3-Phase service vs VFD??

Wondering what the pros & cons are of having 3-phase utility service connected vs using a VFD? The driver would be to open up possibilities for buying 2nd hand industrial machinery, which seem to be going at good prices (probably due to limited availability of power sources for smaller workshops such as we hobbyists). Also widens the range of machines that can be considered.

I have not looked into costs, but assume that the ongoing 3-phase service might attract some sort of connection fees beyond just power use?

I know there will be up-front connection costs, along with wiring costs within the shed. But how would that be likely to balance out against VFD purchase & associated electrician costs? (There is 3-phase in the street).

Also I understand that VFD would require electrical work to get high current rated single phase outlets (32Amp??). I assume there will be an upper limit to the motor sizes that could be powered by VFD. Is that balanced somewhat by VFD being able to better manage in-rush current from motor startup? Or is startup current less of an issue in 3-phase line supplies?

Any technical downsides to using VFD? I've done a bit of reading & seems they are not a straightforward producer of sinusoidal power & may take some significant configuration.

Any technical downsides of 3-phase utility service? I have read that there needs to be some consideration of balancing the phases, but not sure if that would impact a small hobby setup.

Any limitations on using 3-phase outlets vs hard wired?

And if using a VFD, given it seems setup is needed, does that mean one VFD per machine, or can they be shared (only one machine powered at a time of course).

And then there are rotary phase converters??

Go to the electronics forum an read the VFD for newbies doc and it will answer many of your questions.

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Originally Posted by RossM

I have not looked into costs, but assume that the ongoing 3-phase service might attract some sort of connection fees beyond just power use?

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There will be a cost of connection from the street to the house, a new breaker box and meter, and the sparkly will in that process connect different single phase household circuits up to different phases, ie balance the phases.

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I know there will be up-front connection costs, along with wiring costs within the shed. But how would that be likely to balance out against VFD purchase & associated electrician costs? (There is 3-phase in the street).

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We were quoted $1500 a few years ago to install 3 phase from the street to just our house - for that money I bought more than 10 VFDs for my shed. The $1500 cost did not count running the 3P line from the switch board to the shed and installing 3P sockets in the shed which can be expensive.

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Also I understand that VFD would require electrical work to get high current rated single phase outlets (32Amp??). I assume there will be an upper limit to the motor sizes that could be powered by VFD.

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Single phase to 3 phase VFDs can run direct from 10A GPOs when power/driving 2HP or smaller motors.
If the VFD is carefully programmed a 3P 3HP motor can also run on a 10A GPO.
Likewise a 4HP 3P motor on a 4HP VFD can run from a 15A GPO. Some will even run on 10A GPOs but not recommended.
The limit of single phase to 3 phase VFDs is typically 5HP and that will need a dedicated 20A GPO.
It's really unlikely you will need to go above that in a small hobby setup.

If you have 15A GPOs in your shed already you would be covered for most machines suited to a small hobby setup.

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Is that balanced somewhat by VFD being able to better manage in-rush current from motor startup? Or is startup current less of an issue in 3-phase line supplies?

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Yes - that's what I mean by 'carefully programmed VFDs".

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Any technical downsides to using VFD? I've done a bit of reading & seems they are not a straightforward producer of sinusoidal power & may take some significant configuration.

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Modern VFDs out of the box have no problems in terms power quality to run motors used for a small hobby setup. It's more of an issue running sensitive electronic equipment which motors are not.

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Any technical downsides of 3-phase utility service? I have read that there needs to be some consideration of balancing the phases, but not sure if that would impact a small hobby setup.

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See above.

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Any limitations on using 3-phase outlets vs hard wired?

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The biggest advantage of 3P power is being able to use more than 5HP motors and more than 63A total current simultaneously, but let's face, it how often will you need that in a a small hobby setup?
3p power come into its own with things like big welders, multi motor metal work lathes, 4ft wide drum sanders and 16" table saws etc if that is the way you want to go. 3 Phase outlets are more expensive than hardwiring but of course more flexible. If you think single phase cord running across a floor are a PITA then 3P ae significantly worse.

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And if using a VFD, given it seems setup is needed, does that mean one VFD per motor, or can they be shared (only one machine powered at a time of course).

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VFDs work best one per machine , see VFDs for Newbies sticky in the electronics forum. Independent speed control is just one aspect, dedicated motor protection and speed limitations specific to each motor are two other important reasons to have dedicated VFDs.

