3 phase

This topic has 20 replies, 12 voices, and was last updated 6 September 2011 at 23:52 by Jon.

Viewing 21 posts - 1 through 21 (of 21 total)

Author

Posts
31 August 2011 at 13:30 #5639
capnahab
Participant
@capnahab
Advert

31 August 2011 at 13:30 #74262
capnahab
Participant
@capnahab
I am embarking on the sometimes reported painful journey to get 3 phase installed. I will only have it in the garage for a lathe and a milling machine. There is a handy online form for a quote

http://bit.ly/p1K0bu

Can anyone give me an estimate of how much the max power requirements in kVA would be ?. I would probably never use both machines simultaneously so a guess might be 25kVA ?.

Cheers

nick
31 August 2011 at 13:43 #74263
Richard Parsons
Participant
@richardparsons61721
Nick Hi!

How big in Horse Power is your largest motor? For each H.P. allow 1 KVA. _ know it should be 720 VA but 1 KVA allows for inefficiency, heat generated, power factor etc.

I would another 500 VA for your lights etc.

Rgds

Dick

P.S. 25 KVA would power a 25 HP motor!
31 August 2011 at 15:26 #74265
capnahab
Participant
@capnahab
aaahhh. Thanks Dick.

They want the total load for the houses single phase as well. (I think). Single phase can supply up to 20kVA , I thought the machines would be max 2 HP each , then I added 1 for good luck.

I am flying by the seat of my pants so am happy to be told I am wrong.

Nick
31 August 2011 at 15:54 #74266
John Stevenson 1
Participant
@johnstevenson1
I believe the minimum they will install now is 100 amps per phase – don’t quote me on this though.

John S.
31 August 2011 at 16:05 #74268
_Paul_
Participant
@_paul_
I am told it can be quite expensive to have 3 phase installed, as you only intend to use a mill and a lathe (perhaps infequently?) have you considered the alternatives of perhaps a digital inverter or a static or rotary Phase Convertor.

If you are the adventurous type you could even construct your own Convertor.

Regards

Paul

(usual disclaimer about both companies applies)
31 August 2011 at 16:34 #74270
capnahab
Participant
@capnahab
I would probably be wanting to run a lathe and a bridgeport milling machine, tho not simultaneously, possibly a welding machine later.

Are there any advantages to either solution ?.

many thanks

Nick
31 August 2011 at 17:20 #74272
Nick Hopwood
Participant
@nickhopwood71702
I run a lathe and milling machine, both with 2hp motors and find that provided I run the coolant, lights etc at the same time as the main motor, a phase converter will do the lot. I think you will find something like that will be considerably cheaper than having a 3 phase mains supply.

Nick
31 August 2011 at 19:17 #74278
chris stephens
Participant
@chrisstephens63393
A friend was quoted many thousands of Pounds to put 3 phase in his small industrial workshop, well it did involve digging a twenty foot long trench under the pavement. He now has a very large rotary converter instead.

Get a quote , not an estimate, for the cost of installing before giving the go ahead.

chriStephens
31 August 2011 at 19:27 #74280
_Paul_
Participant
@_paul_
If you are going to use a welder then in my opinion a Rotary converter would be a better choice as Inverters are suited to motors.

Pros & Cons:

Inverter: (VFD) gives excellent variable speed control over a 3 phase motor by being able to vary the current frequency, mine goes from 0Hz to 200Hz potentially enabling a 1425 rpm motor turn at 5700 rpm, I find it very convenient originally with my ML7 changing speeds was a stop the lathe and change pulley affair now it’s simply a case of reaching for the control pod.

Dosent like current being interrupted, most manufacturers warn of fitting switches on the outlet side of the unit.

Rotary: Copes with interrupted demands (like you welder) downside it has to be running (idling) all the while you need 3 phase.

Can be scratch built quite cheaply.

Another thing you could look at is “unique3phase” it seems to be a static convertor but 415v and home made, I eventually plan to build one.

