# Three Phase Home AC



## bennettdan (Sep 20, 2007)

Hello, 
I am working on building a 3 phase controller but to start and to test out my power stage I plan to use some of the parts out of a 80Kva battery backup that was give to me due to the company bought a newer one and I would like to build an inverter that would allow me to run my 3 phase welder and milling machine on single phase home power. I have some questions that someone here might help me out with. I know that most three phase drives can't handle the output being switched open it will usually take out the power IGBTs. I seen that the battery backup had transformers inline with the output is this to always keep a small load on the power IGBTs to keep them from open spikes? Thanks


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## Sunking (Aug 10, 2009)

bennettdan said:


> I would like to build an inverter that would allow me to run my 3 phase welder and milling machine on single phase home power.


How large of a welder and mill? I mean how many Kva service do they need.

Anyway to be honest you are kind of wasting your time and a lot of money for something that will likely fail. All you need is a single phase to 3-phase converter transformer and call it done. The seriously big question whether or not if you use a transformer or home brew inverter is; Can your electrical service handle the load? If not you are dead in the water. In which case you would have to upgrade your service and if you did that just as well go with 3-phase service.


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## coulombKid (Jan 10, 2009)

Sunking said:


> How large of a welder and mill? I mean how many Kva service do they need.
> 
> Anyway to be honest you are kind of wasting your time and a lot of money for something that will likely fail. All you need is a single phase to 3-phase converter transformer and call it done. The seriously big question whether or not if you use a transformer or home brew inverter is; Can your electrical service handle the load? If not you are dead in the water. In which case you would have to upgrade your service and if you did that just as well go with 3-phase service.


My home built converter uses a 15 Hp GE tri-clad 55 induction motor to generate the "wild leg". I have a 200 amp residential service. I use 1,500 micro-farads of starter caps to pull this big dog up. When the wild leg gets up to 160 VAC RMS my potential start relay opens disconnecting the starter cap bank. (77% RPM peak torque pull out ) I have a delta ring of run caps connected to the motor to get all three phase voltages within less than 2% of imbalance and to pull a .95 lag power factor at idle as seen from the single phase mains. I start it from a 100 amp load center in my shop and a CT hooked to a fluke says it pulls a 200 amp transient for about 1/2 second on starting. That does not trip the 60 amp 2-pole breaker in front of it. I have started my 15 Hp welder generator and my 10 Hp compressor with it for 2 decades now with out a problem. Auto transformer type converters need to be more closely tuned to the service load. I have an excitation delta ring cap on each load so I never see an appreciable voltage sag as I start each 3-phase load sequentially. With each load power factor corrected down-stream of it's starter the over-all system PF hovers at about .95 lagging as recommended in my 1990 code handbook. At idle the converter uses the same number of watts as the hair drier in my bathroom.


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## Sunking (Aug 10, 2009)

So why not just upgrade to 208/120 service?


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## aeroscott (Jan 5, 2008)

bennettdan said:


> Hello,
> I am working on building a 3 phase controller but to start and to test out my power stage I plan to use some of the parts out of a 80Kva battery backup that was give to me due to the company bought a newer one and I would like to build an inverter that would allow me to run my 3 phase welder and milling machine on single phase home power. I have some questions that someone here might help me out with. I know that most three phase drives can't handle the output being switched open it will usually take out the power IGBTs. I seen that the battery backup had transformers inline with the output is this to always keep a small load on the power IGBTs to keep them from open spikes? Thanks


I wondered what the problem with using a inverter (vfd) for a shop inverter was . sounds simple power up a 3ph transformer then switch on /off your loads . unbalanced loads not a problem ? ps you could hot rod your motors with higher hz .


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## coulombKid (Jan 10, 2009)

Sunking said:


> So why not just upgrade to 208/120 service?


Some residential areas have three phase on the poles. Most don't. In a dual zoned residential-business area you will need to pay the utility to come out and install at least one more transformer on the pole. (two more preferred) That will cost several grand if you're lucky.


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## Tesseract (Sep 27, 2008)

aeroscott said:


> I wondered what the problem with using a inverter (vfd) for a shop inverter was . sounds simple power up a 3ph transformer then switch on /off your loads . unbalanced loads not a problem ? ps you could hot rod your motors with higher hz .


What, you mean run the VFD in "V/Hz" mode and just abruptly switch on and off motor(s) connected to it?! Yeah, the VFD is gonna love that...


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## bjfreeman (Dec 7, 2011)

bennettdan said:


> Hello,
> I would like to build an inverter that would allow me to run my 3 phase welder and milling machine on single phase home power.Thanks


lets start with real world problems.
Most power companies monitor usage, no matter how you attempt to do this they are going to charge you for peak power rates, as they do industrial.
You may even have the police there thinking you have a pot grow operation.
The power company will probably force you to get the 3 phase an will report you to the planning/ zoning commission.
At Any rate you will have a Demand meter put on so you power rates will be industrial, not residential.
you did not say what you KVA requirement is.
Not sure the % of clear skies you have but you might think of a solar farm to provide the power.
Next you might consider a Dyno motor setup.
There are commercial off grid sytems. you would have to get ones with sync so you can make 3 phase and each is powered from 12-48 volts.

now we get down to is it better to have one 3 phase for each machine, or try to power them off one 3phase source.

but that is A good start


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