I have 2 totally different toroidal transformers I want to put in series to make 75vac total. I have a decently large toroidal transformer in which I wound many, many turns of 10 gauge wire around. To give some perspective, the hole in the toroidal was about 3 inches wide(above the 120v primary), and there is only about half an inch left. That gave me 40vac. I have a smaller toroidal transformer that has about a 2 inch hole in the middle(also above the primary). The primary’s are likely different and the secondaries will be different. 40vac on one toroidal transformer and obviously 35 on another to achieve 75vac. I would use the same 10 gauge wire, but again, obviously, less turns on the second smaller toroidal transformer. Can I do this without an issue?

In short, can I connect 2 different transformers in series to get their combined voltage?

  • \$\begingroup\$ Are you asking about connecting the primaries in series, or the secondaries? A diagram might help to make your question more clear. \$\endgroup\$
    – The Photon
    Jun 17 '19 at 0:22
  • 1
    \$\begingroup\$ Both primaries connected in parallel. Same phase. \$\endgroup\$ Jun 17 '19 at 1:11
  • \$\begingroup\$ Pretty sure you can do that but I'm not confident enough to make it an answer. \$\endgroup\$
    – user253751
    Jun 17 '19 at 5:02
  • \$\begingroup\$ Fewer turns LOL. \$\endgroup\$
    – Andy aka
    Jun 17 '19 at 7:34

If you have two transformers, with their primaries in parallel, it's just fine to connect their secondaries in series.

Their output voltages will add algebraically, which means if you have (for instance) a 35v and 40v secondary, you'll get either 75v or 5v, depending on the phasing of the two transformers.

You should limit the current that you draw to the capability of the lower current transformer.

If you have a large and a small transformer, you'll likely find that the small one delivers fewer volts per turn, so you'll need more turns for a similar output voltage.


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