# 7 1/2 hp VFD for cheap guy?



## Allemay (Mar 9, 2018)

Hi Everyone,

I see a lot of discussions about 2-3hp VFD installations, but none for bigger hp situations.  I just picked up a 7.5hp lathe 220/3 phase.  Like most of you I only have single phase in my shop.  It seems like most of the VFD;s I see for 7 1/2 hp are 3 phase input only.

Can anyone suggest one that hopefully isn't $1,000?

I'll appreciate any help any of you can give me.

Brad
Newbie from MN


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## Cooter Brown (Mar 9, 2018)

You dont need a VFD to run a 220 volt 3PH motor with 1PH. I run all of my machines with static phase converters, and 220 volt 1PH. You just wire a bunch of capacitors to one of the wires from the walll and one of the wires from the motor and the other two motor wires go to the wall. it will fire right up.

this guy explains it better......


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## Karl_T (Mar 9, 2018)

Most VFDs rated for 220 3 phase will also run on 220 single phase. You won't get the full power out of it, however. Depending on your application you should oversize the VFD by 25 to75% over the 3 phase motor size. For example, I use a 10 hp. VFD to drive the 7.5 hp spindle on my hardinge CHNC lathe.


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## Ray C (Mar 9, 2018)

Allemay said:


> Hi Everyone,
> 
> I see a lot of discussions about 2-3hp VFD installations, but none for bigger hp situations.  I just picked up a 7.5hp lathe 220/3 phase.  Like most of you I only have single phase in my shop.  It seems like most of the VFD;s I see for 7 1/2 hp are 3 phase input only.
> 
> ...



It would help to know what kind of lathe and if it has other electronics associated with it.   Also, what is the long-term usage likely to be?  Cutting big pieces or little pieces?

If you're not going to be taking 0.250 cuts on 300lb pieces of material, you might consider swapping the motor with a 3 HP unit and driving it with a 220 single phase with a $180 VFD.

Ray


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## chips&more (Mar 9, 2018)

I would try one of those $230 10hp VFD’s from China. Remember, with a static converter, NO variable speed. That’s a big feature to give up/over look…Dave


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## Cooter Brown (Mar 9, 2018)

I do have a VFD on one of my SB H10 Lathes. Its from automationdirect.com. I can set it to run 1-400 Hz its dangerously fast...... and can damage the windings of motors made with older style magnet wire, newer magnet wire is good up to 1000 Hz usually...
VFD's are great for machines that don't have much or any RPM control, like my horizontal mill it only has a range of 1430-3100 RPM.


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## Allemay (Mar 9, 2018)

Thanks for all the great replies!  Everyone had really good ideas to think about.  It's an oddball Sunmax GBL-1760.  It looks like it has 12 speeds between 45-1400 rpm.  It will see very little use so I can get by without the variable speed if it means I save a bunch of money!  And when I do use it I won't be in any hurry so I'm not likely to load the machine up much.  I've never run one before so I'll be playing it safe and probably not use anywhere near the full amount of power it has.  

Here is a link to about the only info I can find about it:
https://nsmachine.com/product/17-x-60-sunmax-engine-lathe/


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## Allemay (Mar 9, 2018)

Karl_T said:


> Most VFDs rated for 220 3 phase will also run on 220 single phase. You won't get the full power out of it, however. Depending on your application you should oversize the VFD by 25 to75% over the 3 phase motor size. For example, I use a 10 hp. VFD to drive the 7.5 hp spindle on my hardinge CHNC lathe.



Really?  That would open up a world of possibilities.  I had no idea you could do that.  I did find one that specifies 1 phase input for $300.  I'm willing to gamble on it.  Seem reasonable?  

https://www.ebay.com/itm/10HP-7-5KW...844487&hash=item33d571b64a:g:xOQAAOSwI6RZw386


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## Allemay (Mar 9, 2018)

Cooter Brown said:


> You dont need a VFD to run a 220 volt 3PH motor with 1PH. I run all of my machines with static phase converters, and 220 volt 1PH. You just wire a bunch of capacitors to one of the wires from the walll and one of the wires from the motor and the other two motor wires go to the wall. it will fire right up.
> 
> this guy explains it better......



