- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Well, you are just going to be making a rotary phase converter then, which you said they already rejected…
3 Phase from Single Phase 120/208
- Thread starter CoolWill
- Start date
Rotary phase converter is not the same as a motor generator. I mean, yes, it is using rotation to make 3 phase, but what is called a "rotary phase converter" is different than a motor generator.
Out here in the sticks people love having these barns with home machine shops or odd farm equipment,
I have converted a handful of machines to 240 single phase against all manufacturer recommendations , voided warranties, voided UL and the sky did not fall. I had much help from folks on here so thanks again MH forums.
For the most part they were 480 machines and the motors could be re-configured to 240, then a large enough VFD to be powered off single phase goes in and a line reactor.
I have converted a handful of machines to 240 single phase against all manufacturer recommendations , voided warranties, voided UL and the sky did not fall. I had much help from folks on here so thanks again MH forums.
For the most part they were 480 machines and the motors could be re-configured to 240, then a large enough VFD to be powered off single phase goes in and a line reactor.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Sort of the difference between a rotary phase converter and a motor generator set. Both are producing three phase from single phase, but one more faithfully looks like the output of a generator than the other.
An inverter based device for generating 3 phase power can produce output of varying levels of fidelity. The simplest is something that only derives the 3rd phase, and that third phase is PWM modulated and depends on the connected motor for filtering. Next is a VFD that synthesizes all 3 phases, but still produces a PWM output that is really only suitable for a motor. Then you get something that is essentially a VFD with filtering tacked on so that the output (more or less) looks like the output from a generator. Done 'perfectly' the three phase output should be indistinguishable from what the POCO provides, but nothing is ever really perfect.
Good luck, and please tell us what the final solution ends up being.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
What would be the difference between a RPC fed from 240V/120V and one fed from 208V/120V?
Would the mfg leg from the 208V be a high/wild leg like it is on 240V?
Would the mfg leg from the 208V be a high/wild leg like it is on 240V?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Hey @CoolWill , do you need a neutral or just the 3 phases? I ask because you did say, " have a request to supply 3 phase 208Y/120 to a new machine." IF you do, note the product above does not supply a neutral, so you would need to feed a delta wye transformer to get one.
Dammit. Yes, there are 120 volt contactors and a couple of receptacles built in. I didn't read much beyond the intro. But still, it will probably be the way to go.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Well if you only need about 3 kva, it won't be a very expensive transformer.
AC\DC
Senior Member
- Location
- Florence,Oregon,Lane
- Occupation
- EC
Zvang said it all!!!!!
Not your issue manufacture messed up they fix it.
Have had that happen on much simpler thing like kitchen equipment,
Owner told manufacturer to fix and they did!
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
The output would be 208v 3ph instead of 240v 3ph. And, I believe all three 120v L-N.
It isn't my issue anyway. I'm just going to make it work one way or another. As long as the check clears, I wouldn't care if a team of mules turned a generator.
AC\DC
Senior Member
- Location
- Florence,Oregon,Lane
- Occupation
- EC
I stand corrected you're getting a paycheck either way. I guess that comment applies to the owner
Flicker Index
Senior Member
- Location
- Pac NW
- Occupation
- Lights
You can not passively derive the third phase from a center tapped single phase transformer, however if you have L1, L2 and N and they're 120 out of phase, the third phase can be created using two transformers.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
A 12 mule team is a force to be reckoned with......
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
I am not sure about a neutral. Don't standard phase converters create the 3rd leg 90° away from the midpoint if the two original legs?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Now you have a phase converter that the machine builders won't cover any warranty with.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
The bean counters don't see the labor their machinists/mechanics put into this project as they get paid to be there regardless of what they may be doing? Why spend $1500 for this item when we have an old generator and an unused motor on hand that will work. BTW the guys used $3000 of their wages and/or other supplies that were on hand when all was said and done dedicated to putting this unit together that otherwise could have been spent on other things.
Oh, the thing is less efficient when all is said and done as well with the moving parts, friction .....
Add: that 10 HP motor they happened to have on hand was probably a spare for something already in the facility, now you need to purchase another one so you still have a spare if needed, and it is probably no less than $1500 to replace
Update: I emailed the engineer at the machine vendor last night with the specs on that digital phase converter. He wrote back this morning saying that he would be OK with it as long as we used a unit that was at least twice the capacity of what a normal 20 amp circuit could supply and the transformer used on the output was twice as large as was required by the machine, so 6 kVA. He was going to put it in writing. So now I'll drop this on the customer in a little while.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Standard phase converters basically create a high leg delta, so yes the 3rd leg is essentially 90° away from the midpoint of the original 2 legs. But in this case the original 2 legs are two 120V 120° legs off of a 3 phase wye system.
If everything works out _perfectly_ the third derived leg would end up at exactly the same voltage and phase angle as the original missing leg from the wye. But it wouldn't actually be connected to the original system neutral by a stiff low impedance coil; it would be derived in the round about way from the other two legs. Sort of the same way that in a perfect open delta system the voltage across the open jaw _should_ be 240V, but even less direct and unstable.
junkhound
Senior Member
- Location
- Renton, WA
- Occupation
- EE, power electronics specialty
Are you going to share the name of the machine vendor and what the machine is?
Or is this some classified military program? Or a laser inferometer or similar where the input impedance of the machine internal supplies work with microvolts of ripple and the control loop gain is above a few kHz and the vendor is worried about Middlebrook stability?