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Registered Member #1733
Joined: Thu Oct 02 2008, 03:17PM
Location: Hamilton, ON, Canada
Posts: 100
Hey All,
I'm a little lost. I have 2 identical transformers. 120V primary, 30V, 60VA secondary, with a 15V centre tap. Think door bell xfmr.
Both 30V secondaries and one of the 15V taps are all run through independant full-wave rectifiers. Output at the rectifiers is 28.7V and 13.8V. I've checked with my scope that all inputs and outputs are the same. When I connect just the two 30V rectifier (-) output, 0V, to a common rail, everything is good. When I add the 15V rectifier 0V output to the common rail, it goes funny on me. The 15v rectifier now registers ~42V.
I've done this with 2 larger xfmrs and a SMPS with no issues. I want to use just the 2 smaller xfmrs, but need to fix this issue.
Registered Member #1316
Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365
What did you expect the output to be? If you expected 45 volts the 3v drop is because of the rectifiers. If you expected 60v or 30v the windings are out of phase.
Registered Member #1733
Joined: Thu Oct 02 2008, 03:17PM
Location: Hamilton, ON, Canada
Posts: 100
I expected no change to the voltage. I want two 30V and one 15V output, sharing a common 0V rail. Only the 0V outputs are common, +V is driving independant components.
I have two 15kg 12V15A transformers, secondarires in series, out to a rectifier, and shared the 0V from that with a SMPS and got the desired results - 24V on the rectifier, 15V from my SMPS.
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