Theoretically possible, but why? You can buy a speed controller with
soft start, dynamic braking, and dozens of features, that also converts
single phase to to 3 phase, for $200 or so. Why bother to make your
own, which will take many hours, might or might not work well, might or
might not fail catastrophically, and will never have all the features of
a commerical speeed controller?

Richard


Ignoramus17647 wrote:
I am thinking about my high capacity transistors. Supposedly they can
be used for making inverters.

What if I build something like this:

1) a 220V to 208 V transformer

fed into

2) a rectifier

fed into

3) three DC to AC inverters that have their outputs shifted by 120
degrees relative to one another.

Would that not become a phase converter (1 - 3 phase)?

i

He is only a little closer to being able to make a VFD from those
transistors than if he'd start with a bucket of sand..

Bob Swinney
"Richard Ferguson" wrote in message
...
Theoretically possible, but why? You can buy a speed controller with soft
start, dynamic braking, and dozens of features, that also converts single
phase to to 3 phase, for $200 or so. Why bother to make your own, which
will take many hours, might or might not work well, might or might not
fail catastrophically, and will never have all the features of a
commerical speeed controller?

Richard


Ignoramus17647 wrote:
I am thinking about my high capacity transistors. Supposedly they can
be used for making inverters.

What if I build something like this:

1) a 220V to 208 V transformer

fed into 2) a rectifier

fed into

3) three DC to AC inverters that have their outputs shifted by 120
degrees relative to one another.

Would that not become a phase converter (1 - 3 phase)?

i

Ignoramus17647 wrote:
I am thinking about my high capacity transistors. Supposedly they can
be used for making inverters.

What if I build something like this:

1) a 220V to 208 V transformer

fed into

2) a rectifier

fed into

3) three DC to AC inverters that have their outputs shifted by 120
degrees relative to one another.

Would that not become a phase converter (1 - 3 phase)?

i

To build your own inverter type phase converter you have to start with
building a big DC power supply. It's much harder than it looks. What would
very likely happen is that you'd go spend $40 on big power rectifiers and
as soon as you fired it up they'd go "BOOM!" and you'd be wondering why.

There is a design for an SCR-based variable frequency power supply in the
back of the old GE SCR Handbook. I did a lot of design work planning to
build one until I found out more about the failure mechanism of large SCRs
(roughly analogous to a hand grenade) and decided I didn't want them in my
house. You can pursue this if you want to and you will likely learn a great
deal but I can tell you this with great certainty: you will never cobble up
something cheaper and more robust than the inexpensive inverters you can buy
now from places like dealerselectric.com - but do keep us posted.

If you decide to press on, make sure you google on the term "snubber" because
a snubber circuit is what you'll have to design and test to keep your power
rectifiers from going boom.

GWE

"Robert Swinney" wrote: He is only a little closer to being able to make a
VFD from those transistors than if he'd start with a bucket of sand..
^^^^^^^^^^^^^^
I had a friend who used to say, "Give me enough sand, and I'll build you a
golden castle."

"Richard Ferguson" wrote in message
...
Theoretically possible, but why? You can buy a speed controller with
soft start, dynamic braking, and dozens of features ...

I'm working on an induction heater (just blew two more transistors, pffbt),
I could just as well buy one, with all the features, temperature control,
ability to run any coil, and be completely load protected, but I won't. I
have more incentive because these things run upwards of $10k, but that's not
my point.

Some people like to build a Gingery lathe too...

Tim

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

You have the block diagram basically right except for the microcontroller
and software to provide transistor control, implement overload protection,
and orderly start-up/shutdown sequences. It took industry about 10 years
to get to where we are today: relatively cheap, bullet-proof, simple to use
VFD's. Phase converters, rotary or static, are obsolete.

Randy


"Ignoramus17647" wrote in message
...
On Mon, 14 Feb 2005 15:05:48 GMT, Richard Ferguson
wrote:
Theoretically possible, but why? You can buy a speed controller with
soft start, dynamic braking, and dozens of features, that also converts
single phase to to 3 phase, for $200 or so. Why bother to make your
own, which will take many hours, might or might not work well, might or
might not fail catastrophically, and will never have all the features of
a commerical speeed controller?

I do not disagree with you, practically speaking, most things are
easier to buy than to build, but I am curious theoretically. Will this
be able to be a basis for a high current phase converter.

i

"Ignoramus17647" wrote in message
...
On Mon, 14 Feb 2005 15:05:48 GMT, Richard Ferguson
wrote:
Theoretically possible, but why? You can buy a speed controller with
soft start, dynamic braking, and dozens of features, that also converts
single phase to to 3 phase, for $200 or so. Why bother to make your
own, which will take many hours, might or might not work well, might or
might not fail catastrophically, and will never have all the features of
a commerical speeed controller?

I do not disagree with you, practically speaking, most things are
easier to buy than to build, but I am curious theoretically. Will this
be able to be a basis for a high current phase converter.

i

i

I really like the idea of your building that device for comverting single
phase to 3 phase. I like it so much that I'd suport your efforts by
supplyimg any parts that I might have. (and I have alot of stuff for
projects like that).
My thought is; you are a smart guy with curiousity. This sure would
become a way for you to get alot of experience with electronics and learn
things that will possibly benefit you in your future.
This is a metalworking news group but there are guys in this group who are
very knowledgeable about the circuits you will use. I hope you build the
phase converter.

J

In article mr5Qd.21348$uc.21332@trnddc08, Jerry Martes says...

