Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Old July 9th 03, 11:02 PM
Ron Coffey
 
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Default were to buy vfd

me too....
thanks,
Ron
"Stephen Young" [email protected] wrote in message
...
Jim Stewart wrote:
Asp3211968 wrote:

i am looking to buy a vfd. i do not need a fancy box just the guts
what would
be a good place to start



I know where you can get new older model Hitachi 1hp units
for a little over $100 shipped. I have one each on my
lathe and mill and am quite happy with them.

If anyone wants the information, let me know and I'll
dig it up and post it.


I'm interested...




  #2   Report Post  
Old July 10th 03, 01:54 AM
Jim Stewart
 
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Default were to buy vfd

David Heidary wrote:
What is a vfd??


Volunteer Fire Department

Variable Frequency Drive

I'm too tired to explain. Maybe Gary C.
will write you an epistle on the subject (:


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Old July 10th 03, 03:04 AM
Jon
 
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Default were to buy vfd

if anybody is looking for a new vfd reasonably priced, try

www.automationdirect.com

they have great deals on industrial controls in general

"Asp3211968" wrote in message
...
i am looking to buy a vfd. i do not need a fancy box just the guts what

would
be a good place to start



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Old July 10th 03, 04:12 AM
Gary Coffman
 
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Default were to buy vfd

On 9 Jul 2003 16:58:57 -0700, (David Heidary) wrote:
What is a vfd??


Variable Frequency Drive. It is basically a rectifier driven inverter. It rectifies
the input AC voltage and uses that to run a power oscillator (in the case of a
3 ph inverter, 3 power oscillators, synchronized and phase shifted to synthesize
3 ph). The outputs of the oscillators drive the load. By varying the frequency
of the oscillators, with a control provided on the VFD, you vary the speed of
the driven 3 ph motor.

Because the VFD first rectifies the line voltage, ie turns it to DC, it doesn't
matter what frequency or phase the input voltage has. The output voltage
will be the frequency, and phases, the inverter control sets it to be.

For relatively small VFDs, the input can be single phase while the output
is made to be 3 phase. For example, I use a VFD to drive my 2 hp mill.
That VFD runs just fine off of 1 ph 230 volts, producing 3 ph 230 volts
for the mill motor. The VFD cost me $200 new from Dealer's Electric.
It is a simple, easy, solution to getting 3 ph power in a shop with only
1 ph power. Plus you get variable speed control of the mill.

For larger VFDs, the input rectifiers and filters are designed for 3 phase
input power only. Using a large VFD on single phase can overstress the
active rectifiers and filters. So you have to *derate* larger VFDs if you
intend to power them with 1 phase. Typically, they shouldn't be asked
to provide more than 2/3 of their nameplate power. In other words, to
power a 5 hp 3 ph motor with aVFD running from single phase power,
you should use a 7.5 hp rated VFD.

Note that since VFDs above about 3 hp are not designed to be run from
1 ph power, you may need to modify them to work that way, as well as
also derating them. Usually this means defeating a phase loss detector
in the VFD which shuts it down when a missing input phase is detected.

Defeating this circuit can be simple, difficult, or essentially impossible,
depending on the design of the particular VFD. You're somewhat on
your own here because you're using the VFD in a way for which it
wasn't designed.

Note also that high power VFDs, greater than about 3 hp, start getting
expensive. If you just need to make 3 ph from 1 ph power, a home made
rotary converter will be much less expensive in the higher power ranges.

I'm currently facing that dilemma. My new lathe is 7.5 hp 3 ph. That
means I'll need a 11.25 hp VFD to run it on single phase. Since that's
not a standard size, I have to go up to a 15 hp VFD. That's $929 from
Dealer's Electric. Then I have to hope I can fool its phase loss detector
into letting it run off of 1 ph power.

But I can build a rotary for nearly nothing, using a used 15 hp 3 ph motor,
some surplus capacitors, and a couple of contactors. That will limit me to
using only the speeds provided by the headstock gearing, but that's not
really a problem with this lathe.

Perhaps I shouldn't make a rotary converter sound like such a casual
no brainer. For a 15 hp rotary, we're talking about 50 amps of running
current, and a starting surge well in excess of 200 amps. Starting it can
tax a 200 amp service panel severely if you don't take steps to soft
start it.

One good way to do that is to spin it up first with a *pony* motor.
That's simply a small 1 ph motor belted to the shaft of the big 3 ph
rotary converter motor. Spin it up with the pony, then hit the big
motor with line voltage. Power can then be disconnected from the
pony. That reduces starting surge down to a more comfortable
range (ie something that can be handled by a 60 A motor rated
circuit breaker).

It can still be cheap if home made from scrounged parts, but it is
starting to become a bit more Rube Goldberg. OTOH, a large
rotary like that can be used to power every 3 ph piece of equipment
in your shop (perhaps not all at once, depending on the total current
draw). That can be considerably cheaper than buying a VFD for
each piece of equipment.

