parrellel inductors, values add up?

[Westrock2000]

hey guys just wondering if parrellel inductors add up like capacitors do. Some of the values I need are little off and was wondering if I could add some, or do you recommend getting one too big and making it smaller?

 

[Christer]

Inductors behave like resistors for series and parallel connection.

Series:

Lser = L1 + L2

Parallel:

Lpar = 1/(1/L1 + 1/L2) = L1*L2/(L1 + L2)

 

[plasmodium]

series inductors add up

parallel inductors are like resistors i think
1/i= 1/i1 + 1/i2 etc

 

[Pjotr]

Hi,

When inductors are paralleled the total value is:

L_tot = L1 x L2 / (L1 + L2)

When inductors are in series:

L_tot = L1 + L2

This is thus the opposite of the case with capacitors.

Chaio


/Edit/

Oops, many answers at the same time

 

[dhaen]

Be aware that most inductors have significant self capacitance and hence a resonant frequency.
When you parallel or series connect inductors, the behavior can become complex.

 

[Westrock2000]

so would it be wiser (as well as cheaper) if for example I need a 1.36 mh and I buy a 1.4 mh and take some off.

 

[peranders]

You but notice the inductance is turn^2. Remove half the turns you will get 70% of the original inductance.

 

[Pjotr]

You but notice the inductance is turn^2. Remove half the turns you will get 70% of the original inductance.

No you get 25% of the inductance: 0.5^2 = 0.25

So remove 30% (and keep 70% ) to get app. half the original inductance.

If it was all that easy… First, how do you know how many turns a given inductor has? Second, the inductance is related to the enclosed cross sectional area of the windings. This is not the same for every turn.

Westrock2000, if you need 1.36 mH and you can get 1.4 mH why bother? That is just a few percent off and accurate enough.

To get an accurate value, the best way is to buy a value to first higher value available. Then indeed trim it down by removing turns AND use an inductor-measuring device by trial and error until you get the value needed.

I am using this one and it works pretty well for LS crossovers:

 

[Westrock2000]

I was looking at LC meters and most (at least ones in PE catalog)seem to only go down to 3 mh and up to 4 h ( ).

 

[till]

I have no L meter. What about take a known capacitor with the unkbown inductance in series. Feed some sine from a signal generator in this, use a scope to look at the waveform. Turn sine generator frequency for lowest amplitude on scope screen . Read frequency on generator and calculate L ?