Go Back   Home > Forums > Member Areas > The Lounge

The Lounge A place to talk about almost anything but politics and religion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 30th May 2012, 10:18 AM   #23501
wahab is offline wahab  Algeria
diyAudio Member
 
Join Date: Nov 2009
Location: algeria/france
Quote:
Originally Posted by Wavebourn View Post
All outputs of all supplies are connected together in one point that is the ground.
This point exact physical position is defined only at iddle
or eventualy in a schematic...
Once the system is in large current mode the said point will be
a moving target.
  Reply With Quote
Old 30th May 2012, 01:28 PM   #23502
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
Quote:
Originally Posted by Wavebourn View Post
I have a scope. And when I short tip of the probe with it's ground crocodile near any wire that charges caps through diodes I see spikes.
You are measuring dB/dt, a consequence of amperes law and faradays law. This effect is why star grounds do not work with low impedance circuitry. Bonzai is very knowledgeable on this aspect, IIRC he drew a 4 wire capacitor on a simple supply schematic..

Quote:
Originally Posted by Chris Hornbeck View Post
If a center tapped transformer is used to establish the center point of a dual polarity power supply, any imbalances, including AC ones, appear as current into the "ground". In a circuit with a single true star ground and no ground loops this is no problemo, but what real circuit has no ground loops?
That is incorrect (in red).

The real problem is this: how does one approach a designated zero potential reference point through a path in 3 dimensional space which has time varying magnetic fields... without inducing differential voltages between two wires ala faradays law of induction?

Simple.

1. via two paths which do not trap time varying magnetic fields.

or

2. via two paths with identical integrated time varying magnetic fields.

For #1, geometry of 3-d space states that there can only be 3 paths which are magnetically orthogonal, so practical circuit design cannot use this. There are some simple ways around this.

For #2, it is almost impossible to do this, and the only practical methods to do this are extremely counterintuitive.

The most important thing here is: star grounds are high impedance constructs. NOT for low impedance with high current slew rates.

ps...btw, this is standard stuff....and works for uV level instrumentation wires buried in 10 tesla magnets running 13 kiloamps, up to 45 kiloamp primary/15 million amp secondary structures over ten meters tall.


j

Last edited by jneutron; 30th May 2012 at 01:34 PM.
  Reply With Quote
Old 30th May 2012, 02:23 PM   #23503
Bonsai is offline Bonsai  Taiwan
diyAudio Member
 
Bonsai's Avatar
 
Join Date: Jul 2003
Location: Taipei, Taiwan
. . . winding temperature measurement with an RTD perhaps?
__________________
bonsai
Amplifier Design and Construction for MUSIC! http://hifisonix.com/
  Reply With Quote
Old 30th May 2012, 02:48 PM   #23504
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
Quote:
Originally Posted by Bonsai View Post
. . . winding temperature measurement with an RTD perhaps?
Milli-kelvin accuracy temperature measurement at 1.8 Kelvin using ceramic-oxy-nitride.

1 part in 10e6 magnetic field measurements in 5 to 10 tesla superconducting magnets.

Quench detection of the 30 gigajoule ITER solenoid during plasma initiation.

As well as some difficult tasks...

j
  Reply With Quote
Old 30th May 2012, 03:18 PM   #23505
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally Posted by wahab View Post
This point exact physical position is defined only at iddle
or eventualy in a schematic...
Once the system is in large current mode the said point will be
a moving target.
Moving in respect to what?
__________________
If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.
  Reply With Quote
Old 30th May 2012, 03:21 PM   #23506
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
Quote:
Originally Posted by Wavebourn View Post
Moving in respect to what?
Detroit.

j
  Reply With Quote
Old 30th May 2012, 03:22 PM   #23507
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Quote:
Originally Posted by jneutron View Post
You are measuring dB/dt, a consequence of amperes law and faradays law. This effect is why star grounds do not work with low impedance circuitry. Bonzai is very knowledgeable on this aspect, IIRC he drew a 4 wire capacitor on a simple supply schematic..
Absolutely right. I always solder 4-wire capacitors on breadboards and in prototypes.
__________________
If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.
  Reply With Quote
Old 30th May 2012, 03:32 PM   #23508
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
Quote:
Originally Posted by Wavebourn View Post
Absolutely right. I always solder 4-wire capacitors on breadboards and in prototypes.
When using a 4 wire capacitor, use a braid to carry the current from one end of the capacitor over it's body. This negates the external magnetic field caused by the physical length of the capacitor. No, it cannot negate the solenoidal field of the internal foil wrap if the manu kept them apart. But the selection of a low ESL will take care of that.

Using the braid option eliminates the mutual inductance.

This technique works on diodes and resistors as well.

j
  Reply With Quote
Old 30th May 2012, 03:46 PM   #23509
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
I once even wanted to buy a loom machine to manufacture high-end resistors, including non-inductive multitap carpets for volume controls.
__________________
If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.
  Reply With Quote
Old 30th May 2012, 04:00 PM   #23510
diyAudio Member
 
vacuphile's Avatar
 
Join Date: Apr 2011
Location: Right behind you.
Quote:
Originally Posted by jneutron View Post
When using a 4 wire capacitor, use a braid to carry the current from one end of the capacitor over it's body. This negates the external magnetic field caused by the physical length of the capacitor. No, it cannot negate the solenoidal field of the internal foil wrap if the manu kept them apart. But the selection of a low ESL will take care of that.

Using the braid option eliminates the mutual inductance.

This technique works on diodes and resistors as well.

j
Braid sounds like great idea. However, wouldn't it go some way already to mount axial stuff vertically with the return lead close to the body? Or, what I have been doing in the PS I am working on, take two resistors of 1/2 the desired value, connect them at the top and mount the two which are now in series vertically on the PCB. This will also keep the junctions balanced and as closely as possible at the same temperature. I just surmised this would be better, but the differences are below what I can measure, so who knows?

vac
__________________
Everything eats everything else, given appetite and opportunity.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 01:44 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2