C-Coil inductance value verfication....

[Wolf]

I have a set of C-Coils, labeled 4.7mH, and low enough DCR to not read on the meter. When I measure them, I get 2.9mH and 2.7mH. While this is measured at 1kHz by my meter I would guess, I'm wondering if they were rated funny, or measured at a different frequency where it matters more.

Also- since these are toroidal, is there a range that is higher inductance than where it was measured? I'm really curious as to why these were ~2mH off spec, especially for the price.

I'll be taking a scan of the impedance to check verfication of the simulated system impedance against it. That should likely answer my question as to the actual value in reality, but I'm curious if anybody else came across this problem or issue.

Later,
Wolf

[ligs]

I recently acquired a few large value ERSE Super Q magnetic core inductors and my initial measurements came out 18.6 vs 20 mh advertised and 9.45 vs 10 mh advertised. Both are just shy of 5% tolerance. Under the same calibration, on Jensen air core I got 2.5 mh vs 2.5 mh advertised. On my generic LCR meter, 2 mh to 20 mh is one range.

I wonder if there is any protocol for measuring large value inductance?

[Jeff B.]

I have a set of C-Coils, labeled 4.7mH, and low enough DCR to not read on the meter. When I measure them, I get 2.9mH and 2.7mH. While this is measured at 1kHz by my meter I would guess, I'm wondering if they were rated funny, or measured at a different frequency where it matters more.

Also- since these are toroidal, is there a range that is higher inductance than where it was measured? I'm really curious as to why these were ~2mH off spec, especially for the price.

I'll be taking a scan of the impedance to check verfication of the simulated system impedance against it. That should likely answer my question as to the actual value in reality, but I'm curious if anybody else came across this problem or issue.

Later,
Wolf

They are spec'ed at 1Khz, so you're meter should be pretty close. Those numbers seem very odd. Try measuring them with your WT2. It should do coils very accurately.

[1100xxben]

I can take a look at them sometime and try to measure them, if you'd like.

[mzisserson]

Change the battery on your meter. Sometimes it may not show weak, but with low DCR coils it cannot supply enough current to get an accurate measurement. Been there before!

[PWR RYD]

Change the battery on your meter. Sometimes it may not show weak, but with low DCR coils it cannot supply enough current to get an accurate measurement. Been there before!

+1

[wg_ski]

My experience with the 390-513 meter (the cheap one everyone uses) is that it tends to read HIGH when the battery is weak.

[Wolf]

Thought of that- other coils register values as I measured them prior.

I plan to check with the WT2 as stated and recommended in a few days.

Thanks all,
Wolf

[Wolf]

Checked with fresh batteries, same scenario.

I'll hopefully be taking some sweeps this evening on the xover with drivers connected to totally verify it.

Thanks, all!
Wolf

[Jeff B.]

Checked with fresh batteries, same scenario.

I'll hopefully be taking some sweeps this evening on the xover with drivers connected to totally verify it.

Thanks, all!
Wolf

OK. I have to ask - why not check the inductor with WT2? It's perfect for this purpose. It should settle this for you, one way or another.

[Deward Hastings]

Were these bought new? Do you still have the receipt? Is it possible that someone unwound them deliberately to get the value you're measuring?

And just as a test . . . do you have any other inductors in that value range to check your meter with?

[Wolf]

OK. I have to ask - why not check the inductor with WT2? It's perfect for this purpose. It should settle this for you, one way or another.

That's one of the sweeps I'll be taking...
Guess that wasn't clear.
Later,
Wolf

[Wolf]

Nope- I got them free as a door-prize. No receipt, and it was 4 tears ago.

They aren't unwindable, as they are surrounded with a melted/bonded cover of plastic to keep them secure and stable. You'd have to remove it first.

Yep- I have several, and all checked as previously measured, I just never measured these before.

The sweep will take care of the issue I hope, telling me one way or another.
Thanks,
Wolf

[Wolf]

Okay- it appears I WT2'd one before and did not remember it.
So- I'm attaching the old plot and the new one.

It looks like the one measured at 2.7mH (second attachment) is closer to 3.2mH, which is still not 4.7mH according to the second plot. I don't know which coil I measured for the first plot, being a while ago. However, I got 2.6mH on the first plot with the measured-2.7mH hooked up, and 3.2 once it settled on the second. The plot on the first is old, but the meter reading is new.

So there you have it... My handheld is probably correct.
Wolf

[Jeff B.]

Okay- it appears I WT2'd one before and did not remember it.
So- I'm attaching the old plot and the new one.

It looks like the one measured at 2.7mH (second attachment) is closer to 3.2mH, which is still not 4.7mH according to the second plot. I don't know which coil I measured for the first plot, being a while ago. However, I got 2.6mH on the first plot with the measured-2.7mH hooked up, and 3.2 once it settled on the second. The plot on the first is old, but the meter reading is new.

So there you have it... My handheld is probably correct.
Wolf

I noticed that Le isn't showing a value on either of those plots. Hook up the inductor and click the "Measure Fs, Q, etc." button. WT2 will post the actual measured inductance that it sees.

[Wolf]

I noticed that Le isn't showing a value on either of those plots. Hook up the inductor and click the "Measure Fs, Q, etc." button. WT2 will post the actual measured inductance that it sees.

It won't finish the sweep, or I would have done it that way. It hits the 10 Hz and 20k, and just remains at the top.

The little scale on the left shows the inductance when you select a freq, so 1kHz verified it for me.

Later,
Wolf

[Jeff B.]

It won't finish the sweep, or I would have done it that way. It hits the 10 Hz and 20k, and just remains at the top.

The little scale on the left shows the inductance when you select a freq, so 1kHz verified it for me.

Later,
Wolf

Wow, what a shame. I used WT3 to measure all of my inductors. I didn't know WT2 couldn't do it too. I hear you guys talking about how it's supposed to be better.......

[Wolf]

Wow, what a shame. I used WT3 to measure all of my inductors. I didn't know WT2 couldn't do it too. I hear you guys talking about how it's supposed to be better.......

It did measure it, Jeff. It's on the left.... You don't have to use the Q test to get your C/L/R values.
Later,
Wolf

[Jeff B.]

It did measure it, Jeff. It's on the left.... You don't have to use the Q test to get your C/L/R values.
Later,
Wolf

OK. I was looking in the wrong area. I stand corrected.