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Old 7th March 2010, 04:36 PM   #1
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Default Hammond DC chokes 193L

I bought 4 pcs of Hammond 139L Chock from Angela.com. They came in white boxes with no printing on them. The seal has printed marks stating 139L, 5H + - 15%, Made in Canada etc. Yet, when I measure them with my LC meter, all of them are between 3.7H to 3.98H and theit DC resistance is stounf 51 ohms instead of 57 ohms on the spec.

Does anyone here have the same experience? Are they sub-standard products? Or am I doing the correct measurement?

LCR meter used: UNI-T UT603 with new battery.

Last edited by Sunsun22; 7th March 2010 at 04:40 PM.
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Old 7th March 2010, 05:54 PM   #2
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Inductance measurement have typo. They ranges from 3.72H to 3.88H. Other particulars remain unchanged.
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Old 8th March 2010, 01:58 PM   #3
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I wrote to Hammond and this is their reply:

Hello Sunny Chan

This is a common question.

The 193L can not be tested with a battery opperated meter.

Lamination steel needs to be excited ( energized ) enough to be in its opperating range .

There needs to be at least 30Vac of AC drive or at least 100 mA DC passing through the inductor during the test to measure correctly. See below.

Test
Conditions
Acceptance Criteria
Specified By






Inductance
@ 30V, 60Hz, 300mADC, BLK BLK
13.84mA 18.72mA



Adjust gap to obtain 5H 15%






Hope this helps.

Doug Hutt
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Old 8th March 2010, 09:48 PM   #4
db! is offline db!  Canada
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I am pretty sure this is the case; my LC meter measures small inductors accurately but gives strange readings when used to measure chokes or transformers. As for the 51 ohm DC resistance; it's still in the neighborhood of a 5H choke, changes in manufacturing processes/materials might be accountable for this... Also, are you sure your meter calibrated properly?
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Old 8th March 2010, 11:51 PM   #5
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I would place a mA meter (ideally one that is internally fused) in series with the choke and throw 120VAC across the chain. Measure the current, you know the voltage, and calculate the henries. Even then, in my experience you get only close. But much closer than what your meter is giving you.
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Old 9th March 2010, 02:00 AM   #6
jrenkin is offline jrenkin  United States
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Try this:

Untitled
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Old 9th March 2010, 11:32 AM   #7
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You can do that, but you will find R is maybe 1% of the total impedance, hence all those calculations taking R into account do NOT change the value of the measured inductance. The in circuit actual inductance will vary anyway; there is no need to split hairs incorporating the DCR of the choke.
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