button to projects menu

UNKNOWN PLATE TRANSFORMER TEST

click on any photo to ENLARGE

When I got this 260 pound beast home I hooked up my variac and put 10 VAC on the primary and read out the secondary voltages. With a little algebra, I calculated the secondary outputs to be 2378-1980-1694-0-1694-1980-2378. The next test was to find out the current rating. The idea of the test was to draw an amount of secondary current and check the internal temperature after 5 or 6 hours. Using the test setup shown in diagram #5, I brought up the primary input voltage until the transformer started to hum and backed it down until it was quiet. (Not scientific but I am after all, a radio AMATEUR).



1 schematic: transformer test setup 2 photo: transformer under test 3 photo: transformer under test 4 photo: transformer under test 5 photo: schematic of test setup
1: The transformer size is approximatly a foot cubed, however, the dimensions of just
    the windings area are 13 x 9 x 9.5 inches.
2: Resistance of the primary between 0 and the 230 tap: .05 ohms. I also put the
    temperature probe down the opening between the primary and secondary
    windings: 180 degrees F after 5 hours.
3: Resistance of the secondary between the highest voltage taps: 11.48 ohms. A full
    wave bridge, capacitive input configuration on these taps would yield: 6047 VDC.
4: Test setup: AC ammeter shorting the secondary. Low voltage applied to the
    primary.
5: Diagram of test setup. I drew 2.7 amps on the secondary for 5 hours, the outside
    winding  temperature was 108 degrees F and the inside between the primary and
    secondary was 180 degrees F. (The temperature rise was gradual, it took hours to
    get to the final value).


FOOTNOTE: After the first set of published results, several guys on amps@contesting.com suggested that the temperature was too high and that the transformer was probably a 2 amp unit. Many hours later when the transformer was again at room temperature, I repeated the test for 6 hours drawing 2.0 amps on the secondary. This time the inside temperature, between the primary and secondary was 144 degrees F which seems reasonable.

Since this transformer can provide 2 amps continuous duty across the full secondary winding, the conservative rating would be 9.5 KVA (2378 VAC x 2 windings x 2 amps). Since the transformer can also provide 2.7 amps without hum and excessive heat in the short term the amateur radio rating could be 12.8 KVA (2378 VAC x 2 windings x 2.7 amps).




button to projects menu     email menu logo