I really wanted to have 3Phase connected to our house some 15 years ago but was waiting for the so called "upgrade" from pole to underground power in our street, which still does not look like materialising in the near future.

In the meantime I've installed more than 10 VFDs (MW Lathe, WW Lathe, 2 in the MW mill, DC, DP, BSander, BSaw, 3 Grinders, and an exhaust fan) in my shed.

Four of these were 3P machines I got for nothing. I like using VFDs so much I deliberately converted the other machines from single phase machines to 3 phase by swapping out the motors as used 3P motors are relatively cheap. Swapping the motors is not always easy - see the VFD installs thread in the electronics forum.
My shed is setup now so that I am not going to bother with installing 3P power when the upgrade arrives.
Admittedly all this does take some technical know how, so is definitely not for the fainthearted, but for me the benefits of using VFDs now far outweighs installing 3P power.

I have 3 phase and use 415V VFD's to control the motor speed and a slow start up is mechanically kinder on the machines.

Thanks for the replies guys.

Chris, if you were setting up from scratch would you just go single phase with VFDs, given you are using VFD on your 3 phase machines anyway?

I didn't look at the electronics forum Bob; I'll read that now (I searched for 3-phase vs VFD but didn't see anything in the Google results). And thanks for the lengthy reply to all my questions. Looks like VFD will be a better way to go for both flexibility & cost. I guess if I did find something I wanted with a larger than 5HP motor, I could probably swap to a smaller motor at reasonable cost. All academic right now! I don't need much running simultaneously - extractor & one large machine is likely to be the extent of it.

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Originally Posted by RossM

I didn't look at the electronics forum Bob; I'll read that now (I searched for 3-phase vs VFD but didn't see anything in the Google results). And thanks for the lengthy reply to all my questions. Looks like VFD will be a better way to go for both flexibility & cost. I guess if I did find something I wanted with a larger than 5HP motor, I could probably swap to a smaller motor at reasonable cost. All academic right now! I don't need much running simultaneously - extractor & one large machine is likely to be the extent of it.

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You can downsize the motors on some machines but not always. DC and Compressor motors cannot usually be downsized. OTOH machines like Bandsaws can be easily downsized as they rarely hit peak power output.

The question of using 3P power V's VFDs depends on a number of semi-interconnected factors like
The sizes of machines you want to operate.
What's the current power situation in your shed?
Do you already have 3P power in your house, if not, how far is the nearest 3P power from the house
How's your electrical/technical skill and interest
Do you want/need the additional features offered by VFDs?

Some examples
1) Shed has a few 10A GPOs attached to an existing house hold circuit and you want to be able to operate 2 x 3HP machines like a DC and another machine at the same time.
In that case (whether its single or 3P) you will need to run a new cable from the house breaker box to the shed
If you have 3P power in the house the added cost of running 3P cable from house breaker box to shed will be minimal. A 3P breaker box for the shed will cost more than a SP breaker box, as will the cost of in installation of 3P outlets. If you want lots of outlets these will be by far the majority cost. AT the mens shed we asked for 13 3P outlets (3 x 32A and 10 x 20A) and I was shocked at the cost. We ended up with the 3 x 32A and 5 x 20A and this was unfortunately not enough so they are constantly swapping over plugs - I hate that.

2) You wish to run 3P machines using single phase + VFDs but don't care about added VFD features.
If your electrical/technical skill and interest are limited, then you will have to pay for sparkies and/or motor rewinders to convert/install 3P motors for every machine
This is likely to work out to be more expensive that getting 3P power where you can just plug in a 3P machine and use it.
EG
The cost per machine could be as high as follows (rices are just estimates)
- VFD $120
- new motor or used motor (checked by sparky) $200 OR conversion of existing motor by rewinder ($50 - 150)
- installation of motor and VFD ($100)
See how it adds up.

If you already have 3P in the house and don't care about added VFD features I'd go with a 3P. You can always add a 3P-3P VFD to a specific machine later if you wish.
The reason for this is there are some machines that have integral motors configured to run only on 3P 415V and cannot be reconfigured to run at full power under 3P 240V as provided by a SP240V to 3P240V VFD. The motors cannot be swapped out because they are integrated into the machine. I think Chris has a nice drill mill machine like this called an Arborgha.

There is a way around this using (expensive) SP240V to 3P415V VFDs. About 10 years ago I was offered an Arborgha for nothing and turned it down and then a few months later I found out about these VFDs so I kicked myself abut it :(

Hi Bob,

Thanks for all this information. A lot to contemplate!