I really like the idea of your building that device for comverting single
phase to 3 phase. I like it so much that I'd suport your efforts by
supplyimg any parts that I might have. (and I have alot of stuff for
projects like that).
My thought is; you are a smart guy with curiousity. This sure would
become a way for you to get alot of experience with electronics and learn
things that will possibly benefit you in your future.
This is a metalworking news group but there are guys in this group who are
very knowledgeable about the circuits you will use. I hope you build the
phase converter.

Are bipolar transistors really the correct device? Aren't some
of the modern VFDs built using hexfets?

Not to discourage him of course - but today the cost of devices is
*so* small in comparison to the rest of the project, it would make
sense to purchase the best transistor for the job because that would
probably only add about ten bucks to the overall cost.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

"Ignoramus17647" wrote in message
...
On Mon, 14 Feb 2005 17:43:46 GMT, Jerry Martes
wrote:

"Ignoramus17647" wrote in message
...
On Mon, 14 Feb 2005 15:05:48 GMT, Richard Ferguson
wrote:
Theoretically possible, but why? You can buy a speed controller with
soft start, dynamic braking, and dozens of features, that also converts
single phase to to 3 phase, for $200 or so. Why bother to make your
own, which will take many hours, might or might not work well, might or
might not fail catastrophically, and will never have all the features
of
a commerical speeed controller?

I do not disagree with you, practically speaking, most things are
easier to buy than to build, but I am curious theoretically. Will this
be able to be a basis for a high current phase converter.

i

i

I really like the idea of your building that device for comverting
single
phase to 3 phase. I like it so much that I'd suport your efforts by
supplyimg any parts that I might have. (and I have alot of stuff for
projects like that).
My thought is; you are a smart guy with curiousity. This sure would
become a way for you to get alot of experience with electronics and learn
things that will possibly benefit you in your future.
This is a metalworking news group but there are guys in this group who
are
very knowledgeable about the circuits you will use. I hope you build
the
phase converter.

Thanks Jerry, the talk about SCRs exploding like hand grenades scared
me a little bit, but I just might do this one day.

i

i

I have some IR SCRs That will handle 1,000 volts and 1,000 amps that I'd
domate to a *real* project. I'd expect these SCRs to be adequet for any
household power requirements without fear of exploding.
I think you can build a fixed frequency unit to convert single phase to
three phase. I also think there are several guys on this group who can
show you how to do it. I know Don Foreman could design something like this
'single frequency converter'. There are probably many other RCMers who
would help you with any design problems you might encounter.
I'd supply the rectifier diodes and SCRs. I am not smart enough to help
with design.

J

jim rozen wrote:

In article mr5Qd.21348$uc.21332@trnddc08, Jerry Martes says...


I really like the idea of your building that device for comverting single
phase to 3 phase. I like it so much that I'd suport your efforts by
supplyimg any parts that I might have. (and I have alot of stuff for
projects like that).
My thought is; you are a smart guy with curiousity. This sure would
become a way for you to get alot of experience with electronics and learn
things that will possibly benefit you in your future.
This is a metalworking news group but there are guys in this group who are
very knowledgeable about the circuits you will use. I hope you build the
phase converter.


Are bipolar transistors really the correct device? Aren't some
of the modern VFDs built using hexfets?

Not to discourage him of course - but today the cost of devices is
*so* small in comparison to the rest of the project, it would make
sense to purchase the best transistor for the job because that would
probably only add about ten bucks to the overall cost.

Of course, it also depends on how many
sets you blow up (:

On Mon, 14 Feb 2005 11:32:46 -0600, "R. O'Brian"
wrote:

You have the block diagram basically right except for the microcontroller
and software to provide transistor control, implement overload protection,
and orderly start-up/shutdown sequences. It took industry about 10 years
to get to where we are today: relatively cheap, bullet-proof, simple to use
VFD's. Phase converters, rotary or static, are obsolete.

It took industry that long to develop cheap power semiconductors that
can handle the voltages. Now they're available. Appropriate
devices for such a design would be MOSFETs and IGBT's.

As Spehro says, "the journey is it's own reward" (or something like
that.) If it interests you, go for it! You will definitely learn
a few things along the way. I've never built an inverter, but I'd be
glad to collaborate by email with such help as I can offer. I don't
think you'd save any money by building one, but that isn't to say you
shouldn't do it anway.

You'll also need enough DC capacitance to keep voltage up to supply
the other phases while the singlephase power goes thru zero.

On 14 Feb 2005 09:57:35 -0800, jim rozen
wrote:

In article mr5Qd.21348$uc.21332@trnddc08, Jerry Martes says...

I really like the idea of your building that device for comverting single
phase to 3 phase. I like it so much that I'd suport your efforts by
supplyimg any parts that I might have. (and I have alot of stuff for
projects like that).
My thought is; you are a smart guy with curiousity. This sure would
become a way for you to get alot of experience with electronics and learn
things that will possibly benefit you in your future.
This is a metalworking news group but there are guys in this group who are
very knowledgeable about the circuits you will use. I hope you build the
phase converter.

Are bipolar transistors really the correct device? Aren't some
of the modern VFDs built using hexfets?

Not to discourage him of course - but today the cost of devices is
*so* small in comparison to the rest of the project, it would make
sense to purchase the best transistor for the job because that would
probably only add about ten bucks to the overall cost.

Right. Depending on power level and voltage level, HEXFET's or
IGBT's are the appropriate devices.

On 14 Feb 2005 18:07:28 GMT, Ignoramus17647
wrote:

On Mon, 14 Feb 2005 17:43:46 GMT, Jerry Martes wrote:

"Ignoramus17647" wrote in message
...
On Mon, 14 Feb 2005 15:05:48 GMT, Richard Ferguson

Thanks Jerry, the talk about SCRs exploding like hand grenades scared
me a little bit, but I just might do this one day.

