# Which size 3 phase converter to use?



## MDR-Maker (Apr 20, 2018)

Is anyone running a surface grinder on anything less than an extreme duty 5hp level converter? I've been told by one company that I should use this level converter yet another says that the system will run fine on the base level 3hp.

The system has a 1hp spindle motor, a 1/2hp hydraulic pump motor, and a lube pump motor that is maybe 1/4hp, I can't find any reference to the hp of it but it only pushes lube oil to the ways. 

Thoughts?

Thanks


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## markba633csi (Apr 20, 2018)

Are you talking about a rotary phase converter or an electronic variable frequency drive? If it's the former I would think 3 HP would be fine
Mark


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## MDR-Maker (Apr 20, 2018)

My bad.

It's a rotary. My understanding is that a static can't handle more than 1 machine at a time and omly allows the motor to develop 2/3 of the rated power.

Thanks Mark.


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## JimDawson (Apr 20, 2018)

For a 1 HP motor I would think a 3HP RPC would be fine.  Each 3 phase motor that is switched into the circuit actually adds to the converter capacity.  What you want to watch is the voltage balance, it should be not more than +/- 10% imbalance.  The closer the better.

A 3HP static converter will run 2 motors, I have done it.  My 3 HP lathe, and 2HP mill.  This is probably not recommended however.


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## MDR-Maker (Apr 20, 2018)

Thanks Jim.

Once I get the RPC and get it hooked up I'll check the voltage balance.


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## mksj (Apr 21, 2018)

Agree with Jim, that a 3Hp RPC would work, the start up load is very light. But given the expense and installation costs, the difference between a 3 and 5Hp is maybe 20%, it may be more worthwhile to go with a 5Hp if you are planning on any other 3 phase equipment with 2-3Hp motors. The difference between something like the PL-3 and PL-5 RPCs  is $34.  You can probably also save a bit by buying a RPC panel and getting your own idler. A few things to consider, one is noise so I would recommend a 1750RPM idler either TEFC or TENV, cast iron frame if you build your own. The other is voltage regulation and quality of the components. If you buy one, I would sequester some recommendations from others that have installed the particular brand RPC you are considering.
https://www.northamericaphaseconverters.com/shop/category/pro-line-rotary-phase-converters/


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## MDR-Maker (Apr 21, 2018)

Thanks for the advise.

Pawing around on the web I found an American Rotary AR5 for just under $400 including delivery on ebay. 

This should keep me going for awhile as I don't have immediate plans for more three phase equipment.


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## projectnut (Apr 21, 2018)

MDR-Maker said:


> Is anyone running a surface grinder on anything less than an extreme duty 5hp level converter? I've been told by one company that I should use this level converter yet another says that the system will run fine on the base level 3hp.
> 
> The system has a 1hp spindle motor, a 1/2hp hydraulic pump motor, and a lube pump motor that is maybe 1/4hp, I can't find any reference to the hp of it but it only pushes lube oil to the ways.
> 
> ...



Are you sure all the motors are 3 phase?  I have a Sheldon lathe that runs on 3 phase, but only the spindle drive  motor is 3 phase.  The gear motor that powers the Worthington drive speed control is single phase.  In addition the voltage for all the controls is only single phase 120.



MDR-Maker said:


> My bad.
> 
> It's a rotary. My understanding is that a static can't handle more than 1 machine at a time and only allows the motor to develop 2/3 of the rated power.
> 
> Thanks Mark.



You are correct as to the number of motors a static phase converter *can start *at one time.  However I just purchased a North America HL-1.5 static converter for use on a Black Diamond drill grinder.  According to the literature it can power multiple machines if the combine load is within the maximum amperage rating of the converter *AND* they are started one at a time.  One caveat is that the motor(s) shouldn't be started more than a combined total of 6 times an hour.  I have not tried using it to start multiple motors, and when using the grinder every time I've started it I run it for well over an hour before shutting it down.  So far it's been used to sharpen over 300 drill bits at about 100 bits per session.  It runs fine, has plenty of power, and doesn't overheat.

The static converter on the mill is a Phase A Matic PAM 300HD.  This model was recommended because of the forward to reverse motor switching when tapping.  It has been in use over 15 years and has had no trouble instantly reversing the motor hundreds if not thousands of times over the years.  The only downside to this converter is that it's almost 4 times more expensive than the North America HL-1.5.

Keep in mind a static converter uses a series of capacitors to generate a temporary 3rd phase only at the startup of the motor.  Once the motor is at speed the capacitors drop out and the motor runs on single phase.  Since the 3 phase motor is running on single phase power only 2/3 of the coils are energized, thus the 1/3 loss of power.

Having said that I have 4 machines in the shop running on static converters, a Bridgeport mill, a Racine power hacksaw, a Sheldon lathe, and a Black Diamond drill grinder.  All are worked hard and none seem to be lacking power.


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## MDR-Maker (Apr 21, 2018)

projectnut said:


> Are you sure all the motors are 3 phase?  I have a Sheldon lathe that runs on 3 phase, but only the spindle drive  motor is 3 phase.  The gear motor that powers the Worthington drive speed control is single phase.  In addition the voltage for all the controls is only single phase 120.
> 
> 
> 
> ...




Good info for the future! 

All three motors are 3 phase with two of them starting at the same time. 

If i kick on all three at once - spindle, hydraulic pump, and the lube which comes on when the unit is turned on, it may pish the limits of the smaller static converters. With the rotary converter i'll have capacity down the road when i get a milling machine or bigger lathe or just more machines


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## Pops (May 11, 2018)

I just got my system hooked up. Bought a 3 hp Phase A matic RPC on eBay for $350. I hooked it up to a three phase breaker panel I had in the shop. Works great for two lathes and two mills. I’m a one man shop so only one machine starts at a time. They all have two or three hp motors on them. I first ran my 220 inlet power to a magnetic starter then to the RPC then to the breaker box. Our house power flashes off and on a lot. I don’t want the RPC and the motor it is driving to start at the same time.


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## MDR-Maker (May 13, 2018)

Thanks for that info Pops.

I got mine wired up the other day and ran the surface grinder for about 30 min or so.

The system worked fine and the witing was really straight forward.

Given what you run on a 3hp unit i'm guessing i have power to spare with the AR 5 i got.


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## Pops (May 13, 2018)

MDR-Maker said:


> Thanks for that info Pops.
> 
> I got mine wired up the other day and ran the surface grinder for about 30 min or so.
> 
> ...


One of my machines is 5 hp so I may be going to a five hourse RPC. I found a kit to build a 5 hp unit on eBay I'm looking into as  I have a spare 5 motor. My shop is two story so I put the RPC upstairs to reduce the noise and have the magnetic starter and breaker box downstairs.


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