Transformer Help

That may work at 120 V AC ip, however, you said that you had to do various frequencies. A rheostat is a variable coil. Its properties will change with frequency. At DC (0hz) it is a short. If you stay with this option I would not rely on the settings of the rheostat for your amperage. The resistance of the rheostat will change with frequency. You should put an ammeter in series or use another measurement technique for your current.

Best setup is a resistor that limits your currrent for the highest current setting plus a Switch to switch in variable resistors for changing the settings. These variable resistors will be used to calibrate each setting. As well use accurate test equipment to measure both the input and output. An oscilloscope is important to ensure clean signals and accurate measurements.

I have to test 100VAC 50/60Hz, 120VAC 50/60HZ, 200VAC 50/60Hz, 208VAC 50/60HZ, 220VAC 50/60Hz, 240VAC 50/60Hz, 250VAC 50/60Hz. Some will be fully loaded at 2.1A and others at 1.6A. As you can see, the frequency won't vary too much. I currently have it set up with an ammeter in series on one leg after the rheostat. Wouldn't the other resistor just be redundant?

The resistor is there for protection to limit the maximum current. If you dial the rheostat too far one way you could drive the current beyond the limit of the transformer coil and damage it. Without knowing the limit of the transformer, I would set the resistor at 20% over your highest current potential. Doing the math:

250VAC RMS X 1.414 = 353.5V Peak

2.1A X 120% = 2.5A

353.5V / 2.5 A ~= 140 Ohms

<A rheostat is a variable coil. Its properties will change with frequency. At DC (0hz) it is a short>

Sorry Mate ! We learnt always that rheostat is a Resistor wound on an Insulated tube ready to slide and vary the tap.

Hence at DC it is 100 OHMs(say). At 50Hz it may be Impedance= 100.05 Ohm. At 60 Hz may be 100.06Ω!

You go ahead-OK

I stand corrected.

I did not know the frequency range or accuracy required. (wire wound = coil)

If The minimum resistance (rheostat adjusted all the way one way) is approximately 140 ohms it would be safe, however, if it is 0 ohms; a current limiting resistor would be prudent.

He better be prudent--

Always begin midway(slider to rear terminal shorting) -go a little left-watch Ammeter-correct the direction-- >>> till test current is there.

Don't rush-spend 2 minutes in 1 test!

Better Late than a burnt TRX winding or a smoked Rheostat!

Unless........ you want to have a little fun

What are you trying to test? Putting a resistor at the output is only loading the XFMR.

There are several standard tests for XFMRs

Resistance Measuremnets, Ratio Test, Polarity and Phase relation(3 Phase), Impedance and load loss, Excitation Loss and Excitation Current and Dielectric tests-Low Frequency (IMPULSE, AKA the BOOM BOOM Test).

Depends on what you want to do.

In stead of using a rheostat and always varying & monitoring all at once may have risk of erroneous accident or atleast burning your test gadget or transformer under test: 1. You should make Fool-Proof Simple Test Loads for each Test & mark properly. 2. It will be safe for you & your assisstants /co-workers and will save your supervision. 3. It will look more professional & will earn dignity of your job to your Clients/ managers. 4. It will be your skill to expand your job & knowledge. Wish you best of luck

In stead of using a rheostat and always varying & monitoring all at once may have risk of erroneous accident or atleast burning your test gadget or transformer under test:

1. You should make Fool-Proof Simple Test Loads for each Test & mark properly.

2. It will be safe for you & your assisstants /co-workers and will save your supervision.

3. It will look more professional & will earn dignity of your job to your Clients/ managers.

4. It will be your skill to expand your job & knowledge.

Wish you best of luck