# Re: Identifying Current and Voltage on vaguely marked MOT. (fwd)

```---------- Forwarded message ----------
Date: Mon, 27 Aug 2007 18:20:35 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Identifying Current and Voltage on vaguely marked MOT. (fwd)

You need to measure to find out actual specs. Most MOTs will be less
than 2600 Vac and many meters will read about 700 Vac. That's a little
less than a factor of 4. But, protect your meter by being smarter than
the voltage. If you have the capability to vary the AC voltage from 0 to
full voltage (like a variac), start at 0V and slowly increase the
voltage until you are just below the meters specifications. Log down the
voltage on both the primary and secondary sides of the transformer.

Here are a few basic calcs from a few simple measurements:

Turns ratio = Vsec/Vpri (as stated above)
Sec Volts = Turns ratio x Vpri (at 120 Vac)
Inductance ratio = Turns ratio x Turns ratio
Primary reactance = Pri Voltage / Pri Current (both measured with the
secondary shorted)
Primary inductance = Pri reactance / (2 x PI x Hz)
Secondary inductance = Pri Inductance x Inductance ratio

Take care,
Bart

PS: As always, becareful with these type of measurments (lots of AC
floating around and easy to get zapped).

Tesla list wrote:

>---------- Forwarded message ----------
>Date: Mon, 27 Aug 2007 00:21:46 -0500
>From: Glen McGowan <glen.mcgowan@xxxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Subject: Identifying Current and Voltage on vaguely marked MOT.
>
>Just curious if there's some super secret math out there that can help me
>identify the rated voltage and current of a MOT.  I only have one variable
>for the equations.... the MOT is labeled with 700W output. That's it......
>
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