• Scam Alert. Members are reminded to NOT send money to buy anything. Don't buy things remote and have it shipped - go get it yourself, pay in person, and take your equipment with you. Scammers have burned people on this forum. Urgency, secrecy, excuses, selling for friend, newish members, FUD, are RED FLAGS. A video conference call is not adequate assurance. Face to face interactions are required. Please report suspicions to the forum admins. Stay Safe - anyone can get scammed.

VFD fundamentals

P

PeterT

Ultra Member
Premium Member
On my long term project list is getting familiar with VFD/motors for some specific applications. I thought about retrofitting my 110v 1/3HP? Taiwan drill press with a suitable motor/VFD to give me some practical experience & of course a useful end result.

One thing I've never understood is there appear to be simpler standalone VFD controls like seen on belt grinders & such. They basically wire them up & go. Then there are installations like Clough42 with a separate enclosure, fans, noise filters, special fuses etc. The components & features vary by project of course, but some of these are in comparable HP range. I don't tend to see many adverse comments from the belt grinders that they are experiencing noisy line glitches or VFD is heating up. Is the enclosure more about the VFD itself, bigger machines & more sophisticated running conditions?



 
PeterT said:
On my long term project list is getting familiar with VFD/motors for some specific applications. I thought about retrofitting my 110v 1/3HP? Taiwan drill press with a suitable motor/VFD to give me some practical experience & of course a useful end result.

One thing I've never understood is there appear to be simpler standalone VFD controls like seen on belt grinders & such. They basically wire them up & go. Then there are installations like Clough42 with a separate enclosure, fans, noise filters, special fuses etc. The components & features vary by project of course, but some of these are in comparable HP range. I don't tend to see many adverse comments from the belt grinders that they are experiencing noisy line glitches or VFD is heating up. Is the enclosure more about the VFD itself, bigger machines & more sophisticated running conditions?



Click to expand...

James went overboard on his installation/conversion. In most cases you dont need a EMI filter. You dont need a separate fast blow fuse. The circuit protection (fuse or breaker) for the plug you use is sufficient for smaller applications.

A simple drill press does not require tuning a VFD... not that you shouldn't do so.

You of course want some way to measure rpm at the spindle....

A drill press is a great project to familiarize yourself with all the settings of a VFD and to learn where a better VFD may be worth the investment on a lathe for instance.

I converted my lathe. I am going to swap the VFD for a better one that allows me to use a "braking resister" to be able to stop the spindle on a dime if needed.

Feel free to ask any questions you may have
 
OH VFDs nor motors will heat up when using the VFD on a grinder because they typically run at above the nominal 60 hz and have full cooling capability of the motor. The VFD circuitry is not absorbing current under braking either... The internal cooling fans on a VFD are fine for that application.

James went for content minutes for revenue ;), his lathe has internal fast blow fuses and he did not need all the torroids he added. An EMI filter was all he really needed.
 
So KB seems to be popular with the belt grinders. This 110V-in control looks to be the smallest they make. 1HP exceeds my 1/3HP by a wide margin. But that's OK, I can foresee a comparable applications in my future. Is it just a matter of screwing the unit to a tasteful color coordinated piece of MDF & then to the wall? I noticed in the first video that particular control module actually pops out like a remote?

So assume first order of business is identify my existing motor bolt pattern/shaft ....all that dimensional stuff in order to spec out a suitable 3P retrofit motor?

I'm guessing this is maybe where shaft/pulley matching issues rear their ugly head, but gotta start somewhere.
 
TorontoBuilder said:
James went for content minutes for revenue
Click to expand...

YES! This is exactly my impression. I actually do like some of his videos but I'm sour on anybody dragging me along for months to hit revenue targets. There is so much more great content he could have added but didn't.

Anyhoo, @PeterT, I personally would not mount my vfd inside another cabinet. It already has its own enclosure and putting that inside yet another enclosure could reduce its self cooling capabilities. Even mounting it inside a plastic case is a mistake because the chassis is a heat sink and works better installed on a metal backplate or at least in open air.

