Yet Another VFD Question...

[David DeCristoforo]

In my last VFD question thread, Colin Prince replied:


"You don't need a 5hp VFD to run your 5hp motor. A 3hp VFD will run it just fine, but obviously it will only deliver 3hp. The VFD will supply up to and including 3hp, and the motor will still work fine, as long as the load on it is 3hp or less."


So here's the new question. Is this verifiable? I would love to keep the 5HP motor against the day I can afford to "upgrade" the VFD to a 5HP model. But if I can safely run the 5HP motor off a VFD with a 3HP rating, that would be excellent. As long as nothing would be damaged, this would be ideal. In truth, a 3HP output would be more than sufficient for my present needs so if it is indeed true that the 5HP motor can be safely run with the 3HP VFD, then I'm keeping this motor!!!

[roger oldre]

Do you read answers to your other posts? I believe this has been answered quite completely.

[David DeCristoforo]

Well... yes, actually, I do read them. And I have to say that your reply has been most helpful. Just loaded with exactly the kind of information I needed. Now I can proceed with total confidence. Thanx!

DD

[Ryan Mooney]

In theory yes.. in practice maybe-probably. The HP isn't the most useful metric to judge by you want to look at full load amps and compare the VFD to the motor and see how far off it is. Depending on the settings you may have trouble spinning up (the inrush requirement looks like a short to the vfd and it can shutdown output) which can somewhat be mitigated by doing a slower ramp up - if the vfd can throw enough juice at the motor to get it to kick over at all (there can be a bit difference between "5HP" motors). If it does spin up and you put sufficient load on it it can draw to much line voltage and also cause the VFD to failsafe shutdown. Much of that can likely be gotten around with clever programming but may be a bit of a pain. If it was way off I'd vote not but 3hp to 5hp seems doable depending on the actual motor requirements.

Google search for "undersize vfd" and you'll get some interesting hits - a big no from automationdirect forums, tentative yes with caveats from practical machinist forums (and lots of good suggestions there about what settings to use to protect the vfd)

Having said all that lots of people do it so it is definitely possible within reasonable confines..

Don't you just love unequivocal answers.

[Mike Cruz]

As I said before, DD, the VFD doesn't know diddly about HP. It knows about amps. So, just program your VFD to recognize the maximum amps of your motor and you'll be fine. As a matter of fact, you can overclock you VFD so that it can deliver more amps and thus more HP to your motor.

[roger oldre]

Well... yes, actually, I do read them. And I have to say that your reply has been most helpful. Just loaded with exactly the kind of information I needed. Now I can proceed with total confidence. Thanx!

DD

Thats great! I would never have known that!you took the time to answer! and in this thread!

If that is true why start yet another thread and ask a question that has been answered in a previously generated thread? I am not trying to be mean. the information is there and you have already generated a following on that(those) threads of interested parties who wish to help. people are tracking those threads to keep up to speed and then you pop up in another thread with a new question that has or will be covered in the original thread. now your energy as well as others has to be split amongst the different threads to find the conclusion. I haven't really gotten involved before because I didn't think it was needed, and I am sure that by now you are convinced that surely it isn't there are those with much more experience than I that can answer your questions. If you want to get your machine going and are working to that end ask the right questions. when questions are asked answer them so that others can figure out where you are in the learning curve. In another thread you said that you didn't understand the low voltage control wiring section or it wasn't clear. You were given answers as to where to find it and without acknowledging that you now did understand moved on to what appeared to me at least "ok I don't understand but I think i can do without learning that right now how do I bypass the classroom and get my diploma". I have read he manual for your VFD. pretty straight forward for many, and understandable if you take the time to understand it. Posting my help at that point would have prooved usless because you would start a new thread about that once you got your VFD functioning Ive built two lathes in the last 6 months. One will take 26" in diameter inboard and 8 feet off the ways, 7 feet between centers, it does fine on two horse. there is no bragging rights to a 5 hp lathe lol. Over the years I have built equipment for ATT, IBM, Rapalla, several sawmills and other companies. I do it all the time. I work with VFD's every day, from fractional to over 100 hp. The VFD isnt the total answer from low speed to high speed one or the other it will fit well with the proper reduction. to combine both you will have to use a reduction system with at least two stages either two different sized pulley arrangements or a jack shaft. Just for the record if you want to fully utilize five horse with sub 100 rpm final you wont do it with small pulleys or a single v belt or poly v drive think about going to a final drive with a chain or wide (like 3 inch wide cog belt) If you want to get right down to brass tacks post some of the specs for the machine you are working with like the pulley sizes and belt cross section swing capability etc and keep all the information in one thread so it is easy to follow and resource. If you really want to make the best you can and not just cobble something together lets get the right info, the right questions and you will get the right answers. Really put to use the combined reference of information you have available to you and listen.

