Here's a money-grubbing question from a hard-case tinkerer:

Leadin:
In order to run a 3-phase motor drive from single phase input,
the user must derate the unit by 50%. This is because the input
rectifier and filter capacitors are too small to handle the increased
peak current of a single phase feed.

There's a "simple" way around this: feed the input with DC (or feed
the internal DC bus).

Furthermore, it's often advisable to isolate the input of a motor
drive with a transformer. This gets large, heavy, and if you have to
buy it new, expensive.

The question:
If I sold a relatively inexpensive fully-isolated power-factor-corrected,
low-harmonic-distortion input multi-kilowatt 310-335V power supply for
220-240V motor drives, would anybody be interested. I'd price it so that
the solution would be cheaper than buying an over-rated drive and a
reasonably priced used transformer.

There would be a 600-700V unit for the 480V crowd as well, though getting
UL to sign off on that one will be a trip and a half.

The gist:
would you buy a box that let you connect a motor drive to a single
phase connection at full rating and fully isolated?

Any ideas (or thrown vegetables)?
geoff

On Thu, 04 Oct 2007 21:30:20 GMT, gwes
wrote:

There's a "simple" way around this: feed the input with DC (or feed
the internal DC bus).


The gist:
would you buy a box that let you connect a motor drive to a single
phase connection at full rating and fully isolated?


Since the difference in price between a 3HP and 7.5HP VFD is only
about $200, I have a hard time believing this would be economical.

--
Ned Simmons

Ned Simmons wrote:
On Thu, 04 Oct 2007 21:30:20 GMT, gwes
wrote:
There's a "simple" way around this: feed the input with DC (or feed
the internal DC bus).

The gist:
would you buy a box that let you connect a motor drive to a single
phase connection at full rating and fully isolated?


Since the difference in price between a 3HP and 7.5HP VFD is only
about $200, I have a hard time believing this would be economical.

Add in a 2000-3000VA transformer and that's worth another couple
of hundred dollars - that's the isolation function.
geoff

On 2007-10-04, gwes wrote:
Here's a money-grubbing question from a hard-case tinkerer:

Leadin:
In order to run a 3-phase motor drive from single phase input,
the user must derate the unit by 50%. This is because the input
rectifier and filter capacitors are too small to handle the increased
peak current of a single phase feed.

Usually, the derating factor is 0.66.

There's a "simple" way around this: feed the input with DC (or feed
the internal DC bus).

You cannot feed a three phase rectifier with DC and utilize all three
inputs. So you have to feed the bus (as you say), which is easy only
if DC terminals are available.

Furthermore, it's often advisable to isolate the input of a motor
drive with a transformer. This gets large, heavy, and if you have to
buy it new, expensive.

Very expensive. But the need for it rare.

The question:
If I sold a relatively inexpensive fully-isolated power-factor-corrected,
low-harmonic-distortion input multi-kilowatt 310-335V power supply for
220-240V motor drives, would anybody be interested. I'd price it so that
the solution would be cheaper than buying an over-rated drive and a
reasonably priced used transformer.

I would suspect that people needing isolation, would have three phase
available.

Interesting.

i

Ignoramus3531 wrote:
On 2007-10-04, gwes wrote:
Here's a money-grubbing question from a hard-case tinkerer:

Leadin:
In order to run a 3-phase motor drive from single phase input,
the user must derate the unit by 50%. This is because the input
rectifier and filter capacitors are too small to handle the increased
peak current of a single phase feed.

Usually, the derating factor is 0.66.
Not according to several manufacturers' web sites. They say 50%.
Work out the peak currents in the rectifiers and the capacitors.


There's a "simple" way around this: feed the input with DC (or feed
the internal DC bus).

You cannot feed a three phase rectifier with DC and utilize all three
inputs. So you have to feed the bus (as you say), which is easy only
if DC terminals are available.

Furthermore, it's often advisable to isolate the input of a motor
drive with a transformer. This gets large, heavy, and if you have to
buy it new, expensive.

Very expensive. But the need for it rare.
Depends - for transformer, read filter reactors. Again the
highly non-sinusoidal input waveform causes problems when you're
drawing 20A because the harmonic currents (like 180Hz and 300Hz)
are pretty high and the rest of your appliances may not like them.

The question:
If I sold a relatively inexpensive fully-isolated power-factor-corrected,
low-harmonic-distortion input multi-kilowatt 310-335V power supply for
220-240V motor drives, would anybody be interested. I'd price it so that
the solution would be cheaper than buying an over-rated drive and a
reasonably priced used transformer.

I would suspect that people needing isolation, would have three phase
available.

