Transformer power question - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 26th November 2011, 07:34 AM   #1
diyAudio Member
merlin el mago's Avatar
Join Date: Sep 2009
Location: Catalonia - Europe
Question Transformer power question

I have a tx dual secondary 9V 30VA (15VA per winding so total power 30VA) & I need to know if the total power configured in series to have 18V is 30VA or 15VA?
  Reply With Quote
Old 26th November 2011, 07:46 AM   #2
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
Mooly's Avatar
Join Date: Sep 2007
Both the total VA rating and the individual ratings must not be exceeded.

So 9 volts at 15VA is 1.6 amps per winding. (15VA).
In series you have 18 volts and can still only draw 1.6 amps (total 30VA)

In parallel you would have 9 volts at 3.2 amps available (30VA)
  Reply With Quote
Old 26th November 2011, 07:50 AM   #3
diyAudio Member
merlin el mago's Avatar
Join Date: Sep 2009
Location: Catalonia - Europe
Thank you Mooly
  Reply With Quote
Old 26th November 2011, 01:48 PM   #4
DF96 is offline DF96  England
diyAudio Member
Join Date: May 2007
VA assumes resistive load. If you are rectifying and smoothing it you need to take into account RMS current and duty factor. In some cases you could end up back in the same place, but for high duty factor (e.g. Class A amp) you might need to derate by a factor of three or four.
  Reply With Quote
Old 26th November 2011, 01:59 PM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
yes, DF,
Many seem to be unaware or forget about the de-rating factor that transformer Manufacturers specify for a capacitor input filter in lieu of resistors passing AC current.

The easiest way I remember the approximate DC current available from a rectified and smoothed supply after applying the de-rating factor is:
Maximum Continuous DC output current = 50% of the rated AC current.
This takes account of the extra resistive heating due to IsquaredR losses being much greater for high crest value currents, cf resistive loaded AC windings.
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote


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
power transformer question woodturner-fran Tubes / Valves 6 9th March 2011 11:04 PM
Power transformer question keithgreenhalgh Tubes / Valves 4 6th August 2008 07:37 AM
transformer power question needtubes Parts 2 9th April 2004 11:13 AM
i am new, power transformer question i_drives Parts 1 25th November 2003 12:53 AM
power transformer question Bill Fitzpatrick Solid State 5 8th June 2001 04:22 AM

New To Site? Need Help?

All times are GMT. The time now is 12:33 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2