transformer ratings... pls help - Page 3 - 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 14th May 2003, 09:05 PM   #21
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Default Thanks for the clarity

Yes, it's true that the manufacturer gives the "on-load" voltage.

JojoD818 has 2 problems that are clouding the issue:

1 He has low mains voltage (easy to calculate the difference)
and,
2 He doesn't know the true RMS current being taken from the secondarys. We can only guess that it about 1.5 x the DC current after rectification.

Cheers,
  Reply With Quote
Old 14th May 2003, 09:13 PM   #22
diyAudio Member
 
bigparsnip's Avatar
 
Join Date: Apr 2003
Location: Cambridge
This may sem like a bit of a crap way to do this, but if you were to conect to high power resistors of around 0.22Ohms in between the transformer and the rectifier diodes (one on the supply for each rail), you could use the AC voltage setting on a multimeter to mesure the voltage drop on the resistors, and try and work back from that to find the current. The only problem with that being the fact the voltage vaveform will not be a sine wave, so the MM might give the wrong reading for the RMS voltage.
  Reply With Quote
Old 14th May 2003, 09:19 PM   #23
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Quote:
The only problem with that being the fact the voltage vaveform will not be a sine wave, so the MM might give the wrong reading for the RMS voltage.
Yes.
  Reply With Quote
Old 15th May 2003, 06:33 AM   #24
diyAudio Member
 
megajocke's Avatar
 
Join Date: Jan 2003
But the 0.22 ohm resistors will lower the RMS current! The diodes will conduct a longer time and the waveform will become less peaky!

I think you should expect about 1.6-1.8 times the DC current. But it depends on the filtering.
  Reply With Quote
Old 15th May 2003, 10:11 AM   #25
diyAudio Member
 
5th element's Avatar
 
Join Date: Oct 2002
Location: England
This may be redundant as I think someone has already mentioned something along these lines before but.

P=V.I
power(watts)=voltage * current

So the VA is volts times current so is the power in watts. Why they dont just call it power i dont know cause its the same thing and can cause confusion as it clearly did earlier on before.
  Reply With Quote
Old 15th May 2003, 02:03 PM   #26
diyAudio Member
 
megajocke's Avatar
 
Join Date: Jan 2003
The reason they don't call it power is that it is actually the current that counts. For example, if you have a transformer with a secondary voltage of 24V and put a capacitor across it that draws 10A, it will use 0W of power (if the cap was ideal), but the transformer would heat up as much as if you put a resistor across the secondary that drew 10A instead.
  Reply With Quote
Old 15th May 2003, 03:31 PM   #27
diyAudio Moderator
 
JojoD818's Avatar
 
Join Date: Mar 2003
Location: searching...
Well, I checked it again and it really is hot. My rectifier and filters are correctly placed.

At least the amp is up and running, maybe I should buy another transformer and just use this for bench testing future amp projects.

I have learned a lot from this project, a friend told me that the design of a power supply in an amp is as important as the amp itself. That is why I am so concerned with my transformers specs.

Thanks guys!

Jojo
  Reply With Quote
Old 17th May 2003, 02:08 AM   #28
diyAudio Member
 
Join Date: May 2003
Location: quebec
maybe the transformer has a short inside betwen wire, remember there is only varnish to insulate the wire, if there is a short winding, the magnetising current will rise. magnetising current is the minimum current needed by the transformer wen there is no load at the secondary. to measure it you remove all loads ( disconect the secondary ) , place a small resistor in series with the primary ( 3-5 ohms ) an measure the voltage drop on the resistor. then calculate the current and do the same on a similar tranfo, if the magnetising current of the transfo is really highier it may be defective.
  Reply With Quote
Old 17th May 2003, 02:35 AM   #29
diyAudio Member
 
Join Date: May 2003
Location: quebec
transformerrating for DC power supply is tricky the transformer supply current only wen diodes are conducting ( during the part of the cycle wen the voltage rise on the cap ) so if this par of the cycle is let say 20% of the time during this time the current must de 5 times higher than the DC current out of the power supply this is why the manufacturers will tell you that if you build a power supply with a 1 AC amp transformer ( standard bridge capacitor configuration ) you will get a 0.55 DC amp supply. But if you use a bigger capacitor there will be less ripple but the diode will conduct a shorter time an the current during conduction will be higher and you will need bigger diode and bigger transfo. several transfo company have chart on the net..........
  Reply With Quote
Old 17th May 2003, 03:54 PM   #30
diyAudio Moderator
 
JojoD818's Avatar
 
Join Date: Mar 2003
Location: searching...
Thanks audiofan for the info. I haven't given up on my transformer yet. Though I am considering buying a new one. Just have to finish evaluation of my amp.

Thanks again,
Jojo
  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
ratings of output transformer??? cbutterworth Tubes / Valves 6 24th January 2008 03:16 PM
Little help understanding Transformer ratings randy5235 Power Supplies 12 11th December 2006 06:43 PM
PSU Transformer ratings? wildswan Power Supplies 6 11th May 2006 07:54 AM
Transformer ratings??? AR1 Power Supplies 2 2nd May 2005 07:02 PM
Torroidal Transformer ratings kestrel200 Chip Amps 2 8th May 2004 04:59 PM


New To Site? Need Help?

All times are GMT. The time now is 08:41 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