3 Phase Workshop Options

[superman22x]

I am planning a solar install for a new build (couple years out at this point...) and I wasn't sure if someone had some feedback on 3 phase. I have a couple tools in my shop now that run 3 phase through VFDs. But in the future, I'd like to be able to easily add a few more, including a ~15hp CNC at some point. Rather than VFDs on everything, these get expensive when you talk about 3+hp motors, I was thinking I'd have a Rotary Phase Converter. Then I got to thinking, maybe there is a better way if I had a solar system with battery backup already planned. Growatt off grid have the option to pair 3 into a 15kw three phase system. I came up with the following diagram. Is this a good way to add a three phase shop off a solar system with a single phase grid-tie? Second advantage would be the ability to add cheaper "Off Grid Use only" panels from Santan to the 3 phase side of things.

I'm thinking the Hybrid inverter would need to maintain the batteries to a minimum state of charge from the grid so the 3 phase equipment has power on days when the solar system isn't putting out.

Sizing, I'm thinking around a 10-12kw array at this point. This will cover most of my household needs in the warmer time of year and require some grid backup in the cold months. Batteries in the 15-20kwh range.

Is there a better configuration that could do the same thing? Or should I stick with the original plan of getting a rotary phase converter (roughly similar price to three Growatt 5ks). I think only the Off Grid Growatts had the ability to do the three phase setup, so the Hybrid inverter is needed on the other side of the battery. I'd be ok with a basic grid-tie on the other side of the battery as well, I could have a circuit off one of the Off-grid inverters that powered critical functions during the 1 or 2 days a year power outage.



Thanks!

 

[Warpspeed]

With individual VFDs you can program in an acceleration ramp and avoid the massive start up surge that some high powered equipment creates.
With a single central three phase inverter, its going to get a real kick in the bum every time you push a "start" button somewhere.

The central three phase supply needs to be sized appropriately for worst case surge, and that may be a lot higher than you expect.
Not much you can do about that either.
Something to consider in the greater scheme of things.

 

[superman22x]

Yes, that's true, some of the stuff would have pretty high starting loads. Other than the CNC, I don't see putting anything larger than about 3-4kw in. The CNC would have a ramped start. So maybe with 15kw of inverters, I would be ok.

 

[Warpspeed]

Only way to know for sure is to measure the peak surge power of each machine.
A multimeter or amp meter that has a peak hold feature should give a pretty clear indication.

 

[superman22x]

This is more to allow for futue expansion. I don't have the machines, but would like to have single source of 3 phase so I dont need to get a VFD for every machine.

 

[Warpspeed]

If its a one man shop, you are not likely to be running two large machines together simultaneously.
Surges can be unbelievably high, its not just a bit more, but is usually many multiples. And that is a lot of grunt.

How about using a single large central VFD set to ramp slowly up to 60Hz, supplying all the larger surge prone machines, with a three pole isolating switch located at each machine, and each machine having its own local start and stop buttons wired back to the central VFD.

Any smaller three phase loads could be powered independently direct off the main three phase inverter bypassing the VFD for flexibility and convenience. The one machine only problem need only be for the biggest and baddest machinery.

 

[superman22x]

If its a one man shop, you are not likely to be running two large machines together simultaneously.
Surges can be unbelievably high, its not just a bit more, but is usually many multiples. And that is a lot of grunt.

How about using a single large central VFD set to ramp slowly up to 60Hz, supplying all the larger surge prone machines, with a three pole isolating switch located at each machine, and each machine having its own local start and stop buttons wired back to the central VFD.

Any smaller three phase loads could be powered independently direct off the main three phase inverter bypassing the VFD for flexibility and convenience. The one machine only problem need only be for the biggest and baddest machinery.

This is a good idea, and an excellent point about a one man shop. A single larger VFD might be a bit pricey up front, but not awful, especially if it's designed for 3 phase in/out. They get pricey when you have to derate them by 50% for single phase in/3phase out.

 

[Warpspeed]

I am theoretically off grid, but have a three phase mig welder, lathe, mill, and air compressor which can run only of the grid.

Its just a retirement hobby workshop, so if the grid goes down for a while, it does not really matter.
The small amount of three phase grid power I use each billing period is enough to keep my grid connection (as available backup).
But my house runs 100% off grid.

 

[superman22x]

Oh nice, that's a great setup. Do you run a single VFD for all the equipment?

 

[Warpspeed]

I do have a 10Hp VFD which is not in use right now for anything kicking around here, but all my three phase machinery runs straight off direct grid power, full load start. Three phase availability is a wonderful thing to have.

I also have a second smaller 3Hp single phase air compressor that runs off solar, which is what I normally use.
My rather noisy 10Hp three phase air compressor is only used very rarely for my media blasting cabinet.
The neighbors don't like that very much, so it only gets very infrequent use during appropriate hours.

 

[superman22x]

Ah ok, three phase grid availability is definitely rare but nice to have!

 

[Warpspeed]

Its not rare here in Australia, every suburban street has 230v/415v three phase power.
Houses can be supplied with one, two, or all three phases for the asking.

The American split phase 110/220v system is pretty unique in the world, and puts you at a bit of a disadvantage for powering large motors.

 

[superman22x]

Its not rare here in Australia, every suburban street has 230v/415v three phase power.
Houses can be supplied with one, two, or all three phases for the asking.

The American split phase 110/220v system is pretty unique in the world, and puts you at a bit of a disadvantage for powering large motors.

Ah, that's interesting. I knew higher voltage was used elsewhere in the world, but didn't realize 3 phase was common place for residential.

 

[Warpspeed]

Its often comes as a bit of a surprise to many Americans that the power distribution system in America is rather unique compared to most other places in the World.

This is a fairly typical Australian suburban street.
In the first picture, each power pole has four wires at the top, three phases plus neutral.
The wires lower down are broadband optical for telephone and internet.

Each residential property gets one, two, or three 80 amp phases plus neutral, which in this case in the first picture run underground from each power pole.
In most older suburbs, power to each house is via overhead wires, underground being the norm for newer suburbs.

Second picture, at the very top three phase high voltage delta connected transmission line, maybe 33Kv ?
Lower down the usual four wires along every suburban street.
Branching off from each pole, overhead drop wires to usually four houses or sometimes six houses per power pole.

All very messy and ugly, which is why they are now going underground.