Tim Williams wrote:
http://webpages.charter.net/dawill/t..._IndHeat1.html

Next, bigger power transformer and active device (aka transmitter tube).
Which reminds me, anyone have a 500-2000W tube on hand? Preferably not
forced-air or water cooled, but if so, then how about a blower for my pair
of 4CX250R's...
That's insane! Try some power FETs! They are ten times better than
tubes for this frequency range (50 - 100 KHz). You can get 600 V 30 A
transistors under $10. Want to compare the price with a 4CX250?

Running conservatively, you could get 4 KW out of such a transistor
(400 V, 10 A).

Jon

On Thu, 26 Aug 2004 17:52:18 -0500, "Tim Williams"
wrote:

http://webpages.charter.net/dawill/t..._IndHeat1.html

Next, bigger power transformer and active device (aka transmitter tube).
Which reminds me, anyone have a 500-2000W tube on hand? Preferably not
forced-air or water cooled, but if so, then how about a blower for my pair
of 4CX250R's...

Tim

Hi Tim.,

Here's some pictures I took of my first run at an induction heater.
Not the greatest construction, but seems to work..

http://lerch.no-ip.com/atm/Projects/...er/page_01.htm
(First runs)

http://lerch.no-ip.com/atm/Projects/...ly/page_01.htm
(Heating Graphite)

The next step is to get this to work inside my vacuum chamber, and use
it to evaporate quartz.

BTW, I found this site to be very helpful during my design phase:

http://dave.golfbuddys.com/hvguy/


Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction, Testing, and Coating site)

Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent.
Calvin Coolidge

"James Lerch" wrote

Here's some pictures I took of my first run at an induction heater.
Not the greatest construction, but seems to work..

Very elegant!

Mark

On Fri, 27 Aug 2004 14:53:00 GMT,
(James Lerch) wrote:


Here's some pictures I took of my first run at an induction heater.
Not the greatest construction, but seems to work..

http://lerch.no-ip.com/atm/Projects/...er/page_01.htm
(First runs)

http://lerch.no-ip.com/atm/Projects/...ly/page_01.htm
(Heating Graphite)

The next step is to get this to work inside my vacuum chamber, and use
it to evaporate quartz.

BTW, I found this site to be very helpful during my design phase:

http://dave.golfbuddys.com/hvguy/


Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction, Testing, and Coating site)



Very impressive - what drive system are you using and what
do you use for tank capacitors?

Jim

I know nothing of the electronics end of induction heating but I know from a
casting point of view, I want one!!! Please here this as a loud voice saying;
What you are doing is really great, please work harder at finding a solution to
heating and melting a pound or so of iron!!!
Rick

I have no idea what this is:
http://home.comcast.net/~bobengelhardt/tube.jpg
but it looks like it would handle a couple of kw. Writing on it:
"Amperex
4 PR 125A"
and
"164A
5L804
9612"

There are 5 pins on the bottom and the top looks like a connection.
Looks like it was never used. I picked it up at the dump 'cause it
looked cool. :-)

You can have it for the postage.

Bob

Tim Williams wrote:

"Jon Elson" wrote in message
servers.com...


That's insane! Try some power FETs!



How 'bout IGBT's?...

IGBT's are great ar 20-25 KHz, but their appeal rapidly drops above that.
There are "ultra fast" version that can go a little higher, but I think
100 KHz
is totally out of range. Also, FETs are massively tolerant of overloads and
short-duration short circuits, while IGBTs are very INtolerant of those
conditions. (Don't ask me how I know that, but it involves parts of IGBTs
passing my head simultaneously on either side, and a noise that sounded like
a pistol shot indoors.)




They are ten times better than
tubes for this frequency range (50 - 100 KHz). You can get 600 V 30 A
transistors under $10. Want to compare the price with a 4CX250?



