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rp181

Tue Aug 19 2008, 09:01PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529

I got my E core today, i have some questions on how to wind it:
Should i put the primary under or over the secondary, or should i put it next to, like a MOT.

If i were to drive it with a half bridge IGBT, i would not use a gap, right?
How tightly do the cores need to be pressed together?

Thanks =)

BTW, its a iron powder core, will this change anything?

Dr. Dark Current

Tue Aug 19 2008, 09:33PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Will the output be a voltage source or a current source (capacitor charging, arc drawing, Tesla coil)?
If it's for a current source, you'll have to limit the current anyways (by external inductor) so the extra leakage by putting the primary next to secondary does not matter, the plus is that you can rewind the primary in future if it has bad turns/wire thickness.
You can put it under the secondary too but this way it will be fixed and unmodifiable in the future.

For a voltage source it should be put under the secondary, or even better, 1/2 primary, secondary and the other 1/2 primary for the lowest leakage. This is hard to do with HV transformers though.

Edit- if it is iron core, it will probably be too lossy above ~100-200hz.

Another hint to the winding tecnique, the best would probably to wind a primary in the center of the E core and two centertapped secondaries on the sides.

rp181

Wed Aug 20 2008, 12:03AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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so i want frequency to be less that 200hz? On wikipedia, it says 10's of khz.

This is for cap charging,arc drawing, and possibly marx gen.

EDIT: heres a pic of the core and 2 bobbins.

EDIT #2: Do you think the core can handel atleast 2000watts? wanna make a welder with 1 of the bobbins.

Yet another EDIT: i found this on the site:

look under the losses chart under 200C, this core is the -66 alloy.

So the best frequency would be 100khz-500khz

Dr. Dark Current

Wed Aug 20 2008, 06:36AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

I thought you said its iron core!
Well that changes things a bit, if its ferrite then of course you can certainly run it at tens of kHz. The center "leg" seems to be around 1"x1", does that sound right? If so, I think it'll be usable to 1-2kVA for low voltage transformer, but much less for HV one because you must count in all the insulation (interlayer and winding-to-core).
I think you'll have difictuttly winding anything over 6kV on that core, what is the planned HV output?

rp181

Wed Aug 20 2008, 12:21PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

50kv =/
the website says Iron powder core, and so does the sheet that came with the package. The center leg is 1 3/8" square. for insulation of the layes, i was going to use 10 mill teflon,that should stand 10kv (on mcmaster, it says .001 can withstand atleast 500v). Icould also put it uner oil, but i have no meansto vacume it

Dr. Dark Current

Wed Aug 20 2008, 12:29PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

rp181 wrote ...

50kv =/
the website says Iron powder core, and so does the sheet that came with the package.

OOPS! Iron powder core is used to make chokes, not power transformers!

Fraggle

Wed Aug 20 2008, 04:29PM

Registered Member #1526 Joined: Mon Jun 09 2008, 12:56AM
Location: UK
Posts: 216

I`m curious as to why it wouldn`t work though. Why is that?

I`d have thought it would be better than a laminated core even.

Dr. Dark Current

Wed Aug 20 2008, 04:55PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Fraggle wrote ...

I`m curious as to why it wouldn`t work though. Why is that?

Because it has low permeability (I hope this is the right word) so it requires a lot of magnetization current, which increases no-load losses in both switching transistors and primary winding. How much I have no idea, but it is frequency dependent.

Fraggle

Wed Aug 20 2008, 05:58PM

Registered Member #1526 Joined: Mon Jun 09 2008, 12:56AM
Location: UK
Posts: 216

Thanks :o)

Steve Ward

Wed Aug 20 2008, 08:43PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

The low permeability is caused by the inherent "distributed air gap" that powdered iron exhibits. It would basically be like making a transformer with lots of air gaps in the core, would offer very poor coupling.

BTW, 50kV straight out of a transformer that size is basically impossible.

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