Phase Converters: Am I missing something?

Phase Converters: Am I missing something?

Post by DanD » Fri, 10 Nov 2000 04:00:00



Hi All,

I've been following this ng for some time now and have read a great
many of the threads about static/rotary phase converters. My version
of the single-to-three phase dilema is to use a 15 HP idler motor
wired in the usual way with starting cap and balanced run caps.
Nothing unique so far. My only 3-ph machine at the moment is a 14" 5
HP CNC lathe with a 5 HP AC inverter drive on the spindle motor sized
to run off 3-ph input of which there isn't any around here. My reason
for selecting a 15 HP idler is to have enough capacity to not only run
the lathe, but also a 3-5 HP mill in the future. The mill will also be
CNC and I expect will have an inverter drive on it's spindle motor as
well. I have been told by several phase converter salesmen that I
should size my rotary converter for at least twice the lathe's HP
rating (FLA = 15.0 Amp) due to the fact that it is a CNC machine and
transients, etc. would be undesirable not only to the CNC control, but
the spindle drive and servo drives as well. What I'm wondering is what
am I missing with regard to the price of static converter (needed to
start/run run my idler motor) prices? For a 15 Hp static converter,
the price is around $500. Unless I'm missing something, there's
nothing to them besides an enclosure, a contactor (or two) and some
caps. Why the big price tag? Before you tell me it's because they want
to make a whopping profit, is there anything else I'm missing here? I
figure I can make one of these rascals for next to cheap. Combine that
with a cheap used idler motor and I'm whistling 'cause I just saved
$700-$900! Sanity check - what did I miss?

Dan

 
 
 

Phase Converters: Am I missing something?

Post by Pete » Fri, 10 Nov 2000 04:00:00


Why the big price tag? Before you tell me it's because they want to make a
whopping profit, is there anything else I'm missing here? I figure I can make
one of these rascals for next to cheap.

Simple economics.

For commodity, very high volume or low value items, such as common integrated
circuits and mechanical fasteners, etcetera, the manufacturers need at least a
four times (of "cost of goods sold") ratio to stay in business.

For specialized, low volume or high value items, including phase converters,
the manufacurers need at least a ten times (of "cost of goods sold") ratio to
stay in business.

A $1000 commercial phase converter can usually be duplicated by a hobbiest for
$100.

Naturally, YMMV.

 
 
 

Phase Converters: Am I missing something?

Post by Rolie Baldo » Fri, 10 Nov 2000 04:00:00


Hello Dan,

You have only looked at the narrow picture. Go look at the broad
picture like not only the interest on the money invested, but the
ongoing cost of this inefficient system. There is no argument when you
take all these factors into account. The cheapest long term solution
is the VFD. They are cheap, efficient(low running cost), quiet and
compact.  


Quote:
>Hi All,

>I've been following this ng for some time now and have read a great
>many of the threads about static/rotary phase converters. My version
>of the single-to-three phase dilema is to use a 15 HP idler motor
>wired in the usual way with starting cap and balanced run caps.
>Nothing unique so far. My only 3-ph machine at the moment is a 14" 5
>HP CNC lathe with a 5 HP AC inverter drive on the spindle motor sized
>to run off 3-ph input of which there isn't any around here. My reason
>for selecting a 15 HP idler is to have enough capacity to not only run
>the lathe, but also a 3-5 HP mill in the future. The mill will also be
>CNC and I expect will have an inverter drive on it's spindle motor as
>well. I have been told by several phase converter salesmen that I
>should size my rotary converter for at least twice the lathe's HP
>rating (FLA = 15.0 Amp) due to the fact that it is a CNC machine and
>transients, etc. would be undesirable not only to the CNC control, but
>the spindle drive and servo drives as well. What I'm wondering is what
>am I missing with regard to the price of static converter (needed to
>start/run run my idler motor) prices? For a 15 Hp static converter,
>the price is around $500. Unless I'm missing something, there's
>nothing to them besides an enclosure, a contactor (or two) and some
>caps. Why the big price tag? Before you tell me it's because they want
>to make a whopping profit, is there anything else I'm missing here? I
>figure I can make one of these rascals for next to cheap. Combine that
>with a cheap used idler motor and I'm whistling 'cause I just saved
>$700-$900! Sanity check - what did I miss?

>Dan


 
 
 

Phase Converters: Am I missing something?