Regards

Paul
31 August 2011 at 20:12 #74282
John Stevenson 1
Participant
@johnstevenson1
Posted by _Paul_ on 31/08/2011 19:27:52:

If you are going to use a welder then in my opinion a Rotary converter would be a better choice as Inverters are suited to motors.

Rotary: Copes with interrupted demands (like you welder) downside it has to be running (idling) all the while you need 3 phase.

Can be scratch built quite cheaply.

Regards

Paul

As Paul says for a rotary you need to have the donkey motor running all the while, however a recent buy of a Hydrovane compressor as a spare for mine revealed that the tripod mounted units do not use an electric switch to turn off.

Instead they rely on an inbuilt unloader valve to stop pumping when pressure is reached in the system. Sooo if you have to run a donkey why not make the donkey work ?

No connection with this sale

Ebay compressor

but read the questions at the bottom and this conforms that they are constant run units.

The tank mounted units are electrically switched, it’s only the remote tripod units that are constant running.

John S.
31 August 2011 at 21:47 #74289
Anonymous
Like it or lump it I suspect you’ll get a minimum of 60kVA for a three phase supply. As JohnS correctly says the standard single phase supply for a residential plot is 100A. I make that 23kVA rather than 20kVA, but there’s probably an allowance for some losses. So, for a three phase supply you’ll get 3 phases, each at 100A, ie, 60kVA. I can’t imagine the electricity supplier fiddling around with smaller cables.

That’s what I got when I replaced my single phase supply with a three phase supply. Three phases, each at 100A. Each machine runs off the three phase supply through an individual 16A/phase breaker. The largest motor I run is 5HP, DOL and I’ve had no problems with breakers tripping.

Regards,

Andrew
1 September 2011 at 07:35 #74295
John Coates
Participant
@johncoates48577
I run a 1hp lathe and 0.5hp mill/drill from digital inverters. Each has a 1kw inverter and they are connected to the consumer unit in series as I only use one at a time.

Edited By John Coates on 01/09/2011 07:36:18
1 September 2011 at 09:55 #74301
Steve Garnett
Participant
@stevegarnett62550
Paul’s quite correct about inverters being more suitable for motors, although with a bit of care over the ratings, they will run things like welders as well. But even if you have three-phase installed, it’s still often worth using inverters to control lathes and mills, etc – you get the advantage of soft starts, rapid stops as well as variable speed operation. And if you look on Ebay, you’ll find that often, three-phase inverters are cheaper to buy, as there doesn’t seem to be anything like the demand for them.

Regards, Steve
1 September 2011 at 18:55 #74322
Jon
Participant
@jon
Why is everyone assuming an inverter is wired for VFD.

That would be useless to him powering a welder, many are only 220V outputs unless you pay.

In fact just get one decent inverter MA7200 7.5KW and it will do the lot as a plug and play, job done £1100. People run workshops from these inc Brideports and Students at same time!

Exactly the same operating as a rotary convertor being plug and play. I have one as a back up but find extremely noisy cant hear yourself think.
6 September 2011 at 00:32 #74525
Anna Jablonska
Participant
@annajablonska79888
You will aslo be consuming less energy….as 3-phase more often than not runs at a lower amperage, so you need less power to move things along….
6 September 2011 at 08:05 #74530
Michael Malleson
Participant
@michaelmalleson22793
For running 3ph machines at home having 3ph installed will cost you a fortune. A good rotary convertor is your best cost/benefit option as you can switch on motors in succession up to the convertor rating , and off, at will without afecting the performance of motors already running. Miles cheaper than mains and you have tha convertor tosell when you no longer need it ! Mike.
6 September 2011 at 10:18 #74536
Steve Garnett
Participant
@stevegarnett62550
Posted by Jon on 01/09/2011 18:55:07:

Why is everyone assuming an inverter is wired for VFD.

That would be useless to him powering a welder, many are only 220V outputs unless you pay.

