Parallel power transformers? - 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 17th October 2001, 02:54 AM   #1
paulb is offline paulb  Canada
diyAudio Member
 
Join Date: Jun 2001
Location: Calgary
In another thread, the topic came up of trying to combine the power from two differently-sized transformers (same nominal voltage). "downhere" was asking about it. I originally said to use two separate bridge rectifiers and combine the outputs at the capacitors, but after thinking about it I'm not so sure. I think there's a good chance that one would grab most/all of the load. Perhaps low-valued resistors to help share the load would be a good idea.
Anyone out there have more thoughts on this?
  Reply With Quote
Old 17th October 2001, 07:17 PM   #2
paulb is offline paulb  Canada
diyAudio Member
 
Join Date: Jun 2001
Location: Calgary
Okay, I thought it through some more. It should work. Anyone have comments on the following:
A transformer's voltage rating is at its full load (at least the Hammond ones are). If a transformer can be considered a linear voltage source, it can be modelled as a voltage source and a source resistance.
Higher power transformers will obviously have a lower source resistance, because they can supply more current. This means their voltage drops less under load as compared to a lower power one. And this, in turn, means they will also have a lower "no-load" voltage (Hammond used to spec this, but they don't seem to any more).
So if two transformers are run through separate bridge rectifiers to a common set of caps, the higher voltage source will supply most of the current. At light loads, this will be the smaller transformer; however, because it droops more rapidly than the bigger transformer at some point the latter will start to supply current as well. The rectifiers plus the internal resistance of the transformers will balance the loads.
So it should work fine, but it NEEDS to have separate rectifier bridges to work properly. Sound correct?
  Reply With Quote
Old 17th October 2001, 10:52 PM   #3
JBL is offline JBL  Canada
diyAudio Member
 
JBL's Avatar
 
Join Date: Aug 2001
Location: Canada, N.-B.
Send a message via ICQ to JBL
Well it's not really going to work. The two transformer must have equal voltage at anytime in any load. If voltage is deifferent the one one with the highest voltage will suply current to the lowest. All this power is lost and the total power output must be subsracted from this current between the two transformer.

Also the smallest one is going to fail at full power.
  Reply With Quote
Old 17th October 2001, 11:38 PM   #4
paulb is offline paulb  Canada
diyAudio Member
 
Join Date: Jun 2001
Location: Calgary
I've done experiments with a variable power supply and a battery that are coupled together with diodes. If their voltages are very close, but not quite identical, both will supply power to the load - both diodes are on the knee of their conduction curve. My thinking was that the source resistances of the transformers would even this out.
But your opinion intrigues me enough I'm going to try simulating it.
The higher voltage transformer cannot supply current to the lowest, because they are isolated by the diodes.
  Reply With Quote
Old 18th October 2001, 12:43 AM   #5
paulb is offline paulb  Canada
diyAudio Member
 
Join Date: Jun 2001
Location: Calgary
A simple simulation (using just a half-wave version) has confirmed that the combination of resistors and diodes shares the load between two voltage sources.
  Reply With Quote
Old 18th October 2001, 08:54 AM   #6
diyAudio Member
 
Join Date: Oct 2001
meaning i can parallel transformers of different va ratings?

sighz having a bit of asthma now... stupid soldering fumes.. I forgot to switch on the ventilation fans..

be continuing the proj next week
I've already soldered one channel
  Reply With Quote
Old 18th October 2001, 01:55 PM   #7
paulb is offline paulb  Canada
diyAudio Member
 
Join Date: Jun 2001
Location: Calgary
I think you can ONLY if the two transformers have almost identical voltage outputs at full load. If they are part of the same line from the same manufacturer, this is probably true. If they are different, it probably won't work, one will supply almost all the power.
downhere, I suggest you just use the larger transformer and just put up with a little less output power. Much simpler.
  Reply With Quote
Old 18th October 2001, 03:04 PM   #8
diyAudio Member
 
Join Date: Oct 2001
yup thanks
what If I ran them into two different capacitor batteries?
won't the capacitors so called distribute the load somewhat
  Reply With Quote
Old 18th October 2001, 03:43 PM   #9
paulb is offline paulb  Canada
diyAudio Member
 
Join Date: Jun 2001
Location: Calgary
Capacitors smooth out current surges to keep the voltage steady. They won't help in combining two different voltage sources. What you would need are two voltage regulators, a complex solution.
  Reply With Quote
Old 18th October 2001, 03:58 PM   #10
diyAudio Member
 
Join Date: Oct 2001
Yup I see..
ah well
thanks for everything
I'll try the Larger unknown transformer..
is there a way to test the transformer without using AC power from mains?
  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
Parallel Output Transformers gerryc Tubes / Valves 20 26th September 2007 06:03 AM
parallel transformers Aunkst Parts 15 29th October 2004 01:16 PM
parallel the transformers billy Pass Labs 36 5th June 2004 02:57 AM
Can I parallel transformers for a LM3886? soundNERD Chip Amps 14 29th October 2003 01:34 AM


New To Site? Need Help?

All times are GMT. The time now is 09:26 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