Digi phase converters......

[frank horton]

furthere to my question about the poss of a rotary converter....
It was suggested here "How about a Digi one"......
well the cost looks pleasing but....
I want one unit to power the whole shop not just indiv machines, as I have 10x 3phase machines.....average is a 3hp motor and a few smaller.....
my question is....
has anyone done this.....
how many hours per week does it gets used and reliability....mine is just hobby shop use.....prob 4-6hrs per week then nothing for months...
recomended supplier...
I'm getting to the point where I need do something about this quite soon.....
I'm not confident to make my own rotary unit from info on youtube....anything better....I think the biggest 3phs motor that's spare is 5hp.....

 

[hotponyshoes]

How many machines do you use at once?
I don't see why you would need a digi convertor for each machine?
Why can't you just get one that's big enough to cope with the maximum load you will draw at any one time and connect it into whatever power distribution system you have now.

You won't be able to use all the extra features (without some extra work) but those are.things you won't get with a rotary anyway

 

[m_c]

Digital phase converters aren't anything that special, but require a VFD that'll run without triggering certain faults.

The big thing is the motor start up currents. A typical motor will require 3-5x startup current, possibly more depending on the load.
Take your 3hp motor (~2.2KW). It would take typically take 6.6 to 11kW startup, which at 240V is 27.5 to 45A, and possibly higher.

An olde rotary phase converter would likely struggle along overloaded while the motor gets wound up, but a digital phase converter would just shutdown if overloaded, so they need to be sized far more conservatively.
For 3HP motors, I would be looking at something at least 11KW, possibly more, at which point you're probably looking at it being cheaper to install individual VFDs on each machine, which would remove the startup surge problem while also giving you more control for each machine.

 

[Guineafowl]

As I mentioned on the other forum, I had a similar need, up to a 4hp motor (big old one, not tiddly new one). Complications were Dahlander switching and a DC brake.

I didn’t get very far with digital phase converters. Not sure what they are, if not hacked or renamed VFDs.

My 7.5 kW (10 hp) rotary converter has no minimum load, so you switch on, and have ‘three phase’. It quite happily starts the 4 hp spindle moulder with a chunky cutter block fitted. It’s also more repairable, IMO.

 

[brewdexta]

I've got a full workshop 10Hp digital inverter, 240 single phase to 415v 3 phase, had it for about 10 years. Runs my 7.5HP Colchester no problem.

It has a soft start function that lowers inrush current. Its on its own 50amp breaker.

https://www.mig-welding.co.uk/forum/threads/lathe-swap.53699/page-26#post-647134

 

[Guineafowl]

I've got a full workshop 10Hp digital inverter, 240 single phase to 415v 3 phase, had it for about 10 years. Runs my 7.5HP Colchester no problem.

It has a soft start function that lowers inrush current. Its on its own 50amp breaker.

https://www.mig-welding.co.uk/forum/threads/lathe-swap.53699/page-26#post-647134

What make/model is it?

EDIT: ah, you added the pics. So you can switch that on, and just have ‘three phase’ sockets, using machines on and off like the real thing?
Would it cope with Dahlander motors and DC brakes?
Does it have a true neutral?

I looked into some devices called DPCs, sold by JFK electrical in NI, and after some chat with the owner, who was great, it turns out the answer to those questions above was ‘no’.

 

[brewdexta]

What make/model is it?

There's a picture of all that in the thread I attached

 

[Guineafowl]

There's a picture of all that in the thread I attached

Cross post edited.

 

[brewdexta]

EDIT: ah, you added the pics. So you can switch that on, and just have ‘three phase’ sockets, using machines on and off like the real thing?
Would it cope with Dahlander motors and DC brakes?
Does it have a true neutral?

I looked into some devices called DPCs, sold by JFK electrical in NI, and after some chat with the owner, who was great, it turns out the answer to those questions above was ‘no’.

I have several machines plugged into 3 phase sockets. The Colchester, a screw compressor, a big band saw and a couple of big Wadkin tables saws. Motors vary from 4 to 7.5hp, but most start with no load, except the compressor, but even that seems to fire up and get up to speed before the valve kicks in and loads it up.

There's only one of me so never use two machines at once. I make sure the compressor is off when using other machines, I'm not sure it would like it if your taking a heavy cut on the lathe then the compressor decides to top up the tank.

I still use VFDs but usually for smaller machines with dual voltage motors where I want speed control other than changing pulleys.

I have a DC brakes on one of the Wadkin tables saws and that works fine.

Not sure about the earth or Dahlander motor question, I got a sparky mate in to wire it up and the machines. The vendors were helpful so give the a call for the specifics.

 

[Guineafowl]

I have several machines plugged into 3 phase sockets. The Colchester, a screw compressor, a big band saw and a couple of big Wadkin tables saws. Motors vary from 4 to 7.5hp, but most start with no load, except the compressor, but even that seems to fire up and get up to speed before the valve kicks in and loads it up.

There's only one of me so never use two machines at once. I make sure the compressor is off when using other machines, I'm not sure it would like it if your taking a heavy cut on the lathe then the compressor decides to top up the tank.

I still use VFDs but usually for smaller machines with dual voltage motors where I want speed control other than changing pulleys.

I have a DC brakes on one of the Wadkin tables saws and that works fine.