If you get one, you will end up playing with it (a good thing) so best to keep it someplace where you can do that.

Don't worry too much about derating. Just get one big enough for your motor and with the features that you want. And make sure your motor and vfd can both breathe properly. You wouldn't want to run a mile breathing through a straw and neither do they.
 
Last edited:
Susquatch said:
Anyhoo, @PeterT, I personally would not mount my vfd inside another cabinet. It already has its own enclosure
Click to expand...

Depends on the VFD. The cheapos on Amazon should go in a cabinet for example although you can certainly buy VFDs that have their own electrical cabinet ($$$).

I'm talking about what you should do....my surface grinder vfd is sitting loose on a bench for example. Haven't had time, we (or I) don't always do what we should do. (I do turn off all the breakers when I leave the shop so mitigate the risk) But that is poor practice, especially in a metal shop with chips everywhere. Basically if the VFD has sealed eletrical connections, you should be good....exposed terminals? It should go in a proper cabinet.
 
Last edited:
PeterT said:
I randomly picked this motor just as example. Generally speaking how do I get data/curve of torque vs RPM assuming something like these VFD's are powering it?

Click to expand...

This is not the best motor to run as is, the constant torque speed ratio is 2:1 ergo you can't run slower than 1800 rpm without worrying about over heating.


Here are the load characteristics
1642974448764.webp
 
Mcgyver said:
Depends on the VFD. The cheapos on Amazon should go in a cabinet for example although you can certainly buy VFDs that have their own electrical cabinet ($$$).

I'm talking about what you should do....my surface grinder vfd is sitting loose on a bench for example. Haven't had time, we don't always do what we should do. (I do turn off all the breakers when I leave the shop so mitigate the risk) But that is poor practice, especially in a metal shop with chips everywhere. Basically if the VFD has sealed eletrical connections, you're good....exposed terminals? It should go in a proper cabinet.
Click to expand...

Cheapo VFDs from amazon are fine for duty on a drill press for instance, BUT they dont have any strain relief. The cheap pull out control panels cant handle a lot of use and the wires are too short to be practical.

This means making separate control box and mounting 10K potentiometer. Then perhaps adding tachometer. Then wiring in such a way as to provide strain relief.

My VFD is outside the added electrical box, but the wires too the VFD run thru the electrical box and provide strain relief. I did this to assure good cooling of the VFD and to ensure heavy wire to motor does not put strain on connections, and so EMI filter with it's bare connections are within the electrical box
 
You really first need to determine what purpose you want to add 3 phase motor for... what speed range you wish to operate at and at what power/torque. Otherwise you end up finding a bunch of shitty motors that can't even provide a decent speed range without over heating.

The source your motor paying careful attention to the variable and constant torque speed ratios. Then buy a VFD to suit the motor. And finally consider that most recommendations on youtube are from americans who preach buy american, even at twice the cost. They're as a nation just as bad as the chinese, so I shop on price and capabilities versus origin
 
Ah! where did you get that data from? I didn't see any spec sheets in the motor web link.

That's kind of the direction I was heading but rather blindly. So as a start, if I get my existing motor specs, 1/3 HP & 3500 fixed RPM (or whatever it is). Then what. I want to keep the belt in fixed mid sheave combination lets say. But in dummy terms, if the RPM knob goes from 0-100% (0=off, 100 = max rpm) and I set knob to 25% for slow RPM, is there something like a motor curve that shows (guessing here) maximum torque at corresponding RPM so I can compare to my fixed rpm motor qualitatively?
 

Attachments

  • EDT-2022-01-23 2.58.17 PM.webp
    EDT-2022-01-23 2.58.17 PM.webp
    19 KB · Views: 1
PeterT said:
Ah! where did you get that data from? I didn't see any spec sheets in the motor web link.

