The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: "Helmut Sennewald"
Subject: Re: parallelling two transformers
Date: Sat, 7 Dec 2002 21:58:29 +0100
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
"Jeff" schrieb im Newsbeitrag
> I have two pcb mount small transformers (about 56 VA max, 18 volt output)
> and I want to parallel the outputs to get a nice low profile unit with
> 80 VA minimum. I think if I de-rate the load then the worst case
> differences between the two won't matter. Anyone try this?
if the transformers don't have low tolerances in the output voltage,
a big current will flow just between the secondary coils. This
causes a high primary current in one of the transformers which drives
the iron of this transformer into saturation. A large tolerance would
be 1V difference in the secondary output. In this case the current
meter in the test circuit below could show about 1A(value from simulation).
If the measured current is 0.1A or less it is ok. I would check it
with zero load and full load(half the full load on each winding).
Be carefully to have the correct phase * of your windings before
you connect the current meter. You can check this with a voltmeter
plugged in the position of the drawn current meter. If it shows
nearly zero Volt, you have the correct phase. Otherwise the voltmeter
will show twice the output voltage of each transformer.
C * | |
Tr1 C | | |
C | | |
C | |
| | A | <-- current meter, choose 10A range
| |_V_| (voltmeter for phase * check)
C * | |
Tr2 C | | |
C | | |
C | |
* means equal phase
I am very interested to read how much current you have measured
between the secondary windings.
You should also check the primary current of each transformer after
parallel connection. As more equal the currents as better the symmetrie.
You shouldn't use it if they are more then than 10% different.
If we see how much effort is necessary to make this arrangement
successful, there is no wonder why it is normally not done.
Let's see what other people will say about may advice.
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup