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Topload, effects on efficiency

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Linas

Thu Jul 24 2014, 08:58PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

Hello, since i am redesigning my top-load, one thing does not make sense. Basically, toroid is short turn on top of coil, so it will degrade performance of last secondary windings.

Does any one investigate this ? One simple solution will be to make toroid with a slot, other is to make topload from tube, by winding it on isolator, like this this

Dr. Dark Current

Thu Jul 24 2014, 11:53PM

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

Yes the topload will divert the magnetic field and cause less induced voltage on the top turns. However from my findings the difference is not that big. Losses in the topload can be a problem with high powers/duty cycles. Making the topload as an incomplete turn could be a good solution but avoid sharp edges which could cause an unwanted break out.

Dago

Fri Jul 25 2014, 05:44AM

Registered Member #538 Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181

I would assume the coupling from the primary to near the toroid will be near non-existent so the effect is very small.

Steve Conner

Fri Jul 25 2014, 07:06AM

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

If the toroid is made out of aluminium, that is a highly conductive metal, so instead of absorbing the magnetic energy it will reflect it. The inductance of the secondary will be reduced slightly, but the losses won't increase a great deal.

Mads Barnkob

Fri Jul 25 2014, 08:15AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Linas wrote ...

Does any one investigate this ? One simple solution will be to make toroid with a slot, other is to make topload from tube, by winding it on isolator, like this this

Goodchilds and Catons coils uses complete rings for the topload which are all connected to eachother and the secondary coil, so they present the same one turn as a large toroid would. The dics material is only chosen for ease of sourcing/machining/weight.

I also doubt that it absorbs much of the energy directly from the primary as we usually have much else metal in the bridge construction underneath that is closer to the primary.

One thing that could be interesting would be to make a ringed topload where every slot in each ring, to not make complete turns, was connected in series so instead of being one big end terminal it worked like an extension of the secondary coil, I do however have no idea how that would affect the coils performance, just a thought.

Linas

Fri Jul 25 2014, 08:53AM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

I just point out idea, i know that in linked picture is compleate short.

same apply for electronics, since i have huge metal box, i will redesign my coil frame so that primary will not see any "shorted turns", because this this does effect coil performance, adding any metal below primary in a way, that it can create eddy currents,it will boost power, but that will go to heat, now sparks

And i did test, my aluminum box get warm if i put it below primary, well, it is induction heater, so nothing new that it gets warm.

Dr. Dark Current

Fri Jul 25 2014, 03:53PM

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

Just put the primary further away from the metal box, or shield only the control electronics into a conductive box (the power electronics will probably be fine with the magnetic field)

OR make the box from a more conductive material, such as aluminium, it will heat less than steel.

Linas

Fri Jul 25 2014, 06:28PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

Linas wrote ...

And i did test, my aluminum box get warm if i put it below primary, well, it is induction heater, so nothing new that it gets warm.

Dr. Dark Current wrote ...

OR make the box from a more conductive material, such as aluminum, it will heat less than steel.

it will be standing close to coil, just like in recent Odin DRSSTC testing

1406055696 30 FT4896 Odin Test Burntisland A1

But how about capacitors, can i put it below coil, or it should be placed near electronic as well ? so equivalent circuit is capacitors in series creating loop, so not a big deal, i just don't know how metal react to changing magnetic field)

GrantX

Sun Jul 27 2014, 05:06AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

I was thinking about this topic recently. I also wondered how great of an effect topload material has on performance. I understand that aluminium is the best choice due to weight, but would non-ferritic stainless steel function identically? And at the extreme end, how much would a mild steel toroid degrade performance? I imagine it would be horrible on a small coil, since the primary isn't very far away.

Dr. Dark Current

Sun Jul 27 2014, 08:01AM

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

The heating is mostly due to eddy currents I believe. A stainless steel topload would heat more than aluminum one. The conductivity is the key parameter.

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