Inductor for magnet power supply - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

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 6th March 2013, 03:19 PM   #1
diyAudio Member
 
Join Date: Mar 2013
Location: SE Michigan
Default Inductor for magnet power supply

Hi folks. I am new to the forum, and my question is not strictly audio but close. I have a power supply I built 30 years ago to power an electromagnet on a home built magnetic drill press. Consisted of a rectifier bridge from a GM car alternator, a 200 mfd motor start capacitor and a 3/8" diameter 9" long steel rod with about a couple hundred turns of 18 ga magnet wire around it as an inductor to help smooth the voltage. The input was direct (fused) from the 120 VAC. It worked fine for years. Then my magnet burned out and I put it aside for a few decades.

I recently found a few spare moments and made a new bigger magnet using a full 10 pound spool of 22ga magnet wire stuffed into a welded cylindrical magnet housing. Has 80 ohms resistance and draws about 2 amps at the 160 v or so DC output from my power supply. Works great generates huge amount of pull.

My problem is the inductor in the power supply is getting quite warm (hot actually) which I do not recall being a problem when used with the old magnet. I don't remember what the old magnet drew, but I know it was a lot less as it was 1/5 the physical size of the current one. The inductor rod buzzes a fair amount, which I don't remember it doing in the former incarnation of my device .

What are the easy solutions - make a bigger inductor - longer? - more turns? - heavier wire? I think the heat is coming from the "induction" action in the core, not resistance in the wire as it is much larger gauge wire than used in the magnet the power supply is driving. One other possible factor is the power supply is now mounted on the drill press itself within a few inches of the magnet so maybe being in the magnetic field of the magnet is having some effect?


Any suggestions would be appreciated. I am not an engineer - I'm a beanie by training and worked as a marketing guy for years, but am moderately handy with simple electronics.
  Reply With Quote
Old 6th March 2013, 03:32 PM   #2
diyAudio Member
 
Osvaldo de Banfield's Avatar
 
Join Date: Dec 2011
Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
Power is voltage times current. So 2A * 160V makes 320W. Is the inductor capable of managing such a power?
__________________
LW1DSE
  Reply With Quote
Old 6th March 2013, 03:55 PM   #3
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
Quote:
Originally Posted by dwlee6vn View Post
My problem is the inductor in the power supply is getting quite warm (hot actually) which I do not recall being a problem when used with the old magnet. I don't remember what the old magnet drew, but I know it was a lot less as it was 1/5 the physical size of the current one. The inductor rod buzzes a fair amount, which I don't remember it doing in the former incarnation of my device . What are the easy solutions - make a bigger inductor - longer? - more turns? - heavier wire? I think the heat is coming from the "induction" action in the core, not resistance in the wire as it is much larger gauge wire than used in the magnet the power supply is driving. One other possible factor is the power supply is now mounted on the drill press itself within a few inches of the magnet so maybe being in the magnetic field of the magnet is having some effect?


Any suggestions would be appreciated. I am not an engineer - I'm a beanie by training and worked as a marketing guy for years, but am moderately handy with simple electronics.
Hilited is the probable reasoning. It sounds like the solid steel rod is dissipating at 120 hz. I would recommend re-doing the inductor using lots of individual smaller steel insulated rods. It is probably eddy current dissipation in the inductor, and using lots of smaller insulated rods will break that up.

jn
  Reply With Quote
Old 6th March 2013, 05:20 PM   #4
diyAudio Member
 
Join Date: Mar 2013
Location: SE Michigan
Default magnet power supply

Thanks, I'll try that. Would 1/32 inch or so wires in a. 1/2" bundle be "many" enough to be effective?. I would cut some pieces out of tig welding filler and spray them with insulating enamel.
  Reply With Quote
Old 6th March 2013, 05:37 PM   #5
diyAudio Member
 
Osvaldo de Banfield's Avatar
 
Join Date: Dec 2011
Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
...or simple iron wire with a natural oxide insulator. I once again ripped and old ignition coil for car ignition which the core was a lot of simple iron wires oxidized.
The transformer has the secondary left open.
__________________
LW1DSE
  Reply With Quote
Old 6th March 2013, 05:59 PM   #6
diyAudio Member
 
jneutron's Avatar
 
Join Date: Jan 2004
Location: away
Quote:
Originally Posted by dwlee6vn View Post
Thanks, I'll try that. Would 1/32 inch or so wires in a. 1/2" bundle be "many" enough to be effective?. I would cut some pieces out of tig welding filler and spray them with insulating enamel.
I don't know if tig filler is magnetic. But yes, I'd spray. Oxidized as OdB said may be good enough, but I wouldn't trust it.

I'd try to duplicate the total cross sectional area so the inductance is similar. But since you're winging it for no exact inductance value, give it a try. Remember, the inductance goes up as the square of the number of turns, so if you're too low in inductance, just add more turns.

jn
  Reply With Quote
Old 6th March 2013, 06:16 PM   #7
diyAudio Member
 
Osvaldo de Banfield's Avatar
 
Join Date: Dec 2011
Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
Quote:
Originally Posted by jneutron View Post
Remember, the inductance goes up as the square of the number of turns, so if you're too low in inductance, just add more turns.

jn
This would be true if there exists AC voltage and current though the col, but if there is only DC, the current is dominated by wiring resistance. IN DC inductance if of no means excepting in transients of switching on or off. Be sure what are you apliying to this electro-magnet.
__________________
LW1DSE
  Reply With Quote
Old 6th March 2013, 06:33 PM   #8
diyAudio Member
 
Join Date: Mar 2013
Location: SE Michigan
Default magnet power supply

Thanks, I'll try that. Would 1/32 inch or so wires in a. 1/2" bundle be "many" enough to be effective?. I would cut some pieces out of tig welding filler and spray them with insulating enamel.
  Reply With Quote
Old 6th March 2013, 06:41 PM   #9
diyAudio Member
 
Join Date: Mar 2013
Location: SE Michigan
Default magnet power supply

Thanks, I'll try that. Would 1/32 inch or so wires in a. 1/2" bundle be "many" enough to be effective?. I would cut some pieces out of tig welding filler and spray them with insulating enamel.
  Reply With Quote
Old 7th March 2013, 06:32 AM   #10
diyAudio Member
 
Join Date: Sep 2010
Location: Melbourne
Why do you use in inductor is series with what is essentially a very large inductor the magnet? The magnet itself is a very effective filter many electromagnet power supplies are unfiltered, for a full wave single phase bridge rectifier with no capacitor input filter the average DC voltage across the magnet will be 0.9 x the supply voltage. With 80 ohms just over an amp will flow. That would reduce the magnet heating from around 300W to 145W. The important thing is how hot the magnet gets for me I would get rid of the capacitor input filter and the inductor and see how that works, there is many a shunt wound DC motor or magnetic chuck using no filtering.
  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
Help with inductor choice in power supply jmillerdoc Solid State 1 24th February 2011 12:03 PM
atx power supply inductor operating max. frequency ? gev Power Supplies 3 10th May 2010 08:55 PM
Which inductor for IC power supply decoupling Banfi T. Parts 1 17th January 2010 07:11 PM
2.2mH inductor in Aleph3 Power supply vsr123 Pass Labs 10 9th April 2003 02:04 AM


New To Site? Need Help?

All times are GMT. The time now is 10:21 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