# coupled inductor in series

I'm planning on using a dual inductor in series mode to increase the inductance.
I realize that the total inductance will be L1+L2+2M where M is the mutual inductance (when the polarity is connected to give aiding, rather than opposing, magnetic flux).

My question, though, is whether the saturation current will decrease by using this arrangement. My initial thought is that it won't change (appreciably) since, although the flux is doubled, the effective core length used is also doubled. Is my thinking correct?

• I wonder if you really need to increase inductance, or energy of saturation? What is the purpose of that coil? Are you building converter or filtering something? – Kamil Apr 22 '14 at 23:15
• Connecting coils in parallel (not series) will increase saturation current. – Kamil Apr 22 '14 at 23:17

## 1 Answer

If both coils share the same core, then the length of the core is the same whether one coil is used or two (aiding). If opposed, then flux is much, much reduced.

If the current reduces because the inductance has increased then there is an overall net reduction in flux despite the number of turns doubling - this is because inductance is proportional to turns squared hence inductance quadruples (current quarters) and turns only double.

Magneto motive force (mmf) halves when the turns double because current quarters. MMF drives flux hence there is an improvement.