# Re: Measuring inductive limits (was Re: Rotary Sparkgap)

• To: tesla-at-grendel.objinc-dot-com
• Subject: Re: Measuring inductive limits (was Re: Rotary Sparkgap)
• From: Wesley Brzozowski <brzozoww-at-rchland.VNET.IBM.COM>
• Date: Mon, 26 Feb 1996 16:47:36 -0500 (EDT)
• >Received: from VNET.IBM.COM (vnet.ibm-dot-com [199.171.26.4]) by uucp-1.csn-dot-net (8.6.12/8.6.12) with SMTP id OAA18037 for <tesla-at-grendel.objinc-dot-com>; Mon, 26 Feb 1996 14:49:26 -0700

``` "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz> wrote:
> I've just sent a post on how to estimate transformer power.
> Some of the ideas expressed therein can be used. But the real
> one is to measure the Q of the circuit. Since you can measure
> R directly, and since Q = Xl/R, you can calculate Xl and hence
> L.
>     More directly, L = (Q x R)/(2 x PI x f)
>
>     You can also use Q = 1/R x SQRT(L/C) in the form :
>
>     L = Q,2 x R,2 x C

Yes, I did see that posting; very clever to do the driving thru
the primary. But for a power transformer, doesn't that add more
measurement problems? There's a certain minimum primary current
needed to make a power transformer work properly; this level of
current is drawn even when there's no load on the secondary. I
seem to remember something about needing some minimum flux in
the core, but I'm going on some really vague memories here. If
the signal generator is not supplying that minimum current,
you'll get measurements, but will they reflect the way the
transformer will perform under real power?

Wes B.

```