I would need to bring in 3-phase from the street for a new shed build.

On the wish list is a euro slider. Second hand Altendorfs etc come up quite regularly from joineries who are shutting down, and prices seem good. An SCM was listed recently for $2k and had 25 just sharpened blades included (300mm & 350mm). The blades alone would be more than the asking prices! The kicker with most of these saws is the 3-phase requirement. That SCM would be a 7HP motor.

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Originally Posted by RossM

Wondering what the pros & cons are of having 3-phase utility service connected vs using a VFD?...

I have not looked into costs, but assume that the ongoing 3-phase service might attract some sort of connection fees beyond just power use?

I know there will be up-front connection costs, along with wiring costs within the shed. But how would that be likely to balance out against VFD purchase & associated electrician costs? (There is 3-phase in the street). ....

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Good Morning Ross

Before you go any further, I suggest that you talk to your electricity supplier.

Like most of Australia, three-phase is available in our street. Twenty years ago I looked at having 3P power connected to my shed and was quoted a connection fee of about $1,000. Perhaps foolishly, I opted for $1,000 worth of tools.

Two years ago, I looked at installing a three-phase heat pump. The electricity supplier quoted a minimum connection fee of $50,000. It seems that the "available power" in my street is fully utilised and a three-phase connection would require an upgrade to the street's reticulation wires; not just the connection to my house. And they would expect muggins to pay for everything.


Cheers

Graeme

7 HP is definitely not 240v territory and I don't really see this as small hobby shop territory either.

GCs comment on available power in the street is increasingly important as more battle axe blocks and appartments are being built. A developer of a new major aged care facility near us had to contribute big $$ to run new HV wires to a new tranny to bring the facility on line. This enabled the aged care facility to installed a 192 kW solar rooftop system. It's interesting to see how many of these facilities are now running large rooftop Solar around Perth and probably elsewhere as well?

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Originally Posted by RossM

Thanks for the replies guys.

Chris, if you were setting up from scratch would you just go single phase with VFDs, given you are using VFD on your 3 phase machines anyway?

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I don't think there are any easy answers to that other than having 3 phase is a big plus and allows more options. I have always had 3 phase because about 40 years ago we installed air conditioning and the service provider installed the 3 phase for free. My K3 slider is 3 phase but I chose single phase for the Hammer A3 simply because I reckoned that a single phase machine has a better re-sale value and buying the 3 phase slider was most probably a mistake. My Clearvue has been run on both 240 & 415 as it is a multi voltage motor. The original Huanyang VFD committed suicide so when I ordered a new Powtran I elected to go 415 for no specific reason than I could. My Arbroga drill press is 415 and can't be changed and it runs from a VFD because it is only four speed gear head machine.

There is one big advantage using 415 and that is if using a welder. 240 goes through a null period of zero volts and that is why a stick or MIG welder is far better because it does not have a null period. I used to do a lot of welding and my stick welder had a 400 amp capacity and my MIG is an industrial machine not an inverter.

Having 3P simply gives more options and the bargains do pop up. I bought my 3P stick welder for $20 simply because they couldn't sell it, my original compressor for about the same but that was a long time ago when VFD's weren't even invented. Converting machine motors and using VFD's is not something I would be bothered with TTTT though it was the 240V VFD that made CV cyclones feasible in Oz.

Thanks Chris.

I'm not ready to pull the plug as yet - a lot of planning & thought to go. Cost may yet be a decider & I'll have to talk to the energy company.

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Originally Posted by Chris Parks

There is one big advantage using 415 and that is if using a welder. 240 goes through a null period of zero volts and that is why a stick or MIG welder is far better because it does not have a null period. I used to do a lot of welding and my stick welder had a 400 amp capacity and my MIG is an industrial machine not an inverter.

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It's interesting to see AC is an added feature these days on many higher end welders with some machine providing a hybrid Pulse, with both DC and AC components. This of course is all done by using inverters (as used in VFDs) which means the type of input AC doesn't make any difference. The AC output is variable AC, with frequencies typically ranging from 0.5 to 250 Hz.

Of course 3P welders can deliver much higher currents and also usually have much better duty cycles but for DIY (especially for anyone starting to weld) and even most light industrial use its hard to beat single phase inverter machines these days.

At the mens shed, back in 2014 when we moved sheds and were able to set up a dedicated metal shop we had 4, 3P welders donated to us, 3 heavy duty stick welders and a 320A Kempi MIG said to be worth more than $6k. The supervisors were really pleased as we had many new members interested in welding including 3 members who were professional welders in a past life. The Kempi was a beautiful machine but even our top pro welder member with 40 years welding/inspection/instructors experience was battling to get a clean Al weld on anything thinner than 6mm.