Post by Steve Smit » Fri, 10 Nov 2000 04:00:00


But its a mighty nice enclosure, with paint and everything.

Steve Smith

Quote:

> Hi All,

> I've been following this ng for some time now and have read a great
> many of the threads about static/rotary phase converters. My version
> of the single-to-three phase dilema is to use a 15 HP idler motor
> wired in the usual way with starting cap and balanced run caps.
> Nothing unique so far. My only 3-ph machine at the moment is a 14" 5
> HP CNC lathe with a 5 HP AC inverter drive on the spindle motor sized
> to run off 3-ph input of which there isn't any around here. My reason
> for selecting a 15 HP idler is to have enough capacity to not only run
> the lathe, but also a 3-5 HP mill in the future. The mill will also be
> CNC and I expect will have an inverter drive on it's spindle motor as
> well. I have been told by several phase converter salesmen that I
> should size my rotary converter for at least twice the lathe's HP
> rating (FLA = 15.0 Amp) due to the fact that it is a CNC machine and
> transients, etc. would be undesirable not only to the CNC control, but
> the spindle drive and servo drives as well. What I'm wondering is what
> am I missing with regard to the price of static converter (needed to
> start/run run my idler motor) prices? For a 15 Hp static converter,
> the price is around $500. Unless I'm missing something, there's
> nothing to them besides an enclosure, a contactor (or two) and some
> caps. Why the big price tag? Before you tell me it's because they want
> to make a whopping profit, is there anything else I'm missing here? I
> figure I can make one of these rascals for next to cheap. Combine that
> with a cheap used idler motor and I'm whistling 'cause I just saved
> $700-$900! Sanity check - what did I miss?

> Dan

 
 
 

Phase Converters: Am I missing something?

Post by Eric R. Sn » Sat, 11 Nov 2000 10:12:24


Quote:

>Hi All,

>I've been following this ng for some time now and have read a great
>many of the threads about static/rotary phase converters. My version
>of the single-to-three phase dilema is to use a 15 HP idler motor
>wired in the usual way with starting cap and balanced run caps.
>Nothing unique so far. My only 3-ph machine at the moment is a 14" 5
>HP CNC lathe with a 5 HP AC inverter drive on the spindle motor sized
>to run off 3-ph input of which there isn't any around here. My reason
>for selecting a 15 HP idler is to have enough capacity to not only run
>the lathe, but also a 3-5 HP mill in the future. The mill will also be
>CNC and I expect will have an inverter drive on it's spindle motor as
>well. I have been told by several phase converter salesmen that I
>should size my rotary converter for at least twice the lathe's HP
>rating (FLA = 15.0 Amp) due to the fact that it is a CNC machine and
>transients, etc. would be undesirable not only to the CNC control, but
>the spindle drive and servo drives as well. What I'm wondering is what
>am I missing with regard to the price of static converter (needed to
>start/run run my idler motor) prices? For a 15 Hp static converter,
>the price is around $500. Unless I'm missing something, there's
>nothing to them besides an enclosure, a contactor (or two) and some
>caps. Why the big price tag? Before you tell me it's because they want
>to make a whopping profit, is there anything else I'm missing here? I
>figure I can make one of these rascals for next to cheap. Combine that
>with a cheap used idler motor and I'm whistling 'cause I just saved
>$700-$900! Sanity check - what did I miss?

>Dan

Greetings Dan,

  When I needed to put 3 phase in my shop for cnc stuff I was told to
get a 30 hp converter because my lathes were 10 hp. However, I
contacted Molitor and they said that their 15 hp model would start my
10 hp lathes one at a time and run (2) 10 hp cnc lathes, (1) 3 hp
manual lathe, (1) 2 hp manual mill and (1) 5 hp cnc mill all at the
same time. With some to spare. And they were right. So I know that you
could build the same thing and it should work just as well if you do
it right. Especially because the inverter drives can be adjusted for a
"softer" start than just using a contactor connected to the line. In
fact, before I got my big phase converter I was using a 7.5 hp unit to
start my first 10 hp cnc lathe. I set the spindle drive for the
longest acceleration time (i.e. "softest" start) and was able to run
the lathe and mill at the same time.
ERS

 
 
 

Phase Converters: Am I missing something?