When power elex are being developed, things do go POW -- but they're
little POWs, more like a smallish caliber pistol than a grenade.

Eye protection at the bench is a very good idea.

"Jerry Martes" wrote in message
news:796Qd.32647$Dc.14953@trnddc06...
I have some IR SCRs That will handle 1,000 volts and 1,000 amps that I'd
domate to a *real* project. I'd expect these SCRs to be adequet for any
household power requirements without fear of exploding.

How fast are they? I've been curious about building an SCR inverter as Dan
experimented with:
http://www.dansworkshop.com/Induction%20Heating.shtml
At that current rating, I could pump what, a good couple of kilowatts
through a coil without that thing breaking a sweat! The only problem is the
capacitance needed, I'll have to drop a lot of change to get enough
capacitance rated for that kind of current and voltage.

Tim

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

i

I like your idea of synchronizing the three output voltages by triggering
them with a rotating machine. But, are you able to manufacture the three
output voltage sources??

J



"Ignoramus17647" wrote in message
...
On Mon, 14 Feb 2005 18:32:35 GMT, Jerry Martes
wrote:

I have some IR SCRs That will handle 1,000 volts and 1,000 amps that
I'd
domate to a *real* project. I'd expect these SCRs to be adequet for any
household power requirements without fear of exploding.

Jerry, I must say that these are worth real money on ebay. Try
looking into this. 300 amp ones sell like hot cakes for $25 each.

While I appreciate the donation offer, I want you to be aware that
these things are not just cute garbage, that they have high value. I
do not want you to not be aware of it.

I can guarantee that if I embark on this project, I will not sell any
donated products on ebay, but would either use, accidentally destroy,
or return them back.

I think you can build a fixed frequency unit to convert single phase to
three phase. I also think there are several guys on this group who can
show you how to do it. I know Don Foreman could design something like
this
'single frequency converter'. There are probably many other RCMers who
would help you with any design problems you might encounter.
I'd supply the rectifier diodes and SCRs. I am not smart enough to
help
with design.

Regarding the control circuits, what I am curious about is whether I
can control the process with a regular small 110V motor spinning at
the regular RPM. That is, the motor, and some wheel with contacts and
such, would tell the system which circuits to turn on and off.

A wheel of that motor would be made of dielectric, with some copper
pieces on it that would at certain points close some switches that
would then supply various phases etc. I can draw a picture but you may
be getting the idea.

If the control current is 3-4 amps, then arcing on the contacts should
not be (I hope) too bad.

Various contact points would be touching that cylinder at different
position along the spinning axis. One position may say "turn phase 1
PLUS on", another would say "turn phase one MINUS on", another one
would say "turn phase 2 PLUS on", another would say "turn phase 2
MINUS on",another one would say "turn phase 3 PLUS on", another would
say "turn phase 3 MINUS on". These copper strips will be positioned
with 120 degree offset.

That same motor could drive a fan that would cool the transistors.

This cannot really go wrong unless, something falls off, or there is a
short. (or so I think)

The issue that I see right now is that the inverted current will not
be sinusoidal .-'~`-._.-'~`-._.-'~`-._.-'~`-._.-'~`-._, , but instead
will be ~~~~____~~~~____~~~~____~~~~____ -- basically a combination of
plus or minus voltage and not a smooth curve. Perhaps a curve can be
smoothed with some capacitors and isolation transformers. My memory of
relevant school physics is quite dim.

That would be the Kalashnikov style solution, simple, stupid, and more
easy to understand than a complex circuitry. I would prefer that to
building a sophisticated control circuitry that I would be most likely
to get wrong anyway.

i

Tim

The biggest SCRs I have are marked IR A2 88-4208. They are about 2 inch
diameter and 1 inch high, hockey puck style. I am completely ignorant
about the speed of these things.

Jerry


"Tim Williams" wrote in message
...
"Jerry Martes" wrote in message
news:796Qd.32647$Dc.14953@trnddc06...
I have some IR SCRs That will handle 1,000 volts and 1,000 amps that
I'd
domate to a *real* project. I'd expect these SCRs to be adequet for any
household power requirements without fear of exploding.

How fast are they? I've been curious about building an SCR inverter as
Dan
experimented with:
http://www.dansworkshop.com/Induction%20Heating.shtml
At that current rating, I could pump what, a good couple of kilowatts
through a coil without that thing breaking a sweat! The only problem is
the
capacitance needed, I'll have to drop a lot of change to get enough
capacitance rated for that kind of current and voltage.

Tim

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

Jerry Martes wrote:

"Ignoramus17647" wrote in message
...


On Mon, 14 Feb 2005 15:05:48 GMT, Richard Ferguson
wrote:


Theoretically possible, but why? You can buy a speed controller with
soft start, dynamic braking, and dozens of features, that also converts
single phase to to 3 phase, for $200 or so. Why bother to make your
own, which will take many hours, might or might not work well, might or
might not fail catastrophically, and will never have all the features of
a commerical speeed controller?


I do not disagree with you, practically speaking, most things are
easier to buy than to build, but I am curious theoretically. Will this
be able to be a basis for a high current phase converter.

i



i

I really like the idea of your building that device for comverting single
phase to 3 phase. I like it so much that I'd suport your efforts by
supplyimg any parts that I might have. (and I have alot of stuff for
projects like that).
My thought is; you are a smart guy with curiousity. This sure would
become a way for you to get alot of experience with electronics and learn
things that will possibly benefit you in your future.


