage. PWM of modern VFDs should break the sine wave period into a bunch of increments of time, pulses, each of which is smoothed by inductance/capacitance to approximate a sine wave at the programed output frequency and voltage. When you want to run the motor at low RPM both the voltage and the frequency is changed. My Hitachi WJ-200-022SF will put out upper frequencies of around 400 Hz. This means that to work properly the PWM frequency must be considerably faster. In fact it is in the kHz range: From the manual:

"The internal switching frequency of the inverter circuitry (also called the chopper frequency). It is called the carrier frequency because the lower AC power frequency of the inverter “rides” the carrier. The faint, high-pitched sound you hear when the inverter is in Run Mode is characteristic of switching power supplies in general. The carrier frequency is adjustable from 2.0kHz to 15kHz. " This frequency, is in fact programmable via the setting b083 . See page 3-69 and others of the manual: https://www.hitachi-iesa.com/sites/default/files/supportdocs/WJ200_Instruction_NT325X.pdf

By the way, the best I can tell all of the modern LED lighting that you just plug into your house wiring also uses PWM to convert from the house 110Vac to the ~3Vdc that goes to the LED. If you have multiple (N) LEDs in a fixture the approach is the same, but sometimes the N LEDs are connected in series so the ~3Vdc becomes N * 3Vdc. Anyway, the 110 is rectified and again a very high frequency (100s of KHz) PWM is used to charge a capacitor to a given level and this charge bleeds off through the LED, to power the LED at the low voltage. (LEDs are far more tolerant to low low voltage than motors, but the concepts are similar). In fact, many of the rheostats that you can buy to control your lighting also uses PWM to drive the light fixture but most of these doe not run at very high frequencies. Hence, the wall mounted switch containing the rheostat supplies a reduced power level to the LED fixture/bulb which then uses its own PWM to convert from this power to the LED power. The story that I have heard is that one engineer came up with the circuit design, on his own and owns the design, to drive the LED fixture and he and his company are now quite wealthy!

Dave L.

 

[Batmanacw]

As far as the wire to feed 220v to the vfd, do I need 12-3 with ground or is 12-2 w/ground good enough?

 

[Batmanacw]

You do not need to upsize your VFD, but you need to make sure your VFD can provide the 3 phase output current and maybe +10% of your motor FLA at the voltage and duty cycle of the machine/motor. Single phase input VFD's are common up to and including 3Hp running in what is typically heavy duty (constant torque mode). There are very few single phase input VFDs at 5Hp and above, and almost all are 3 phase input and require derating to run on single pahse. Things get a bit more murky when you look at VFD's Hp ratings/output amps and derating for running a 3 phae input VFD off of single phase. Almost all three phase input VFD's need to be derated by a factor of 2 or more to run on single phase, most require the use of a DC choke. Example below, is for the Hitachi SJ-P1 VFD's which are 3 phase input VFD's but can run off of single phase power if derated. A 3 Hp 3 phase motor is rated at 2.2kW and typically requires between 8-9.5A @208-230VAC. Based on the output current rating on single phase input power you would need either the 00330 (their 7.5Hp model) or their 00460 (10Hp model) to run off of single phase to run your 3Hp motor. Some VFD might also indicate a range of Hp say 5Hp for constant torque (machinery, ND or HD) and 7.5Hp for variable torque (fans and pumps, VLD, LD). Yaskawa's drives and many others are also the same, their 3 phase input VFD's require a derating 2-3X depending on the model and if a DC choke is used (see attached document). One needs to factor in all the deratings required for the specific VFD model under the operating conditions/load.

But for most single phase input VFD's, you are fine using a 3Hp VFD for a 3Hp motor. Most single phase VFD's also have a bit of headroom on the output amps, so match the motor Hp to VFD Hp. But always worthwhile to keep in mind that it is the output amps at the rated voltage that matters. CHeaper (generic) VFD brands people do tend to go to the next size up, as there ratings and reliability tend to be a bit over rated. I will also recommend the newer line GS20/GS21 VFD's from Automation Direct as being easier to install and offering a lot of VFD at the price point. I recommend them over the Teco L510 that are also commonly recommended. Hitachi WJ-200-022SF is also often used but probably not worth the extra $ for your application. Automation Direct also provides very good tech. support, I have installed a few of these drives and they have worked equivalent to the Hitachi WJ200. Choise of VFD also depends on the application and the VFD finctions required.

View attachment 481714

I can get a

Huanyang Vfd,Single to 3 Phase,Variable Frequency Drive,3Kw 4HP 220V Input AC 13

For $110 shipped. It has enough to power the f.l.a. of the 3 hp motor at around 10 amps so there is some wiggle room.

I cannot afford an expensive vfd. I'm hoping this one will do for the limited hobby use this lathe will see.

 

[Gaffer]

The neutral isn’t needed for the VFD because it only feeds the motor. If your pulling a new circuit, you might want a neutral for circuits requiring one.

 

[Batmanacw]

The neutral isn’t needed for the VFD because it only feeds the motor. If your pulling a new circuit, you might want a neutral for circuits requiring one.

I was planning on running a circuit just for the lathe. Maybe overkill but 12-2 is considerably cheaper than 12-3.

 

[Gaffer]

Should you later want to add a DRO or anything else wanting 110 VAC, lighting etc., you'll appreciate it. You can always use an extension cord, too.