Re: more MOT calc trouble (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Wed, 24 Oct 2007 20:47:24 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: more MOT calc trouble (fwd)

Hi Kris,

Sorry, to get to this late (involved in some offline discussions). The 
inductance meter is "not" going to give you accurate readings. The small 
9V battery and oscillator circuit in the meter just can't excite the 
iron core to a degree needed to take direct measurements from the meter. 
You've got to pass some real current through the transformer to 
accomplish that. I learned this by doing and Terry Fritz was kind enough 
to hold my hand at the time.

On a particular MOT experiment for a Microsim model, I wanted to measure 
the MOT to properly insert the transformer. I measured 0.0173mH for 
input inductance with my LCR. Well, that would indicate the open circuit 
current would be:

240 / (2 x pi x 60 x 0.0173) = 37 amps!!

Obviously, way too high! Terry told me to measure the input current under a no load condition with the 240Vac input and measure the current. Once I did that, I could find the input inductance as:

L = 240 / (377 x I)

He was right. You'll find your meter is vastly different from the real case. Since then, I've used these particular open and short circuit tests for transformer modeling. However, the LCR is a great meter to have for numerous coil experiments, so if you did win the item, it's a good tool to have in your arsenal.

Take care,
Bart





Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Tue, 23 Oct 2007 14:15:32 -0700 (PDT)
> From: Kris Grillo <kristianisawesome@xxxxxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: more MOT calc trouble (fwd)
>
> I need to measure the leakage inductance of my MO transformers. Would a
> cheap hand held LCR meter like this
> http://cgi.ebay.com/Digital-LCR-MultiMeter-Inductance-Meter-Tester-NEW-AR_W0QQitemZ150174276416QQihZ005QQcategoryZ25421QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
> connected to the transformer primary with the secondary winding shorted
> give me a reasonably close measurement? Close enough for me to figure a
> good LTR cap size? Just wondering. It seems the more I read up on this
> seemingly simple measurement the more complex the problem gets.
>
>
>
>
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