Huh? Unless he has a degree in electrical engineering, with a strong
background
in power conversion circuits, he will convert all his transistors back
into sand,
and then some! This stuff is REALLY quite tricky, and every wire (or
bus bar)
has parasitic inductance that will drive you crazy (and burn out components)
at every turn! I go through this in designing some of my products, and
still find
it quite difficult. If he doesn't know how to write loop and node
equations for
electrical circuits, and have a foundation in AC circuit analysis, he
will never
get anywhere with this, except possibly hurting himself. I have had
MUCH SMALLER
circuits explode on me, with fragments embedded in the walls. I would
really
be afraid of working on gear this big without extensive safety precautions
like ear protection, face shields, even protective walls.

It is insane to try to learn the intricacies of power electronics when a
VFD is
available off the shelf for a few hundred $.

Jon

Jerry Martes wrote:

I have some IR SCRs That will handle 1,000 volts and 1,000 amps that I'd
domate to a *real* project. I'd expect these SCRs to be adequet for any
household power requirements without fear of exploding.
I think you can build a fixed frequency unit to convert single phase to
three phase. I also think there are several guys on this group who can
show you how to do it. I know Don Foreman could design something like this
'single frequency converter'. There are probably many other RCMers who
would help you with any design problems you might encounter.
I'd supply the rectifier diodes and SCRs. I am not smart enough to help
with design.


To build a phase converter, ONLY, not a VFD, you need a 90 degree phase
shift,
and a Scott Tee transformer. I tried to design a very simple, all
passive converter
this way, but ran into a problem. It would draw a HUGE imaginary
current from
the mains to work. You could build the inverter stage for this with
SCRs, but that
is REALLY doing it the hard way. First, you'd need "inverter grade"
SCRs, not
standard-type ones. These turn off much faster. The commutating
capacitors needed
to turn these SCRs off will likely cost more than a 5 Hp VFD, brand-new,
with
factory warranty! That's why manufacturers stopped using SCRs in motor
drives
almost as soon as the first big power transistors came out in the late
60's - early 70's.

Jon

Ignoramus17647 wrote:

Regarding the control circuits, what I am curious about is whether I
can control the process with a regular small 110V motor spinning at
the regular RPM. That is, the motor, and some wheel with contacts and
such, would tell the system which circuits to turn on and off.

A wheel of that motor would be made of dielectric, with some copper
pieces on it that would at certain points close some switches that
would then supply various phases etc. I can draw a picture but you may
be getting the idea.


WHAAAAAT??!!! You are going to control power semiconductors with
mechanical switches?

If the control current is 3-4 amps, then arcing on the contacts should
not be (I hope) too bad.


Yes, but the first "arc" really a bouncing contact, will destroy the
transistors.
So, that's the end of that! You need to turn these transistors on HARD,
and then off
HARD, to keep the power losses within the limits. So, the base junction
needs
to be driven with several amps that has a rise time of no more than one
microsecond,
both on and off. You will never do this with mechanical switches.

A "regular small 110V motor" sounds like an induction motor, which is NOT
synchronous to the power line. Your switching control would need to be
synchonized to the power line to generate the 3rd phase.

Various contact points would be touching that cylinder at different
position along the spinning axis. One position may say "turn phase 1
PLUS on", another would say "turn phase one MINUS on", another one
would say "turn phase 2 PLUS on", another would say "turn phase 2
MINUS on",another one would say "turn phase 3 PLUS on", another would
say "turn phase 3 MINUS on". These copper strips will be positioned
with 120 degree offset.

That same motor could drive a fan that would cool the transistors.

This cannot really go wrong unless, something falls off, or there is a
short. (or so I think)



How long are your mechanical switches going to last at 60 operations/second?
If you can get 1 million operations, that is 277 hours, or 11 days. I'd
suspect
a mechanical switch will not last even that long at such a rate.

Jon

"Ignoramus17647" wrote in message
...
On Mon, 14 Feb 2005 20:22:37 GMT, Jerry Martes
wrote:
I like your idea of synchronizing the three output voltages by
triggering
them with a rotating machine.

I am glad to hear it.

But, are you able to manufacture the three output voltage sources??

I do not understand the question.

The schematic is that input voltage will be converted to appropriate
voltage, then rectified to DC, then rectified DC will be inverted by
three inverters, according to what the rotating cylinder tells the
transistors (120 degree shift). The inverted current will then be
again transformed with isolation transformers, with three output legs
tied with a common neutral.

Which parts of this scheme are you referring to?

i

i

I wasnt thinking properly. I was thinking that you were intending to have
three semisinewave voltage sources. Now I see it. You will have a DC
voltage source that is supplied systematically to the 4 terminal three phase
load.

Although *I* wouldnt have considered pulsating DC to be adequet for
providing power to three phase machines, maybe it would work. Try it.
I'd think the rotating source of triggering could be holes in a disc mounted
on a 60 rev per second synchronous motor. LED light sources could provide
triggering vlotages. If you do want to investigate the feasability of this,
you could get any old 3750 RPM induction motor. It would provide a
triggering rate that would remain fairly constant since its load would be
constant too.

I am sure *I'd* learn something from your efforts. So, I volunteer any
help I might offer.

J

I wonder how long it will be before this thread gravitates to perpetual
motion? That concept may be more easily grasped than some of the ideas set
forth.

Bob Swinney

"Jon Elson" wrote in message
...


Ignoramus17647 wrote:

Regarding the control circuits, what I am curious about is whether I
can control the process with a regular small 110V motor spinning at
the regular RPM. That is, the motor, and some wheel with contacts and
such, would tell the system which circuits to turn on and off.
A wheel of that motor would be made of dielectric, with some copper
pieces on it that would at certain points close some switches that
would then supply various phases etc. I can draw a picture but you may
be getting the idea.

