Do I need a ROTARY PHASE CONVERTER or a DIGITAL PHASE CONVERTER or an INVERTER? 2

[ExpatIreland]

This is a new thread from my initial 'Phase Converter question - 1ph to 3ph'. (To all those that answered thanks very much). Instead of continuing that thread I thought it best to start a fresh one.

I have more data now. Our 3 phase 7.5hp/5/5kw coffee grinder's motor plate is at this link so you can see the specs on it.

I am going to run the grinder on house current (IRELAND) of 230V/50HZ.

The load on the motor will be steady and there will only be this one piece of equipment being serviced by the converter/inverter.

One friend, who runs a lot of 3ph equipment says to buy an INVERTER to change the power from 1ph to 3ph. He says the power delivered will be more steady and my motor will last longer. Two or three other people say the exact opposite. They say the INVERTER will have a lot of distortion and won't be as 'harmonic' as the ROTARY/DIGITAL converter.

Another says I need a ROTARY PHASE CONVERTER because if the input to the INVERTER is 230V I'll only get 230V coming out the other end.

Another says I should look into a DIGITAL PHASE CONVERTER as it is better than the ROTARY even though it costs about £400 more. He says the DIGITAL converter is quieter and delivers more even power.

The ROTARY PHASE CONVERTER company says they're the best way to go.

The DIGITAL PHASE CONVERTER company says they're the best way to go.

I'm completely confused. What's the difference between ROTARY and DIGITAL converters, and which would you purchase given the information provided? And if you lean toward the DIGITAL CONVERTER is the higher price justified? If you need additional information please let me know.

Thank you in advance for your insights!
William

 

[waross]

First you may want a transformer to boost your voltage up to the 400 Volts that the motor wants.
Then let's talk about a digital inverter.
We generally make a distinction between an inverter and a Variable Frequency Drive.
An inverter generally puts out set frequency and a set voltage. If you run a motor on an inverter the inverter will have to handle the starting surge. Either it will be more robust to handle the surge or it must be oversized or both.

nput to the INVERTER is 230V I'll only get 230V coming out the other end.

Actually the same holds true for the rotary converter. Some rotary converters may be connected to deliver double voltage, but it will have to be twice as large. The other little hitch is that if the rotary machine is used as a voltage doubler, that is what you will get, double voltage, 460 Volts, not the 400 Volts that the motor wants.
The VFD on the other hand, is optimized to control and protect a motor.
Sure it is a type of inverter but if varies both the voltage and the frequency.
That gives you the advantages of speed control and avoiding starting surges.
VFDs are readily available and probably a lot cheaper than an inverter, even before you start oversizing the inverter.
Think:
Transformer, 230 Volts to 400 Volts.
VFD, avoid the starting surge.
Starting that motor DOL on either a rotary converter or a standard inverter will develop a starting surge at 230 Volts of 120 Amps to 150 Amps.
A VFD may be able to keep the starting surge down to 25 Amps.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

A Rotary Phase Converter (RPC) is a 3 phase motor driven by a single phase motor, or a 3 phase motor STARTED by a single phase source using capacitors and a special circuit. In either case once the 3 phase motor is running and two of the windings are energized by the single phase source, they induce a voltage onto the "missing" phase and you can use that to power YOUR motor. So overall, this is the lowest efficient option because you are going to be running TWO motors (or 3 depending on the design) to power one machine, plus you add the mechanical wear and tear on everything.

A "Digital Phase Converter" is a nebulous term with no official definition, but generally means something like a "Phase Perfect" brand of device. This works by taking in the single phase source and tapping off of it to power up a SINGLE inverter module, so it ADDS the third phase to go along with the other two. But the problem is, in a single phase source, the two "hot" lines are really opposite ends of the SAME phase, so are displaced from one another by 180 degrees. In a 3 phase system, the 3 phases are each displaced from one another by 120 degrees. So in digitally adding the "third phase" with an inverter, that third phase is neither 90 nor 120 degrees from the other two, its a compromise. Ultimately this slightly affects the efficiency of your motor, but is not as bad as with the RPC and because there is only ONE pole of an inverter, is less expensive than a VFD. It's also usually OK with powering up other loads on the same machine.

