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SSTC toroid heating up

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MRacerxdl

Thu Apr 29 2010, 09:13PM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

Hi all, today I was testing my new setup, and it works good, but one thing makes me worried about.

My topload is heating up, and its much for a toroid. With my Ambient Temperature at 22ÂºC my toroid heats up to ~45ÂºC with a few minutes turned on... Its not a trouble even for the PVC tube, but what is causing that heat up its that worries me. And I dont know why is heating.

Someone knows what can be, or if I need it really worrie about that?
The coil with the toroid:

Unassembled toroid:

The coil without Toroid:

The smaller toroids fits perfectly at the secondary, I fit it on the aluminium at the top of the coil, so the contact is made good. I started to think there maybe is some corona between the last turns and the smaller toroid, but it isnt only the smaller toroid that heats up. Its ALL of parts get at ~45ÂºC in a few minutes. So I dont know what is it.

If some data of the coil helps:
FullBridge of IRFP250N running at 150V 10A Interrupted
The secondary coil doesnt get any heat. 30cm sparks output.
125KHz of Fres

Thanks!

ScotchTapeLord

Thu Apr 29 2010, 09:35PM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635

Is that aluminum tape on the top? It looks like there might be a break in it on the far side, but if there isn't, it'd be like having a shorted turn at the top of the secondary. You could consider getting rid of it and making a way to raise the toroid slightly to reduce its coupling with the primary.

Dr. Dark Current

Fri Apr 30 2010, 10:53AM

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

The toroid is one big shorted turn too, thats probably why it heats up...

Herr Zapp

Fri Apr 30 2010, 05:05PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

MRacerxdl -

I think the "toroid as a shorted turn" hypothesis has been analyzed previously, and determined that typically the toroid was too far away from the primary's magnetic field to have much current induced in it.

A few questions:
1. How are you measuring the 23 deg C temperature rise? This seems to be a very significant heating.
2. What is the temperature rise in your primary coil and driver heratsinks during the same period that the toroid is seeing it's 23 deg rise?
3. Can you post a photo of the base of the coil, when fully assembled and in the same configuration as when the toroid heating is seen?

It seems more likely that any temperature rise the toroid experiences is the result of heated air rising from the driver circuitry and/or the primary, rather than the result of circulating currents within the toroid itself.

Regards,
Herr Zapp

dex

Fri Apr 30 2010, 07:29PM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147

Herr Zapp wrote ...

I think the "toroid as a shorted turn" hypothesis has been analyzed previously, and determined that typically the toroid to too far away from the primary's magnetic field to have much current induced in it.

Obviously,it can be close enough to secondary's magnetic field to be heated up.

Herr Zapp

Fri Apr 30 2010, 09:04PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

dex -

Could you provide some estimates of the current that might be present in the upper portion of this secondary, and the magnitude of the current that could be induced in a single "shorted turn" conductor at the location of the toroid? The reported 23 deg C temperature rise of the toroid, in an aluminum conductor with as much surface area as this toroid has, would seem to be too great to be caused by induced current from the secondary. The power being dissipated in the toroid would need to be (my estimate here) 10 - 15 watts or more to cause this much of a temperature rise, wouldn't it?

An analysis of the actual current in the toroid would useful.

Herr Zapp

Arcstarter

Sat May 01 2010, 03:37AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

dex wrote ...

Obviously,it can be close enough to secondary's magnetic field to be heated up.

That is debatable. In a typical secondary, only the bottom of the coil is acting like an actual transformer, hence the heating only at the bottom. The rest of the coil is acting as a resonator. So, it is like a magnifier Tesla coil, with a primary, 'secondary', and 'tertiary' coil.

MRacerxdl

Sat May 01 2010, 04:35AM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

Raising all the toroids, drops the temperature a little but not much (I think 5ÂºC).
The coil in the test assemble:

The heatsink stays cool, at temperature ambient, but I didnt measure the temperature, as the secondary coil same thing.

I am measuring the temperature with the multimeter sensor (here on brazil we call termopar, I dont know what is english. Its to different metals soldered together, when it heats it gets a few mV of differencial voltage.), with the coil turned off, and I used thermal grease to help the heat dissipation for the sensor.

Herr Zapp

Sat May 01 2010, 06:18AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

MRacerxdl -

OK, so you are using a thermocouple and a multimeter on the DC millivolt range to measure the thermocouple output, correct?

There are many different types of thermocouple wire, each type using a different pair of alloys, and each with a different millivolt output characteristic. Are you sure that you are using the correct mv/degree output factor or lookup table for your specific type of thermocouple wire? What are the colors of the insulation on each of the thermocouple wires?

Information on the various thermocouple types and their color codes can be found at:

Information on the mV output per degree for the mosr common thermocouple types can be found near the bottom of this page:

What is the secondary grounded to? Is there a chance that your multimeter is measuring noise on your ground connection? Does the indicated mv reading change if the toroid is electrically disconnected from the top winding on your secondary?

Regards,
Herr Zapp

raff

Sat May 01 2010, 11:19AM

Registered Member #2315 Joined: Tue Aug 25 2009, 02:35AM
Location: Leyte, PH
Posts: 161

isnt it proper way of adding "distance" from tip of secondary winding(top end of wire) to torroid with at least HALF the diameter of the torroid?

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