WHAAAAAT??!!! You are going to control power semiconductors with
mechanical switches?

If the control current is 3-4 amps, then arcing on the contacts should
not be (I hope) too bad.

Yes, but the first "arc" really a bouncing contact, will destroy the
transistors.
So, that's the end of that! You need to turn these transistors on HARD,
and then off
HARD, to keep the power losses within the limits. So, the base junction
needs
to be driven with several amps that has a rise time of no more than one
microsecond,
both on and off. You will never do this with mechanical switches.

A "regular small 110V motor" sounds like an induction motor, which is NOT
synchronous to the power line. Your switching control would need to be
synchonized to the power line to generate the 3rd phase.

Various contact points would be touching that cylinder at different
position along the spinning axis. One position may say "turn phase 1
PLUS on", another would say "turn phase one MINUS on", another one
would say "turn phase 2 PLUS on", another would say "turn phase 2
MINUS on",another one would say "turn phase 3 PLUS on", another would
say "turn phase 3 MINUS on". These copper strips will be positioned
with 120 degree offset.

That same motor could drive a fan that would cool the transistors.

This cannot really go wrong unless, something falls off, or there is a
short. (or so I think)


How long are your mechanical switches going to last at 60
operations/second?
If you can get 1 million operations, that is 277 hours, or 11 days. I'd
suspect
a mechanical switch will not last even that long at such a rate.

Jon

"Ignoramus17647" wrote in message
...
I am thinking about my high capacity transistors. Supposedly they can
be used for making inverters.

What if I build something like this:

1) a 220V to 208 V transformer

fed into

2) a rectifier

fed into

3) three DC to AC inverters that have their outputs shifted by 120
degrees relative to one another.

Would that not become a phase converter (1 - 3 phase)?

i

Sure, but how do you plan on ensuring the three inverters stay in sync??
Greg

jim rozen wrote:

Are bipolar transistors really the correct device? Aren't some

of the modern VFDs built using hexfets?

Not to discourage him of course - but today the cost of devices is
*so* small in comparison to the rest of the project, it would make
sense to purchase the best transistor for the job because that would
probably only add about ten bucks to the overall cost.

Jim



Bipolar transistors have traditionally out performed fets. Back when I
was designing switching power supplies, we used bipolars in the high
power supplies because good enough fets just weren't available. A few
years later I designed a supply with fet switches. It was really amazing
how much easier the fet was to deal with than the bipolars. Far easier
to drive, much more forgiving about over driving, etc. I think IGBT's
are a best of combo, but they arrived after I (thankfully) escaped power
electronics. As a general rule, when you're trying to amplify a bipolar
is going to perform better. When you're trying to switch, pick a fet.

Steve

Grant Erwin wrote:


If you decide to press on, make sure you google on the term "snubber"
because
a snubber circuit is what you'll have to design and test to keep your
power
rectifiers from going boom.

GWE


Then there was the talk a friend of mine gave at work one time "How to
build a power amplifier without going blind". I had the good fortune to
be wearing goggles when the power fet in the circuit I was working on
fried. It didn't explode, but the 5V chip driving it did when it got hit
with 300VDC.

Steve

"Greg O" wrote in message
...

"Ignoramus17647" wrote in message
...
I am thinking about my high capacity transistors. Supposedly they can
be used for making inverters.

What if I build something like this:

1) a 220V to 208 V transformer

fed into

2) a rectifier

fed into

3) three DC to AC inverters that have their outputs shifted by 120
degrees relative to one another.

Would that not become a phase converter (1 - 3 phase)?

i

Sure, but how do you plan on ensuring the three inverters stay in sync??
Greg

On 14 Feb 2005 19:19:33 GMT, Ignoramus17647
wrote:

What is an IGBT?

Insulated Gate Bipolar Transistor. Google IGBT for more info.

a much simpler approach is to have a counter (base 3 would be good) so you
can turn on each phase in sequence. Drive it with an oscillator and you
have variable frequency.
But, you will have incredibly nasty harmonics and it won't be kind to
motors.

A "single phase" example of this kind of converter is the CD ignition
schematic on my web page (www.wbnoble.com, look under "articles I wrote") -
it works nicely, I built it because I couldn't find anything commercially,
but it has a major amount of RFI - multiply the power levels by 1000 and you
will seriously annoy the neighbors.

There are books written on commutating circuits and power inverters - you
need to at least somewhat approximate a sine wave - 3 transistors per phase
will give you 8 levels, that ought to be enough (think binary, 2**3 = 8),
just add snubber circuits and logic


"Ignoramus17647" wrote in message
...
On Mon, 14 Feb 2005 20:22:37 GMT, Jerry Martes
wrote:
I like your idea of synchronizing the three output voltages by
triggering
them with a rotating machine.

I am glad to hear it.

But, are you able to manufacture the three output voltage sources??

I do not understand the question.

The schematic is that input voltage will be converted to appropriate
voltage, then rectified to DC, then rectified DC will be inverted by
three inverters, according to what the rotating cylinder tells the
transistors (120 degree shift). The inverted current will then be
again transformed with isolation transformers, with three output legs
tied with a common neutral.

Which parts of this scheme are you referring to?

i

Use a tone wheel and 3 pickups 120* apart. Amplify the pickups to control
the inverter circuit. Control the frequency by varing the motor speed.
Old Tube theory stuff.
Glenn
"Greg O" wrote in message
...