A VFD / Inverter drive converts your single phase source to DC and recreates the 3 phase as an entirely NEW source for the motor. The phase are balanced, the motor is soft started, the VFD typically comes with better motor protection than any other option etc. etc. Don't get excited about "harmonics" with regard to the motor, someone telling you that is all wet. Yes, there are some, but it's not a big deal. There are some serious issues worth considering IF you were running the motor at 380-480V, but not at 230V 3 phase. The down side of the VFD option, as I told you in the other thread, is that you have to double the size of the VFD for the motor (in you size range) and it can only be used for that ONE motor, you can't use it to power up other devices that are connected to the motor circuit, like other electronics, relays etc. So you often must get into the guts of your machine to separate the circuits and have the VFD supply ONLY the motor portion of it.

In my opinion the Digital Phase Converter may be the answer for your situation though.

PS: After reading Bills post, I may have to amend this vis-a-vis the 230V vs 400V issue. But I don't see where you ever actually STATED the motor nameplate voltage rating. What is it?


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[ScottyUK]

jraef,

On the nameplate.

I'd go with the transformer to step up the supply voltage, then a use 400V in, 400V out inverter. You'll probably pick a used VFD up on ebay for £150 - £200 or so. Buy some extra capacitors for the DC link - you'll need types rated at 600V or greater. The transformer might take a bit more finding, or you might have to buy one specially: at that power rating it will be quite a big one.

 

[ExpatIreland]

jraef, the motor voltage rating, the way I read it on the nameplate, is 400v/50hz or 480v/60hz. But I am assuming you can see the picture of the motor nameplate above in my original post to start this thread. If that is the case I'm thinking you are asking a different question than what appears obvious to a non-electrical mind like mine. If you can clarify exactly what you mean by the stated motor nameplate voltage rating I will chase that down with the manufacturer.

 

[waross]

400 Volt delta at 50 Hz on the nameplate pictured. If it was 400 Volt star, we could go 230 Volt delta, but the 400 V delta leaves us with needing a transformer.

Re the digital add-a-phase converter.
If you supply the circuit with 120/240 Volts single phase, you can add 208 Volts to the center tap at 90 degrees and get true four wire delta out. (A combination of 240 Volts delta and 120/240 Volts single phase.)


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

But I don't see where you ever actually STATED the motor nameplate voltage rating. What is it?

Further, the OP is stating that the inverter is £400 MORE than a rotary. This leads me to think this may be a full-on three phase inverter and NOT just an added single phase unit.

Can this motor be reconnected to offer 200/230V operation? I suspect it might since the plate actually states " Δ " what do you guys think on that? It would save the hassle of a transformer.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ExpatIreland]

The kit that is £400 more is -- and apologies if I misspoke earlier -- a DIGITAL PHASE CONVERTER. Drives Direct in the UK is the manufacturer I'm speaking with although I'm sure there are others.

 

[ExpatIreland]

Oh, I did talk to a manufacturer in the U.S. (because it was after hours here) and he recommended phase converting 230v 1ph to 230v 3ph and then transforming that output to 400v 3ph. The kicker though is he thought the phase conversion part would require a 60A to 70A service for my 7.5hp motor. My mains power is 63A. I have to check with the electric company tomorrow but I was told by a local INVERTER supplier that most homes in Ireland have a 2.3kva supply and that with that power the INVERTER could manage a 3.5hp motor but not much more. As I said originally, he may have been a very informed person . . . . or maybe not. Just more fuel to add to this fire.

