Try as the Diabolical Artificer suggest.
I use this method for years, with, or without DC current pushing.
I use this method for years, with, or without DC current pushing.
I used a no-name DMM in 2mA AC range. I tried your suggestion using an 1k resistor, the voltage drop was 1.9V on it. The calculated inductance is 400H.
Feeding the secondary with 13.3VAC the current was 16.5mA. The calculated secondary inductance is 2.5H, which is transformed by n^2 that is 20*20*2.5 = 1000H.
So it must be somewhere between 400H and 1000H. Both measurements were at high level.
Basically you measure the idle current of a transformer, somewheare there is a systematic error because obtining a 1000 H inductor with a magnetic core used in mains transformers is un realistic
IMO the 1k is too much if the primary DCR only 238R.
Try 100R, and repeat the measuring.
The 3k2 PP transformers primary inductance is rather in the 50..150H range, than few hundred Henrys.
Try 100R, and repeat the measuring.
The 3k2 PP transformers primary inductance is rather in the 50..150H range, than few hundred Henrys.
Secondary inductance 2,5H is highly unrealistic too . as it should have only around 100-200 turns . This is somewhere around 100 mH range .
To get 400H with 1.9mArms of current you must have had about 240Vac 50Hz across the total primary winding - which I think aligns with your setup?
400H is nominal of a reasonable modern hi-fi OPT PP primary which has not been pushed partly into its saturation region as the excitation voltage is high at 240Vac.
Any ESR, whether from the winding itself or a sense resistor will introduce some minor error - which can be removed by some simple maths. Even 1k is not significant compared to the impedance of the primary (of circa 125kohm at 50Hz).
The meter may have a relatively high shunt impedance when measuring on the 2mA range - that can be checked by using a safer low ACV like 10Vac and loading the 10Vac with a 5k6 resistor in series with the meter on 2mA range, and noting the displayed current.
Measuring values from the secondary side and then translating to the primary side is fraught with uncertainty.
400H is nominal of a reasonable modern hi-fi OPT PP primary which has not been pushed partly into its saturation region as the excitation voltage is high at 240Vac.
Any ESR, whether from the winding itself or a sense resistor will introduce some minor error - which can be removed by some simple maths. Even 1k is not significant compared to the impedance of the primary (of circa 125kohm at 50Hz).
The meter may have a relatively high shunt impedance when measuring on the 2mA range - that can be checked by using a safer low ACV like 10Vac and loading the 10Vac with a 5k6 resistor in series with the meter on 2mA range, and noting the displayed current.
Measuring values from the secondary side and then translating to the primary side is fraught with uncertainty.
For E+I laminations inductance beyond 100H is extremely hard to achieve , you would need 4000+ turns even for a big core .
Probably all the error is because of a faulty multimeter ...
Probably all the error is because of a faulty multimeter ...
SOLVED! It was my mistake as it is center tapped transformer on both primary and secondary. Measuring the resonance peak at the end terminals of the tranformer winding by a grounded oscilloscope is not a good idea.
Today I measured the half secondary (center to one end) by the LC resonance method by using a 1uF capacitor and a series 10k resistor. There was a sharp peak at 600Hz which gives 70.4mH, and it transforms to the half primary as 28H. It is more realistic 😉
I think the full primary inductance is 4x this value, i.e. 112H.
Today I measured the half secondary (center to one end) by the LC resonance method by using a 1uF capacitor and a series 10k resistor. There was a sharp peak at 600Hz which gives 70.4mH, and it transforms to the half primary as 28H. It is more realistic 😉
I think the full primary inductance is 4x this value, i.e. 112H.
The resonance method is the safest in the case of low frequency transformers because the choice of capacitors with value above 1uF minimalizes the error due parasitic capacitance
Try the Owen bridge by Steve Bench
http://diyaudioprojects.com/mirror/members.aol.com/sbench101/#Inductance
http://diyaudioprojects.com/mirror/members.aol.com/sbench101/#Inductance
A little bit old thread, but the simplest method is a resistor in series with the inductor, and voltage from a variance or a small transformer.
Given the monstrous size and the 3000+ turns (!!!) I can not see any practical reason to measure primary inductance. It is surely more than enough for every purpose.
Given the monstrous size and the 3000+ turns (!!!) I can not see any practical reason to measure primary inductance. It is surely more than enough for every purpose.
I measured the half primary using the resonance method. The test voltage was 1V, the series resistor=10k, C=22nF. The resonance peak was 133Hz, the resulting L=65H. The full primary should be then 4x65H=260H.
Now I really don't know which measurement should I believe.
Since the primary is constructed by 2x3 series connected windings, I measured one (p11), two (p11+p12) and three windings (p11+p12+p13) against the center tap. Here are the results:
p11=7.4H
p11+p12= 26.1H (theoretically it should be 4x Lp11)
p11+p12+p13=65.1H (theoretically it should be 9x Lp11)
End-to-end it should be 4x9x Lp11 = 266.4H
Remember you will be measuring inductance at different core excitations. You will need to be aware of the Vrms value on the measured coil and the Vac flux density on the core.
Even when using the capacitor resonance method, you need to monitor the voltage across the coil. HiB has quite low permeability in the bellow 0.1T region, can go less than 10 times than average, depending on the grade. Only nanocrystalline and high-nickel score well and can be relied on micro-excitation measurements.
I find the most useful method the simplest. Inductor with resistor in series, where the resistor's voltage drop is monitored. Using a stabilized Vac adjustable from 0 to 120V AC, 25 to 100Hz, although I'm using 50Hz most of the time. From there I have the parameters entered inside a spreadsheet, including Bac being calculated.
Even when using the capacitor resonance method, you need to monitor the voltage across the coil. HiB has quite low permeability in the bellow 0.1T region, can go less than 10 times than average, depending on the grade. Only nanocrystalline and high-nickel score well and can be relied on micro-excitation measurements.
I find the most useful method the simplest. Inductor with resistor in series, where the resistor's voltage drop is monitored. Using a stabilized Vac adjustable from 0 to 120V AC, 25 to 100Hz, although I'm using 50Hz most of the time. From there I have the parameters entered inside a spreadsheet, including Bac being calculated.