measuring output transformer inductance?

mctavish · 27th September 2009, 07:16 PM

So I am attempting measuring inductance on a 5k to 8ohm single ended output transformer with an LCR meter, Should i load the secondary with an 8 ohm resistor or leave it open? thanks everyone.

Shoog · 27th September 2009, 08:30 PM

Any reading would be meaningless unless it has the standing DC current going through it. Without this the reading will b e very high.

Shoog

Yvesm · 27th September 2009, 08:49 PM

Quote:

Originally Posted by Shoog

Any reading would be meaningless unless it has the standing DC current going through it. Without this the reading will b e very high.

Shoog

Yes . . . or very low

Iron permeability is level sensitive.

jechentau · 27th September 2009, 08:57 PM

and, it depends which inductance; leakage inductance, afaik short the secondary.

primary inductance, secondary open. but i never tried measuring inductance yet though.

disco · 28th September 2009, 03:01 AM

Took measurements with an tubed bridge last week and got almost identical readings using 40mA bias and no bias current. This bridge uses a transformer to compare (unknown) impedance to a known.

BudP · 28th September 2009, 03:47 AM

If you use a standard 1vac @ 120 Hz inductance bridge with a SE opt you should know how much DC current the transformer is designed for.

Actual working inductance, with 20 to 40 ma flowing through an appropriate gap, will be approximately twice the rest value (1 vac @ 120 Hz is a rest condition for OPT's. For a PP OPT you can count on about 10 times of this rest inductance.

If the SE OPT is designed for even higher current, 60 to 180 ma, the gap will keep the working inductance to about 1.3 times the rest voltage. Larger gaps than this (physical gap of .015 for E/I or .030 for C Core) and currents out to 320 ma DC, will give a flat inductance out to saturation, from rest conditions.

Bud

27th September 2009, 07:16 PM	#1
mctavish diyAudio Member Join Date: Feb 2008 Location: Niederösterreich	measuring output transformer inductance? So I am attempting measuring inductance on a 5k to 8ohm single ended output transformer with an LCR meter, Should i load the secondary with an 8 ohm resistor or leave it open? thanks everyone.

28th September 2009, 03:01 AM	#5
disco diyAudio Member Join Date: Apr 2006 Location: Holland	Took measurements with an tubed bridge last week and got almost identical readings using 40mA bias and no bias current. This bridge uses a transformer to compare (unknown) impedance to a known. __________________ jaap

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27th September 2009, 08:30 PM	#2
Shoog diyAudio Member Join Date: Aug 2002 Location: Eire	Any reading would be meaningless unless it has the standing DC current going through it. Without this the reading will b e very high. Shoog

27th September 2009, 08:57 PM	#4
jechentau diyAudio Member Join Date: Feb 2005 Location: Gelderland	and, it depends which inductance; leakage inductance, afaik short the secondary. primary inductance, secondary open. but i never tried measuring inductance yet though.

28th September 2009, 03:47 AM	#6
BudP diyAudio Member Join Date: Feb 2007 Location: upper left crust, united snakes	If you use a standard 1vac @ 120 Hz inductance bridge with a SE opt you should know how much DC current the transformer is designed for. Actual working inductance, with 20 to 40 ma flowing through an appropriate gap, will be approximately twice the rest value (1 vac @ 120 Hz is a rest condition for OPT's. For a PP OPT you can count on about 10 times of this rest inductance. If the SE OPT is designed for even higher current, 60 to 180 ma, the gap will keep the working inductance to about 1.3 times the rest voltage. Larger gaps than this (physical gap of .015 for E/I or .030 for C Core) and currents out to 320 ma DC, will give a flat inductance out to saturation, from rest conditions. Bud

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