re: MMC Loss Measurement

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Charles Hobson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <charles.a.hobson-at-btinternet-dot-com>

Hi Ted
----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, June 03, 2001 4:19 AM
Subject: MMC Loss Measurement


> Original poster: "tesla by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<tesla-at-paradise-dot-net.nz>
>
> Team
> On the list recently I'd asked if anbody had directly measured the loss
> angle of their caps. (With a view to checking MWO caps  to see if any
brands
> might be MMC capable)
>
> Calorific measurements were considered (heat production) as the loss angle
> is generally small and would be hard to measure directly.
>
> The answer of course is easy don't know why not thought of sooner.
>
> Make a parallel resonant cct with cap under test using good quality
inductor
> resonating at freq  interest.
> Measure Q by measuring -3dB bandwith

That's a good practical way of doing it Ted. I used polyester drawing film
as a dielectric in my first home made capacitor.Value 100nF.  Connected it
in parallel with 20uH coil (8mm diameter helically wound copper tubing) and
measured frequency at -3 dB points. Q was 17.  (Fr ~ 110kHz and delta f ~
6.5kHz). Made identical capacitor using polyethylene dielectric. Q measured
at 53. Used 10k resistor between signal generator and parallel circuit to
minimise loading effect.

> Need to check the maths but R can be derived.
> Even if not strictly accurate can make quick easy check and comparison of
> candidate caps as losses mostly in caps

Yes indeed. I used an ordinary oscilloscope, frequency counter. and a
slightly drifty home made VCO in my measurements.  I estimated the
tolerences at +/-5% but the comparisons told me not to use polyester. in
this case.

Chuck
Dorset, England

> Best
> Ted L in NZ
>
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