# Can two transformers be connected in parallel? **URL:** \ **Category:** Factual Questions\ **Created:** [September 29, 2007, 7:23am UTC](https://boards.straightdope.com/t/can-two-transformers-be-connected-in-parallel/420911 "2007-09-29T07:23:52Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Dusty](https://avatars.discourse-cdn.com/v4/letter/d/a183cd/32.png) [@Dusty](https://boards.straightdope.com/u/Dusty)\ **Post date:** [September 29, 2007, 7:23am UTC](https://boards.straightdope.com/t/can-two-transformers-be-connected-in-parallel/420911/1 "2007-09-29T07:23:52Z")
Can two identical transformers be connected in parallel? That is, could I plug in two 12 volt, 1 amp transformers, join them together, and get an output of 12 volts, 2 amps? Or would, I don’t know, the whole thing blow up? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [September 29, 2007, 2:01pm UTC](https://boards.straightdope.com/t/can-two-transformers-be-connected-in-parallel/420911/2 "2007-09-29T14:01:01Z")
Yes, BUT–and it’s a big but–both transfomers must have identical output. For very small transformers, you can get away with a smallish difference, since the DCR (DC resistance) of the windings will limit the current somewhat, but for large transformers with heavy windings and low DCR, even a difference of less than a volt can creat very large circulating currents, which is very bad. The regulation of both transformers should also match closely, especially if you expect to load them close to max. You must also be careful to match phase. As a general rule, it’s not recommended and is considered bad practice. If you need a higher output current, the best thing to do is get a larger transformer. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [September 29, 2007, 2:38pm UTC](https://boards.straightdope.com/t/can-two-transformers-be-connected-in-parallel/420911/3 "2007-09-29T14:38:05Z")
Yes, as QED said, but it is highly unrecommended. Electric utilities connect voltage sources in parallel as a matter of routine. However, they use sophistacated control systems to ensure proper load sharing and to avoid large circulating currents within the sources. If you were planning on doing it, I wouldn’t. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [September 29, 2007, 2:58pm UTC](https://boards.straightdope.com/t/can-two-transformers-be-connected-in-parallel/420911/4 "2007-09-29T14:58:35Z")
Yes, but we should add that the turns ratios and impedances should be compatible. There is actually a practical difference between primary and secondary coils on transformers, and that is that the voltage ratio marked on a transformer does not necessarily represent the turns ratio, because on primary and secondary the losses contribute in different directions. That is, a 10:1 stepdown transformer does not do a 10:1 stepup if you wire it the other way. If you wire one side of the transformers in parallel, and energize that, and tie one terminal of each other side together, and don’t see zero volts between the remaining leads, then tying them together will cause some heating at least. ---
**Author:** ![Electronic\_Chaos](https://avatars.discourse-cdn.com/v4/letter/e/bbe5ce/32.png) [@Electronic\_Chaos](https://boards.straightdope.com/u/Electronic_Chaos)\ **Post date:** [September 29, 2007, 3:30pm UTC](https://boards.straightdope.com/t/can-two-transformers-be-connected-in-parallel/420911/5 "2007-09-29T15:30:06Z")
You must also be sure not to pair a Decepticon with an Autobot, as the combination could be disastrous.