Can I use a single primary 120V transformer with 240V? - 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 24th January 2008, 03:24 AM   #1
diyAudio Member
 
Join Date: Oct 2007
Default Can I use a single primary 120V transformer with 240V?

Say if I have a 120V primary 42VCT 100VA transformer - can I use it with 240V input to get a 84VCT output and 1/2 max (at the limit) current output to maintain same max 100VA rating?

Any problems or dangers of doing so?


thanks

her shann
  Reply With Quote
Old 24th January 2008, 03:53 AM   #2
diyAudio Member
 
Join Date: Apr 2006
Location: Minnesota
You cannot do this. The transformer will saturate and the primary currents will be very large. This will damage the transformer or blow a fuse if you have one.
  Reply With Quote
Old 24th January 2008, 03:57 AM   #3
diyAudio Member
 
Join Date: Sep 2004
Location: hobart tasmania
Hi Hershann

Stop !!, you will need two transformers rated at 120v then wire the
primaries of two identical transformers in series to get Sec + Sec Voltage

if you don't have two transformers the only other option is to use a step down transformer to reduce 240v to 120v then feed 120v to your existing
tranformer.

If the step down is the way to go you could use a 240v transformer with CT 63v 0 63v secondaries, ( sadly 60v 0 60v transformers are rare) wire the secondaries in series to make 126v Ensure any such step down or other transforner is rated at sufficient current for your project

Hope this helps / Chris
  Reply With Quote
Old 24th January 2008, 04:24 AM   #4
diyAudio Member
 
Join Date: Oct 2007
Thanks all for the reply, just wondering about it. Gotta read about saturation then - it not as simple as the ratio of primary coil over the secondary coil then.

her shann
  Reply With Quote
Old 24th January 2008, 05:01 AM   #5
diyAudio Member
 
JohnAtwood's Avatar
 
Join Date: May 2006
Location: Rural Nevada
Default Core saturation

The majority of core losses in a power transformer are caused by the magnetizing current, a highly non-linear current that is dependent only on the voltage, not the load current. As the transformer core nears saturation, the magnetizing current starts to dramatically go up. Good transformers are designed to have low magnetizing currents (although doubling the primary voltage would still be way out of bounds), while cheap ones (i.e. Stancor and Triad filament transformers) have pretty high magnetizing currents. You can tell because they get hot even with no load on them.

You can run a 240V transformer on 120V with no problem, except that there is "extra" windings, so it is not quite as economical to build.

- John Atwood
  Reply With Quote
Old 24th January 2008, 01:52 PM   #6
star882 is offline star882  United States
diyAudio Member
 
star882's Avatar
 
Join Date: Mar 2007
It is pretty straightforward to convert 240v to 120v with the help of a half bridge converter. (Or even more straightforward to get 120v from hot to neutral as 240v is from hot to hot.)
You can also turn up the frequency (while keeping voltage about the same) with a H bridge to avoid core saturation, but insulation might be a problem.
__________________
"Fully on MOSFET = closed switch, Fully off MOSFET = open switch, Half on MOSFET = poor imitation of Tiffany Yep." - also applies to IGBTs!
  Reply With Quote
Old 24th January 2008, 02:02 PM   #7
Warp Engineer
On Holiday
 
AudioFreak's Avatar
 
Join Date: Oct 2001
Location: Queensland, Australia
Quote:
Originally posted by star882
(Or even more straightforward to get 120v from hot to neutral as 240v is from hot to hot.)

That may well be the case in the USA but alot of the rest of the world that has grown up on 220-240V AC mains supply runs 230V on the hot and the other conductor is at ground potential.
__________________
- Dan
  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
F5 Single Primary Transformer NV&H Pass Labs 15 28th June 2009 09:57 PM
Dedicated 6.3v filament transformer 240v primary DrewP Tubes / Valves 17 23rd June 2009 12:05 PM
WTB: 750-800vct Plate Transformer (120V primary) pjanda1 Swap Meet 0 23rd March 2009 06:43 PM


New To Site? Need Help?

All times are GMT. The time now is 12:58 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