Perhaps. Isolation is a good thing - otherwise you can get very
substantial ground currents from the transformer frame even on a
lowly 1 or 2 HP motor. Doesn't do the bearings any good, for instance.
This is true with a 3-phase feed as well.
It -will- work without isolation. It works better and longer with it.


geoff

Robert Swinney wrote:
gwes sez: "If I sold a relatively inexpensive fully-isolated power-factor-corrected,
low-harmonic-distortion input multi-kilowatt 310-335V power supply for
220-240V motor drives, would anybody be interested. I'd price it so that
the solution would be cheaper than buying an over-rated drive and a
reasonably priced used transformer."

Get real ! It seems you are describing a VFD. Or did you mean a plain, ordinary rotary phase
converter?

Are you also selling plans for a steam powered pickup truck?

Bob (seen it all before) Swinney

Nope. Just a front end which lets you use a smaller VFD,
smaller input wiring because of lower harmonic currents,
isolates it so you don't draw sparks in the bearings or your
hand or have big ground currents, and keeps the RFI down.

If it's not what people want or need I'm certainly not going to
bother making any, that's for sure.
geoff

gwes wrote:
Here's a money-grubbing question from a hard-case tinkerer:

Leadin:
In order to run a 3-phase motor drive from single phase input,
the user must derate the unit by 50%. This is because the input
rectifier and filter capacitors are too small to handle the increased
peak current of a single phase feed.
You need to consider that many hobby-garage shop types buy used
VFDs on eBay for a fraction of new cost. The cost to them of
derating the drive is quite small. I've been running a 1 Hp
Bridgeport from a 1 Hp-rated, 3-phase-only Magnetek drive for
years, because I didn't know any better when I bought it. It
has not had any problems at all, and runs cool. When all this
stuff about derating the drive came out, I looked up the power
module in it, and it has rectifiers rated at 30 A continuous.
As a 1 Hp drive, it shouldn't draw more than about 4 A RMS.
Given the worse power factor for a single-phase input, I'm
guessing the peaks may be around 10 A at full load. I had to
put a line filter in the input to keep it from trashing some
equipment in the shop, that probably helps limit the peak I.
So, the rectifiers look like they are more than adequate for the
job. If the capacitors ever croak, I can replace them, although
the whole bank could get expensive.

You have to remember that these units are designed to run in
enclosed cabinets at 50C ambient for 10 years continuously,
sometimes with a motor start every minute. That is so much more
severe than what most hobby-garage shop users put it through.

Jon

Jon Elson wrote:
gwes wrote:
Here's a money-grubbing question from a hard-case tinkerer:

Leadin:
In order to run a 3-phase motor drive from single phase input,
the user must derate the unit by 50%. This is because the input
rectifier and filter capacitors are too small to handle the increased
peak current of a single phase feed.
You need to consider that many hobby-garage shop types buy used
VFDs on eBay for a fraction of new cost. The cost to them of derating
the drive is quite small. [...]

You have to remember that these units are designed to run in enclosed
cabinets at 50C ambient for 10 years continuously, sometimes with a
motor start every minute. That is so much more severe than what most
hobby-garage shop users put it through.

Jon

Good point. And the low-HP drives keep getting cheaper.
More than one net discount drive supplier has 1 and 2 HP 1-to-3 drives for
under $200. The box I was thinking of making would allow running 220V
units from 110 or 440 from 220, but that's very much a niche.

There are these really cute power control and PFC ICs and planar transformers
these days so it would be a lot of fun to find a good application to tinker
with....
geoff

minarik already offers a drive that runs 220V units of 110, I have one
sitting in my "test drawer" - I use it for testing 3 phase pumps


"gwes" wrote in message
news:LZsNi.11$C2.5@trnddc02...
Jon Elson wrote:
gwes wrote:
Here's a money-grubbing question from a hard-case tinkerer:

Leadin:
In order to run a 3-phase motor drive from single phase input,
the user must derate the unit by 50%. This is because the input
rectifier and filter capacitors are too small to handle the increased
peak current of a single phase feed.
You need to consider that many hobby-garage shop types buy used
VFDs on eBay for a fraction of new cost. The cost to them of derating
the drive is quite small. [...]

You have to remember that these units are designed to run in enclosed
cabinets at 50C ambient for 10 years continuously, sometimes with a motor
start every minute. That is so much more severe than what most
hobby-garage shop users put it through.

Jon

Good point. And the low-HP drives keep getting cheaper.
More than one net discount drive supplier has 1 and 2 HP 1-to-3 drives for
under $200. The box I was thinking of making would allow running 220V
units from 110 or 440 from 220, but that's very much a niche.

There are these really cute power control and PFC ICs and planar
transformers
these days so it would be a lot of fun to find a good application to
tinker
with....
geoff



--
Posted via a free Usenet account from http://www.teranews.com