All inverter devices are inherently VFDs – it’s a part of the control circuitry. Your MA7200 is as well. The only real issue with using an inverter to power a three-phase welder is that apart from being able to stand the load, you’d have to reprogram it so that it behaves more like ‘normal’ three-phase, without being variable frequency, or with controlled ramp-ups and downs, or DC braking. Don’t want to think what applying DC braking to a welder might do!

Unless you pay more for the voltage-doubling types, all inverters give out essentially what goes in, up to the design limits. So if you put 240v into a single-phase inverter, you’ll get 3 phases of 240v each out of it.

Posted by Anna Jablonska on 06/09/2011 00:32:53:

You will aslo be consuming less energy….as 3-phase more often than not runs at a lower amperage, so you need less power to move things along….

Sorry Anna, but that’s not really true. Single phase supplies running a three phase motor through an inverter are remarkably efficient, one way or another. If a motor is rated at 750W, then that 750W is what it will consume, regardless of where it comes from. It may be spread across 3 phases, each effectively supplying 250W each, but the total will remain the same. You don’t get free energy, and you really don’t lose much by running an inverter. Indeed the performance control gains are more significant than the losses, I’d say.

Posted by Michael Malleson on 06/09/2011 08:05:45:

For running 3ph machines at home having 3ph installed will cost you a fortune. A good rotary convertor is your best cost/benefit option as you can switch on motors in succession up to the convertor rating , and off, at will without afecting the performance of motors already running. Miles cheaper than mains and you have tha convertor tosell when you no longer need it ! Mike.

The rotary converter option is rather more suitable for a small commercial operation, because that’s the situation where you might be wanting more machines to run simultaneously. In most home workshops, this isn’t the situation at all, and in that case, running a rotary converter isn’t that good, because they are remarkably inefficient. It’s certainly true that a rotary is generally cheaper than having 3-phase installed, but that’s about the only thing going for it in a domestic situation, I fear. The reason that inverters outsell all of the other devices available in this situation is that the other benefits are regarded as well worth it.
6 September 2011 at 14:24 #74554
Jon
Participant
@jon
Mines unprogrammed, straight out the box running 400V from 240V input untouched but checked.

The benefit of my digi inverters is i can plug any 380V to 440V machine in and fire them all up all at same time, because its not wired as a VFD, no reason to. Why settle for second best i dont potter about i have geared machines with easy to change speeds retaining the torque. Only this morning have been plunging in and facing 14mm deep cuts on alum 6082, far from your typical hobbiest.

Its meant to power complete workshops where 3 ph 440V machinery is used and not installed.

True it could be wired direct to the motor negating the essential ‘must have’ controls in VFD format.

All i would say to the OP is have a word with Dave at Drives Direct and state your requirements.

Rotary convertors are more expensive, i have a 5KW one as a backup, its easy to get it to moan and not deliver the goods.

All i do is unplug from output of inverter and plug direct into Transwave box outlet socket.

I did note both efficiencies or deficiencies some time back on both rotary and digi inverter.

There are losses in the conversion with both under no load.
6 September 2011 at 15:49 #74563
chris stephens
Participant
@chrisstephens63393
Hi Jon,

Why settle for second best i dont potter about i have geared machines with easy to change speeds retaining the torque

Why settle for second best indeed, but by having an inverter and not using its VFD facility are you not doing just that? I too have an all geared lathe but i bless the day I fitted a VFD.

christephens
6 September 2011 at 23:52 #74602
Jon
Participant
@jon
VFD is no use to me except a hindrance. I certainly dont want to keep faffing about constantly adjusting coolant flow dependant on speed of motor not to mentioned getting drowned.

If i want a different speed i change gear, takes 2 secs.

Secondly as with the OP wired for VFD you can only run that specific machine.

Unless all wiring is removed from the inverter from the machine along with all the other wires for stop/start (7 wires), emergency stops, foot brake, lighting, etc.

Likewise would have to wire in the new machine the same and configure each time used.

In my instance it would have been far cheaper to buy a cheap 4 or 5KW 220V 3ph inverter plus pot and buy a dual voltage 2.25KW motor.

Great if only using for one specific machine and can put up with the pitfalls.
Author

Posts