The same member also became one of 2 shed welding instructors and after persisting with these machines for a few months the instructors advised us to replace the 3P welders with 160A and 220A SP inverter machines. We sold the Kempi for $900, but despite extensive advertising we could not even give the 3P stick machines away and they eventually went to scrap.

I tried one of the better 3P stick welders out at work that was being thrown out and thought I would grab it for my shed for possible high current welding use and put it in storage until I got 3P power. My home machine at that time was a spare welder from my boiler maker BIL who loaned me his 150A Rainbow Stick/Tig inverter (it's not much bigger than loaf of bread) which was much easier to use than the 3P stick machine I was intending to bring home so I let it go. Eventually I had to give BIL back his welder and following advice on the MW forum I bought myself a 210A AC/DC/TIG/Stick inverter machine which runs from a 15A GPO. This has been an excellent machine and I have not needed anywhere near the max currents provided by this machine.

A similar fate happened to the 50 year old 450A stick welder at work - it was as big as a large freezer and weighed as much as large safe and we had to pay $$$ just to have it removed :oo:
With space becoming more of a premium, few folks want that size stuff in their sheds these days.

I do agree with Chris that unless you have the bent, installing VFDs are not many peoples' cup of tea as they'd much rather be doing something else. As the threads on VFDs in the Electronics explain, it can considerable expertise and at times is not for the faint hearted.

Moved into our new house in December. It is 225m from the road and power line. Quoted cost to run single phase in ground (sharing trench with storm water and water mains) was $8,800, upgrade to 3 phase (same shared trench and conduit, extra 2 cables same size and material, but harder to pull through conduit) was an extra $8,200. Went with the 3 phase because the single phase was adequate for the house but very light on for house and shed about to built. No issues with 3 phase at the street, plenty available there and town substation is 0.5km up the road with 4 homes between it and us.

Overall $17K for 225m in a shared trench, retrofitting would be a dedicated trench (more $), and rewiring the breaker box to current 3 phase standards, plus whatever your wholesaler charges to upgrade supply and meter. Prices are rural Vic.

Prior to the move we were in a small house 1Km away for 5 yrs, same retailer. No difference in unit costs for daily service fee or power consumed before/after the move, so there is no significant price variation between single and 3 phase other than potential for increased consumption.

A heads up on costs for 3P. It is one thing to get it connected to the house but it does not end there. My workshop and what was my original workshop in the lower floor (it is two story) each have a sub board which are not cheap things to install and the power points can be expensive also, contactors if used also add to the expense. I was lucky that I found a lot of plugs and wall power points years ago that a bloke was throwing out so saved some serious dollars there.

I have contemplated this many times. I am looking at moving in about 1 year from now so won't bother for the time being. One thing that sways me to getting it installed is that fact that not all 3P motors are compatible with VFDs. In the case of me acquiring 4 bandsaws recently it turns out all but 1 is compatible with a VFD. I've looked at other machines on my wish list and I don't think their motors can run off a VFD either ( Example: Wadkin MF mortiser).

Another option you could consider is a getting Rotary Phase Converter. I think they start at about ~$2k and on the rare occasion can be found second hand for cheaper or there are kits and plans you can buy to make your own - I wouldn't be up for it personally as I am not a sparky and my knowledge is limited. I knocked a Rotary Phase Converter back recently due to it needing to draw an enormous amount of amps (60 amps) which wasn't going to be suitable given my switch board (maxed out at 100amps) couldn't handle (have a bunch of stuff in the house, a few air con systems, shed, pool totalling about 60amps). BUT in hindsight should have just bought it ($400) as A) The next house may have been able to cater for it B) I could upgrade my switchboard at the new place if needed for probably cheaper than the installation of 3P. Worse case scenario I could have sold it.

As mentioned you can make 3P a lot cheaper by:
- Installing all the hardware
- Running lines; digging tenches to shed, etc
- Buying secondhand leads, plugs etc
Then when time comes just get your provider + sparky to hook it all up

I've had a growing itch for old BIG machines and whilst I am a hobbiest I know I'll always have 3P machines in my life so personally having 3P plumbed in takes out any workaround options that will possibly get you by but never be the real deal. I don't care much for what a VFD provides (slow start etc). I just want to run machines as they were designed for their intended use.