"Ignoramus17647" wrote in message
...
I am thinking about my high capacity transistors. Supposedly they can
be used for making inverters.

What if I build something like this:

1) a 220V to 208 V transformer

fed into

2) a rectifier

fed into

3) three DC to AC inverters that have their outputs shifted by 120
degrees relative to one another.

Would that not become a phase converter (1 - 3 phase)?

i

Sure, but how do you plan on ensuring the three inverters stay in sync??
Greg

On Mon, 14 Feb 2005 22:38:28 -0800, "william_b_noble"
wrote:

a much simpler approach is to have a counter (base 3 would be good) so you
can turn on each phase in sequence. Drive it with an oscillator and you
have variable frequency.
But, you will have incredibly nasty harmonics and it won't be kind to
motors.

A "single phase" example of this kind of converter is the CD ignition
schematic on my web page (www.wbnoble.com, look under "articles I wrote") -
it works nicely, I built it because I couldn't find anything commercially,
but it has a major amount of RFI - multiply the power levels by 1000 and you
will seriously annoy the neighbors.

There are books written on commutating circuits and power inverters - you
need to at least somewhat approximate a sine wave - 3 transistors per phase
will give you 8 levels, that ought to be enough (think binary, 2**3 = 8),
just add snubber circuits and logic


"Ignoramus17647" wrote in message
...
On Mon, 14 Feb 2005 20:22:37 GMT, Jerry Martes
wrote:
I like your idea of synchronizing the three output voltages by
triggering
them with a rotating machine.

I am glad to hear it.

But, are you able to manufacture the three output voltage sources??

I do not understand the question.

The schematic is that input voltage will be converted to appropriate
voltage, then rectified to DC, then rectified DC will be inverted by
three inverters, according to what the rotating cylinder tells the
transistors (120 degree shift). The inverted current will then be
again transformed with isolation transformers, with three output legs
tied with a common neutral.

Which parts of this scheme are you referring to?

i

I don't know very much about electronics but couldn't the transistors
be set with epoxy to act as feet for the motor for a rotary phase
convertor?
ERS

You can put the capacitors in series and each sees the applied voltage
divided by the number in series.

Ignoramus17647 wrote:

On Mon, 14 Feb 2005 13:05:53 -0600, Don Foreman wrote:

On Mon, 14 Feb 2005 11:32:46 -0600, "R. O'Brian"
wrote:

You have the block diagram basically right except for the microcontroller
and software to provide transistor control, implement overload protection,
and orderly start-up/shutdown sequences. It took industry about 10 years
to get to where we are today: relatively cheap, bullet-proof, simple to use
VFD's. Phase converters, rotary or static, are obsolete.

It took industry that long to develop cheap power semiconductors that
can handle the voltages. Now they're available. Appropriate
devices for such a design would be MOSFETs and IGBT's.


What is an IGBT?

As Spehro says, "the journey is it's own reward" (or something like
that.) If it interests you, go for it! You will definitely learn
a few things along the way. I've never built an inverter, but I'd be
glad to collaborate by email with such help as I can offer. I don't
think you'd save any money by building one, but that isn't to say you
shouldn't do it anway.

You'll also need enough DC capacitance to keep voltage up to supply
the other phases while the singlephase power goes thru zero.


Yep, I wondered about that also. I have 4 10,000 mF 200V (250 surge)
capacitors, but they would be unlikely to handle 246 or so utility
volts, so the voltage would need to step down a bit. Not sure if they
are DC or AC.

If this idea moves further towards implementation, I may keep the
caps, if not, I will sell them.

If I am going to go ahead with this, I will keep a project page
similar to my generator restoration page

http://igor.chudov.com/tmp/onan/Diesel/

What is becoming clear is that old junk UPSes are in fact a real gold
mine. Power cords, contactors, switches, circuit breakers, SCRs, IGBTs
(I mined some also), all of those are quite valuable. The real
difficulty is handling heavy items and throwing away what is not
needed.

I will from now on bid on all large UPS lots from the military,
regardless of condition.

thanks to all.

i

"Ignoramus29573" wrote in message
...
I have another idea. Scratch the idea about having a rotating cylinder
with brushes. What I need is a small 1 phase motor (1/3 hp) connected
to a small 3 phase generator (again, low power). If the 3 phase
generator generates 1 or so amps, the transistors could amplify that
85 times, and I get a smooth wave on top of that. The result would be
70 amps of 3 phase, enough for more or less anything. All I need is a
source of clean DC, AC motor ($15), small 3 phase generator ($???,
maybe I can make it from a regular 3 phase motor), the transistor
units, and 2 isolation transformers.

i

i

Good idea. Make it and send some reports.

Jerry

If I remember my electronics correctly then this should make quite an
efficient space heater. I think in the configuration you are talking
about you will dissapate a great deal of your input power as heat. This
is the reason for using switching technique due to the much greater
efficiency possible. At this point i'll hope someone else chips in who
can remeber more of the detailed electronics involved.

Ignoramus29573 wrote:

I have another idea. Scratch the idea about having a rotating cylinder
with brushes. What I need is a small 1 phase motor (1/3 hp) connected
to a small 3 phase generator (again, low power). If the 3 phase
generator generates 1 or so amps, the transistors could amplify that
85 times, and I get a smooth wave on top of that. The result would be
70 amps of 3 phase, enough for more or less anything. All I need is a
source of clean DC, AC motor ($15), small 3 phase generator ($???,
maybe I can make it from a regular 3 phase motor), the transistor
units, and 2 isolation transformers.

i

"Ignoramus29573" wrote in message
...
On Tue, 15 Feb 2005 18:31:33 GMT, Jerry Martes
wrote:

"Ignoramus29573" wrote in message
...
I have another idea. Scratch the idea about having a rotating cylinder
with brushes. What I need is a small 1 phase motor (1/3 hp) connected
to a small 3 phase generator (again, low power). If the 3 phase
generator generates 1 or so amps, the transistors could amplify that
85 times, and I get a smooth wave on top of that. The result would be
70 amps of 3 phase, enough for more or less anything. All I need is a
source of clean DC, AC motor ($15), small 3 phase generator ($???,
maybe I can make it from a regular 3 phase motor), the transistor
units, and 2 isolation transformers.

