VFD Confirmation Questions

David Schott

David Schott

Joined
Sep 27, 2004
Messages
3,041
Hello,
Will be going VFD very soon and look at options, as always. Have a single phase 1.5hp right now and three step pulley system.

Reason for question is I have found a 3hp Baldor 1750 motor for $50 locally which seems a steal. Here's a pic of specs:
ndAx5DU.jpg


I have access to normal home 220 in my shop so no problems there.

I am planning to skimp and add filters to one of the chinese VFDs. I realize a KBAC-27D is probably the "proper" long term solution here but sometimes money talks.

At that point I had been planning for a ~2hp motor as I know I dont need more than that. I had planned on getting this VFD:
https://www.ebay.com/itm/390919779712?38280

I'm a bit concerned going for a 3hp chinese VFD and maxing it out with this 3hp motor. I was planning on this VFD with a 2hp motor to give me some breathing room on a less quality VFD.

That being said, I will RARELY use the full 3hp of this motor. I was using my 2hp wired 110 for years and never really noticed losing all that HP, either.

Am I right that pushing the limit of a VFD would really only occur if I was drawing the max amps and such from it? IE running my 3HP at max rate and leaning into the belt with a big bar of steel type application? I could always go to the 4hp version here for $40 more https://www.ebay.com/itm/313182985703?5384499

Alternatively I'll just keep motor searching for a 1.5-2hp.

Other than the recommended 1750rpm and the HP rating, anything else I need to worry about on the motor beyond it being three phase?

Lastly, in my conversion from step pulleys am I seeing that I lose the pulley/belt altogether and somehow mount the drive wheel directly to my motor? I have a 4" rear drive wheel on my grinder that attaches to that 3 step pulley on the other side right now.

Much appreciated! I know bits and pieces of this have been covered over the years but specific applications are hard to gauge as I'm not a real expert in how these things are normally set up and/or converted.
 
It's the VFD the one who limits the current to the motor, so if it's a 1.5kw VFD, the motor will behave like a 1.5kw/2hp motor.
OTOH some years ago I changed my 1400rpm motor for a 2800rpm one because that is the speed I work the most.

Pablo
 
PEU said:
It's the VFD the one who limits the current to the motor, so if it's a 1.5kw VFD, the motor will behave like a 1.5kw/2hp motor.
OTOH some years ago I changed my 1400rpm motor for a 2800rpm one because that is the speed I work the most.

Pablo
Click to expand...

So if my end goal was around 2hp power and I went with a ~3hp rated chinese VFD (2.2kw) and a 3HP motor it sounds like I really wouldn't be asking for any more issues than using the same rated VFD with a 2HP motor? It sounds like a silly question when I write it out like that but my backwards logic was that if I was cutting a corner with a lower quality VFD, I wouldnt want to run it at max rating like I would a high quality one. Perhaps I should just not worry about that given the application I'm using this for (part time, and I make folders.)
 
PEU said:
It's the VFD the one who limits the current to the motor, so if it's a 1.5kw VFD, the motor will behave like a 1.5kw/2hp motor.
OTOH some years ago I changed my 1400rpm motor for a 2800rpm one because that is the speed I work the most.

Pablo
Click to expand...

Not entirely true. While the VFD does have a current limit feature, there is nothing preventing the larger motor from trying to draw more current (depending on load applied), and if it draws too much too fast, the VFD will end up tripping out to protect itself. If the load is too high, but not high enough to trip immediately, then the next protective feature that comes into play is the overload timer, which will typically allow 150% load for one minute before tripping.
 
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Buy the vfd that will give you the 3hp.

You'll never regret having more hp. It's not like more hp will speed up your grinder. It's gonna go the same speed regardless. It'll just be harder to stall. And that's good!

As you get better and better at grinding, you'll use more and more pressure to get the job done. You'll never say, "dang this grinder is just to hard to stall"!
 
A.McPherson said:
Buy the vfd that will give you the 3hp.

You'll never regret having more hp. It's not like more hp will speed up your grinder. It's gonna go the same speed regardless. It'll just be harder to stall. And that's good!

As you get better and better at grinding, you'll use more and more pressure to get the job done. You'll never say, "dang this grinder is just to hard to stall"!
Click to expand...