[John Keeton]

Let's keep it civil folks. Perhaps David wanted additional input and felt the title to the other thread might hamper responses.

Thanks.

[David DeCristoforo]

The thing is, I know little about this stuff. I know how to install a breaker, run a wire, connect a receptical, that sort of stuff. When Mike says "adjust the out put to match the amperage of the motor, I look in the manual but I don't see anyplace where it tells how to make this adjustment. Maybe I'm missing it or maybe Mike's unit ius different. But I end up being baffeled by it all. Sorry if this seems dense to you but I'm fishing for very specific information. If you don't have the time to bother with it, that's fine but then maybe you coulod make better use of your time than by spending it writing a 20 minute diatribe about how offended you are by it all.

[Brad Adams]

Actually when you over clock a motor with a vfd you aren't increasing the hp. You are increasing the cycles, thus increasing the speed. A 5 hp motor pulls a lot more than a 3 hp motor, and frequency drives are pretty sensitive. I would bet something burnt out in the vfd with the five hp motor on it.

[Mike Cruz]

Welcome to the Creek, Roger.

I know you are new here. I understand your frustration. Please understand that there are no "rules" around here saying that you have to stay within a thread. DD isn't doing anything that 100 people before him haven't done. Not saying it is right, but he isn't a trail blazer with this supposed issue. Heck, I've done it, too.

If you do some research (or maybe DD or someone else will post the links), you'll see that this whole lathe project that DD is working on goes back YEARS. He didn't build the lathe. Another Creeker did. That Creeker gave up on the project and "gave" the lathe away. DD decided to salvage it. IIRC, DD DID post the specs of the pulleys (pics and all) of what he conjured up.

The problem is, adding everything (continuing new questions, etc) in one thread would mean that only the die-hards would follow the thread, and DD wouldn't get the audience needed to answer individual questions. If all of DD's questions regarding VFDs were in his original thread about this lathe, many to most would never have seen it because they would have perceived that the thread had run its course already. For that matter, if DD's new VFD questions weren't in new threads (assuming the questions weren't answered in the old threads), then posting the new VFD questions would pose the same problem...smaller audience, and only those that were interested enough in the first question to pop back in to see how it is going. On that note, please understand that just because someone answers a "question" here on the Creek, (or anywhere on the Net for that matter) doesn't mean they know what they are talking about. Nothing personal, but with 5 posts (and that includes your personal address to DD), clout and respect haven't been "established" yet. Not to say that 5000 posts here makes you a genius or that it means you know what you are talking about, but it DOES mean that people get an understanding of you. They get a feel for your MO. They can figure out what your strengths and weaknesses are. And they can figure out who to trust and who to blow off.

Hey, this is my two cents regarding your "rant". Not that I'm against rants...I've had my share here. Just my observations about yours. And as I just noticed JK's opening words to his last post here about "keeping it civil", let me leave you with this... The Creek is very PC. This is not a place for vulgarity, accusations, slander, and attacks. Not saying you did any of that or implying that you will/would. Rather that, since you are new and knowing how some other forums are, I just wanted to give you some insight.

Again, welcome to the Creek! BTW, I'd love to see pics of your lathes!!!!! Built my own, too! Well, with some UBER help...