Post by mulli.. » Sat, 11 Nov 2000 12:18:08




Quote:
> Hello Dan,

> You have only looked at the narrow picture. Go look at the broad
> picture like not only the interest on the money invested, but the
> ongoing cost of this inefficient system. There is no argument when you
> take all these factors into account. The cheapest long term solution
> is the VFD. They are cheap, efficient(low running cost), quiet and
> compact.

And I would consider them to be consumables.  As they contain
active devices, and are basically engineered to just fulfil their
ratings, I suspect the MTBF is about 2 or 3 years.

Besides, I think the NC machine he has contains more than just
a spindle motor that requires a 3~ input.  And I am unaware of
the inefficiencies you mention.  When the idler motor is not
driving a machine, there is practially no power dissipated.

I would think a 15 hp idler, properly tuned with running capacitors
to get the third leg up to***for the NC stuff, would run his
shop for a long, long time.  This is the way I would go.  I might
even consider a 10 hp motor.

Jim

Sent via Deja.com http://www.FoundCollection.com/
Before you buy.

 
 
 

Phase Converters: Am I missing something?

Post by Robert Swinne » Sat, 11 Nov 2000 12:40:53


Rolie,
Wrong again!  You obviously have not priced any15 HP VFDs, now have you?
Bob Swinney


Quote:
> Hello Dan,

> You have only looked at the narrow picture. Go look at the broad
> picture like not only the interest on the money invested, but the
> ongoing cost of this inefficient system. There is no argument when you
> take all these factors into account. The cheapest long term solution
> is the VFD. They are cheap, efficient(low running cost), quiet and
> compact.


> >Hi All,

> >I've been following this ng for some time now and have read a great
> >many of the threads about static/rotary phase converters. My version
> >of the single-to-three phase dilema is to use a 15 HP idler motor
> >wired in the usual way with starting cap and balanced run caps.
> >Nothing unique so far. My only 3-ph machine at the moment is a 14" 5
> >HP CNC lathe with a 5 HP AC inverter drive on the spindle motor sized
> >to run off 3-ph input of which there isn't any around here. My reason
> >for selecting a 15 HP idler is to have enough capacity to not only run
> >the lathe, but also a 3-5 HP mill in the future. The mill will also be
> >CNC and I expect will have an inverter drive on it's spindle motor as
> >well. I have been told by several phase converter salesmen that I
> >should size my rotary converter for at least twice the lathe's HP
> >rating (FLA = 15.0 Amp) due to the fact that it is a CNC machine and
> >transients, etc. would be undesirable not only to the CNC control, but
> >the spindle drive and servo drives as well. What I'm wondering is what
> >am I missing with regard to the price of static converter (needed to
> >start/run run my idler motor) prices? For a 15 Hp static converter,
> >the price is around $500. Unless I'm missing something, there's
> >nothing to them besides an enclosure, a contactor (or two) and some
> >caps. Why the big price tag? Before you tell me it's because they want
> >to make a whopping profit, is there anything else I'm missing here? I
> >figure I can make one of these rascals for next to cheap. Combine that
> >with a cheap used idler motor and I'm whistling 'cause I just saved
> >$700-$900! Sanity check - what did I miss?

> >Dan



 
 
 

Phase Converters: Am I missing something?

Post by goo195 » Sat, 11 Nov 2000 04:00:00


With all this talk about converters being easy to make, where do you get the
information to do so??
Greg


Quote:
> Hi All,

 Unless I'm missing something, there's
Quote:
> nothing to them besides an enclosure, a contactor (or two) and some
> caps. Why the big price tag? Before you tell me it's because they want
> to make a whopping profit, is there anything else I'm missing here? I
> figure I can make one of these rascals for next to cheap. Combine that
> with a cheap used idler motor and I'm whistling 'cause I just saved
> $700-$900! Sanity check - what did I miss?

> Dan

 
 
 

Phase Converters: Am I missing something?

Post by KD6J » Sat, 11 Nov 2000 04:00:00


Quote:
>With all this talk about converters being easy to make, where do you get the
>information to do so??
>Greg

  Greg
  To me, rotary converters are simple and easy to make because I'm 'crude'.
  Three phase 220vac can be obtained by "properly connecting" 220vac single
phase to a spinning 3 phase motor.
  That is; you get 3 phase voltage across the 3 wires of a *spinning* 3 phase
motor.
  And; a 220vac, 3 phase motor, will continue to spin with only 2 of its leads
energized with 220vac single phase.