Not sure about the earth or Dahlander motor question, I got a sparky mate in to wire it up and the machines. The vendors were helpful so give the a call for the specifics.

Cheers. Just asking for my own interest, in case my rotary sets on fire.

The Dahlander problem is that you can disconnect the motor while it’s running, then re-connect in a different configuration. VFDs don’t like that. Yours sounds like it would cope.

DC brake issue is similar - during braking, only two phases are used. Ditto.

Roughly how much did your set-up cost? A new 10 hp one from DD is about £4400, but I see you have added options like sine wave and RFI filters and soft start.

 

[brewdexta]

It was 1575 +VAT ten years ago.

 

[Guineafowl]

It was 1575 +VAT ten years ago.

Wow, so either the price has more than doubled, or I’m looking at the wrong one. £4,399:

Pardon our interruption...

(10 hp as listed, picture is of 7.5 hp one for some reason. When I was researching these, I was slightly put off by DD’s 1990’s-style website.)

 

[Agroshield]

The Dahlander problem is that you can disconnect the motor while it’s running, then re-connect in a different configuration.

Why are you assigning the problem to Dahlander in the above statement?

The problem is the "you" between 'that' and 'can'. If you, the 200lb gorilla, are stupid enough to try to change speed while the VFD is active, frankly, you deserve the consequences.

Human being are supposed to be intelligent beings. Thus, if you know that changing the speed while the VFD is on is discouraged, the smart thing to do is to eliminate the possiblity by carrot or by stick. Use a metal knob on the speed change switch and wire it up to the VFD's output. You will only touch it once.

The carrot version is a cover over the speed change switch that is interlocked to the VFD control circuitry so that as soon as you lift the cover to access the switch, the VFD goes low.

As VFDs have more computing power than sent man to the moon, with some thinking and manual reading, it would be possible to do the speed change via the VFD's own controls - but would need a relay not a mechanical switch. A VFD can do the 'swap any two wires to reverse' trick internally without breaking a sweat and a two-speed change is not much more than that but using an external component.

 

[m_c]

What make/model is it?

EDIT: ah, you added the pics. So you can switch that on, and just have ‘three phase’ sockets, using machines on and off like the real thing?
Would it cope with Dahlander motors and DC brakes?
Does it have a true neutral?

I looked into some devices called DPCs, sold by JFK electrical in NI, and after some chat with the owner, who was great, it turns out the answer to those questions above was ‘no’.

Dahlander is no different from starting/stopping any other comparably sized induction motor.

If you need a neutral, you can add a "neutral generator" aka 3 transformers connected in a star configuration, however very few 3 phase machines actually need a neutral connection.

The big benefit of DPCs, is you get a more balanced 3 phase. Rotary phase converters are rarely perfectly balanced, as phase timing and phase voltage vary as the applied load changes.

I've now been running a home brew DPC for over 5 years.
It's a 7.5kw boost VFD, although I kept the idler motor to provide a bit load and smoothing, and to provide a neutral if needed.
I also added a Sine wave filter, as it powers my CNC lathe.
Biggest motor it used to hard start was my old manual mill, which IIRC was 2hp, and it would start it quite happily in top gear. The old rotary would chatter for a few seconds while it gradually got wound up, whereas with the DPC, it would spin up quicker and smoother.

Now the DPC only runs my CNC lathe, which has a VFD controlled 5.5kw spindle, 1.2kw sub spindle, and 1.2kw servos. It does dim the lights a bit when winding the spindle.up though

 

[Guineafowl]

Why are you assigning the problem to Dahlander in the above statement?

The problem is the "you" between 'that' and 'can'. If you, the 200lb gorilla, are stupid enough to try to change speed while the VFD is active, frankly, you deserve the consequences.

Human being are supposed to be intelligent beings. Thus, if you know that changing the speed while the VFD is on is discouraged, the smart thing to do is to eliminate the possiblity by carrot or by stick. Use a metal knob on the speed change switch and wire it up to the VFD's output. You will only touch it once.

The carrot version is a cover over the speed change switch that is interlocked to the VFD control circuitry so that as soon as you lift the cover to access the switch, the VFD goes low.

As VFDs have more computing power than sent man to the moon, with some thinking and manual reading, it would be possible to do the speed change via the VFD's own controls - but would need a relay not a mechanical switch. A VFD can do the 'swap any two wires to reverse' trick internally without breaking a sweat and a two-speed change is not much more than that but using an external component.

It’s more the inconvenience. I didn’t like spinning up the big 6.5kg cutter block on the full speed setting (6000 rpm), the spindle moulder being a simple, flat-belt affair. Much nicer to spin up to 3000 first, then switch up.

Second, the power feed unit on the same machine, which has two forward and two reverse speeds. During setup, it’s handy to run it on its own - test run a piece, change speed, maybe reverse if it jams.. etc.

A VFD could be set up to do all that, as I’ve done on the mill and lathe, but the ‘DPCs’ I was looking at (JFK), as far as I could tease from the owner, were not able to.

 

[frank horton]

well thanks for the replies....a lot of info to think about ....
Looking at the DPC cost at 4 grand'ish I thinking v seriously about a Diesel Generator....plus as we get reg power cuts, I'll have some back up.....