No, because I already have said tubes, curtesy of Mark Winlund.
Forgot to mention, I also have a dead printing arclight supply, 10kW.
Damage seemed to be on a contactor so I'm sure the 200/220/240 800V
transformer is still good, as well as the several chunky capacitors. If I
FWB that winding, I get 1200V at oh, 5A? Obviously I can't use too much of
that on a pair of 4CX250R's, so it'd be nice to have some beefier things.
If I go with a doubler, I've got 2.4kV. Anyone got a 2kW pentode on hand?



Running conservatively, you could get 4 KW out of such a transistor
(400 V, 10 A).



Unforunately, 600V is not only under the minimum output voltage (say I did
choke input filtering, and wow....what a nice choke that would have to
be....) but well under the peak voltage seen in such a circuit. Not sure
about 30A either, but in class C things come in short bursts, I've got to
imagine such a transistor would only be able to run +250VDC 5A... 1.25kW
ain't bad, but if I'm going to buy some parts I might as well get some that
can handle the whole thing.


You can get 1200 V and higher FETs, only a little more expensive. You
could definitely
go higher on the current and voltage. If you are running the FETs on
short pulses,
the usable current would go up, too. Also, the drive requirements could
be much
simpler, and you could probably have 12 V CMOS control circuits that
could shut it
off within microseconds if overloaded. I guess you could do all that
with tubes, too,
with only a little translation circuitry.

Jon

Bob Engelhardt wrote:

I have no idea what this is:
http://home.comcast.net/~bobengelhardt/tube.jpg
but it looks like it would handle a couple of kw. Writing on it:

I doubt it. Besides, real power tubes have carrying handles or maybe
even hoisting points.

-G

Bob Engelhardt wrote:

I have no idea what this is:
http://home.comcast.net/~bobengelhardt/tube.jpg
but it looks like it would handle a couple of kw. Writing on it:
"Amperex
4 PR 125A"


Nope, 125 W in class A, maybe twice that, max, in class C. The 125
is the wattage.

Jon

Bob Engelhardt wrote:

I have no idea what this is:
http://home.comcast.net/~bobengelhardt/tube.jpg
but it looks like it would handle a couple of kw. Writing on it:
"Amperex
4 PR 125A"
and
"164A
5L804
9612"

There are 5 pins on the bottom and the top looks like a connection.
Looks like it was never used. I picked it up at the dump 'cause it
looked cool. :-)

You can have it for the postage.

Bob


It is a Pulse Rated tetrode vacuum tube that has a rated plate
dissipation of 125 Watts

Bill K7NOM

Greg wrote:
Bob Engelhardt wrote:

I have no idea what this is:
http://home.comcast.net/~bobengelhardt/tube.jpg
but it looks like it would handle a couple of kw. Writing on it:


I doubt it. Besides, real power tubes have carrying handles or maybe
even hoisting points.

And water connections.

On Fri, 27 Aug 2004 03:14:03 -0500, "Tim Williams"
wrote:

"Jon Elson" wrote in message
servers.com...
That's insane! Try some power FETs!

How 'bout IGBT's?...

They are ten times better than
tubes for this frequency range (50 - 100 KHz). You can get 600 V 30 A
transistors under $10. Want to compare the price with a 4CX250?

No, because I already have said tubes, curtesy of Mark Winlund.
Forgot to mention, I also have a dead printing arclight supply, 10kW.
Damage seemed to be on a contactor so I'm sure the 200/220/240 800V
transformer is still good, as well as the several chunky capacitors. If I
FWB that winding, I get 1200V at oh, 5A? Obviously I can't use too much of
that on a pair of 4CX250R's, so it'd be nice to have some beefier things.
If I go with a doubler, I've got 2.4kV. Anyone got a 2kW pentode on hand?

Running conservatively, you could get 4 KW out of such a transistor
(400 V, 10 A).

Unforunately, 600V is not only under the minimum output voltage (say I did
choke input filtering, and wow....what a nice choke that would have to
be....) but well under the peak voltage seen in such a circuit. Not sure
about 30A either, but in class C things come in short bursts, I've got to
imagine such a transistor would only be able to run +250VDC 5A... 1.25kW
ain't bad, but if I'm going to buy some parts I might as well get some that
can handle the whole thing.

As soon as I install a 240V circuit...

