Measure unknown choke?

coldcathode · 13th October 2009, 12:38 PM

I picked up a very beefy power supply at a flea market for $2 last weekend.

The Power tranny is 1150CT @ 350mA
The chassis appeared to be homemade but not sure
The choke and PT are both potted in squarish metal cases (military type).
The choke has no info on it.

Is there a simple way to measure its inductance without an LCR meter?
I have a DMM can I use this somehow?

Tom Bavis · 13th October 2009, 01:17 PM

Apply 10VAC and measure the AC current (if it's too low, use 100VAC...). Impedance is V/I. Inductance (ignoring R) is Z/(2*pi*60). Inductance will not be the same with DC current, but this will get you in the ballpark.

coldcathode · 13th October 2009, 01:26 PM

Quote:

Originally Posted by Tom Bavis

Apply 10VAC and measure the AC current (if it's too low, use 100VAC...). Impedance is V/I. Inductance (ignoring R) is Z/(2*pi*60). Inductance will not be the same with DC current, but this will get you in the ballpark.

Tom,

Excuse my ingnorance. Is Henries a unit of Inductance or Impedance?

I know this choke is sufficient current wise for the PS I am building but I am looking for the Henry number to use in PSU designer. The DCR of the choke is about 150Ohms

coldcathode · 13th October 2009, 01:35 PM

Tom,

Applied 16.5VAC 60hz to the choke
Got 2.8mA AC thru it.
So Impedance is 5892 (16.5/.0028)?
So Inductance is aproximately 15 hy (5892/(120*pi)?

peranders · 13th October 2009, 02:01 PM

You'll have to measure the DC resistance also if the Q is low.

zigzagflux · 13th October 2009, 03:18 PM

Quote:

Originally Posted by coldcathode

So Inductance is aproximately 15 hy

Correct. With 150 ohms of DCR, the true inductance will not be much different, so don't bother incorporating into your calculation. In fact, the change in inductance due to actual DC current while in circuit will affect the inductance more than the DCR will.

Modelling 15H and 150 ohm in PSUD will be a very good model.

coldcathode · 13th October 2009, 03:34 PM

This turned out to be a GREAT find at the Flea market. $2.00 can't be beat!

I finished taking this apart and found that it was probably "homebrew" stuff, found marking on the aluminum sheet used to make the chassis that indicate it is much younger than the transformer and choke.

It appears that it was also a bit of OVERKILL for whatever they were powering because of a 40K and 19K 25Watt resistors I found in the RC filter section.

I now have a decent PS for my 829B "Triode" Push Pull amp (4 tubes) that I have been toying around with in the back of my head.

coldcathode · 13th October 2009, 03:40 PM

First Load is input/splitter/driver sections ~40ma + regulated by 3 VR tubes to 450V (thats the other 24 odd mA)

Second load is the (4) 829B's "Triode Strapped" at 60mA each

coldcathode · 13th October 2009, 03:46 PM

I will use (2) 5U4GB in Parallel

13th October 2009, 12:38 PM	#1
coldcathode diyAudio Member Join Date: Jan 2009	Measure unknown choke? I picked up a very beefy power supply at a flea market for $2 last weekend. The Power tranny is 1150CT @ 350mA The chassis appeared to be homemade but not sure The choke and PT are both potted in squarish metal cases (military type). The choke has no info on it. Is there a simple way to measure its inductance without an LCR meter? I have a DMM can I use this somehow?

13th October 2009, 02:01 PM	#5
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	You'll have to measure the DC resistance also if the Q is low. __________________ /Per-Anders (my first name) or P-A as my friends call me

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13th October 2009, 01:17 PM	#2
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	Apply 10VAC and measure the AC current (if it's too low, use 100VAC...). Impedance is V/I. Inductance (ignoring R) is Z/(2pi60). Inductance will not be the same with DC current, but this will get you in the ballpark.

13th October 2009, 01:35 PM	#4
coldcathode diyAudio Member Join Date: Jan 2009	Tom, Applied 16.5VAC 60hz to the choke Got 2.8mA AC thru it. So Impedance is 5892 (16.5/.0028)? So Inductance is aproximately 15 hy (5892/(120*pi)?

13th October 2009, 03:34 PM	#7
coldcathode diyAudio Member Join Date: Jan 2009	This turned out to be a GREAT find at the Flea market. $2.00 can't be beat! I finished taking this apart and found that it was probably "homebrew" stuff, found marking on the aluminum sheet used to make the chassis that indicate it is much younger than the transformer and choke. It appears that it was also a bit of OVERKILL for whatever they were powering because of a 40K and 19K 25Watt resistors I found in the RC filter section. I now have a decent PS for my 829B "Triode" Push Pull amp (4 tubes) that I have been toying around with in the back of my head.

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