Transformer VA rating?? - 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 7th November 2006, 03:44 AM   #1
RyanW is offline RyanW  Canada
diyAudio Member
 
Join Date: Apr 2005
Location: Vancouver, BC
Default Transformer VA rating??

Some time ago, I purchased a transformer from a surplus sale... I have no specs or anything. Can anyone take a guess at the VA rating?

Dimensions: EI style with laminate plates
Overall
3.75"x6.75"(x6" tall)
Core
3.75"x2.25"(x4" tall)

Windings:
2.25mmx2.25mm square copper secondary
~3mmx3mm square copper primary
(Note that I am removing windings from what was originally step up to get it down to an appropriate amplifier voltage... Also, I need to create a CT)

This monster is quite heavy, ~15 to 20pounds

Any thoughts on loss of performance due to removing windings?
  Reply With Quote
Old 7th November 2006, 11:30 AM   #2
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Hi

If I remember correctly, the power of a transformer can be (crudely) evaluated by squaring the iron area (ie. center leg or twice outer legs) expressed in cm². The relation is valid for good quality laminations; a derating factor of 0.9 or 0.8 might be prudent for unknown materials. Also, this applies for 50Hz; I suppose for 60Hz you can multiply by 6/5.
LV

PS power can also be estimated by weight, but I have no conversion factor at hand.
  Reply With Quote
Old 7th November 2006, 11:49 AM   #3
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
If you can find a wire gauge table, you can make an informed judgement what current the designer was running at, hence work out VA.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 7th November 2006, 12:48 PM   #4
RyanW is offline RyanW  Canada
diyAudio Member
 
Join Date: Apr 2005
Location: Vancouver, BC
Thanks for the input. Based on your equation, I find that this transformer is ~2700 VA. Can anyone provide a sanity check here? I am surprised by this huge value. Does it sound reasonable that this transformer could be 2.7kVA. I have further confirmed this value with an equation I found online.

in sq.in, VA=(Area/0.16)^2 = 2780VA

I suppose if these equations are somewhat valid then I should have sufficient power for one or two 150W amps (Note sarcasm)
  Reply With Quote
Old 7th November 2006, 01:17 PM   #5
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
2700VA seems quite large for only 20lb, but the figure is compatible with the primary gauge size, thus I guess it must be correct.
LV
  Reply With Quote
Old 11th November 2006, 10:17 PM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
Silvio Klaic transformer calculator shows 2.9kVA for a 95mm by 57mm core. Each limb should be 95mm by 28.5mm. The top I and leg of the E should be about 28.5mm or just a little less.

But there is something wrong with the quoted dimensions and/or weight.

The core alone is about 1.9litres from those sizes and should weigh about 15.1kg (about 34lbs).
Then there is all the copper to add in.

Can you confirm the size of the plates in the stack and how thick the stack is?
__________________
regards Andrew T.
  Reply With Quote
Old 11th November 2006, 10:23 PM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
removing some of the windings will reduce the VA rating.

Take off 50% of the secondary and you take off 50% of the VA. It's that simple.

It's similar for the primary except that if you remove 50% of the primary you reduce the input voltage by 50% as well, but at the same current, so it equals 50% of the VA.

Increasing the copper on the primary and/or the secondary gives a very small increase in VA rating but the core becomes the limiting factor.

I think the increased VA comes from the reduced losses due to less Isquared R loss.
__________________
regards Andrew T.
  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
Transformer rating ? woody Parts 0 31st July 2008 05:44 PM
Zen transformer rating!! sandstorm33 Pass Labs 13 14th December 2007 02:42 PM
Transformer Rating sushi Pass Labs 12 15th August 2007 04:05 PM
Transformer rating xplod1236 Chip Amps 3 7th July 2004 12:58 AM
Transformer VA Rating vs. Current Rating JhonDoe Chip Amps 45 5th June 2004 01:11 AM


New To Site? Need Help?

All times are GMT. The time now is 04:41 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