# RE: [TCML] Calculating transformer output at lower voltages

```Since I also have no high voltage meter,  I figured out an easy way to use
my multi-meter in the ohms, then volts AC scales....

TRx = Rs/Rp

We can then use the tested ohms ratio (TRx:1) to calculate the voltage
coming out of the secondary, when a specified test voltage is applied.

Hypothetical value example...
Secondary measures 1250 ohms
Primary measures 10 ohms.

Ratio (as per above math): 125:1  (125 is now our multiplier)

120v in X 125 = 15,000v out (normal NST)
4v in X 125 = 500v out (within the range of most multi-meters)

I even threw together a small Windows application to do the math for you.

http://www.msbministries.org/blog/2011/11/17/new-software-transtest/

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of mrapol@xxxxxxxxxxxx
> Sent: June 07, 2012 8:30 AM
> To: Tesla Coil Mailing List
> Subject: [TCML] Calculating transformer output at lower voltages
>
> I know the usual formula Vs/Vp = Ns/Np for calculating transformer voltages,
> but I have a problem in that I am dealing with a sealed NST and don't know
> the number of secondary or primary turns. What I am trying to do is
> calculate the output of a 12kV NST when it's getting less than 110 volts
> input. For example, if I feed the NST 30 volts AC, what does it put out? Is
> there any way to figure this out without a high voltage meter (which I don't
> have) and without knowing the number of primary or secondary turns?

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