2 trafos tied in the middle

[kbeist]

I know it is here somewhere on this site.
I read over about 4 different ideas on multiple trafos, earlier this summer, and how to tie them. But I can't seem to find the right search expressions to enter. And of course like always with my favs and hot bar all filled up I didnt add them to reference to.
Could some one either point me in the right direction?? please.
Is it better to tie the 2 trafos before rectification or after, for a +p and -n supply?
Thank you all.

[kbeist]

Just came across an APPnote that answered my question; tied prior to rectifier.

[Elvee]

Originally Posted by kbeist

Just came across an APPnote that answered my question; tied prior to rectifier.

That's the obvious, common sense answer, but some audiophiliacs on this site seem to disagree.
It would be nice to give the reference of this appnote, to contribute to the sanitation of the subject.
It will not convince the opponents, but it will help newcomers make up their minds.

[kbeist]

I am sorry for not being thorough on this as you are absoutely correct Elvee.
I cam across the first snippet on this thread:
(gootee posted some refs in post# 3)
~700w ampifier
I can't seem to find the actual diyaudio references that led me to the national LME appnotes.
And viola national has it right there in black and white:
App Note: AN1849 - An Audio Amplifier Power Supply Design - for their LME49811&LME49830 Chipamps.

I still think it is ironic to note that while schematics list the transformer with a dot denoting the common connection, most transformer manufactures do not even paint a dot on one end of the windings.

I do hope that is a tad bit more complete for others to reference.

[AndrewT]

Use a bulb tester to power up the transformer/s.
You can't damage your self, nor your transformer/s no matter how badly you wire up the various windings.
If the bulb lights, you have an error.

[kbeist]

RIGHT!!! SAFETY FIRST!!!
Just remember that any electrical circuit can be Extreemly hazardous to your health/property/family/lifestyle or well being. Murphys Law still applies to everyone and everything.

I would usually do that anyways. (Residential/Commercial Electrician background with additional naval electronics training hast taught me much but....) Just finished moving into a new place and my whole bench is still not set up correctly.

(Disclamer)
I am still ONLY responsible for MY OWN actions and outcomes. I will for now take the off chance that a puff-o-smoke with the notable flamage can happen.

Yeup, did it last night. Trafo1: 112VACin-13.47VACout / Trafo2: 112VACin-14.32VACout (primaries tied parallel-secondaries tied series gives 26.8VACout then rectified through 4x 1N4001's gives ~35VDC-ish (i think it was more like 38VDC).

[HOPHANTHIET]

HAPPY NEW YEAR EVERY ONE ,
Suppose 1 have 2 trafos 110V input ,24V out,Can i connect them to a bridgerectifier ,with one trafo in reverse polarity ,to achieve a +-35V DC out put OR it will blow up?

[kbeist]

Originally Posted by kbeist

I still think it is ironic to note that while schematics list the transformer with a dot denoting the common connection, most transformer manufactures do not even paint a dot on one end of the windings.

Please anyone with more info or corrections to my posting please, PLEASE interject!!!

That which I stated refers to the fact that Transformers are not nececerily polarized (alternating current in - alternating current out)(alternating current references from a 0-volt reference point then traveling in the positive region then traveling back down and past the 0-Volt reference and continuing down into the negative region then back up to the 0-volt reference point) This example is reversed in a polarized version(ie. current travels down then back up then down to the 0-volt reference). This is precisely the reason for using safety measures when doing ANY and ALL wiring! (litebulb/circuit breaker/fuse/deadman switch/etc.) A transformer is polarized in reference to the direction that the windings are wound on the former, causing an expanding then collapsing magnetic field, inducing (aka. inductance) of a current in a seperate coil of wire. The directions in which these coils primary/secondary is the cause of most concern. (either you wire it right and get an additive voltage out or you wire it "backwards" and the pulsing current sine wave cancels the other out and you get a subtractive voltage out). The subtractive effect will cause your transformers to overheat then smoke and eventually burst into FLAMAGE!
Do yourself and your loved ones a huge favor, ALWAYS USE SAFETY!
(fwiw. the time it takes for ones transformers to go from cold to overheating and right into and into the , putiing you in either a or , depends on a few factors; transformer rating, age of trafo, quality of manufacture, Oh and how fast can you flip the switch off, there are a few others but this is just a brief.)
As to your question and an answer: Measure the resistance of each winding, also doing a continuity check in both directions helps with transformers that have internal diodes, fuses, breakers, resetable fuses, etc. -> connect safety devices -> wire the transformers individually test the voltage (note the primary/secondary) -> Disconnect from wall power -> wire transformers according to your application -> reapply wall power -> quickly test for voltage measurement then disconnect from wall power -> compare results to your estimated results - if lower than estimated rewire transformer -> reapply power do a quick check and dissconnect wall power again -> recompare your estimates.
NOTE: listen to the transformers making sure you do not hear them making a loud "buzzing". Loud buzzing denotes a loose winding and prone to failure. Also touch the surface of the transformers while disconnected noting the temperature. [rule of thumb] A small transformer should be no more than +1-+2 deg above room temp. A medium trafo sould never rise above +3 - +5 deg above room temp. And a Large transformer sould never rise above +5 - +8 deg above room temp. (temps are referencing transformers not connected to anything else, (aka. non-loaded).


Safety is an uderused action that requires you to be proactive.

I hope this helps you on your journey into our world!

[kbeist]

(I like the way it loooks, and the sound! Oh man the sound is amaizing! ) Using a 50KVA ballast transformer is way cool with #4AWG!!! You can light a few things up.

[kbeist]

Originally Posted by kbeist

I can't seem to find the actual diyaudio references that led me to the national LME appnotes.

I found It!!!
Bridge tied load amplifier

Post #4 by gootee.

And now the references are complete.