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DRSSTC shielding and capacitor location

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chris_inkubate

Sun Jan 31 2016, 10:53PM

Registered Member #46007 Joined: Wed Apr 30 2014, 08:02PM
Location: Walsall, UK
Posts: 36

Hello,
A little while back when having issues with my DRSSTC I put some shielding around my electronics in the form of plastic sheet with foil tape attached. I have since solved the problems by optimising other areas but left the shielding in place anyway. However when running 700-800A peak primary the below happened - looks like the shielding is picking up the primary field and heating up!

This is interesting as I have read discussion about the potential for this happening but never seen it and there is always some amount of metal under the coil in most cases. I'm a little concerned however as my tank capacitors are in much the same position as this shield was - and they are essentially foil and plastic too!

Has anyone else seen heating effects like this?

Chris

1454280797 46007 FT0 Img 20160130 144429993

Perezx

Mon Feb 01 2016, 05:31AM

Registered Member #54263 Joined: Thu Jan 15 2015, 09:54AM
Location: Perth
Posts: 35

Hm... You have HF EM field and a conductor in it... Why shouldnt it heat up?

loneoceans

Mon Feb 01 2016, 09:09AM

Registered Member #4098 Joined: Fri Sept 16 2011, 09:26PM
Location:
Posts: 236

This is expected behavior - the primary coil is essentially a big induction cooker, and also works pretty well as one. :)

Mads Barnkob

Mon Feb 01 2016, 09:27AM

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

I failed to find the pictures, but I think it was Dr. Spark that had shielding around the electronics underneath the primary that he burnt all the paint off when running high peak currents.

Try using net instead of flat planes. If I recall correctly you will have most current running along the edges and it will look like a 1 turn coil to the primary, much like the currents tends to run at the upper and lower part of a copper ribbon primary.

What was the distance to your primary, could you prove pictures with a better overview, than just the detail of damage.

chris_inkubate

Mon Feb 01 2016, 01:10PM

Registered Member #46007 Joined: Wed Apr 30 2014, 08:02PM
Location: Walsall, UK
Posts: 36

Thanks for the replies. I've removed the shield anyway and runs ok. Primary is about 100mm above the shield. More worried now about the capacitors which are within the same distance. Think im going to raise the coil all up by 100mm or so more then use nesh as suggested for safety.

Mads Barnkob

Mon Feb 01 2016, 02:56PM

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

A guess on why the foil would be burning is that is simply has much less mass and gets heated very easily compared to a thicker plate that would be able to dissipate more heat than it absorbs.

loneoceans

Mon Feb 01 2016, 05:30PM

Registered Member #4098 Joined: Fri Sept 16 2011, 09:26PM
Location:
Posts: 236

chris_inkubate wrote ...

Thanks for the replies. I've removed the shield anyway and runs ok. Primary is about 100mm above the shield. More worried now about the capacitors which are within the same distance. Think im going to raise the coil all up by 100mm or so more then use nesh as suggested for safety.

Another good method is to make a shield with breaks located radially away from the middle to open up loops, but moving the primary coil up works great as well. Your caps are most likely fine - they have a much smaller flux linkage compared to your huge piece of foil and will probably be heating up much less than how they already be heating up from the tank current during operation.

Perezx

Tue Feb 02 2016, 05:05AM

Registered Member #54263 Joined: Thu Jan 15 2015, 09:54AM
Location: Perth
Posts: 35

Perhaps you have noticed that without this shield your sparks are a bit longer :)

chris_inkubate

Tue Feb 02 2016, 01:27PM

Registered Member #46007 Joined: Wed Apr 30 2014, 08:02PM
Location: Walsall, UK
Posts: 36

I saw a slight increase in output but not huge as was mentioned i doubt it was taking too much power. Just the thin aluminium was vulnerable. I may be able to tune it better now though and get more. Probably pushing my luck though as using mains ground with big arcs!

flyboy7777

Sun Feb 07 2016, 04:17AM

Registered Member #58118 Joined: Sat Dec 12 2015, 12:34AM
Location: Sanger, Texas
Posts: 14

This makes me chuckle a bit... I was reading the user's guide to my induction stove today. One of the warnings was to never put any silverware on top of it. I guess the same applies to coils too!

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