 

[waross]

Hi Keith. 400 Volt delta will be 690 Volts star. No help there.
I'm looking at a motor rating of 5.5 kW.
With about 80% overall efficiency that will be about 30 amps at 230 Volts.
On a total available service of 63 Amps it doesn't look good for DOL starting.
The effect of the staring surge of a 7.5 HP motor going DOL on 230 Volts is one reason I suggested a VFD.
The phase converter will have to have double the current rating if it goes on the 230 Volt side.
Over here in NEMA land, there are a lot of single phase transformers available in that size range. Not so many small three phase transformers available off the shelf.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Crazy. 3 posts in before I finished mine. Now I look like I just piled-on to poor Jeff. LOL


Expat: I hate to tell you this but I think you're... nutz to do this. A coffee grinder? You essentially have a machine that you run for a minute that is a monster not sized for your application or location. You are going to spend a fortune getting this to all work right. It's like you bought a semi truck to do daily deliveries of a crate of apples!

You should step back and re-assess the logic of this whole thing. I suspect a 1HP grinder will do a very nice job for you without all the phase crap and humming, house-heating transformers it won't need. Sure it will take a little longer but why would you care? Just make sure what you want to grind will all fit in the hopper so you don't have to babysit the operation closely.

Every boutique grocery store I go in has coffee grinders the patrons can use that munch large bags of ground coffee almost instantly that are surely less than a horsepower as they're just "plugged in".

I suggest you find a nice smaller machine that will be quieter, less of a space hog, and not require an acre for transformers and phase converters. Also it won't ultimately have your neighbors reporting you because their TV's reboot or they hear buzzing out of their speakers every time you fire up the monster. You will save a bundle of money by disposing of the non-optimal choice now instead of after you've been visited by pitch-forks and torches.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ExpatIreland]

itsmoked,

Would that I could. I'm a wholesale coffee roaster. Right now I run 3, 1hp grinders and I run them just about all day, every day, shutting them down for long periods to cool. It's just past 10pm here and my son is still outside grinding coffee. This is a huge bottle-neck for us.

To replace the grinders would run me about £2k each for an equivalent grinder.

Just this past Friday I ground all day but didn't keep up with my orders. This meant grinding 1/2 day Saturday and 1/2 day Sunday. All this grinding takes it's toll on the grinding discs. So when the grind quality deteriorates I have to remove the discs (the grinders are no longer made by the way) and send them off to a great guy in the UK to be sharpened. And sometimes he has to make me new discs when they are beyond sharpening. In fact I'm waiting on a new set right now. This downtime of one grinder puts more strain on the other two grinders and round and round we go. So I know I'm spending a lot to make this work but as my son likes to say, 'It has to be done'.

The grinder I'm buying will keep up and beyond which I need because of some new markets opening up for me. The grinder is costing me X. An alternative grinder, that I could just plug in and go on my house current would cost me XXX. So spending X or half-X to convert the power seems to make economic sense.

All that said I really appreciate all the comments here. With all the input I'm really starting to be able to get my head around this. It is starting to get down to choosing the best option. I think the best choice based on all the folks I've talked to and all of your comments -- and I welcome a correction as I'm less than a layman -- is to phase convert 230v 1ph to 230v 3ph and then use a VFD to go to 400v 3ph. To me this is great because it doesn't require more amps than I can deliver. WAROSS suggests I'd be pulling 25A at start.

My second option, the Digital Phase Converter, is the one I may go with for two reasons. 1. it seems simpler than option 1. The way I understand it, I plug in 230V / 1ph / 50hz into the DPC and out comes 415v / 3ph / 50hz with a soft start so that I'm not tripping breakers on start-up. And 2. I just can't seem to find an electrician here in the rural West of Ireland who can get their head around what I'm trying to do. The ones I've spoken with are great guys but their experience mainly extends to wiring-up a house and that's it. I know there is a guy, multiple guys, around here who could do this in a snap, I just haven't come across them. Hopefully I will.

So there is my long-winded explanation of why I'm doing something that seems nutty on the surface but hopefully this look behind the curtain explains my need.

 

[FreddyNurk]

That looks like a standard motor frame, it would be conceivable to swap the motor for a 230V 3 phase unit and then get the 230V 1 phase in 3 phases out unit, although its getting up there in terms of size of a single phase (input!) VSD. This may well be cheaper than getting a transformer.
Admittedly, it might also be possible to replace it with a single phase unit, although its generally a less than optimum solution. That option will get around the issue of having to rewire the unit to split the VSD output from any control equipment that is fitted, although in order to start and stop it you'd probably need to do that anyway.

