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Have Question, Need help... Ferrite volume.......

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Patrick

Wed Oct 28 2009, 10:39PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Hey All,

I have been looking on the internet in general , and TI/Unitrode but am uncertain as to what power ferrite can handle before saturation.
Does power vary with core leg surface area, or total volume of magnetic material? (given all other conditons are the same)

And, what about the larger ferrites i can buy $$$ like Marco Denicolai's seen below. (Approx 120mm square!!!

)

The reason you ask, My PhD thesis may require 10-100KW+

(Experimental devolpement of electrostatic lifters)
My current best is a 900W to 1KW SMPS.

EDIT adding new info: Mag-Inc.com has the 0P49928EC core which is an E type Quite big and tech notes i am and reading now.

Ty all,
-Patrick

Steve Conner

Wed Oct 28 2009, 11:40PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The power handling capacity of ferrite cores is limited by heating from core losses, not saturation. If you don't understand the difference, better learn before you try making that 100kW SMPS! :P

Metglas make some truly enormous cores, I believe they're used in pulse transformers to drive particle accelerators and the like.

Patrick

Wed Oct 28 2009, 11:44PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Yes, Steve MCconner, I dont want to die in a firey burst of plasma at 100Kw, thats why I ask several years before construction starts

Oooo!.... the Metglas website is useful.

Dr. Slack

Thu Oct 29 2009, 12:39PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Is volume of the overall power supply a problem? If not, you may want to consider an air-core design, especially as you have a couple of years to come up with the goods. The design would start as a DRSSTC, but with a much lower target voltage for the secondary. The point about air is that it is a lot cheaper, lower loss and unlike ferrite has accurately known magnetic and electrical parameters - but - it would be bigger. I've seen examples of aircraft radar supplies that use this principle - using a conical secondary so that clearences increase just where needed. As it's not intended to create streamers, they won't alter the secondary tuning, so that's easier than a TC. A large discrete capacitance on the secondary would be benefical to keep the frequency down, both for driving as well as for rectification efficiency.

Just a thought, please ignore if your heart's set on ferrite.

Patrick

Thu Oct 29 2009, 05:55PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Hmm ... i dont know about an air core SMPS, it wont be a DRSSTC , I also Need high power density, so ferrite maybe the only option.
I would need a much higher frequency too. like 1Mhz+(aircore) instead of 30-80Khz.(ferrite) how much power density
(kW per cubic meter) could i expect from a well made air inductor? I am also considering a "bank winding" technique as seen elsewhere on the forum. Radiative magnetic fields would be a concern too, many kW potentially coupled far away to delicate circuits.

Ty DR.slack
-Patrick

Sulaiman

Thu Oct 29 2009, 07:23PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

For a lifter you need a very high dc voltage ... how high in your case?

You will probably have to build the secondary in several segments with a diode for each, in effect you will be stacking several dc voltages.

I'd start with the diodes !
.. see what voltage and current rating FAST diodes you can purchase economically,
then design each secondary for the diodes.

Then there is output current limiting, typically a series resistance (ballast),
if you don't have a 'ballast' resistor the first flashover will kill your eht diodes and probably the electronics driving the primary.

The power transistors for 100 kW will also be non-trivial,
maybe you should consider a modular approach - several inverters in parallel.
This would allow (relatively) simple development of a medium power unit,
far less expensive when prototypes fail !

You could then phase them to operate sequentially to reduce output voltage ripple and primary current ripple = smaller HV DC BUS capacitance.

Ferrite (or iron powder etc.) cores need to dissipate heat, for a given flux density and frequency the core loss (mW/cm3) can be determined.
A transformer will generate heat proportional to volume and dissipate it proportional to surface area ... hence several smaller units are easier to cool.

Just a few ideas to mull over ......

Patrick

Thu Oct 29 2009, 07:54PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Yep suiliman,

I am using a modular approach, your point about core volume and core SA is taken well, any way...

first, i built my PFC 1kW section with inductor + Transforemer.
then, Segmented 1kW (i hope) ferrites from Fair-Rite Corp. 50kv transformers i wind myself
next, my diodes may be the HER108 1KV type Super-dooper fast.(though i would rather not have any components on the high side)
Finnaly, it works like this...[1kW pfc @200 vdc -> 1kW boost txfmr @ 500vdc -> High voltage txfmr 50kv -> lifter device]

soooo, each secotion can be operated synchronously Parallel

...[1kW pfc @200 vdc -> 1kW boost txfmr @ 500vdc -> High voltage txfmr 50kv -> lifter device] 1kW
...[1kW pfc @200 vdc -> 1kW boost txfmr @ 500vdc -> High voltage txfmr 50kv -> lifter device] 2kW
...[1kW pfc @200 vdc -> 1kW boost txfmr @ 500vdc -> High voltage txfmr 50kv -> lifter device] 3kW etc......

but right now i am happy with 1-4kW, besides 100 modules @ 1kW is a lot i was thinking of 5kW modules ...
so 20 modules x 5kW =100kW, but am 2 years away from needing 100kW.

I need to master 1-2kw's first

(because of $$$ and i don't want to have my body parts exploded all over the place...)

TY
-Patrick

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