# Electrical savings, RPH versus VFD



## flutedchamber (Sep 5, 2012)

My lathe needed a 20 hp RPH to operate it.  The lathe has a two speed 240v 3 phase 7.5/8 hp motor, no clutch.  The motor is made by WEG, and according to the companies I talked to, they are not the easiest starting motors around.  I guess you would call them electrically 'thirsty'. 

The RPH powers my lathe and Bridgeport with zero problems.  My question is, what would my electrical savings be if I converted to a VFD?  I assume by what I read that I would actually need two, one for the lathe, one for the mill.

Any ideas??

Thanks all.


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## Tony Wells (Sep 5, 2012)

Well, considering that a VFD that would handle the lathe motor could easily be well over $1,000, I'd consider carefully just how much operating it would take to "earn" back that much money if it is more efficient. I would assume that it is, due simply to the fact that there are no moving parts, but I don't know that.

And, yes, you'd want one for the mill too, so that would need to be figured in.


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## Dlance (Jan 28, 2013)

the vfd will lower your overall power usage for sure, but in addition to needing two, you will also most likely have to rewire both the mill and the lathe's control system to be routed through the VFD. 

What HP is the phase converter you have now? In most cases it is possible to put two phase converters together to increase the output instead of buying a single much larger one.


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## Kennyd (Jan 29, 2013)

When you have a motor over 3hp, it gets real pricey trying to power them with VFD's-and often you need 440v input.


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## rdhem2 (Feb 16, 2013)

Call your local power company.  Ask for the *"ENERGY CONSERVATION SPOKESMAN".  *They will have a young under used electrical genius/engineer there who will (or at least try to) explain the computer calculated billing procedure for kw usage.  Your applicable rates, base rates, penalty rates, over use rates, power factor disruption penalty and anything else they can tack on and give you the answer you desire.  Having a lathe using a 20hp motor takes you out of the home fiddler class immediatly.  So being a commercial user, they like you.  Very, very well.

Have you ever studied your phone bill?  And wonder why you have to pay a subsidy to Uganda for phone installation to mud huts.  Or pay for Obama phones with free usage minutes when every cell phone ever made will call 911 for free if the battery works.  Power Co. has some of the same charges.  Why do you think they have a State Utilities Commission.  Somebody must keep an eye on them or the would have monthly charges like a hospital does not blink to send out.  And you would have no choice but pay, pay, pay.

Just a sad fact of life.


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## 8ntsane (Feb 16, 2013)

I would stick with you RPC being your lathe is 7.5 HP. The cost for a VFD for you lathe will be expensive. If you could find a lower HP motor for your lathe,that still had enough HP to drive it, then the cost would come down. My Sidney lathe has a 5 HP motor, and I needed to power it, and the cost of the 10 HP VFD was out of my price range. So, I used a 7.5 VFD knowing it was under powered. That was a few years ago now, and the machine has been great on VFD. 

The cost of VFDs for your machines would be costly enough that what your spending on hydro now is atleast a monthly charge. To purchase VFDs now, you will have to use them for years to pay them selfs off. I did have one draw back with my setup. My lathe does have a clutch, and VFDs don't like the abrupt hit from a clutch. But for me I also have a 600 volt transformer in the mix, but sure miss using the clutch.


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