# Wiring a transformer's coils together?

just a couple quick questions. My goal is to make a powerful inductor and I was wondering if it is possible to this by connecting the primary and secondary windings of a microwave transformer in parallel. The question is: this is only possible if the coils were wound in the same direction, right? And what would happen in this configuration if they were wound in opposite directions?

Major noob here, so sorry if these are stupid questions! Any advice is highly appreciated, thank you in advance!

• what's the purpose of the battery? Commented May 16, 2021 at 19:32
• Seconding @jsotola, what is the purpose of the battery? Commented May 16, 2021 at 19:53
• Putting say 100 mH in parallel with 1mH makes it less than 1mH. N.G. Commented May 16, 2021 at 19:57
• @jsotola, mentioning the battery was irrelevant to my question, so my mistake. Its just the power source for my circuit, sorry for the confusion :) Commented May 16, 2021 at 20:11

This wouldn't work very well, but it would work.

A transformer is designed to keep as much flux as possible contained inside its core (microwave transformers specifically are an exception to this, so it might work better than most, but it's still optimized for use as a transformer, not an inductor.), while large-value inductors rely on having some sort of air gap to avoid saturation and increase energy density; most of the energy in an inductor is stored in the air gap.

As for winding direction, you can always swap the wires to correct a mismatch. If they're wound oppositely and connected in parallel, the flux would just cancel and you'd get a lower inductance than you would otherwise, but like I said, you can just swap the wires.

As an additional point, to maximize inductance you should connect the windings in series, not in parallel. Connecting them in parallel would lower the inductance compared to putting them in series.

• So although it would not be an ideal inductor, the configuration would work right? You also mentioned the config's use as an electromagnet, would the wiring need to be changed at all to use it efficiently for this purpose? Commented May 16, 2021 at 19:45
• It would work, it just wouldn't be a great inductor. Better than most transformers would, at least. Putting the coils in series would give you more inductance than in parallel. When this answer was about using it as an electromagnet, it was a much firmer "no, you can't do this"; an electromagnet needs to have an open end, which would be a very detrimental characteristic for a transformer to have. Commented May 16, 2021 at 19:48
• The secondary has many times more turns than the primary, so there would be minimal gain over just using the secondary.
– Frog
Commented May 16, 2021 at 20:02
• @Frog Also true. Not much point in it, but technically it does increase the inductance! It'd be much higher inductance than putting them in parallel, though. Commented May 16, 2021 at 20:03
• @x7benihana I mean that it needs to be, roughly, a rod-shaped or U-shaped core, rather than a box-shaped or O-shaped core. The ends of the rod or U are where things get magnetically pulled towards. You couldn't make an electromagnet out of a transformer without hacking apart the core and re-winding it, and at that point it's probably easier to use something else for a core. Commented May 16, 2021 at 20:15