Gary

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Old July 10th 03, 06:12 AM
Jon Elson
 
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Default were to buy vfd



Gary Coffman wrote:

Note that since VFDs above about 3 hp are not designed to be run from
1 ph power, you may need to modify them to work that way, as well as
also derating them. Usually this means defeating a phase loss detector
in the VFD which shuts it down when a missing input phase is detected.


I'm sure there are VFDs that have this feature, but I haven't run into
one yet.
I have run a number of VFDs from single phase, and never had any trouble
with it.

Defeating this circuit can be simple, difficult, or essentially impossible,
depending on the design of the particular VFD. You're somewhat on
your own here because you're using the VFD in a way for which it
wasn't designed.

Note also that high power VFDs, greater than about 3 hp, start getting
expensive. If you just need to make 3 ph from 1 ph power, a home made
rotary converter will be much less expensive in the higher power ranges.


New, straight from the distributor, yes, they are quite expensive. But,
new units that are last year's model or overstock are plentiful, and can be
found on eBay all the time.

I'm currently facing that dilemma. My new lathe is 7.5 hp 3 ph. That
means I'll need a 11.25 hp VFD to run it on single phase. Since that's
not a standard size, I have to go up to a 15 hp VFD. That's $929 from
Dealer's Electric. Then I have to hope I can fool its phase loss detector
into letting it run off of 1 ph power.


Well, you really don't need one that big, unless you really plan on
running the
lathe at full power for an extended time. 7.5 Hp is a lot!

Jon



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Old July 10th 03, 02:38 PM
Gary Coffman
 
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Default Idle Current Draw was were to buy vfd

On Thu, 10 Jul 2003 06:47:54 -0400, Brian Lawson wrote:
Hey Gary,

Nice little treatise on the VFD versus rotary convertor. Thanks.

Does anyone know what the IDLING current draw is for a rotary where
the idler motor is in the ranges you speak of, typically 5 to 15 HP?
My lathe motor is 5HP , so I expect I'll be needing a 7.5 HP rotary
convertor idler motor, but it turns out a 15 HP wound rotor may be
more readily available to me. I've wondered about which way to go
for long term economy. My hope for the proposed new shop is that if
I go rotary, that I'll "power up" the convertor sometime in the early
part of the day, and it will run for hopefully 5 or 6 hours on a
regular basis. I can see this helping a bit to heat the shop in the
winter, but cost even more to cool it in the summer, but I'm wondering
just about the costs of operating it.

And so my question is, can anyone give us the amperage on their
particular 220/240 line feeding their particular rotary when there is
no "machine" operating from it? And some details as to what sizes
everything is?


Just knowing the current won't tell you the power. That's because
at idle most of the current is reactive, ie the power factor is far from
one. The easiest way to know the actual energy consumption at idle
is to watch the watt-hour meter with everything off but the rotary.
In other words, see how much the reading changes after an hour
with nothing running but the idler.

I think you'll be surprised at how little energy is consumed. System
losses are mainly due to windage, bearing losses, and resistance
losses of the wiring. Windage (air drag) is typically the largest loss.
Using the lowest speed motor you can find will minimize this.

Gary

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Old July 10th 03, 05:47 PM
John Normile
 
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Default Idle Current Draw was were to buy vfd

Bryan
I have a 15hp idler running thru a 40 amp breaker. Idling it draws;
L1=18 Amps L2=21 amps L3=23 amps

After starting the 12.5hp motor on my harrison the amps won't change
by more than an amp or so. Contact me privately if I can be of any
help.

John Normile jnormile (at) cswnet.com

On Thu, 10 Jul 2003 06:47:54 -0400, Brian Lawson
wrote:

Does anyone know what the IDLING current draw is for a rotary where
the idler motor is in the ranges you speak of, typically 5 to 15 HP?
My lathe motor is 5HP , so I expect I'll be needing a 7.5 HP rotary
convertor idler motor, but it turns out a 15 HP wound rotor may be
more readily available to me. I've wondered about which way to go
for long term economy. My hope for the proposed new shop is that if
I go rotary, that I'll "power up" the convertor sometime in the early
part of the day, and it will run for hopefully 5 or 6 hours on a
regular basis. I can see this helping a bit to heat the shop in the
winter, but cost even more to cool it in the summer, but I'm wondering
just about the costs of operating it.

And so my question is, can anyone give us the amperage on their
particular 220/240 line feeding their particular rotary when there is
no "machine" operating from it? And some details as to what sizes
everything is?

TIA.

Brian Lawson,
Bothwell, Ontario.
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX


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Old July 10th 03, 06:03 PM
Gunner
 
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Default were to buy vfd

On Wed, 09 Jul 2003 11:00:58 -0700, Jim Stewart
wrote:

Asp3211968 wrote:
i am looking to buy a vfd. i do not need a fancy box just the guts what would
be a good place to start


I know where you can get new older model Hitachi 1hp units
for a little over $100 shipped. I have one each on my
lathe and mill and am quite happy with them.

If anyone wants the information, let me know and I'll
dig it up and post it.

Please post it.

Gunner


Liberals - Cosmopolitan critics, men who are the friends
of every country save their own. Benjamin Disraeli


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