  If you do want to make a good rotary converter, contact Fitch Williams. He
has a lot of helpful information on how to build a converter.

             Jerry    

 
 
 

Phase Converters: Am I missing something?

Post by Rolie Baldo » Sat, 11 Nov 2000 04:00:00


Hello Jim Mulligan,

If as you say you know nothing about them then who is going to take
notice of you?  I just bought a small VFD for $AUS225. and my friend
has had one on his mill for a long time without any problems. You
obviosly know nothing about losses in electrical machines. Being an
experienced professional electrical engineer in the middle of
redesigning a polyphase induction motor, I think I know a little about
this topic.

Quote:



>> Hello Dan,

>> You have only looked at the narrow picture. Go look at the broad
>> picture like not only the interest on the money invested, but the
>> ongoing cost of this inefficient system. There is no argument when you
>> take all these factors into account. The cheapest long term solution
>> is the VFD. They are cheap, efficient(low running cost), quiet and
>> compact.

>And I would consider them to be consumables.  As they contain
>active devices, and are basically engineered to just fulfil their
>ratings, I suspect the MTBF is about 2 or 3 years.

>Besides, I think the NC machine he has contains more than just
>a spindle motor that requires a 3~ input.  And I am unaware of
>the inefficiencies you mention.  When the idler motor is not
>driving a machine, there is practially no power dissipated.

>I would think a 15 hp idler, properly tuned with running capacitors
>to get the third leg up to***for the NC stuff, would run his
>shop for a long, long time.  This is the way I would go.  I might
>even consider a 10 hp motor.

>Jim

>Sent via Deja.com http://www.FoundCollection.com/
>Before you buy.


 
 
 

Phase Converters: Am I missing something?

Post by Rolie Baldo » Sat, 11 Nov 2000 04:00:00


Hello Robert Swinney,

My electric car has two 15.8Kva invertors one for each front wheel. I
have designed and am building them. It is not my first invertor design
and my friend who does it professionally has also built some big ones.
They are now old hat. We had a pair of 50Kva units when I was working
and some of the ones discarded from mine sites,which I have
***ised have ratings like 170Kva. Hate to have to pay for them
when new, but they are fun to ***ise. At least I prevent those
big semiconductors and ferrite cores from going into the BIG hole in
the ground.



Quote:
>Rolie,
>Wrong again!  You obviously have not priced any15 HP VFDs, now have you?
>Bob Swinney



>> Hello Dan,

>> You have only looked at the narrow picture. Go look at the broad
>> picture like not only the interest on the money invested, but the
>> ongoing cost of this inefficient system. There is no argument when you
>> take all these factors into account. The cheapest long term solution
>> is the VFD. They are cheap, efficient(low running cost), quiet and
>> compact.


>> >Hi All,

>> >I've been following this ng for some time now and have read a great
>> >many of the threads about static/rotary phase converters. My version
>> >of the single-to-three phase dilema is to use a 15 HP idler motor
>> >wired in the usual way with starting cap and balanced run caps.
>> >Nothing unique so far. My only 3-ph machine at the moment is a 14" 5
>> >HP CNC lathe with a 5 HP AC inverter drive on the spindle motor sized
>> >to run off 3-ph input of which there isn't any around here. My reason
>> >for selecting a 15 HP idler is to have enough capacity to not only run
>> >the lathe, but also a 3-5 HP mill in the future. The mill will also be
>> >CNC and I expect will have an inverter drive on it's spindle motor as
>> >well. I have been told by several phase converter salesmen that I
>> >should size my rotary converter for at least twice the lathe's HP
>> >rating (FLA = 15.0 Amp) due to the fact that it is a CNC machine and
>> >transients, etc. would be undesirable not only to the CNC control, but
>> >the spindle drive and servo drives as well. What I'm wondering is what
>> >am I missing with regard to the price of static converter (needed to
>> >start/run run my idler motor) prices? For a 15 Hp static converter,
>> >the price is around $500. Unless I'm missing something, there's
>> >nothing to them besides an enclosure, a contactor (or two) and some
>> >caps. Why the big price tag? Before you tell me it's because they want
>> >to make a whopping profit, is there anything else I'm missing here? I
>> >figure I can make one of these rascals for next to cheap. Combine that
>> >with a cheap used idler motor and I'm whistling 'cause I just saved
>> >$700-$900! Sanity check - what did I miss?