The other consideration is that there's no way around the 5.5kW size of the grinder. Whatever VSD you use will need a suitable supply for it, and if Ireland is anything like Australia, single phase socket outlets only allow a certain size (about 2.4kW here) to be powered from them. Thus, no matter what you do, there's modifications to the house wiring to be done, you'd likely need a 25A socket outlet (or get the electrician to hardwire in the VSD).



EDMS Australia

 

[ExpatIreland]

Yes, whatever we do we'll have the appropriate breaker put in and run a dedicated line off of that for the system to plug into.

 

[itsmoked]

Ah, forgive me, your comment,

We drink all we can and sell the rest.

did not adequately paint the picture you just did.

Let's look for, perhaps, an out-of-the-box solution since it's very possible you simply cannot support that load with what you have as a domestic supply.

Do you have any idea how long The Monster would take to do a day's grind?

Got a picture of it and its motor overall?

Use the

above if you post some pictures.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[zlatkodo]

The cheapest solution could be to buy a portable 3 phase generator.

Winding Design and Motor Repair

 

[waross]

The VFD will accept single phase and output three phase. It will have to be oversized.
The motor takes 10.8 Amps at 400 Volts.
Now bear with me until the end;
5.5 kW at 75% combined efficiency and power factor = 7.5 KVA
7.5 KVA at 400 Volts = 18.75 Amps single phase.
You need a 7.5 KVA, 230V:400V transformer.,
OR
Use an auto-transformer connection.
You will need a 4 KVA or 5 KVA transformer. 230V:230V. The output will be 460 Volts, single phase.
Then connect a VFD to drive the motor. The VFD will have no trouble driving and protecting a 400 Volt rated motor with 460 Volts supplied.
A 230:230 Volt transformer may be easier to find than a 230:400 Volt transformer.
I have done a lot of voltage adjustment for motors with auto-transformers, both single phase and three phase.
Others here have more experience than I in sizing VFDs for single phase supplies, so I will stand down now and let the others help you with the VFD sizing.
You are going to need about 40 Amps, at 230 Volts. I hope that an additional 40 Amps is available from your 63 Amp Mains Service.
By the way, if you can post an internal wiring diagram for the machine or a make and model number we may be able to help with the connections to power the control circuits.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

The motor swap is a fair suggestion. I can't tell from the photo if it's foot mounted or flange, or a hybrid, but there are plenty 230V[Δ]/400V Y motors available from reputable brands at ~£300 or so. 132S is a standard IEC frame size, so it should be any easy swap, and would open up the option to use a 230 in / 230 out phase converter or a VFD without the additional cost and complication of a transformer.

 

[ExpatIreland]

This is the grinder. It will cut my grinding time by 75% (and this is taking the manufacturer's throughput claims and halving them).

 

[itsmoked]

It looks to be really easy to change motors on. I'd sure consider switching to a motor that's 230V/50Hz.

It appears to have no other controls other than ON/OFF so a VFD is certainly a clean option.

With a 230V motor this is what a typical doubled (as Jraef states) VFD would be new:
230V 15Hp VFD
You have to add the cost of swapping in a more appropriately voltaged motor.

If you added the boost transformers as waross describes, kept the existing motor and used a 460V VFD this is what you'd be looking at:
460V 15HP
You have to add the cost of the transformers.

With either VFD you leave them powered up so there is rarely a big surge on your service and the neighbor's services who share your service transformer. You always leave the motor on. In fact you make it so the motor can never be turned off while the VFD is running it as that can harm the VFD.

Then to run the grinder you press run on the VFD and if it's setup correctly it will quietly ramp up the grinder motor with no shock to your electrical network and actually no mechanical shock to your motor or the bearings.

A VFD also allows you not to have a motor starter involved, which is not seen in your picture but must be there somewhere?

Keith Cress
kcress -

http://www.flaminsystems.com