Tim
IIRC many years ago (mid '50s) Life magazine had an article about
induction heating of exotic allows, I would assume this would occur in
a specialized atmosphere. I seem to remember pictures of a sphere of
molten metal suspended in the field created by two water cooled coils.
Does anyone recall this article? I did save the magazine at the time,
but as "they" say "three moves is equivalent to a major fire" and I
have moved at least twelve times since then.
Gerry :-)}
London, Canada

James Lerch writes:

http://lerch.no-ip.com/atm/Projects/...er/page_01.htm

Is that a Sony camera making that purple fringe in the photos?

In article ,
"Tim Williams" wrote:

I seem to remember pictures of a sphere of
molten metal suspended in the field created by two water cooled coils.
Does anyone recall this article?

No, but I've seen it before. You put two short solenoid coils a small
distance away; the magnetic field inbetween them has a high uniformity. Put
some conductive object in the middle and you've got a levitator! Since it
has to carry AC, it helps for said object to be low resistance
(aluminum/copper/silver) so it makes a nice BEMF. A few more tesla of field
and you can levitate nonconductive (diamagnetic) things like frogs!


Yeah, but can you induction-heat the frogs? And will the field
successfully contain the results of that heating?

--
B.B. --I am not a goat! thegoat4 at airmail.net

Bob Engelhardt wrote:

I have no idea what this is:
http://home.comcast.net/~bobengelhardt/tube.jpg
but it looks like it would handle a couple of kw. Writing on it:
"Amperex
4 PR 125A"
and
"164A
5L804
9612"

There are 5 pins on the bottom and the top looks like a connection.
Looks like it was never used. I picked it up at the dump 'cause it
looked cool. :-)

You can have it for the postage.

Bob
I'll have to dig out some Acorn and RF Transmitter tubes :-)
They are cone shaped and are silver plated ceramic...

Klystrons and the like :-) just in case I need to build a Radar trap!

Martin

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

Greg wrote:

Bob Engelhardt wrote:

I have no idea what this is:
http://home.comcast.net/~bobengelhardt/tube.jpg
but it looks like it would handle a couple of kw. Writing on it:


I doubt it. Besides, real power tubes have carrying handles or maybe
even hoisting points.

-G
The big ones have SS bolt covers that a man can climb in to work!

Raytheon makes some really big tubes for transmitting.

Martin

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

On Sat, 28 Aug 2004 07:48:39 +0800, David R Brooks
wrote:
Bob Engelhardt wrote:

:I have no idea what this is:
:http://home.comcast.net/~bobengelhardt/tube.jpg
:but it looks like it would handle a couple of kw. Writing on it:
:"Amperex
:4 PR 125A"

It's a tetrode, with anode dissipation 125W. Given a Class-C stage has
a best efficiency of 66%, that means you could get 300W max. from it.

I guessed that much - but what's the useful operating frequency
range, and how much power does the driver stage need to push it?
Enquiring minds want to know... ;-)

(Not that I know someone who used to get annoyed at being talked
over, warm up a 10KW amp on 11M CB, and calmly continue the
conversation where they left off...) :-0

Oh, and is it one of the ones that requires a special socket and
glass airflow chimney, or other expensive bits? Even if the tube is
free, buying the socket for it might kill the deal.

-- Bruce --
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

On Fri, 27 Aug 2004 17:40:16 -0400, Bob Engelhardt wrote:
I have no idea what this is:
http://home.comcast.net/~bobengelhardt/tube.jpg
but it looks like it would handle a couple of kw. Writing on it:
"Amperex
4 PR 125A"

That's a 125 watt plate dissipation tube. Half that of the
4CX250s Tim already has. Max rating operated Class C
is 4 kV at 65 mA, in other words, 260 watts plate input
power, about 170 watts output power. We used to use
the 4-125A as a low level driver in our transmitters.

Gary

Gary Coffman wrote:

Bob Engelhardt wrote: ...
4 PR 125A"

... about 170 watts output power. ...

