# Re: Fw: Tesla List - Micro Wave Oven Transformers

```Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Greg,

```
Yes, inexpensive LCR meters can be used to measure inductances. However, for inductances with large iron cores, The LCR meter probably wont be able to magnitize the core. For these cases, it is best to energize the inductor like you will in the "real" application and measure the voltage across the inductor and the current thru it. Impedance (V/I) will mostly be in the inductive reactance of the inductor and the L can be calculated from XL = 2 * pi * freq * L. Therefore L is:
```
L = V / (I * 2*pi*freq)

```
An AC volt meter and AC amp meter is all that is needed. You may also want to use a variac to control the voltage
```
Gerry R.

```
```Original poster: G Hunter <dogbrain_39560@xxxxxxxxx>

calculate the correct size ballast for MOTs?  Is your
goal to wind your own ballast, or are you merely
trying to figure out what kind of ballast to buy?

Yes, one can measure inductance with simple equipment.
A digital LCR meter comes to mind.  In the US one can
be bought new for under \$100.  They are probably about
the same price over there.  A digital multimeter with
an inductor function is probably even cheaper. Check
e-bay and Amazon.

ballasts or guitar amp chokes for example), you won't
need to measure their inductance as it will be a known
value.

Cheers,

Greg

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: "James Howells"
> <james@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Thanks for the "primer" on MOT
>
> As I will construct a power supply from my MOT
> eventually .... can
> anyone help with how to determine the size of
> ballasts ... I have
> e-mail 4 UK universities and spent 50 or so hours
> surfing for
> information but still do not understand how to
> determine their size (
> can one measure inductance with simple equipment ?
> ... i.e NO scope)
>
> James Howells   ( England )
>
>
>
> Protected by www.Spamjab.com
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>
>

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```

```