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Joined: Jan 2004
Posts: 2
Junior Member
Main Building Power
Single Phase 237v

The Equipment Electrical Requirements are:
208-228 3 Phase 60hz 7 KVA

We are using a 15 HP Rotary Phase Converter CNC
It Converts 230volt Single Phase to 230volt 3-Phase


Under No Load Voltage Measured;
L1 to G = 118v
L2 to G = 119v
L3 to G = 205v

L1 to L2 = 236v
L2 to L3 = 237v
L3 to L1 = 235v

Under A Load
L1 to G = 117v ... "Changed -1 volt"
L2 to G = 119v ... "No Change"
L3 to G = 199v ... "Changed -6 volt"

L1 to L2 = 235v ... "Changed -1 volt"
L2 to L3 = 228v ... "Changed -9 volt"
L3 to L1 = 233v ... "Changed -2 volt"

Power then goes through a set of

Square D Company (Transformer Catalog # 500SV43B) Two Transformers Required
.500 KVA
(Its to buck the voltage from 237 to 213v)

Then To Equipment (2 Color Press Hamada c248cx-sf)

Measured Power at Equipment Panel

Under No Load I Measured;
L1 to G = 109v
L2 to G = 108v
L3 to G = 204v (WHY?)

L1 to L2 = 213v
L2 to L3 = 211v
L3 to L1 = 214v

Under A Load
L1 to G = 109v ... "No Change"
L2 to G = 106v ... "Changed -2 volt" (WHY?)
L3 to G = 198v ... "Changed -6 volt" (WHY?)

L1 to L2 = 210v ... "Changed -3 volt" (WHY?)
L2 to L3 = 210v ... "Changed -2 volt" (WHY?)
L3 to L1 = 204v ... "Changed -10 volt" (WHY?)
I NEED TO STAY ABOVE 208v on all phases

Thank you for your INFO & HELP!

Joined: Apr 2002
Posts: 2,527
NWD — With due respect, if you expect any help here, answer in detail the followup questions posted in

Blindly respamming mostly useless numbers won’t magically solve your problem.

Realize that participation here is voluntary, and you need to help with reasonable effort on your part.

Joined: Dec 2003
Posts: 886
Without even looking too closely at your numbers I can tell you that a rotary phase converter, unless it is a true motor/generator (a single phase motor coupled to a 3 phase generator) will not give you true 3 phase power. Any of the ones I have seen use the two existing "phases" as A & B which are at 180 deg and create a third phase. How do you get 120-120-120 deg out of that?

I think your buck/boost transformer is seeing this phase descrepancy, which may change under load, and not provide the proper correction.

Joined: Oct 2000
Posts: 2,722
Broom Pusher and
I kind of smell a Delta connected cornverter here! Odor remnants of a Center Tap Grounded type Animal! (or the Ø Offset is verrrry harsh!).

Can see that the Autotransformer setups for Voltage Reduction are in Delta - Open Delta that is! (specs list Two 500 VA Xformers).

Appears that the EMF levels listed are within tolerance for said piece of Polyphase Machinery.

Speaking in many tongues...


p.s. This message is simple to decipher - just use a good book to reference [Linked Image]
BTW; 208-228 VAC sounds kinda stange, unless this is something set directly for use on a 208Y/120 VAC 3Ø 4W system.
I'm commonly seeing specs at 200-208 VAC (200-208-215 VAC), or 200-208/230 VAC.
Not that this is default for every North American Equipment rating, only what's been seen by me.

Scott35 ... again

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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