Multiple transformers in one power supply - Page 1
Forum section: electronics / beginners

author: TCPMeta
author_rank: Newbie
timestamp: December 31, 2015, 07:16:19 am
content: I am currently building a high power bench power supply. The question is can I use two mismatched transformers on the output? One transformer to handle constant current and the other handle constant voltage. IE one transformer has a output of 12 volts 12 amps while the other outputs 24 volts 2 amps. The only info I can find is that two transformers can share a input AC connection and putting them in series or parallel. I want to know if I can use basically two supplies with floating outputs but each one doing it's own part. At the same time I think it might be a no or I would have to lower the output voltage from 24 to 12 or check and see if the other transformer can extend to a 24 output. Any help would be lovely.

author: ivaylo
author_rank: Frequent Contributor
timestamp: December 31, 2015, 07:41:02 am
content: A diagram of what you are trying to do would help. It kinda sounds like you are talking about a two channel supply where the channels "are doing their own thing", but can't be sure...

author: jeroen79
author_rank: Frequent Contributor
timestamp: December 31, 2015, 09:01:50 am
content: If you connect the secondary windings together in parallel then there will be a short with a 12V difference.But you could use a relay or semiconductor to switch between the two transformers depending on the need.If you connect the transformers in series then you could switch between 12V/12A, 24V/2A and 36V/2A.You could even use the secondary of one as primary powerd by the secondary of the other.Then you could go up to 480V/200mA.Building two seperate supplies with seperate CV/CC regulators is also possible.If you connect them in parallel then they could smoothly transition between 24V/2A and 12V/12+2A.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 31, 2015, 11:10:03 am
content: Constant current and constant voltage mode depend on the load. So you cant use different transformers for both parts. There is a chance to combine the two as describeb above. Just the 480 V don't look plausible and are to dangerous for a beginner anyway.Many regulator circuits use one supply for the main output and an auxillary one to power the regulator circuit itself. So the smaller transformer might be useful for this purpose - though something like 8-12 V and 0.5 A would be mormally enough for this.Also keep in mind that after rectifier and buffer cap, the 12 V 12 A (AC) transformer will provide something like 14-16 V with a maximum current of about 6-8 A.

author: jeroen79
author_rank: Frequent Contributor
timestamp: December 31, 2015, 11:57:03 am
content: Quote from: Kleinstein on December 31, 2015, 11:10:03 amYou feed the 24V trafo from the mains.Then you add the 12V secondary trafo to the 24V secondary.That way the 12V secondary becomes the primary.The primary -now the secondary- will now have 460V on it. (230V mains)Then the 24V winding and 460V winding are placed inseries to yield 484V.QuoteDefinitely.

author: retrolefty
author_rank: Super Contributor
timestamp: December 31, 2015, 12:21:17 pm
content: Quote from: jeroen79 on December 31, 2015, 11:57:03 amCould be dangerous for anyone. If the insulation voltage rating of the output winding is not specified?

author: dom0
author_rank: Super Contributor
timestamp: December 31, 2015, 12:28:48 pm
content: Quote from: jeroen79 on December 31, 2015, 11:57:03 am200 % rated voltage will drive even generously dimensioned transformers into saturation and the fuse pops.If you want a 'HV' lab supply, go get a decent transformer. Industrial control transformers used to supply 230 V equipment in 380/400/690 V environments are often available with various power ratings and have the necessary winding voltages and insulation strength to support such an application on their own. Plus, they are often cheaper NOS than multiple new transformers hacked together.