Wow! This big thing will only drive a couple of light bulbs?! Thanks
goodness for transistors. Bob

Very impressive - what drive system are you using and what
do you use for tank capacitors?

Jim

Jim,

I'm using a TL494 for the frequency and duty cycle generator. The
output of the frequency generator feeds a pair of Mosfet gate drive
chips, thru a 1:1 transformer to the gates on the 4 corners of the
h-bridge.

My first experiments didn't use tank capacitors, but I found I HAD to
have them to heat the graphite efficiently. Currently I'm using 12x
0.1mf caps in parallel as the tack capacitor, but this is a problem.
The capacitors can't handle the REALLY HIGH ripple current (100 amps
or more?) and I keep melting the legs off.

I'm currently on the hunt for a nice water cooled 2mf cap, but not
having much luck. Most of the ones I'm finding or for high voltage,
not high ripple current.


Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction, Testing, and Coating site)

Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent.
Calvin Coolidge

On Fri, 27 Aug 2004 16:27:03 -0500, "Tim Williams"
wrote:

"James Lerch" wrote in message
. ..
Here's some pictures I took of my first run at an induction heater.
Not the greatest construction, but seems to work..

What's the deal, I don't see a capacitor... just going on transformer
action?

The first runs heating the poor allen wrench didn't use a tank
capacitor. When I moved onto the graphite they became really
important. Current problem is I'm melting the legs off the
capacitors!

http://lerch.no-ip.com/atm/Projects/...er/page_01.htm
(First runs)

http://lerch.no-ip.com/atm/Projects/...ly/page_01.htm
(Heating Graphite)

Neato! How much power and what dimensions are the load?

II'm pulling 10amps @ 24vdc from my power source during the graphite
heating experiments. The graphite is 1/2" in diameter and 1 1/2" in
length. Takes about 7 seconds to bring it up to orange heat while
running at 150mhz.

H-bridge circuit?

Yup, 3x paralleled IRFZ44 mosfets at each corner of the bridge



Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction, Testing, and Coating site)

Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent.
Calvin Coolidge

On Fri, 27 Aug 2004 21:02:49 -0500, Richard J Kinch
wrote:

James Lerch writes:

http://lerch.no-ip.com/atm/Projects/...er/page_01.htm

Is that a Sony camera making that purple fringe in the photos?

LOL, yes it is. Sony DSC-F707.

For the most part I'm real happy with the camera. Zero problems in
the last two years & 6k+ images. (other than occasional chromatic
error you observed while at fast F/Ratio near field imaging)
Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction, Testing, and Coating site)

Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent.
Calvin Coolidge

James Lerch writes:

Is that a Sony camera making that purple fringe in the photos?

LOL, yes it is. Sony DSC-F707.

For the most part I'm real happy with the camera.

Yeah, I have that one and the F828 too, which exhibits the problem to a
greater degree. Wonderful instruments other than that oddity.

On Sat, 28 Aug 2004 15:51:42 GMT,
(James Lerch) wrote:


Very impressive - what drive system are you using and what
do you use for tank capacitors?

Jim

Jim,

I'm using a TL494 for the frequency and duty cycle generator. The
output of the frequency generator feeds a pair of Mosfet gate drive
chips, thru a 1:1 transformer to the gates on the 4 corners of the
h-bridge.

My first experiments didn't use tank capacitors, but I found I HAD to
have them to heat the graphite efficiently. Currently I'm using 12x
0.1mf caps in parallel as the tack capacitor, but this is a problem.
The capacitors can't handle the REALLY HIGH ripple current (100 amps
or more?) and I keep melting the legs off.

I'm currently on the hunt for a nice water cooled 2mf cap, but not
having much luck. Most of the ones I'm finding or for high voltage,
not high ripple current.


Take Care,
James Lerch


Sounds pretty good but I'd follow your present
route and use multiple paralleled small capacitors - the
extra surface area is useful and, if you're using extended
foil capacitors, a fin on each leadout wire helps to get rid
of the heat.

I expect you've already researched this but the breed of
extended foil polypropylene capacitors used for snubber duty
is ideal for this duty. The extended foil results in a much
lower series R than with metallised film, and the loss
tangent of polypropylene is less than 1/10th of that of
polyester or polycarbonate.