Good idea. Make it and send some reports.


Two questions.

1. Can I use a small 3 phase motor (dirt cheap on ebay) to be a
generator? (if it is driven by something else)

Example:

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=3870194621

2. How can I construct a source of relatively smooth DC from regular
AC. Say I can convert 250V into 208VAC, how can I make 208 VDC? I
understand that, obviously, I need a rectifier. But what else to
stabilize voltage as the input phase goes through zeroes?

i

i

I have messed up again. I assumed that you had already figured out all
the complex electronics. I dont know how to design these things. I have
enough trouble trying to fix them.

Did you notice the shipping charges for thet "cheap" 1 HP 3 phase motor?

I'm pretty sure you can make your idea work. And, I'd also bet that
it'll keep you busy for the best part of a year learning how to get it
working right.
All the guys I know who are able to design devices like this had spent
years and years in school and designing circuits before making complex
systems like this 3 phase power generator.

Jerry

Steve Smith wrote:



jim rozen wrote:

Are bipolar transistors really the correct device? Aren't some

of the modern VFDs built using hexfets?

Not to discourage him of course - but today the cost of devices is
*so* small in comparison to the rest of the project, it would make
sense to purchase the best transistor for the job because that would
probably only add about ten bucks to the overall cost.
Jim



Bipolar transistors have traditionally out performed fets. Back when I
was designing switching power supplies, we used bipolars in the high
power supplies because good enough fets just weren't available. A few
years later I designed a supply with fet switches. It was really
amazing how much easier the fet was to deal with than the bipolars.
Far easier to drive, much more forgiving about over driving, etc. I
think IGBT's are a best of combo, but they arrived after I
(thankfully) escaped power electronics. As a general rule, when you're
trying to amplify a bipolar is going to perform better. When you're
trying to switch, pick a fet.

IGBTs are a dream, from the performance standpoint. Unfortunately, they
are a
NIGHTMARE from the tricky design details view. Yes, they definitely can be
made to work reliably, but just wiring them up, without attention to
transients,
dv/dt and the worst characteristic, the positive temperature
coefficient, will end
up with a big POP! The IGBT must be driven hard into saturation, and then
driven hard into cutoff, in the space of 50 - 75 nS maximum. Any period of
linear operation, even for 100 nS can cause current hogging, usually to
the center
of the die, and the transistor fails shorted. I had a great (and REALLY
frank)
discussion with an International Rectifier applications engineer who
told me all
the stuff that they don't publish in the data sheets. It was very eye
opening!
After that, I did get a pretty nice 1 KW inverter running reliably.

Darlington bipolar power transistors have gone to that place in the sky with
ignitrons, Mercury Thyratrons, etc. for a good reason. They can never reach
the low forward voltage drop of a properly driven single bipolar or IGBT.
They are simpler to drive, of course, but the power loss is a real killer.

Jon

On 15 Feb 2005 18:45:18 GMT, Ignoramus29573
wrote:

On Tue, 15 Feb 2005 18:40:20 +0000, David Billington wrote:

Can you explain in which part the heat will be lost?

Obviously, transforming 250V into 208V will use up some heat, also 2
isolation transformers will also dissipate some heat. But what else
would waste energy?

The biggest loss would be in the transistors. The best
(theoretical) efficiency you can hope for in the method you describe
is 50% just in the transistors, (class B amplifier) so if you're
producing 1000 watts you are also dissipating 1000 watts. The
rectifier(s) will also dissipate some.

Ignoramus17647 wrote:

On Mon, 14 Feb 2005 15:06:07 -0600, Jon Elson wrote:


Ignoramus17647 wrote:



Regarding the control circuits, what I am curious about is whether I
can control the process with a regular small 110V motor spinning at
the regular RPM. That is, the motor, and some wheel with contacts and
such, would tell the system which circuits to turn on and off.

A wheel of that motor would be made of dielectric, with some copper
pieces on it that would at certain points close some switches that
would then supply various phases etc. I can draw a picture but you may
be getting the idea.




WHAAAAAT??!!! You are going to control power semiconductors with
mechanical switches?



That's what I thought of doing, not knowing much better.

I defer to superior knowledge of more informed individuals.



If the control current is 3-4 amps, then arcing on the contacts should
not be (I hope) too bad.




Yes, but the first "arc" really a bouncing contact, will destroy the
transistors. So, that's the end of that! You need to turn these
transistors on HARD, and then off HARD, to keep the power losses
within the limits. So, the base junction needs to be driven with
several amps that has a rise time of no more than one microsecond,
both on and off. You will never do this with mechanical switches.



Any way around this that is compatible with the mechanical approach?
Ergo, place some quick electronic switch that ignores the
first "arcing" instant, but then switches the current to the
semicondctors HARD?



A "regular small 110V motor" sounds like an induction motor, which is NOT
synchronous to the power line.



Since I am going to invert DC, synschronicity with the power line is
of secondary importance (I am not going to make power line one of the
legs of 3 phase)..



