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LL1683, what to do with unused windings

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Posted on October 17, 2009 at 06:11:26
KurtP
Audiophile

Posts: 217
Joined: January 25, 2007
 What is the general recommendation for unused windings? The 5V and 48V windings are not needed in my design. I can leave them floating or ground one end. My leaning is that they should not be left floating.

Suggestions?

With large power transformers, posted on October 17, 2009 at 19:21:53
KurtP
Audiophile

Posts: 217
Joined: January 25, 2007
 and I'm speaking of transformers rated in MVA, running a winding unreferenced is a big no-no, primarily because of the risk of insulation puncture from static buildup. Of course we are talking apples and oranges.

I have been experimenting with the stray capacitances in this unit (and the LL1685 choke) to try and determine optimal hot/neutral polarization. And I believe I've found it. Just thinking that maybe the stray capacitance from one winding or the core to the unused winding might build up and stress the insulation, or cause transient behavior. I will probably try some tests with/without ground references to see if there is any difference in stray capacitance.

Results, posted on October 18, 2009 at 17:29:53
KurtP
Audiophile

Posts: 217
Joined: January 25, 2007
 Well, there was definitely an increase in stray capacitance when the unused windings were grounded. I guess this wasn't a huge surprise, but now what to do about it. I took the simplistic idea that by grounding these unused windings, they were providing some degree of electrostatic shielding between primary and secondary, a good thing in my mind. As it turns out, the used 6.3V windings are also grounded on one end, so there is further benefit. Now I have a floating primary and non-grounded but referenced HV secondary with all other windings effectively grounded.

Of course, not knowing exactly how the windings are layered, there is no guarantee of performance improvement, but it makes me feel better. Really look forward to seeing how this improved power supply with all Lundahl iron works out. I need a quiet mechanical and magnetic supply with low RF hash. I'll keep updating with any significant findings.

RE: LL1683, what to do with unused windings, posted on October 17, 2009 at 08:50:44
KevinC
Manufacturer

Posts: 1999
Joined: April 19, 2001
Contributor
  Since: October 7, 2002
 I've always left them floating, so I have no experience with the difference.

Kevin Carter
K&K Audio
www.kandkaudio.com
I know that is what Dave Davenport does, posted on October 17, 2009 at 08:18:56
rickmcinnis@dogwoodfabrics.com
Audiophile

Posts: 723
Location: Atlanta
Joined: December 15, 2003
 due to having a DAVENPORT LINE STAGE. His instructions do not include doing anything with them.

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