After 15 years making im still a grinder wuss and hardly use top speed pulley for anything but hogging profiles. I now only make tiny folder blades, though, so thats scary at 50 grit. I actually really desire the high torque low speed from the VFD most.

I guess the bottom line question is if its ok to use a chinese VFD right at its max rating or should I always buy a bit higher rating?
 
THose are good Chinese VFD drives. I've used that one (or very similar) for several years, got 3 of them in service now. Easy to setup and works good. Do put filters over the air inlet or mount in a box for dust protection.

Either the 2.2KW or 3.0KW will work just fine with the 3hp motor. You might not get the full 3hp from with the 2.2KW VFD but that should still have plenty of power. Just call the 3hp motor with the 1.15 service factor a 2 hp with a 1.5 service factor {g}.

Interesting there are now 110vac input VFD, been needing those for a long time.
 
182T frame

That's probably a seven eighths shaft, drive wheel will change

I don't know what the T is for, make sure it's a keyed shaft and not some weird threaded stub or something.
 
OK! Here is where I’m at: $35 for this motor. 3hp 60hz 1750rpm 3phase tefc Baldor. 7/8ths keyed shaft with a ~2.5” drive pulley mounted.

Its wired for 3ph directly with an on/off switch and a 20 foot section of wire im sure I can re-use. Spins like it is on glass rollers but i have no way to fully test it till i get the VFD.

Is it true i can wire a 220 basically to one pole somehow to see if it spins under power? I may just wait a week for the VFD.

Assuming the pulley is same width can I just throw a belt from this to a pulley on my current drive shaft and be done with things? I have a three step pulley on that shaft now.

For $35 seemed impossible to pass up:
4m5avHX.jpg

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Researching a bit it does seem I may be losing out some top speeds if I use this motor and a simple shaft coupling to my existing KMG with its 4" drive wheel and this 1750rpm motor. Looks like they make couplings specifically made to connect any two different motor shafts and they are pretty cheap.

Is there any reason why I cannot put a pulley on the new motor, hook it to the "middle" slot in my triple pulley on the KMG and effectively permanently mount it that way? It may be less than ideal using a pulley to double my speed vs a direct drive but I dont see a better way since I'm not getting a 7-8" drive wheel.

I may try both as neither is too much work to test out. I may not even care about the top end speed enough to do anything but direct drive it with the coupling.

VFD was in stock on amazon, locally and should be coming tomorrow.
 
Ken what are you using for filters or a box for dust protection?

Ken H> said:
THose are good Chinese VFD drives. I've used that one (or very similar) for several years, got 3 of them in service now. Easy to setup and works good. Do put filters over the air inlet or mount in a box for dust protection.

Either the 2.2KW or 3.0KW will work just fine with the 3hp motor. You might not get the full 3hp from with the 2.2KW VFD but that should still have plenty of power. Just call the 3hp motor with the 1.15 service factor a 2 hp with a 1.5 service factor {g}.

Interesting there are now 110vac input VFD, been needing those for a long time.
Click to expand...
 
David Schott said:
Is there any reason why I cannot put a pulley on the new motor, hook it to the "middle" slot in my triple pulley on the KMG and effectively permanently mount it that way? It may be less than ideal using a pulley to double my speed vs a direct drive but I dont see a better way since I'm not getting a 7-8" drive wheel.
Click to expand...

Hey David,
You'll lose some hp going that route. Will it be noticeably different? I have no idea. But at the very least, you'll be losing some to heat, vibration and slippage because of the belt.
 
A.McPherson said:
Hey David,
You'll lose some hp going that route. Will it be noticeably different? I have no idea. But at the very least, you'll be losing some to heat, vibration and slippage because of the belt.
Click to expand...

Makes sense! I will try this route just to see how it goes since its the least amount of work for me to set up. If that doesnt work I can easily get a 1+1/8 to 5/8 coupler with a spider at any tractor supply and make it effectively direct drive and see how the speed feels.
 
Wanted to update here that all went well. Motor worked, runs almost silent at max RPM. VFD arrived, wired with fear but without incident. Old motor pulled and replaced. Still need to work out some wiring logistics on where I'll located the VFD long term.

Using 1:1 pulley ratio on my grinder for now. Can't direct drive it easily as motor and grinder shaft different height (motor higher.)
 
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