[Harry Robinette]

When I put mine in the guy's at Automationdirect said that running the vfd at a slow speed would burn the vfd way befor it should.I believe you said your motor is a 3450 rpm isn't that going to cause a problem.Just asking.

[Mike Cruz]

Brian, let me explain my statement... AND let me clarify, too. I've added 4 VFDs to pieces of equipment. Two on lathes, one on a disc/belt sander, and one on a band saw. Let me rephrase that. I've HAD THEM PUT ON...by someone else. Me being me, I was there for every step of the hook up. I ask questions. I get answers. I understand it enough to know what was done, but still probably couldn't go through the hook up myself.

What was explained to me was this... A 2 hp motor pulls about 6 amp. A "1.5 hp" VFD is rated up to 4.5 amps. If you over clock it (meaning that it will allow a "surge" of power), it will for small bursts (30 seconds or so) before "failing". So, a 1.5 hp VFD, (designed to regulate 4.5 amps) will/can surge up to 6 amps (I'm pulling numbers here for the sake of an example) for up to 30 seconds. Now, on a lathe, that would/could work. On a planer, not a good idea! Even if you are hogging out a large blank, you won't put a continuous load that would largely exceed the overclocked amp output of the VFD...not for extended periods.

Now, that said, the TECO FM50 (which is what I used for 3 of my machines) asks (in one of the setup steps) for a setting of your motor's amp capacity. DD this is for you, buddy!: I'm going to use the opposite example here... If your VFD was a 2 hp (6 amp) and your motor was a 1.5 hp (4.5 amp), you would set the VFD for 75% because the motor cannot keep up with the VFDs capabilities at 100%...you'd likely burn out your motor. So, if you make that setting 100% (in DD's case), his VFD would put out 9 amps to his motor (likely something like a 15 amp motor). The motor is fine, it isn't being taxed at all. Now, I BELIEVE that setting can go higher (past 100%) which would overclock the VFD...putting out more amps (than 9) but only for short bursts...otherwise it will shut down to protect itself.

I want to add that it has been a year of so since I built my last lathe and had to think of all this stuff, so, please forgive me (but feel free to correct me) if I've mutilated things. Likewise, IIRC it is 3 amps per hp in 220v, and 6 amps per hp in 110. So the numbers above were assuming 220v...

[Sid Matheny]

DD I would be in the same boat as you! I don't blame you for asking for more guidance.


Sid

[David DeCristoforo]

Ya see? That's just what I'm talkin about. One guy says sure, hook it up… it'll run fine. Then the next guy says you hooked a 5hp motor up to your 3hp VFD??? Woah dude… you probably toasted your VFD! Then another guy says hey, dummy… you already got your answer. Why are you still askin'? Scheech!

[Mike Cruz]

DD, under no load, your motor, albeit 5 hp, isn't putting out 5 hp. So, even if your VFD wasn't "configured", I don't see (though I'm no expert) how your motor would be pulling more than 9 amps (what I'd imagine your "3 hp VFD" is rated for). I don't see how you fried your VFD with that motor. Now, that said, TECO may say that you should NEVER start the VFD up without first configuring it or else you might fry the VFD (because maybe it comes pre programmed at 1000% or something stupid like that).

As long as I understand this whole thing correctly, your motor "can put out 5 hp/15 amps". Your VFD can output up to 3 hp/9 amps. If anything, your VFD will not be able to supply your motor enough power to allow it to be "all it can be".

If your situation were reversed, and you had a 3 hp motor and a 5 hp VFD, I can see how you could overwork/overheat/fry your motor.

If you don't configure your VFD to allow it only put out enough power to equal its rating, I don't see how you can fry it.

If you overclock your VFD to allow it to put out as much power as the motor is able to "suck up", I can see how you would/could fry your VFD.

The secret is to properly program your VFD. There are certain sections that need attention. If I get time tomorrow, I'll look for my manual that I wrote down my parameters in. IF I find it, I'll let you know which part is dedicated to this discussion.