That's kind of the direction I was heading but rather blindly. So as a start, if I get my existing motor specs, 1/3 HP & 3500 fixed RPM (or whatever it is). Then what. I want to keep the belt in fixed mid sheave combination lets say. But in dummy terms, if the RPM knob goes from 0-100% (0=off, 100 = max rpm) and I set knob to 25% for slow RPM, is there something like a motor curve that shows (guessing here) maximum torque at corresponding RPM so I can compare to my fixed rpm motor qualitatively?
Click to expand...

There is a PDF download with technical info

Note on motors.

There are 3 main classes we look at when considering VFDs

Inverter Only motors... usually the best 1000:1 speed ratios are common (moderately expensive)

Inverter Duty a compromise that is usually not too bad, 15:1 speed ratios are common. (usually most expensive)

Inverter Ready, basically a POS when it comes to variable speed applications due to terrible 2:1 speed ratio. (cheap)

Use the sites filtering under "Inverter rating"
 
Mcgyver said:
Depends on the VFD. The cheapos on Amazon should go in a cabinet for example although you can certainly buy VFDs that have their own electrical cabinet ($$$).

I'm talking about what you should do....my surface grinder vfd is sitting loose on a bench for example. Haven't had time, we don't always do what we should do. (I do turn off all the breakers when I leave the shop so mitigate the risk) But that is poor practice, especially in a metal shop with chips everywhere. Basically if the VFD has sealed eletrical connections, you're good....exposed terminals? It should go in a proper cabinet.
Click to expand...

All bets are off with cheapo units..... I agree with your advice in that respect. That said, best to make sure your cabinet has adequate cooling if you are gunna put a VFD in there - especially one without its own cooling.

FWIW, both mine are not yet mounted so I play the same game as you and they are unplugged before I leave the shop. I plan to permanently mount the one for my Hartford on the base pillar of the mill itself with a shutoff switch between it and the wall. The one currently used for the Bridgeport will either be sold with the mill or will be moved to my lathe if the buyer doesn't want to pay for it.

I am also planning a cabinet for switches, rheostats, and displays that will mount above the mill. Even without a VFD in it, it might end up with a cooling fan too if the internal temp goes up too much. TBD based on actual temperature measurements.

But ya, I'm not recommending that temporary practice either. In that sense I'm a little like Clough. I like to wire everything up, fine tune it, and make sure it works before I start mounting things permanently.
 
I forgot to add that in the case of a drill press, for what I do, which is drilling many different materials (woods, plastics, metals) from large holes to tiny holes in model engineering, I want the best possible range of speeds.

I'd opt for a 3600 rpm motor that has a high constant torque ratio so I could turn the motor down very low if needed, or overclock it at up to 500 hz potentially
 
Susquatch said:
All bets are off with cheapo units..... I agree with your advice in that respect. That said, best to make sure your cabinet has adequate cooling if you are gunna put a VFD in there - especially one without its own cooling.
Click to expand...

Agree. There are few things a cabinet should do for you. Paramount imo, especially in a machine shop with chips flying, is to stop something shorting across the terminals. To do it properly (to code) ventilation would be through a screen and filter....can't have any openings where a chip would get in. Actually, to do it properly, you buy a cabinet, rated etc...not supposed to make them yourself, they need the sticker :rolleyes:.

Have you had over heating problems with a VFD? We put a lot of VFD's in cabinets, can't remember what the ventilation situation typically is...I'll ask the electrician.
 
Last edited:
dfloen said:
My L510 will overheat after a few hours if i keep the cabinet door shut. I need to add ventilation and a fan.
Click to expand...
That is interesting. What is the size of your cabinet? I have mine mounted in a repurposed fire alarm cabinet with ventilation holes in the bottom and top and have never had any issues with heating. I use the same cabinet for my RPC controls.
 
Hacker said:
That is interesting. What is the size of your cabinet? I have mine mounted in a repurposed fire alarm cabinet with ventilation holes in the bottom and top and have never had any issues with heating. I use the same cabinet for my RPC controls.
Click to expand...
 

Attachments

  • 20220123_195629.jpg
    20220123_195629.jpg
    345.6 KB · Views: 19
You must log in or register to reply here.
Back
Top