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# Determining coil characteristics

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## Determining coil characteristics

(OP)
I have an over molded coil that I have been using to finalize a prototype.  I scavenged the coil from a solenoid and now I have to determine the coil characteristics so I can spec out the production coils.

I can get a rough idea of the wire size and number of turns based on the dimensions of the coil and its resistance, but is there a simple test to nail down the number of turns a little better?

Thanks

### RE: Determining coil characteristics

cut it in two and count, it is the only way that you will know.
How about buying coils from the other company?

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Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm

### RE: Determining coil characteristics

(OP)
Thanks EdStainless.

I was hoping that there was a little simpler solution.  If I measure the inductance of the coil, how close do you think I could come to the actual number of turns?

I would buy the coil from the original company if I could figure out who it is.  There are no markings on the coil and the manufacture of the solenoid is not longer in buisness.

John

### RE: Determining coil characteristics

Check inductance, resistance, size and wire gage. then wind one and see if it works.  You should be able to fine tune from  that one.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm

### RE: Determining coil characteristics

If the solenoid was originally designed for 60 hertz,
Wind say 10 turns over the coil. Use small wire say #30 film insulated.
Put the original steel back in the solenoid with the solenoid closed.
Excite the coil at some low voltage. Use 60 hertz line and the original coil.
Measure the voltage of the coil and the added turns.
The voltage ratio should be the same as the turns ratio.
Double the applied voltage and repeat the test.
The results should be the same for both voltages.

If 10 turns gives too low a voltage, use 100 turns.

### RE: Determining coil characteristics

(OP)
Thanks CarlPugh,

Let me make sure I understand.

1)Measure the voltage across the original coil, V0, at 60 Hz.
2)Add the extra loops around the coil and measure the new voltage, Vn.

The number of coils should be:  coils_new/coils_old = Vn/V0

### RE: Determining coil characteristics

Test the same as you would test the ratio of a transformer. (Which it is when the additional turns are added)
Wind the 10 turns on.
Assemble the core. The solenoid should be closed for all tests.
Apply 1/4 rated coil voltage to the molded coil.
Measure the voltage of the molded coil and the voltage of the 10 turns.

turns molded coil/10 = applied voltage/voltage 10 turn

Solenoid should be closed so exciting current is not excessive.
Test at less than 1/2 rated voltage to avoid core saturation.

Do the check at two (three or four would be better) different input voltages. The calculated turns ratio should be the same. If turns ratio is different, there is some sort of problem.

Don't apply voltage to the small wire. There may be dangerous voltage in the molded coil and the small wire may evaporate.

Don't short the small wire.

The preceding should work for most solenoids, however there is no guarantee that it will work for some odd types of solenoids.

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