Genius!  That guy is awesome and so are you.  He's even cheaper than I am.  Your idea is in the lead now.  I'm going over to all my friend's houses and steal the capacitors out of their A/C units.


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## Ray C (Mar 9, 2018)

Allemay said:


> Genius!  That guy is awesome and so are you.  He's even cheaper than I am.  Your idea is in the lead now.  I'm going over to all my friend's houses and steal the capacitors out of their A/C units.



They even have air conditioners in Minnesota?


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## Allemay (Mar 9, 2018)

Ray C said:


> They even have air conditioners in Minnesota?



Yeah, we run them if it gets above 40 degrees F just so we don't get spoiled.


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## Ulma Doctor (Mar 9, 2018)

this is about as inexpensive as it gets for a single phase 220v input 5.5Kw output (7.5HP) VFD ...
https://www.ebay.com/itm/5-5kw-7-5H...985802?hash=item28475d418a:g:BbUAAOSwTO9aF47W

or if you want a homebrew RPC have a look at my design- (the units i have built are robust, and the oldest is 20 years old and still operates like new)
https://www.hobby-machinist.com/threads/rpc-simple-design-unbalanced.12712/


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## gr8legs (Mar 11, 2018)

When I got my Clausing 1500 lathe with the 7.5 HP 3-phase motor I was advised that I needed a 15HP VFD to run it from single-phase power and still maintain most of the motor power. It's been long enough ago that I don't exactly remember why but the reason made sense at the time. And now, 3 years later, it's still running beautifully. 

Stu


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## mksj (Mar 11, 2018)

gr8legs said:


> When I got my Clausing 1500 lathe with the 7.5 HP 3-phase motor I was advised that I needed a 15HP VFD to run it from single-phase power



That is correct, as a general rule if you look at VFD manuals, you should upsize by a factor of 2. You can fudge down to 1.5x a by adding a DC choke or input reactor to decrease the harmonic distortion.  The issue is increased current spikes and harmonic distortion running a 3 phase input VFD on single phase can lead to premature failure of the VFD. Even if running a 7.5 Hp motor on a 15 Hp VFD, the input wiring and fusing need to be rated at 15Hp x 125%. Other than the HY and other generic VFDs listed on eBay, the largest single phase VFD is 5Hp. Speedstar does make a 7.5Hp but at $1k it is expensive. I would stick with an RPC to start out with.


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## Karl_T (Mar 11, 2018)

The amount to upsize VFDs when using single phase "depends".

If you need absolute full power and 100 % duty cycle, double the size.

If you don't need that, then you can back off. Most lathes seldom run full power, 50% oversize is plenty conservative.


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## Dabbler (Jun 12, 2018)

Funny about the 2 times the rated motor thing.   I contacted Westinghouse to size my my TECO 510, and they got my motor specs and recommended a 2HP unit for my 2HP bridgeport pancake motor.  They must have built in a 'safety factor'  It has been running flawlessly for 2 years now.


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## Bob Korves (Jun 12, 2018)

Ray C said:


> They even have air conditioners in Minnesota?


I am originally from Minnesota.  They only have two seasons there, called shovel and swat.  The humidity gets so high that you need A/C even at 70F. We never had A/C, and melted at night in a pool of sweat.  The high here today in Sacramento was 99F, but only 21% humidity.  Feels fine, no A/C needed.  We also get a nice sea breeze that comes in from the coast most evenings, cools things down a lot.  IMO, Minnesota is a great place to be from, far from...


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## tq60 (Jun 13, 2018)

To properly size a vfd never derate...always RTFM...

Look in the manual and select the size indicated for the unit in service.

Just derating by getting larger unit may get close but it is a guess at best.

Everyone brags about being precise but just guesses on these...RTFM...

Sent from my SAMSUNG-SGH-I337Z using Tapatalk


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