inductor problem

I tried two of the 1010VS-141 parts in series to get about 300 nH (we have a nice sample kit) but they also got real hot at well below my target pulse rate. Again, skin effect apparently wrecks the current capability. If I change the PCB, I could maybe use four or six of them, and maybe cool them from below with gap-pads to my baseplate.

Putting these air-core resistors over my PCB ground plane is another interesting complication. The mag fields may be heating the board. Gotta investigate that.

I still don't know if some core material might help. I've requested some powder toroids from Micro-metals, and I guess I'll buy an assortment of ferrite-core inductors from Mouser.

Nobody seems to publish current-vs-frequency specs for their inductors.

Maybe a milliohm-range axial-lead vitreous-enameled power resistor would have the right inductance, but that would be hard to find. I could let that just get hot.

Fortunately, my customer is slow getting his gear together, and we can demo at a low pulse rate and hand-wave about the next spin.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin
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Silver oxide is a conductor, so if you keep sulphur out of the box, the conductivity holds up better over time. Silver-plated connections also exhibit lower transient intermodulation at high powers. (Nickel plating is a disaster for that.)

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Phil Hobbs

In this application even at low frequencies only as a space heater or for defrosting purposes :-)

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I remember when we built our big fat shortwave power amplifiers for ham radio one of the most important items on the shopping list was metal polishing paste. For that reason. If you let the coil in the Pi-filter or the matchbox become too dirty someone might comment "Where does that amperage smell come from?".

Still using it and this is IMHO the best stuff for the job:

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Skol!

Currently enjoying a homebrew Autumns Amber Ale. Yes, I know it's only lunch time but it's Saturday and only half a stein.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

If your liver starts to suffer you'll have to go back to full-time engineering, though. ;)

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

Why not try a copper strip about 2cm wide and 0.25 mm thick? with paper isolation? Might be better for reducing skin effect problems, and can carry lots of current.

Reply to
Sjouke Burry

30MHz is tough. I remember that inductors in ham radio amps occasionally unsoldered themselves when operating in the 10m band (which is 28-30MHz). Every few months I polished the Pi-filter coil in my amp with Wenol paste which lowered the operating temperature. For a while.

You need to notch out all planes underneath if they sit close to the PCB surface.

It will help if they make the resulting fewer turns from wider material. Otherwise not.

I know, and that has tripped me up a few times. It's usually trial and error, especially when trying to gauge core losses.

It's the same with a copper coil. As long as there is no lacquer on the copper it can be run hot as long as it won't give the PCB a tan or unsolder itself. With lacquer that's a different story and depends on what kind they used. Could give off a stench.

If you could free up some real estate in that area of the board that would greatly help.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

No kidding, that was my concern when my ALT values kept being too high. However, months of total abstinence and diet changes did absolutely nothing. What the heck? Then I started bicycling again just to stay in shape. Bingo ... ALT value in the middle of the normal range. So ... I could happily brew now.

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Regards, Joerg 

http://www.analogconsultants.com/
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Joerg

Check out this series, they are for operation at high frequencies:

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Regards, Joerg 

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Joerg

It feels like I'm backing up against something fundamental here, how much copper it will take to do the job. I've wound several coils myself, and all of them behave a lot like the various Coilcraft combinations that I've tried. Either I need to add a core to store more energy with less copper, or I just need a lot more PCB area to pave over with more coils.

Or I need to push the copper and get the heat out somehow.

The 1010VS is a good candidate for heat sinking.

I'm already using a TO-220 size aluminum nitride insulator for one fet. The difference in cooling is amazing. I've got three quotes so far: $25 each, $5 each, and 80 cents from China.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin

It's a rather small difference, and remarkably hard to measure.

That kind of precision resistance measurement is the sort of thing that national bureaus of standards do with ratio transformers.

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Bill Sloman, Sydney
Reply to
bill.sloman

At some point you might want to push some numbers around. Maybe you need to try some 12 gauge house wire. I've seen coils made from copper tubing.

George H.

Reply to
George Herold

I don't have room to wind the coil from 12 gage. And even a 12g coil is going to get hot.

I think the real problem is that I have to get rid of a lot of heat from the inductor(s).

The Coilcraft 1010VS is a lot of copper

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but two of them in series get pretty hot at 1 MHz pulse rate... and I want to go to 4.

I need to somehow figure out how much heat these inductors are dissipating per MHz pulse rate, so I can do approximate thermal calculations. And find a way to conduct the heat away.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin

Is there room for a small fan? It doesn't have to be on the pcb itself.

Reply to
Pimpom

No room for a fan; the small inductors would need a hurricane of air to keep them cool. But the aluminum baseplate will be water cooled.

I can use vias to move heat from the surface-mount inductor pads to the bottom of the board, to copper pours on the bottom. Then conduct the heat to the baseplate through a thermally conductive insulator. Silicone gap-pads might work, and aluminum nitride would almost surely work but is expensive and harder to get.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin

Clearly you need high temperature superconducting tape formed into your inductors. You'll have to keep in a bath of liquid nitrogen to keep them suoer-conductive, but liquid nitrogen is as cheap as milk per litre.

Problem solved. Jan Panteltje may want a royalty, but the idea of using high temperature superconductors for low loss inductive elements has been around for a while.

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Bill Sloman, Sydney
Reply to
bill.sloman

What about coil dimensions. Those Coilcraft coils seem to have low Q or higher losses. Coil dimensions and winding pitch have an effect on losses. That is inductance/wire lenght

Reply to
LM

Right.

There is no such thing as a small high-power HF coil. You do need the space to keep the losses down. The old ham rule of thumb is a spacing of half the coil diameter from anything conductive.

--

-TV
Reply to
Tauno Voipio

to try some 12 gauge house wire. I've seen coils made from copper tubing.

Not sure if this idea is practical or not. But you could wind a coil out o f aluminum and then plate the aluminum coil with copper. And then remove t he aluminum using Lye. And make a heat pipe or pump water through the holl ow copper. You would probably have to start with aluminum tubing so the ly e solution could be circulated thru the coil. Other wise it would take for ever to disolve the aluminum.

This probably sounds like an impossible task. But Varian made grids for TW T's this way. Starting with electroplating copper onto aluminum wire. The n putting sections of the wire into copper pipe and swaging the pipe to col d weld the copper together. Then twisting the pipe to the same spiral as t he electron beam would have. Then slicing the pipe into wafers and etching out the aluminum. The result was copper grids.

Since Varian is just down the street ( more or less ) Maybe you could con vince them that they should get into making hollow copper coils.

Dan

Dan

Reply to
dcaster

maybe you could use the mag field in the coil to turn a rotor :) But not at 30MHz.

Flat copper or parallelled smaller gauge would get more sa per xsa of course.

NT

Reply to
tabbypurr

Maybe you could wind some skinny hardline coax and use the shield? Clean it, then spray or plate it to prevent oxidation? Or use some #12 bare Cu?

I got Q's over 300 @ 900MHz from bare copper tubing (1/4" IIRC) in a "helical" resonator (mine was straight, not wound). I was going to silver plate my resonator until I realized that silver just wasn't that much better than copper. There's only ~5% difference in the clean metals.

But count me with Phil. Your tin-plating is very unhelpful--less conductive than copper by a factor of six, and located exactly where you need it least.

A fatter bare copper wire would be a big step in the right direction.

Cheers, James Arthur

Reply to
dagmargoodboat

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