Unclear Transformer Specifications

[teroenza]

Can someone help me better understand the specs for this old transformer I found? I'm confused why the input and output power see to differ greatly (115V*1.2A ~140W while 40,000V*2mA~ 80W).

Also, the fuse rating is unclear to me. Does that mean 1 and 2/10 amp?

 

[Tom.G]

Here is a basic description.

The input is rated in Volt-Amps, not Watts. Using the nameplate ratings, the Power Factor (PF) is about 0.57. Since a transformer is coils of wire, it has Inductance, and an Inductance opposes any change in the current flowing thru it. That means, for instance, that the peak current in an inductor (the primary of the transformer) lags, or occurs later than, the voltage peak.

A PF of 0.57 means the phase angle between the input voltage and the input current is about 55 degrees; with a full electrical cycle of the input AC being 360 degrees.

In an actual, physical, transformer there are also losses in the core and in the resistance of the windings that need to be accounted for to get a precise answer. For this specific transformer one of the limiting factors for output current is likely the temperature of the secondary winding. It uses very fine wire to get many more turns to step up the input voltage. A long piece of small diameter wire has a relatively high resistance which means it gets hot with just a little current flowing thru it.

 

[Asymptotic]

It doesn't appear to be a transformer per se. Output is 0 to 40 kV DC at 2 mA max.

0-115/125 V AC at 60/400 Hz suggests it may have been made to operate from aircraft (400 Hz) as well as from 60 Hz U.S. line supply.

It is probably old; been awhile since nameplates used "CY" (cycles) or CPS (cycles per second) instead of Hz (Hertz).

Primary fuse is a Bussmann type MDL (250V, slow blow, 1/4 x 1-1/4", glass tube) rated one and two-tenths (1-2/10) amps.

Be careful. Handling 40 kV at 2 mA requires a respectful nature.

 

[arydberg]

It doesn't appear to be a transformer per se. Output is 0 to 40 kV DC at 2 mA max.

0-115/125 V AC at 60/400 Hz suggests it may have been made to operate from aircraft (400 Hz) as well as from 60 Hz U.S. line supply.

It is probably old; been awhile since nameplates used "CY" (cycles) or CPS (cycles per second) instead of Hz (Hertz).

Primary fuse is a Bussmann type MDL (250V, slow blow, 1/4 x 1-1/4", glass tube) rated one and two-tenths (1-2/10) amps.

Be careful. Handling 40 kV at 2 mA requires a respectful nature.

It also might mean there is only one fuse of a rating 2/10 amp.

 

[Asymptotic]

It also might mean there is only one fuse of a rating 2/10 amp.

True, but primary current rating is 1.2 amps. This is 100% of a 1-2/10 amp rated fuse, but 600% of a 0.2 amp fuse.

 

[Asymptotic]

Couldn't find this particular supply, but suspect it is similar to several available at Surplus Sales of Nebraska like the one pictured below.

 

[teroenza]

Thank you all for the information. I should have noticed off the bat that it's output was DC. After finding it, my original idea was to build a Jacob's ladder, but <2mA of output current seems too low.

 

[Tom.G]

but <2mA of output current seems too low.

Try it and see.

Oh, and let us know too.