I have a 7.5 horse RPC and use it to run my Sheldon VS Lathe. The lathe
motor is 2HP 3 phase. I was looking at VFD's and could pick up a 2HP
VFD that is 3phase in/out for $179.

My question is: If I run the VFD from the RPC do I need to derate the
VFD or will I get close to 2HP from the VFD running on the rotary phase
converter?

Thanks, Steve

In article .com,
wrote:
I have a 7.5 horse RPC and use it to run my Sheldon VS Lathe. The lathe
motor is 2HP 3 phase. I was looking at VFD's and could pick up a 2HP
VFD that is 3phase in/out for $179.

My question is: If I run the VFD from the RPC do I need to derate the
VFD or will I get close to 2HP from the VFD running on the rotary phase
converter?

It depends on what the manufacturer did when designing it. And
how conservative the ratings are. The part which probably makes more
difference than anything else is how much capacitance is there to hold
the DC voltage generated from the power line before it is used to
generate the three phase.

With true three phase input, you can get away with aobut 1/3 the
capacitor size needed for single phase to control the ripple.

Some makers also tend to way overdesign, so it will run at full
specified load when the input power is a bit on the low side and when
the shop is too hot for any office person to stay there long. :-)

Personally, I like to buy about 50% more horsepowewr rating than
I really expect to use when I plan to us a VFD for generating three
phase from single phase.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
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wrote in message
oups.com...
I have a 7.5 horse RPC and use it to run my Sheldon VS Lathe. The lathe
motor is 2HP 3 phase. I was looking at VFD's and could pick up a 2HP
VFD that is 3phase in/out for $179.

My question is: If I run the VFD from the RPC do I need to derate the
VFD or will I get close to 2HP from the VFD running on the rotary phase
converter?

Thanks, Steve

That would be a huge waste when you could just buy a larger VFD or one that
is rated for 100% of single phase input for a few dollars more.

I don't understand the problem. Buy a single phase in, 3 phase out VFD. Same
price.
Steve

wrote in message
oups.com...
I have a 7.5 horse RPC and use it to run my Sheldon VS Lathe. The lathe
motor is 2HP 3 phase. I was looking at VFD's and could pick up a 2HP
VFD that is 3phase in/out for $179.

My question is: If I run the VFD from the RPC do I need to derate the
VFD or will I get close to 2HP from the VFD running on the rotary phase
converter?

Thanks, Steve

Steve Lusardi wrote:
I don't understand the problem. Buy a single phase in, 3 phase out
VFD. Same
price.
Steve

wrote in message
oups.com...
I have a 7.5 horse RPC and use it to run my Sheldon VS Lathe. The
lathe
motor is 2HP 3 phase. I was looking at VFD's and could pick up a
2HP
VFD that is 3phase in/out for $179.

My question is: If I run the VFD from the RPC do I need to derate
the
VFD or will I get close to 2HP from the VFD running on the rotary
phase
converter?

Thanks, Steve


The problem is price. I already have the 7.5HP RPC. The next problem
is: if running a VFD from 230v single phase you have to derate the VFD
usually by 50% is my understanding. I can pick up a 3ph in/ 3ph out for
$179. A single phase in to 3 phase out is twice that much. If I can use
the RPC to generate the 3 phase and use the $179 VFD then I can save
$$$.

My question is will I get 2HP out of the VFD if I run it from the RPC
outputting 3 phase???

how many HP is the largest VFD single phase input unit?? the largest i
can find is a 3HP unit, he is running a 7.5 HP unit.

So if he wants a VFD and he has the RPC already inducing the third leg,
wouldn't it be easier to buy a 3 phase in/3 phase out 7.5 HP unit?

-S

There is a new class of VFD inverters. They are expensive in the states and
in Europe, but I have sourced some made in China that are very well priced.
This new class converts the input power directly to DC. Internally, they use
a microprocessor to construct a variable frequency sinosoidal AC signal
which is then amplified to drive a 3 phase inductive load. These generate
very little heat and virtually no RF noise. They are very efficient and
small in size. I am going to the Canton Industrial fair in April and try to
put a deal together. I will gladly let you know how successful I was when I
return. Standby.
Steve

wrote in message
ups.com...

Steve Lusardi wrote:
I don't understand the problem. Buy a single phase in, 3 phase out
VFD. Same
price.
Steve

wrote in message
oups.com...
I have a 7.5 horse RPC and use it to run my Sheldon VS Lathe. The
lathe
motor is 2HP 3 phase. I was looking at VFD's and could pick up a
2HP
VFD that is 3phase in/out for $179.

My question is: If I run the VFD from the RPC do I need to derate
the
VFD or will I get close to 2HP from the VFD running on the rotary
phase
converter?

