Need help selecting a VFD for 3/4hp 230V 3phase motor

I Know almost nothing about VFD's other than I know I need one and I know what I want it to do. I want to replace the 3/4hp 120V motor on my mill (bigger than a bench top mill but smaller than a bridgeport) with a 3/4hp 230V 3phase motor that I have. I want to do this for variable speed control using the VFD. I would prefer one that is 120V single phase input because I have an outlet right there and that would make life easier but if I have to run a 230V line then I will. My question is what size or type of VFD do I need? I have seen some things that say I need one larger than the motors hp and some things that say they should match. My concern is will it loose all its torque at slower speeds? it will conect to the spindle still with a v belt so I can change the pulley ratios to try and help it. I just don't know anything about VFD's when looking at them online. I'm guessing there is a little more to selecting on than just finding one rated for 3/4hp with single phase input.

Thanks for any advice and help you can give me.

This is a picture of the motor label that I have.

Matched HP is generally fine, but check the rated current of the VFD against the motor rated current, make sure the VFD is good for a bit over the motor rating.

120V input is available at that power level. NOS 1 HP rated units are available surplus, I have seen them from $100 to $160 or so. The 1 HP would be fine for 3/4 HP, and no issue with current. You would set it up using the motor ratied current etc and all would be well.

Without pulleys, you do not so much "lose" torque, as you do not GAIN any from the RPM reduction. You normally gain torque in proportion to the reduction in speed. Half speed, double torque.

I'd keep the belts, and use the VFD as an adjustment within each range. You will be much happier that way

Hi!

That's a perfect motor for what you want to do.

Any VFD that's rated for single-phase input, and 3/4hp output will be sufficient... and they will have ratings for capacity in that arrangement.

It is also possible to use some brands/models of VFD that are NOT identified as single-phase input, but when doing so, one must realize that the VFD is designed to have it's incoming power spread across THREE wires, instead of two, which means expecting full output is actually overloading the input. It's also important to realize that many VFD manufacturers have their equipment designed to detect phase loss, and when they see it, they automatically shut down. Some VFDs have a parameter which can be set to ignore phase loss, and some cannot. IF you choose to go this way, the popular suggestion is to 'oversize' the VFD a bit, in order to make up for that circumstance. Going to a 1hp VFD, for example, would bring it closer-in-line.

As for 120v input... you will be needing about twice the current, than if you were running 230-240v. A common 120v/20A receptacle is capable of 2400w, which is technically a smidgen over 3hp, but wiser to expect around 2hp. You could easily run the 3/4hp unit from a 120v/20A receptacle, except for the fact that a 230v VFD would not like being fed only half it's input voltage. I have used an ordinary dry transformer intended for stepping down 240/480 to 120 BACKWARDS, thus yielding the higher voltage, and had no issues at all.

Notice that your motor is labeled for 230-460... you could use a dry transformer to step 120v up to 460, then use a 1hp 460v 3ph VFD, and drive your motor (wiring configured for 460, of course).

As for torque at lower speeds, programming and planning is most of this issue. The VFD can run motors at very low speeds, and yield some amazing results... there's also some things you can do with a VFD'd motor that you simply cannot do with a constant speed setup... like overspeeding.

overspeeding is when you program the VFD to run at a frequency HIGHER than 60hz. For example, if you program the VFD to run to 120hz, and you have it connected to a 60hz 1800rpm motor, that motor will run to 3600rpm. IF you run an additional 2:1 drive reduction on the motor, you'll have a spindle that, at 60hz, is only going half it's original speed... that means 30hz is a quarter of the speed, but your leverage from that drive ratio is doubled. My Johannsen radial drill has a Bridgeport J-head, which runs a Gates Polychain toothed belt 3:1 reduction, with a 2hp Baldor like yours, also 1800rpm. I have it programmed to 200hz, which means the motor runs 1800/60*200=6000rpm... and the spindle is running 2000rpm. Without the backgear, that drill has an immense amount of torque at ANY speed. From a stalled start, with the backgear engaged, I it will easily twist a 3/4" tap in half.