Have a look at
http://www.wima.com/product.htm
http://www.wima.com/navig/menue/prsu...hcr/forhcr.htm

They're a European outfit but I think Intertechnical Group
inc is a USA stockist.

Jim,

In article ,
James Lerch wrote:

Currently I'm using 12x
0.1mf caps in parallel as the tack capacitor,

[ ... ]

I'm currently on the hunt for a nice water cooled 2mf cap, but not
having much luck. Most of the ones I'm finding or for high voltage,
not high ripple current.

Am I reading this correctly? You're looking for two
*milli*-Farad capacitors? (0.002 Farad or 2000 uF (micro-Farad)?
(Granted, back in the old days, 'm' was used as an abbreviation for
"micro", but that got dropped about the time that they started calling
the really small ones 1.0 pF instead of 1.0 uuF).

Normally, I ignore spelling in postings, but when it can change
the meaning, I have to ask.

For large capacitors made for both high voltage and high
current, check out Maxwell Labs (if they are still around). They made
the caps which we used to use for high-speed flash discharge to pump
Nd-YaG lasers. They were probably not cheap -- but since I never had to
buy them myself, I don't know what they cost. :-)

Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 28 Aug 2004 18:27:56 -0400, (DoN. Nichols)
wrote:

In article ,

James Lerch wrote:

I'm currently on the hunt for a nice water cooled 2mf cap, but not
having much luck. Most of the ones I'm finding or for high voltage,
not high ripple current.



Am I reading this correctly? You're looking for two
*milli*-Farad capacitors? (0.002 Farad or 2000 uF (micro-Farad)?
(Granted, back in the old days, 'm' was used as an abbreviation for
"micro", but that got dropped about the time that they started calling

Yes, no, maybe... ahhh dang it

(after some research, I say) YES.... 2000uf or 0.002 Farad.

This is almost as bad as measuring air pressure.. PSI / ATMs / Torr /
mmMg / Pascals and a few I probably don't even know about yet... :0


Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction, Testing, and Coating site)

Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent.
Calvin Coolidge

On Sat, 28 Aug 2004 07:38:59 -0400, Bob Engelhardt wrote:
Gary Coffman wrote:

Bob Engelhardt wrote: ...
4 PR 125A"

... about 170 watts output power. ...

Wow! This big thing will only drive a couple of light bulbs?! Thanks
goodness for transistors. Bob

Glass envelope tubes are generally much bigger than ceramic
envelope tubes of the same power rating (especially the ones
without heaters which we call transistors). That's because they
needed to keep envelope temperature below 400 degrees, but
the cathode had to be at 2300 degrees.

Back in the day, the 4-125A worked at 200 MHz when transistors
were straining to do milliwatts at 1 MHz. Of course that's all changed
now. About the only place for tubes today is when you *have* to
deal with very high voltages. Otherwise, transistors are preferred.

Gary

"James Lerch" wrote in message
...
On 28 Aug 2004 18:27:56 -0400, (DoN. Nichols)
wrote:

In article ,

James Lerch wrote:

I'm currently on the hunt for a nice water cooled 2mf cap, but not
having much luck. Most of the ones I'm finding or for high voltage,
not high ripple current.



Am I reading this correctly? You're looking for two
*milli*-Farad capacitors? (0.002 Farad or 2000 uF (micro-Farad)?
(Granted, back in the old days, 'm' was used as an abbreviation for
"micro", but that got dropped about the time that they started calling

Yes, no, maybe... ahhh dang it

(after some research, I say) YES.... 2000uf or 0.002 Farad.

This is almost as bad as measuring air pressure.. PSI / ATMs / Torr /
mmMg / Pascals and a few I probably don't even know about yet... :0


Millimetres of magnesium????? Surely that's mmHg ;-)
Martin

--
martindot herewhybrowat herentlworlddot herecom

On Sun, 29 Aug 2004 02:27:33 GMT, "Martin Whybrow"
wrote:


"James Lerch" wrote in message

This is almost as bad as measuring air pressure.. PSI / ATMs / Torr /
mmMg / Pascals and a few I probably don't even know about yet... :0


Millimetres of magnesium????? Surely that's mmHg ;-)
Martin

LOL.

