VFD. Sorta confused, now totally.

T

ToddInMn

Joined
Mar 9, 2020
Messages
7
Ok, just when I sorta thought I had things figured out, I dont.
Went to pick up my motor yesterday, a single phase 2 horse. It was only a 1725 rpm, but thought that would be good enough to get things rolling.
Talking with the owner if the store about 3 phase motors, he told me that a vfd needs to be at least the rating of the hp of the motor being used. Last week, another person told me that a vfd needs to be DOUBLE the hp of the motor being used.

So, I held off on buying a motor until I inderstsnd this. I have the opportunity to buy a brand new baldor tefc 3 horse 3 phase 3450 rpm motor for 125 bucks which I THINK would be a good choice.

So what is the requirements for a vfd?
 
Don't get a single phase unless you want no speed control or use pulleys.

The 3 horse motor should run on a 3 horse VFD. Three horsepower will require a 220V outlet. I think the KBAC-29D is what you need to run it if you want a NEMA 4 VFD.

Make sure the motor has the right shaft size and mounting. Are you using the motor for a belt grinder? Do you have the model number of the motor? The price sounds too good to be true...
 
Both people could be right depending on the quality of VFD you buy. If you buy a cheep Chinese VFD then yeah the twice rating could be a safe bet. If you buy a good quality VFD like what’s used on most high end grinders then You can get them at max rated HP.

Case in point I was running a 10hp forging press off a 10hp Chinese VFD. It worked ok till it didn't. Thy replaced it after tons of back and forth emails and videos: it now lives happily running my mill and the 7.5hp motor on my lathe.
 
JTknives said:
Both people could be right depending on the quality of VFD you buy. If you buy a cheep Chinese VFD then yeah the twice rating could be a safe bet.
Click to expand...

Well that makes sense, thanks.
Hubert S. said:
I think the KBAC-29D is what you need to run it if you want a NEMA 4 VFD.

The price sounds too good to be true...[/QUOTE)

That is the vfd I was looking at. Yes the price is correct. Bought new but never used. Still in box.
Click to expand...
 
In some cases, VFDs designed for 3-phase input can be run from single-phase supplies. Doing this may need a substantial derate, somewhere along the lines of 50%, because all the power will be going through one rectifier instead of all three.

To be honest, this is pretty much history now. Most current drives designed for 3-phase supplies either have beefed up input stages which allow full power on single phase and will specify they can be used on single- or 3-phase input, or they will fault if they do not have all 3 phases present on the input and will not run at all on single phase.

It is probably still worth oversizing the ultra-cheap Chinese drives somewhat, particularly if the measures taken to protect the drive from metal dust are likely to have an effect on cooling airflow.
 
I normally try to get a 2.2KW Chinese VFD for a 2hp motor just to have a little "fudge" factor. BUT, let's face it, seldom is the full 2hp used from a 2X72 grinder motor for very long periods of time anyway. The VFD has no clue what HP motor is connected, all it knows is how many amps the motor is pulling. The Chinese drives are amazingly good values for the cost, just gotta put filters over the air inlet, or mount them in dust proof box.
 
So what would a good cheap Chinese vfd be then for the following? Am looking at the KBAC ones but money is money :)

3 horse. Amps are 8.9-8.6 208-230. rpm 3510
 
Before you decide on the price only, consider the other things you get with KBAC. You get top grade tech service and repair if needed. They know the answer to pretty much every question you ask. If they don't know, they will find out. If it needs repair or replacing, you don't have to sent it to China.
If you had called them with this question they would have taken the info for your motor and told you exactly which VFD is the right one for running your grinder.
 
Skip 3 HP and go 1.5 or 2 HP

If you go chinese vfd, you need 220 outlet to plug into
Outlet, wire, breaker



If you go kbac-27d
you can go 1.5 hp three phase motor and plug into any 110 outlet.
Comes out even money and more flexible.
 
The "Count" above stated it pretty good ^^^^if you buy that 3 hp Baldor you WILL NEED 220v outlet regardless. Both The KBAC 29 or a Chinese VFD Require that voltage to drive the VFD and Motor combination.
 
Busto said:
The "Count" above stated it pretty good ^^^^if you buy that 3 hp Baldor you WILL NEED 220v outlet regardless. Both The KBAC 29 or a Chinese VFD Require that voltage to drive the VFD and Motor combination.
Click to expand...
Yup,motor bought, and yes, 220 in the shop.
Always wished I paid more attention to electronics , circuits, wiring etc in school so I very much appreciate the help you ALL have provided.
 
ToddInMn said:
So what would a good cheap Chinese vfd be then for the following? Am looking at the KBAC ones but money is money :)

3 horse. Amps are 8.9-8.6 208-230. rpm 3510
Click to expand...
Todd, nobody gave you a response to your question. "IF" money is a concern you might try this Chinese VFD for $145 shipped, it's rated for a 4hp. You can get a 2.2kw (3hp) for $110 shipped, https://www.ebay.com/itm/321298739141? I'm running the same VFD on two motors and a 1.5kw VFD of the same manuf on a different motor. They're VERY easy to setup and for the last yr have given good service. If you're already got the 3hp motor I might spring for the extra $35 and get the 4hp rated drive. Since you'll be using well less than 2hp 99% of the time I suspect the 2.2kw drive would work just fine. "IF" you've not ordered the motor yet, then take Count's advice and go with a 2hp - all you'll ever need, UNLESS you plan to run more than 6,000 SFPM belt speed, then a 3hp "might" be a good idea.

realize with the NEMA 1 enclosure the Chinese drives have you'll need to put a filter over the air inlets (easy to do) or mount in dust proof box.
 
Thanks ken, very much appreciated. Yes, I already have the motor, couldn't really pass it up as the price and brand name were good. I will for sure check out the link you sent for the Chinese vfd.

As far as a box and filter goes, yeah that wouldnt be a problem
 
Ken, is it definitely the Vevor drive in the link that you have?

I have had very good experiences with the 2.2 kW/3HP HuanYang drives, which look virtually identical and have been around for a few years. The manual is actually pretty good.

I vaguely recall a discussion with someone who had a different drive that looked the same as the HuanYang drives in the ebay listing but didn’t share the same parameter list and had a really poor manual. I said I’d have a look at the manual if he could send me a link to it. I don’t think he could find one because I never got the link. It may have been the Vevor.

I have run into cheap Chinese knock-offs of Cheap Chinese pyrometers: The first dozen or so TM902C pyrometers I bought were boringly accurate to 1370 degC (2500 degF) when checked against the calibrator at work. I then bought another ten and they were ok to 800 degC, but then deviated from the calibrator. I can’t remember whether they read 1370 degC at 1290 degC or read 1290 degC at 1370 degC, but either way they were no good. It seems quite possible that something similar is happening with VFDs.
 
Ooops, I just realized I didn't include the link to the 4hp, 3KW drive and don't see it right now. The link I provided is the same drive (same model number anyway) as a couple I have, and I also have a 1.5kw drive of the same manuf (model number different to reflect smaller drive. I find the manuals one of the best around. I'll be happy to send a pdf file to anyone who wishes it. Is it a Vevor drive? I have no idea, the manual doesn't list a manuf at all. There are two size formats, one is the 2.2kw drive which is the same size as a 2.2 kw HuanYang drive, the 1.5kw is a physically smaller enclosure.

So far, I'm a fan of these drives - easy to setup, runs quiet (fan is OFF when motor isn't running), and display programmable to display RPM, or SFPM belt speed - and CHEAP! I think I paid $62 for one of the 1.5kw drives. $70 or so for the 2.2kw, but they've gone up some since.
 
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