tripod inductor modification ?

[snk]

Hello

Due to an order error on my side, i received today a couple of tripod inductor, while what i need is inductors with two legs.
I do not know how i am supposed to use tripod inductors, and if i can "adapt" them to fit into a circuit expecting inductors with two legs ?
Can i use them, or are they useless ?

Thank you in advance !

[Rob Strand]

It would help to get a  links to what you wanted and what you got.

You can use two legs of a three pin inductor.   
There's three combinations you can use to get three inductances:
- outer pins, highest inductance (highest DC resistance)
- tap and outer pin, one will be higher inductance and the other low inductance. 
  The higher inductance will normally be less than the inductance on the outer windings *unless* it's a transformer where the "non-dots" are connected to a common terminal.

If the inductor is center tapped the two inductances to the tap will be the same but the DC resistance might be slightly lower on one winding.  Use the lower resistance winding.

(There some caveats but I won't bog you down with the details.)

[snk]

Thank you.

It would help to get a  links to what you wanted and what you got.

This is what i wanted : https://www.rapidonline.com/murata-ps-22r476c-47mh-10-radial-leaded-inductor-88-1684
https://www.ebay.fr/itm/INDUCTOR-47MH-0-055A-10-RADIAL-RLB0913-473K-Fnl-/352066923766
https://www.mouser.fr/ProductDetail/Murata-Power-Solutions/13R476C?qs=sGAEpiMZZMsg%252By3WlYCkU%252B0DGp0rEzrkkwRbFAMQIfs%3D

This is what i ordered (the main picture shows only two legs, which is misleading) :

I haven't used inductors much (only in a Renometer clone), so i am not familiar with them.

[snk]

You can use two legs of a three pin inductor.   

That's good to know

There's three combinations you can use to get three inductances:
- outer pins, highest inductance (highest DC resistance)
- tap and outer pin, one will be higher inductance and the other low inductance.
  The higher inductance will normally be less than the inductance on the outer windings *unless* it's a transformer where the "non-dots" are connected to a common terminal.

If the inductor is center tapped the two inductances to the tap will be the same but the DC resistance might be slightly lower on one winding.  Use the lower resistance winding.

I don't really understand, as each pin seem similar to me (well, one is short, one is medium and one is long)... I mean : which is the "tap", and which one is the "outer" pin ?
(all i want is to get the 47MH inductance i bought them for

[Rob Strand]

I don't really understand, as each pin seem similar to me (well, one is short, one is medium and one is long)... I mean : which is the "tap", and which one is the "outer" pin ?
(all i want is to get the 47MH inductance i bought them for

Exactly what pin is the tap I don't know.  But don't worry, the important thing is how to find it:

- Set your multimeter to ohms  (use auto ranging.  If your meter isn't autoranging, start with the set to 2k scale. If the reading is less than 200ohm flip it back to 200 ohms (for more accuracy), then flip it back to 2k scale for the next measurement.)

- measure between each pair of terminals

- choose the terminals with the highest resistance.  Those should be the 47mH terminals.

If there's no tap on the inductor you might even find you only get a measurement between two of the terminal.  That means one terminal is open and only used for mechanical support.

The one you wanted was:
47.0mH   115.0Ω   0.03A

So you might expect measurement of around 115 ohms.  (A bit higher if it's a "cheaper" inductor.  The inductor you bought is larger so it could be lower.)

[snk]

Thank you very much, ROb !

[snk]

I tested today.
It gives me these values :
58Ω
81Ω
23Ω
So if i understand correctly, 81Ω is the right pair, that's it ?

The one you wanted was:
47.0mH   115.0Ω   0.03A

Oh, it was a reference only : i only had the 47mH value in mind

[Rob Strand]

It gives me these values :
58Ω
81Ω
23Ω
So if i understand correctly, 81Ω is the right pair, that's it ?

Yes that is correct.

For 47mH bobbin style inductor of that size (8mm diam x 10mm high) 81 ohms looks very reasonable to me.  So without any more information I would expect that to be true.   

Just a heads-up though.  There's a small possibility it is not true.  Here's why:
The 47mH inductance specification is not complete. An inductor with three connections has three inductances depending on which terminals are used (just like you have three resistance measurements).  If you know two of those you can work out the other one  but only if the specifications have a diagram showing how the windings are done.   By reversing a winding the inductance across the terminals with the 81 ohms could be less than the inductance across the 58 ohm terminals.

The seller should know all that and put up the full data, but if they did you wouldn't be here! (Sometimes datasheets appear to give you all the information but the often there's something wrong making it completely useless - datasheets from China are particularly bad in this way.)

So I am assuming the fact they only give one inductance means they are giving the largest one.  The size, the DC resistance of 81 ohms kind of backs that up.   Since your DC resistances 23 and 58 are not equal I know it's not a 1:1 transformer.  If it were I might have some suspicion that the 47mH inductance spec was for the smaller windings.

So in the bigger picture there's plenty to go wrong but it looks like you should be OK  .   If it were me I'd measure the inductance!