Sorry for the silly question but, Do you have 3 phase on your street?
If so It might be worth it to have the power company run it to the house...
Putting the cart before the horse…..Three Phase power question???????
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If so It might be worth it to have the power company run it to the house...
ken erickson
Well-known member
Equipment
B7100 hst, 2650 front mount snowblower, L2501 hst qa loader
In my situation with low HP machines, Bridgeport and Harig surface grinder, I had good results with static converters. They were an inexpensive solution , easy to wire and served me well.
Now if I was running large industrial machines running lots of hours and hogging big chips the rotary converters would have been the way to go.
No internet myth. Here are some experts explaining why. Pay close attention to Forrest Addy who is an expert of experts.
VFD Derating and the Math
I have searched the achives and haven't seen this addressed. If for example I have a 5hp 3phase input VFD and am using single phase. The maximum output hp is 5/(sq rt 3)= 2.88hp. I assume that using a 3 hp motor is acceptable, but only would be capable of creating 2.88hp. So could one use a 5hp...
www.practicalmachinist.com
You will find that same info straight from the OEM sites
Basically when using single phase input you are increasing input current draw on L1 and L2 beyond the 3 phase design rating. You have to be very careful when shopping to read the manufacturers fine print. Most headline ratings are for 3P input and the derating number is hidden in the fine print.
Dan
It depends on the converter.
I say they suck because with most low cost units you only get 2/3 the rated motor HP and the motors run hot when loaded. The cheap units are simply motor starters and you are actually running the motor on just two of the three legs. Not at all good for the motor. Better ones also have run caps and you get a third leg and about 80% power. At this point you have an RPC minus the idler motor. Adding an idler motor gets you an RPC, roughly 98% power and better balanced legs.
Higher end solid state converters generate quality three leg power and are a different and much more costly animal.
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I'm sure your right.
So, what is the advantage of a 3ph machine?
Other than they are cheaper because very few folks can power them.... (correctly)
I mean, for a hobbiest guy wouldn't it be more practical to buy a single phase machine OR swap out the motor for a single phase lump?
That has to be possible... No?
There are a multitude of advantages to 3 phase induction motors. Ask Google for a list.
But the biggy is single phase motors top out around 5-7 HP and even at that relatively small size require "massive' input current draws.
Take a look at the big green mill in my earlier post. It has 4 motors, a 7.5HP main spindle, a 3 HP vertical head, a 3HP knee motor, and a 1/8 HP coolant pump. Converting it and all the electrical controls to single phase is not practical but powering it with a El Cheapo DIY rotary phase converter is.
Dan
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Russell King
Well-known member
Lifetime Member
Equipment
L185F, Modern Ag Competitor 4’ shredder, Rhino tiller, rear dirt scoop
Just to clarify…How many converters did you use? If more than one why?
I can swear when I was discussing the use of small single phase input converters to get three phases out I was told by a power electronics engineer that more than one would be required but I may have been understanding this incorrectly or maybe it was to change the voltage also and go to three phases. I was just discussing it casually as in ”is that possible and what people are doing now”.
I worked at an electric motor (large industrial motors - usually 4000V 3 phase) that also designed and built adjustable speed converters to drive the motors. So they would commonly use “more slices” to increase power output where a slice was similar to a slave drive that all communicated to each other through a master control slice that was the “brains” that controlled most everything.
As a mechanical engineer they were interesting devices that just made my job a bit more complicated due to the various speeds the motors could be operated on (two pole motors on 60 Hz power usually went through the first critical shaft speed and ran fine at 3600 RPMs but not well at 70 to 80% synchronous speed for example)
In the class of motors abd inverters we are talking about an inverter produces 3 phase output. Period. You only need one to convert 240v single phase input to 240v 3 phase output.
If your machine has mulltiple motors and you want to use the inverter to CONTROL each one separately you need multiple inverters - one for each motor.
Dan
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I have been running my Bridgeport on a static phase controller for 30 years without a problem but getting ready to switch to a VFD. For my CNC spindles I use Chinese VFDs. I switched to a single phase motor on my southbend lathe.
When I first got my vertical mill, I built a rotary phase converter for it. It was fine and, at the time, the least expensive way to go. I long ago ditched the RPC and switched to VFD (actually two VFDs - one for the feed motor and one for the spindle). Hell - I've put VFDs on my belt sander and bandsaw too...
Hooking up a VFD takes a different skill set than building a rotary phase converter - a skill set that involves reading and understanding the Chinglesh owner's manual that'll come with the VFD. But lots of folks have done it.
Anyway - get the VFD. All the cool kids are doing it...
Hooking up a VFD takes a different skill set than building a rotary phase converter - a skill set that involves reading and understanding the Chinglesh owner's manual that'll come with the VFD. But lots of folks have done it.
Anyway - get the VFD. All the cool kids are doing it...