>> >Dan




 
 
 

Phase Converters: Am I missing something?

Post by mulli.. » Sun, 12 Nov 2000 11:29:55




Quote:
> Hello Jim Mulligan,

> If as you say you know nothing about them then who is going to take
> notice of you?  I just bought a small VFD for $AUS225. and my friend
> has had one on his mill for a long time without any problems. You
> obviosly know nothing about losses in electrical machines.

I am very glad your friend is pleased with his set-up.

Apparently you are sure my skills as an engineer are lacking - so
be it.  I would respectfully suggest you ignore my comments from
now on, though I will continue to make them.  Just skip over my
posts.

Jim

Sent via Deja.com http://www.deja.com/
Before you buy.

 
 
 

Phase Converters: Am I missing something?

Post by aafra.. » Sun, 12 Nov 2000 04:00:00


Quote:

> > You
> > obviously know nothing about losses in electrical machines.

Well, I would be very careful about that assertion, Rolie, as I know Jim
to be a superb engineer.  It's ill advised to make blanket
characterizations about someone else's knowledge based on an infinitesimal
sample of a few words, though I admit I see it all the time in the
Usegroups.   Though I don't think Jim needs any defending, what *I* read
between the lines in his post are twofold - he prefers the KISS principle
(so do most of us, for that matter) and I suspect he was reflecting (as he
repeatedly demonstrates) on behalf of most of the denizens of this
newsgroup, who would have some degree of difficulty in repairing a VFD if
something went bad in it.  I would agree that the MTBF on a properly
maintained and operated  VFD *with conditioned (surge protected) power* is
arguably higher than a rotary converter.  Anything with moving parts
eventually wears and those parts will need to be replaced.  However, when
a VFD *does* go bad, finding the chips for the control circuitry or a
replacement for an offshore power transistor can be a chore requiring the
patience of Job and sometimes a solid state design engineer's skills.  I
switched from a rotary to a VFD simply because of the noise, but I don't
worry about repairing it either - I have most of the parts down in the
ba***t, along with a Tektronix curve tracer and scads of other pieces of
HP test equipment.  That doesn't describe most of the folks on this list,
however.  Replacing an idler motor bearing, however, now that something
almost *all* of us can do.

Best wishes,
Mike Hanz
Herndon, VA

 
 
 

Phase Converters: Am I missing something?

Post by DanD » Sun, 12 Nov 2000 04:00:00


For those interested in VFD's, be sure to check out
www.automationdirect.com. They carry a full line of Hitachi drives and
the prices are very competetive. I just ordered one of their 5 HP
SJ100 drives for my CNC lathe. The cost was $399 and currently they
are shipping UPS free with orders over $300. Not a bad deal. I'll let
the group knw how the 15 HP rotary converter project comes out. Also,
just foir grins, I'm going to test the new VFD on 220 single phase to
see if it can run the lathe. In case some of you don't know this,
virually all VFD's can be run on either single or three phase input
power. The general rule of thumb is to up size the VFD by a factor of
2 when running on single phase. IE - if the VFD is rated at 5 HP with
230V 3-phase input, then the same performance on single phase input
can be obtained by selecting a 10 HP VFD. Again, this is what the VFD
folks recommend, but they are also in the business of selling drives.
The cost is just about double (makes sense?) for a 10 HP drive over a
5 HP. I have a sneaking suspecion that the 5 HP drive might do just
fine on single phase. Will let you know soon... Dan
 
 
 

Phase Converters: Am I missing something?

Post by Fitch R. William » Sun, 12 Nov 2000 04:00:00


Quote:

>If as you say you know nothing about them then who is going to take
>notice of you?  I just bought a small VFD for $AUS225. and my friend
>has had one on his mill for a long time without any problems. You
>obviosly know nothing about losses in electrical machines. Being an
>experienced professional electrical engineer in the middle of
>redesigning a polyphase induction motor, I think I know a little about
>this topic.

When are you going to reveal what you know?  So far I am
considerably under whelmed by your grasp of the situation,
or your understanding of what is available that will run a 3
phase 5hp CNC machine from single phase input.

Jim's input was excellent, yours was not very good for the
original posters situation.  

Fitch
In So. Cal.

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