Yea, what Martin wrote!


Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction, Testing, and Coating site)

Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent.
Calvin Coolidge

On Sun, 29 Aug 2004 02:44:25 -0500, "Tim Williams" wrote:
"Gary Coffman" wrote in message
.. .
Back in the day, the 4-125A worked at 200 MHz when transistors
were straining to do milliwatts at 1 MHz. Of course that's all changed
now. About the only place for tubes today is when you *have* to
deal with very high voltages. Otherwise, transistors are preferred.

They still find a niche in FM and TV transmitters, although I don't know
what kind of proportions are used right now. Also still popular with HAMs.

There hasn't been a new FM or VHF TV transmitter built using tubes in
the last 10 years. Those markets are all solid state today.

UHF TV transmitters mainly still use depressed collector klystrons or
klystrodes, though transistors are starting to invade that market too.

Hams do use tube amps, though more and more are switching to solid
state amps.

Certainly, with the transformer I have, I need tubes... unless someone can
dig up a 2.5kV FET.

Yep.

Gary

In article ,
says...

I expect you've already researched this but the breed of
extended foil polypropylene capacitors used for snubber duty
is ideal for this duty. The extended foil results in a much
lower series R than with metallised film, and the loss
tangent of polypropylene is less than 1/10th of that of
polyester or polycarbonate.

Have a look at
http://www.wima.com/product.htm
http://www.wima.com/navig/menue/prsu...hcr/forhcr.htm

They're a European outfit but I think Intertechnical Group
inc is a USA stockist.


The Wima capacitors are good stuff. I use them a great deal here
at work.

Jim


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

James Lerch wrote:

The first runs heating the poor allen wrench didn't use a tank
capacitor. When I moved onto the graphite they became really
important. Current problem is I'm melting the legs off the
capacitors!

You need RF rated capacitors, or at least very low ESR types. They
are available, but they cost quite a bit more.


II'm pulling 10amps @ 24vdc from my power source during the graphite
heating experiments. The graphite is 1/2" in diameter and 1 1/2" in
length. Takes about 7 seconds to bring it up to orange heat while
running at 150mhz.
I'm assuming you mean 150 KHz.

Jon

James Lerch wrote:
On 28 Aug 2004 18:27:56 -0400, (DoN. Nichols)
wrote:


In article ,


James Lerch wrote:


I'm currently on the hunt for a nice water cooled 2mf cap, but not
having much luck. Most of the ones I'm finding or for high voltage,
not high ripple current.



Am I reading this correctly? You're looking for two
*milli*-Farad capacitors? (0.002 Farad or 2000 uF (micro-Farad)?
(Granted, back in the old days, 'm' was used as an abbreviation for
"micro", but that got dropped about the time that they started calling


Yes, no, maybe... ahhh dang it

(after some research, I say) YES.... 2000uf or 0.002 Farad.

This can't possibly be right! 2000 uF as a parallel resonator (tank)
capacitor? For 25 - 100 KHz? It sounds way too high! Or, is this
in the DC power supply? If you are burning up the caps on the DC
supply side of the power transistors, it is because you have "shoot
through" currents. That is where both the power transistors in each
half bridge are turned on at the same time. The currents could be a
pulse of 10 - 50 nS width and thousands of amps!

You need a MUCH better circuit to control "dead time" between the
two transistors. I use a pair of IR2113 FET gate drivers, and use
a resistor-capacitor circuit at the input of the driver to delay
the turn-on signal. I put a doide across the resistor to make the
turn-off transition faster than the turn-on. (In my particular designs
for servo amplifiers, I use 3.3 K Ohms and 100 pF, and get about 100 nS
delay between the turn off of one transistor and the turn on of the
other. It works really well.)