OK, I thought that you were going to try to make a real phase converter, and
just supply the 3rd phase. That would make some sense, since you can't buy
one that I know of. But, now, you are just trying to make a VFD! Thatr
is totally
insane. If you know where to look, you can probably find them in dumpsters!
Sell your SCRs or Darlington transistors on eBay, and use the money to buy
a commercial VFD! It will work, all yuou have to do is connect the wires.

Having developed power electronics myself, is it really worth a year (if
you are not
experienced in power electronics, make that about FIVE years) to develop
this?
What happenbs when you blow out all those transistors? Do you abandon the
project, or do you plow ahead, buying more transistors, etc. and keep
trying?
Do you have a digital storage oscilloscope? You certainly need one, as you
will need to record the signals as the transistors blow, so you can
determine
what went wrong.

When I did my 1 KW inverter, I blew somewhere in the neighborhood of FORTY
$8 power transistors before I got the startup problems under control! I
learned
something every time one blew, too!

Jon

In article ,
says...
On 15 Feb 2005 18:45:18 GMT, Ignoramus29573
wrote:

On Tue, 15 Feb 2005 18:40:20 +0000, David Billington wrote:

Can you explain in which part the heat will be lost?

Obviously, transforming 250V into 208V will use up some heat, also 2
isolation transformers will also dissipate some heat. But what else
would waste energy?

The biggest loss would be in the transistors. The best
(theoretical) efficiency you can hope for in the method you describe
is 50% just in the transistors, (class B amplifier) so if you're
producing 1000 watts you are also dissipating 1000 watts. The
rectifier(s) will also dissipate some.


This photo gives a clue about the amount of heat to be dissipated...
http://www.suscom-maine.net/~nsimmon.../Cal1503TC.JPG

That's a 1.5kVA, 3 phase AC power source I just sold. It was really just
a 200 pound, 3 channel, 45-1000Hz amplifier. Manuals are still available
from California Instruments and would be helpful to anyone seriously
considering building such a beast.

Ned Simmons

Ignoramus29573 wrote:

On Tue, 15 Feb 2005 14:29:29 -0600, Jon Elson wrote:



OK, I thought that you were going to try to make a real phase
converter, and just supply the 3rd phase. That would make some
sense, since you can't buy one that I know of. But, now, you are
just trying to make a VFD! Thatr is totally insane. If you know
where to look, you can probably find them in dumpsters! Sell your
SCRs or Darlington transistors on eBay, and use the money to buy a
commercial VFD! It will work, all yuou have to do is connect the
wires.



Well, I hate to say it, but your opinion makes sense from a practical
POV and, quite possibly, I will do what you say -- sell my transistor
stuff and just buy a VFD whenever a need arises. (or perhaps buy a
nice .22 gun with the money)

So, I want to thank you for your frank opinion.



I have another suggestion. You seem to be interested in learning about
electronic design. Take a smaller bite. Your transistors might make
excellent power amplifiers for your stereo. This way you're lots less
likely to fry the transistors, and there will be no chance of
accidentally leaning on the 300VDC buss.

Steve
who still remembers how much that hurt

i

calculate power dispation in the transistors, then you will see why this
isn't done very often



"Ignoramus29573" wrote in message
...
On Tue, 15 Feb 2005 18:31:33 GMT, Jerry Martes
wrote:

"Ignoramus29573" wrote in message
...
I have another idea. Scratch the idea about having a rotating cylinder
with brushes. What I need is a small 1 phase motor (1/3 hp) connected
to a small 3 phase generator (again, low power). If the 3 phase
generator generates 1 or so amps, the transistors could amplify that
85 times, and I get a smooth wave on top of that. The result would be
70 amps of 3 phase, enough for more or less anything. All I need is a
source of clean DC, AC motor ($15), small 3 phase generator ($???,
maybe I can make it from a regular 3 phase motor), the transistor
units, and 2 isolation transformers.

Good idea. Make it and send some reports.


Two questions.

1. Can I use a small 3 phase motor (dirt cheap on ebay) to be a
generator? (if it is driven by something else)

Example:

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=3870194621

2. How can I construct a source of relatively smooth DC from regular
AC. Say I can convert 250V into 208VAC, how can I make 208 VDC? I
understand that, obviously, I need a rectifier. But what else to
stabilize voltage as the input phase goes through zeroes?

i

Ned Simmons wrote:

In article ,
says...

On 15 Feb 2005 18:45:18 GMT, Ignoramus29573
wrote:


On Tue, 15 Feb 2005 18:40:20 +0000, David Billington wrote:

Can you explain in which part the heat will be lost?

Obviously, transforming 250V into 208V will use up some heat, also 2
isolation transformers will also dissipate some heat. But what else
would waste energy?

The biggest loss would be in the transistors. The best
(theoretical) efficiency you can hope for in the method you describe
is 50% just in the transistors, (class B amplifier) so if you're
producing 1000 watts you are also dissipating 1000 watts. The
rectifier(s) will also dissipate some.



This photo gives a clue about the amount of heat to be dissipated...
http://www.suscom-maine.net/~nsimmon.../Cal1503TC.JPG

That's a 1.5kVA, 3 phase AC power source I just sold. It was really just
a 200 pound, 3 channel, 45-1000Hz amplifier. Manuals are still available
from California Instruments and would be helpful to anyone seriously
considering building such a beast.

Ned Simmons
That would have been (or is) a nice 3 phase 50 or 60 Hz power source for a
big toy. - 3 phase motors, 3 phase 1.5KVA welders....

Martin

--
Martin Eastburn, Barbara Eastburn
@ home at Lion's Lair with our computer
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder