mains frequency//secondary current - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 2009, 08:10 AM   #1
diyAudio Member
 
Join Date: Feb 2004
Location: Queensland Australia
Default mains frequency//secondary current

Here in Australia the mains power is around 240 volts at 50 c/s.

I picked up some secondhand PS transformers that were salvaged from equipment made in the US of A and designed for 60c/s. They have multi-tapped primaries (115v,120v and 125vs) and secondaries of 36 volts @ 3 amps. Now they seem ideal for my purposes and I hope to run the primaries in series and use the secondaries to power some "double mono" power amps. But there is a question about the current that is now available in their adopted country. I have been getting two opposing pieces of advice.

The first opinion says that as they were designed for 60c/s I will need to DERATE the secondary current 20% if they are run on Aussie mains of 50c/s.

The second opinion states the opposite and suggests I now have access to 20% MORE current.

Both sets of advice are coming from well qualified people. Anyone come up with a definitive answer please?

Thanks, Jonathan
__________________
"It was the Springtime of the year when aunt is calling to aunt like mastodons bellowing across primeval swamps." P.G. Wodehouse.
  Reply With Quote
Old 24th January 2009, 10:05 AM   #2
diyAudio Member
 
Join Date: Feb 2004
Location: Queensland Australia
Pleeeeeese. Someone must know.
Jonathan
__________________
"It was the Springtime of the year when aunt is calling to aunt like mastodons bellowing across primeval swamps." P.G. Wodehouse.
  Reply With Quote
Old 24th January 2009, 10:42 AM   #3
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
you will certainly not get more current (VA) by going down from 60Hz to 50Hz.

If the transformer is designed to only run on 60Hz then you will have to de-rate it for 50Hz use. But you are never likely to run the transformer at near maximum rating after start up.

One clue to whether it's suitable for 50Hz use is to check running temperature when the output is open circuit.
If it seems to get too hot then maybe it really is a 60Hz transformer.

I think that adding primary windings will help reduce that heat, but I suspect you will not need it.

Can you safely measure the no load primary current? I guess it should be <=10mA. If it's a lot less then 50Hz is OK.
__________________
regards Andrew T.
  Reply With Quote
Old 24th January 2009, 11:04 AM   #4
diyAudio Member
 
Steerpike's Avatar
 
Join Date: Jan 2006
Location: Johannesburg, South Africa
The seriesed primaries will be good for 2x125=250V at 60Hz, so 240V input is already giving a bit of leeway.

One other thing to note: if you are running the primaries in series, you should ensure both transformers are loaded equally - either by wiring the secondaries in series too, or in parallel.
  Reply With Quote
Old 24th January 2009, 11:53 AM   #5
MondyT is offline MondyT  United Kingdom
diyAudio Member
 
Join Date: Dec 2008
Hi Jonathan

If the transformer is designed for standard 60Hz mains input then you are going to need to reduce the input voltage by a factor of 50/60=0.833 at 50Hz or you will more than likely saturate the core. If you have a 250v tap for 60Hz, then the maximum 50Hz voltage you can apply is 208v. Manufacturers do not normally give much leeway except say a 10% over voltage capability as copper costs money!

The loading on the secondary does not have any bearing on this as the magnetising current for most part remains the same despite loading and therefore the flux density in the core remains the pretty much same from no load to full load

Cheers
Ray
  Reply With Quote
Old 24th January 2009, 09:39 PM   #6
Banned
 
Join Date: Apr 2005
Location: Stockholm
Ray,
nice explanation.
  Reply With Quote
Old 25th January 2009, 04:15 AM   #7
diyAudio Member
 
Join Date: Feb 2004
Location: Queensland Australia
Thanks guys. Appreciated. Jonathan
__________________
"It was the Springtime of the year when aunt is calling to aunt like mastodons bellowing across primeval swamps." P.G. Wodehouse.
  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
Low Frequency Mains Noise ruffrecords Tubes / Valves 6 31st October 2008 07:26 PM
Mains frequency variation Circlotron Everything Else 11 3rd March 2008 10:49 AM
Why is mains frequency so low? Nixie Parts 3 29th November 2006 11:13 AM
Change in frequency mains Raka Analog Line Level 49 17th January 2006 04:59 PM
Mains frequency stability Prune Parts 10 26th November 2004 05:09 PM


New To Site? Need Help?

All times are GMT. The time now is 11:56 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