Jon

On Sat, 28 Aug 2004 15:51:42 GMT,
(James Lerch) wrote:


I'm currently on the hunt for a nice water cooled 2mf cap, but not
having much luck. Most of the ones I'm finding or for high voltage,
not high ripple current.

Polypropylene capacitors like Sprague 715P "orange drop" handle high
ripple current better than most. From their literatu

"Type 715P capacitors are ideal for applications where high AC current
flow is found...."

http://www.vishay.com/docs/42018/715p.pdf

Use the higher voltage caps. Those rated for higher voltage also
can handle higher current due to the larger physical size and ability
to dissipate heat. I've run these at several amps each at about 35
KHz. They're not expensive.

Jon Elson wrote in message rvers.com...

This can't possibly be right!

Perhaps I've found something new :0 (Yea, I know better, aint gonna
happen!)

2000 uF as a parallel resonator (tank) capacitor?

Yes, and more.. Last run had 10x 0.47uF caps in parallel, also wired
in parallel with the induction coil. For specs on the caps goto
www.digikey.com and search for part number 495-1396

For 25 - 100 KHz?

actually the induction coil was running at just under 150KHz, 80v p-p,
with a very attractive sinusoidal shape.

It sounds way too high!

It might be, but I imagine the induction coil has rather low induction
value as its only 8 turns of copper wire around a graphite core... I
just kept adding capacitors and watched the resonant freq drop until I
got it down below 150KHz. Seemed like the right thing to do

Or, is this
in the DC power supply? If you are burning up the caps on the DC
supply side of the power transistors, it is because you have "shoot
through" currents. That is where both the power transistors in each
half bridge are turned on at the same time. The currents could be a
pulse of 10 - 50 nS width and thousands of amps!

Nope, my DC source for the H-Bridge is JUST two 17Ah 12vdc batteries
in series for 24vdc. (plus two 6 amp battery chargers to try and
recharge between runs.)

You need a MUCH better circuit to control "dead time" between the
two transistors.

The TL494 frequency generator already takes care of the dead time
between pulses. In addition the mosfets in the H-Bridge don't really
get all that hot. Especially now that I have the Tank capacitors
added in parallel to the induction coil AND I set the frequency
generator to match the resonance of the IC tank circuit.

In the end, who knows. My approach to electronic design is along the
lines of "Playing with Legos (tm)" While I have some official
training in electronics thanks to the military, it was a LONG time
ago!

One thing I worry about is my H-Bridge mosfets are rated for 60Vdc
max. I use a 24VDc source, but I measure 80v Peak to Peak across the
inductor - capacitor tank circuit that is being DRIVEN by the
H-Bridge. Will this 80vpp damage my Mosfets? (Hasn't yet...)

Take Care,
James Lerch

Jon Elson wrote in message news:c79f0$4132b9f3
I'm assuming you mean 150 KHz.

(Sigh) Yes indeed, I meant 150Khz...

I think I have found a problem with my computer's keyboard actuator.
I believe the problem is somewhere between the keyboard and the
computer chair... Unfortunatly, I'm still working on a fix...


Jon

I have three, small, older induction heating power supplies available.
$500./ea or $1000. for all three. Located in Costa Mesa, CA and not
guaranteed except to be all there. Call me at (949) 645-7601 if
interested. Leigh at MarMachine

In article ,
James Lerch wrote:
Jon Elson wrote in message rvers.com...

This can't possibly be right!

Perhaps I've found something new :0 (Yea, I know better, aint gonna
happen!)

2000 uF as a parallel resonator (tank) capacitor?

Yes, and more.. Last run had 10x 0.47uF caps in parallel, also wired
in parallel with the induction coil. For specs on the caps goto
www.digikey.com and search for part number 495-1396

That's not even *near* 2000 uF -- that's only 4.7 uF. Now,
we're back to more reasonable values. :-)

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

James Lerch wrote:

I think I have found a problem with my computer's keyboard actuator.
I believe the problem is somewhere between the keyboard and the
computer chair... Unfortunatly, I'm still working on a fix...

When you find it, please pass it on. I frequently have the same
problem. :-)

Ted