I used the tooth-belt drive so that I would not be faced with slipping V-belt issues or excessive side-loading of the spindle or motor bearings. I also removed the motor's factory cooling fan, and mounted a constant-speed fan on the motor shroud. When a VFD is running a fan-cooled motor slow, it's fan is moving very little air, hence, they'll get hot. By using a constant speed fan, I never have that issue. Furthermore, if you run an 1800rpm motor to 6000rpm with the original fan, it'll sound like an air-raid siren. Not polite to the shop-kitty.

I run the same drive concept on my Monarch 10EE, on my Bridgeport J-mill, and on my Whiteman 42" power-trowel... but the Monarch and the Whiteman run 480v single-phase instead of 240 single.

I have a Clausing drill press for small-bit work that uses a dry transformer to step 120 to 480 to run a 3/4hp toothed-belt drive to the spindle... and with a foot pedal, it's a handy hole-drilling animal.

Thanks for all the advice. Can anyone recommend an affordable VFD and where I can order one from? Amazon or ebay or is there somewhere better to order from. I should probably mention I am in Canada.

mega arc 5040dd said:

Thanks for all the advice. Can anyone recommend an affordable VFD and where I can order one from? Amazon or ebay or is there somewhere better to order from. I should probably mention I am in Canada.

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Fast-changing field these days,, small VFD.

Best to do yer "short list" research at sites such as Wolf Automation, Drives Warehouse, Automation Direct, Galco, etc.

Old line name brands get that way by making fewer greivous tactical errors than those as never earn the right to become "old" brands. Warranty coverage, and their reputation for it, also matters.

Download maker's .pdf's and make a shorter list.

THEN do yer shopping for best all-around deal for the features you care most about.

You may not care, prefer sumthin' else, but some among us like KB's in the washdown NEMA-4X housing, configuration set by screwdriver instead of keypad, for example.

Even if their VFD's are only so-so, that's a lot of hassle already managed right out of the box 'coz ya can mount it where yah can reach it and need no further protective enclosure nor DIY remoted controls.

To each his own...

Order a KB Electronics KBAC24D and never look back! I use both the KBAC24D and the larger KBAC27D on a baldor 3PH grinder and a 2x72" belt grinder respectively. They both take 120V input and will drive a 230V 3 phase motor smoothly at all speeds. The 24D will do up to 1HP and the 27D up to 2HP.

The HP rating of the motor is really easy to set inside the drive as there is simply a jumper that you move. All of the 'parameters' (accel, decel, etc...) are 'programmable' by adjusting pots or changing jumpers inside the drive, which I find a lot more user friendly than annoying menus on a silly LCD screen!

You can attach a braking resistor if you need faster braking, but you likely won't as the VFD has regenerative braking as well.

They are sensorless vector drives which means they can measure the motor RPM via feedback they receive electronically from the windings of the motor (to state it simply) and then maintain the motor speed under load, eg: the motor won't 'bog down' as you enter a cut nearly as much as it would with a simpler VFD.

The enclosures on those drives are Nema 4X/IP65 (washdown) rated so you never have to worry about metal chips/dust getting in them...

There is one on ebay for $300 canadian right now.

Just get a Teco L510 VFD. They work fine for a mill.
L510-101-H1-U | Teco Westinghouse | AC Drives
Teco-Westinghouse, L510-101-H1, 1 HP, Variable Frequency Drive 115 Volt, 1 Phase Input, IP20, at D

I'll x2 on the KB drives, I bought one after seeing Greg Menke's Bridgeport motivated from a KB... not having the sophicsticated display screen with menus does not hurt their ability to do the job, and your shop probably has at least a half-dozen of the 'human interface' tools necessary to adjust those pots.

The TECO/Westinghouse drives work nice, too... and I've got an Omron on one of my small machines, too... long since obsolete/discontinued, but it still makes the belt go 'round.

I buy old surplus, most would call it junk, but it works very well, too... no nightmares. First and foremost, if you can't GET them in your area, then scratch 'em off your list. If you can't get support for them (either online, or live) but you think they're obvious and simple enough to do without, then you've got more options.

If you wind up with an Allen-Bradley 1336 or 1305 drive, I can help you with those... I even have simple wiring diagram and programming setups I made for 'em somewhere...