I have a pair of plate chokes I got on Ebay many years ago. I know that they were intended for low current and the resistance is about 5.5kohms. The maximum inductance on my meter is 20 henrys which these exceed. Any way to determine the inductance?🙂
LC100-A Digital LCD High Precision Inductance Capacitance L/C Meter Capacitor | eBay
Inductance meter - says it goes up to 100H. Most LCR meters just go to 20H like you say.
Inductance meter - says it goes up to 100H. Most LCR meters just go to 20H like you say.
Inductance in parallel is akin to resistance in parallel. So I measured a power supply inductor of a magnitude my meter can read, 1.620 H, then measured that in parallel with the unknown and get 1.613 H. This gives me an inductance of 373 H😕 It is at least of the order of magnitude I was expecting but I don't believe it is really that high, I put it down to the accuracy of the measuring instrument😉
Thanks for the info on the meter Andy. Certainly not expensive🙂 My very vague recollection is that the inductance was about 200H so the results of my not very accurate experiment seem to support that😀
You could use the mains voltage as the signal generator , put the inductor in series with a ( variable ) resistor and measure how much voltage is droping on each . When the voltage drop is equal than R = 2*pi*f*L . Or you can calculate anyway with a fixed resistor a little more complicated . If the inductance is high as you say than the current is small , you could use a normal 100K pot as the variable resistor
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Yes … actually.
Hook a 1000 Ω resistor in series with the inductor.
Hook household 120 VAC (America) or 240 VAC (Europe, etc.) to it.
An inductor has an equivalent resistance of
If it were 2 resistors in series, the divided voltage would be
Take an example. Europe, VIN is measured at 237.5 V, your resister is 1000 Ω, and VOUT is only 18.5 V on the multimeter:
Is this safe? For a few seconds with any choke larger than a lemon, just fine. You'll drive quite a bit of current through the thing, but for short quick measurements, it is still safe.
How much current at 237.5 VAC? Kind of like Ohm's Law …
The value of 1,000 Ω was chosen (by me!) because you said, 'my meter doesn't test above 20 henries'. It is a good safe value.
Give it a whirl.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
Hook a 1000 Ω resistor in series with the inductor.
Hook household 120 VAC (America) or 240 VAC (Europe, etc.) to it.
An inductor has an equivalent resistance of
Z = 2πFL;
so you have to figure your nominal impedance factor '2πF'. In North America, that is 2 × 3.1415 × 60 = 377
In Europe just change 60 to 502 × 3.1415 × 50 = 314
Then it becomes fairly obvious what you should then expect to see:If it were 2 resistors in series, the divided voltage would be
VOUT = VIN Z₂ / (Z₁ + Z₂)
Therefore, if you measure VOUT and VIN, and Z₁ is unknown, then with a little algebra we getZ₁ = (VIN/VOUT - 1) • Z₂
Take an example. Europe, VIN is measured at 237.5 V, your resister is 1000 Ω, and VOUT is only 18.5 V on the multimeter:
Z₁ = ((237.5 ÷ 18.5) - 1) × 1000
Z₁ = 11,837 Ω
Now, work that back to an inductance from the frequency factor. Being in Germany (as is this example), we then get Z₁ = 11,837 Ω
Z = 314ℓ
11,837 ÷ 314 = L
37.7 henries = L
And that is the answer. 11,837 ÷ 314 = L
37.7 henries = L
Is this safe? For a few seconds with any choke larger than a lemon, just fine. You'll drive quite a bit of current through the thing, but for short quick measurements, it is still safe.
How much current at 237.5 VAC? Kind of like Ohm's Law …
E = IR
237.5 = I • (314 × 37.7)
I = 0.020 A
I = 20 mA
So, really not bad at all. 237.5 = I • (314 × 37.7)
I = 0.020 A
I = 20 mA
The value of 1,000 Ω was chosen (by me!) because you said, 'my meter doesn't test above 20 henries'. It is a good safe value.
Give it a whirl.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
The DCR of the choke is 5,500 Ohms
Even if you removed the laminations to grossly reduce the inductance (do not do that) . . .
230V/5,500 Ohms = 42mA
20H @ 50 Hz has 6,283 Ohms of inductive reactance.
The complex impedance of 20H and 5,000 Ohms is well over 7k Ohms at 50Hz.
I say the best test is to breadboard a triode tube stage, use 10mA, and find where the low frequency response is -3dB.
Go to the tube curves, and find the plate resistance, rp,* at 10mA plate current (you will need this value later).
The choke either goes down to 40Hz (bass guitar) 30Hz, 20Hz, 10Hz, or it does not.
Then test where the high frequency response is - 3dB. It either goes to 10k, 20k, 30k, or beyond.
Note that you got a certain low frequency response, and a certain high frequency response, when the choke was driven with the plate impedance, rp, from above *.
Now you can see if that rp gives the response you want; or whether you need a lower rp;
or whether you can use a tube that has a higher rp, and still give you the response you want.
Guess what, the OP does not have a signal generator, and does not have a scope.
He has to find somebody in his area who does.
Otherwise, forget about using the unknown chokes, and purchase some chokes of known value to use.
Or, let him build the circuit he wants with those chokes, and see if it sounds good to him.
Real test equipment is required
Or, Real ears are required
Pick one.
Even if you removed the laminations to grossly reduce the inductance (do not do that) . . .
230V/5,500 Ohms = 42mA
20H @ 50 Hz has 6,283 Ohms of inductive reactance.
The complex impedance of 20H and 5,000 Ohms is well over 7k Ohms at 50Hz.
I say the best test is to breadboard a triode tube stage, use 10mA, and find where the low frequency response is -3dB.
Go to the tube curves, and find the plate resistance, rp,* at 10mA plate current (you will need this value later).
The choke either goes down to 40Hz (bass guitar) 30Hz, 20Hz, 10Hz, or it does not.
Then test where the high frequency response is - 3dB. It either goes to 10k, 20k, 30k, or beyond.
Note that you got a certain low frequency response, and a certain high frequency response, when the choke was driven with the plate impedance, rp, from above *.
Now you can see if that rp gives the response you want; or whether you need a lower rp;
or whether you can use a tube that has a higher rp, and still give you the response you want.
Guess what, the OP does not have a signal generator, and does not have a scope.
He has to find somebody in his area who does.
Otherwise, forget about using the unknown chokes, and purchase some chokes of known value to use.
Or, let him build the circuit he wants with those chokes, and see if it sounds good to him.
Real test equipment is required
Or, Real ears are required
Pick one.
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