Thanks, Steve


The problem is price. I already have the 7.5HP RPC. The next problem
is: if running a VFD from 230v single phase you have to derate the VFD
usually by 50% is my understanding. I can pick up a 3ph in/ 3ph out for
$179. A single phase in to 3 phase out is twice that much. If I can use
the RPC to generate the 3 phase and use the $179 VFD then I can save
$$$.

My question is will I get 2HP out of the VFD if I run it from the RPC
outputting 3 phase???

In article .com,
says...
how many HP is the largest VFD single phase input unit?? the largest i
can find is a 3HP unit, he is running a 7.5 HP unit.


I've seen VFDs at least as large as 30HP that would run on single phase.
Most manufacturers don't specifically mention running on single phase in
their literature, but will make a recommendation if you ask. Yaskawa is
one mfr that does give derating numbers in their manuals.

While oversizing is the conservative way to go, for intermittent use in
a home shop I expect most drives would be just fine at full rated output
with single phase input.

Ned Simmons

VFD's have always done what you describe below. They may be new to your
Chinese sources, but this kind of VFD has been around for quite a few
years. The "new class" aspect may refer to price.

Not complaining, just making sure you aren't getting the wool pulled
over your eyes.

Steve

Steve Lusardi wrote:

There is a new class of VFD inverters. They are expensive in the states and
in Europe, but I have sourced some made in China that are very well priced.
This new class converts the input power directly to DC. Internally, they use
a microprocessor to construct a variable frequency sinosoidal AC signal
which is then amplified to drive a 3 phase inductive load. These generate
very little heat and virtually no RF noise. They are very efficient and
small in size. I am going to the Canton Industrial fair in April and try to
put a deal together. I will gladly let you know how successful I was when I
return. Standby.
Steve

wrote in message
oups.com...


Steve Lusardi wrote:


I don't understand the problem. Buy a single phase in, 3 phase out


VFD. Same


price.
Steve

wrote in message
egroups.com...


I have a 7.5 horse RPC and use it to run my Sheldon VS Lathe. The


lathe


motor is 2HP 3 phase. I was looking at VFD's and could pick up a


2HP


VFD that is 3phase in/out for $179.

My question is: If I run the VFD from the RPC do I need to derate


the


VFD or will I get close to 2HP from the VFD running on the rotary


phase


converter?

Thanks, Steve


The problem is price. I already have the 7.5HP RPC. The next problem
is: if running a VFD from 230v single phase you have to derate the VFD
usually by 50% is my understanding. I can pick up a 3ph in/ 3ph out for
$179. A single phase in to 3 phase out is twice that much. If I can use
the RPC to generate the 3 phase and use the $179 VFD then I can save
$$$.

My question is will I get 2HP out of the VFD if I run it from the RPC
outputting 3 phase???

Why bother with the RPC? Buy a VFD single phase in, 3 phase out.
I wouldn't go through all that monkey motion .... also you wouldn't be
paying for electric to run the RPC.

Carl


On 20 Mar 2005 20:22:25 -0800, wrote:

I have a 7.5 horse RPC and use it to run my Sheldon VS Lathe. The lathe
motor is 2HP 3 phase. I was looking at VFD's and could pick up a 2HP
VFD that is 3phase in/out for $179.

My question is: If I run the VFD from the RPC do I need to derate the
VFD or will I get close to 2HP from the VFD running on the rotary phase
converter?

Thanks, Steve

Yeah, but . . . . he'd already have a RPC ready to run more than 1 machine;
whereas if he chucks his RPC and goes with a VFD, he'll have to buy a
seperate one for every new machine he might add to his shop. IMO, the best
route, since he already has the RPC, is to go ahead and balance it out,
optimized for the lathe. RPC's, when idling, aren't very bad consumers of
"electric". For example, the single-phase load of my 7-1/2 HP RPC, when
idling, is 3.5 amps at 240 volts. That is 840 watts. At 10 cents per KWH,
the standby (idling) cost of the machine would be 8.4 cents per hour. In
actuality, it would be even less, because unloaded induction motors have a
relatively poor power factor.

Bob Swinney
"CarlC" wrote in message
...
Why bother with the RPC? Buy a VFD single phase in, 3 phase out.
I wouldn't go through all that monkey motion .... also you wouldn't be
paying for electric to run the RPC.

Carl


On 20 Mar 2005 20:22:25 -0800, wrote:

I have a 7.5 horse RPC and use it to run my Sheldon VS Lathe. The lathe
motor is 2HP 3 phase. I was looking at VFD's and could pick up a 2HP
VFD that is 3phase in/out for $179.

My question is: If I run the VFD from the RPC do I need to derate the
VFD or will I get close to 2HP from the VFD running on the rotary phase
converter?

Thanks, Steve