regarding to the design of iron-cored inductors (chokes) - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 13th August 2004, 07:30 AM   #1
diyAudio Member
 
Join Date: Feb 2004
Location: Istanbul/TURKEY
Default regarding to the design of iron-cored inductors (chokes)

Hi,

Is it possible to design a choke working in dc current (lets say 100mA) -to say in another way, to design a choke with dc flux- without an air gap ?

Reading Radiatron Designers Handbook Chapter 5-Section 6-Page 242-Iron Cored Inductors, what I understand is:
1) First design the choke assuming an initial permeability
2) Check if your assumption is correct
3) If it is correct, no problem. If it is not correct, try to correct it by changing number of turns.
4) If you can correct it by changing the number of turns, it is ok. If you cannot, try to put an air gap to reduce flux densities in the core.

I am asking this because I have contacted to a local transformer design company to design a choke. They have said they can design the choke with and without the air gap. Is it possible ? If it is possible, can I assume that the one without air gap will have more turns than the one with air gap ?

The AC voltage across the core is the harmonics of rectified AC, isnt it ? (that is about 0.544Vinrms according to Morgan Jones ?)

Thanks in advance...

MB
  Reply With Quote
Old 13th August 2004, 10:25 AM   #2
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
In practice, all wound components using E and I laminations have an air gap, even if it's unintentional. Transformers alternate the Es and Is, but there is still a slight gap. Toroids don't have a gap because the core is wound from a continuous strip.

The more turns you have, the more Ampere Turns of magnetising force you apply, but an air gap is effectively a magnetic resistance and reduces the resulting flux density. An ideal choke design juggles air gap against turns and core size for a set current to give lowest cost, or reduced resistance. Decide what you want. Bear in mind that if you request 20H at 100mA with DC resistance of 10R, it can be done, but it will be enormous (and expensive).

Assuming that you are following the choke with a capacitor down to 0V, then the AC voltage across the choke will simply be the AC harmonics leaving the rectifier.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 13th August 2004, 06:54 PM   #3
diyAudio Member
 
Sch3mat1c's Avatar
 
Join Date: Jan 2003
Location: Milwaukee, WI
Send a message via ICQ to Sch3mat1c Send a message via AIM to Sch3mat1c
You can go without a gap in some circumstances, low or no DC current for example; but to keep it within ratings over a wider range, especially with say a choke input, you need a gap to reduce the flux. This reduces mu and requires a few more turns, but you handle more signal in the process.

Almost zero chokes designed to handle DC have no air gap.

Tim
__________________
Seven Transistor Labs
Projects and Resources
  Reply With Quote
Old 14th August 2004, 12:58 AM   #4
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
go to National Semi's site:

http://www.national.com/onlinesemina...magnetics.html

Sanjaya has developed an algorithm which is very helpful for dealing with "the gap"
  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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Marconi TF2700 LCR bridge and measuring iron-cored chokes resident Parts 80 20th April 2014 04:56 PM
Good source of Chokes/Inductors pjpoes Parts 12 18th May 2007 04:51 PM
Amp rating of Chokes/Inductors pjpoes Parts 20 17th May 2007 10:44 PM
four high-power iron-core chokes 3mH cocolino Swap Meet 0 14th May 2007 12:42 AM
Neosid chokes/inductors roibm Swap Meet 3 20th October 2004 08:12 PM


New To Site? Need Help?

All times are GMT. The time now is 11:35 PM.


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