Transformer Capacitor Question

[KaptainKarst]

I'm in the process of building a 48 volt power supply.
I was able to scronge a big transformer from an old optical comparitor machine at the scrap yard today (could not find anything on the number NTC-9312).

What is puzzling me is this. On the secondary there are 4 out puts. Two of the outputs went directly to an 8 MF 660Vac capacitor.

When I measured the voltage off of the first two outputs on the secondary WITHOUT the cap., I get 52 volts AC (not true RMS). The second two outputs (where the capacitor was connected I get 500 volts (both measurements without load). If I put the capacitor back ON, the voltage at the first two has gone up from 52 volts to 81 volts.

I then connected (just for some kind of load) a 250 watt halogen work light on the 52 volt leads and measured voltage. It remained constant while the light was on.

Other than the obvious increase in voltage at the first two outputs, what is the capacitor doing? Is this some sort of surge suppression, or is is just a cheaper way to boost voltage without extra windings?

I would rather NOT have the cap inline and get just the 52 volts for the ~48 volt supply that I am building.

Interesting puzzle. I may even get motivated and put it on the scope to see if the waveforms are changing with/without the cap....

Any old timers out there that has seen this before? I would place the age of this design around the early 60's based on the other components in the unit.

Thanks,
Jim

[Al_The_Man]

That is very likely a CVS, Constant Voltage Source transformer, it use a ferro-resonance as a principle of operation, basically it is a power conditioner and regulator, because the current is always high due to AC currents circulating in the capacitor, they run very hot, in saturation, when a load is applied the resonant circuit current reduces proportionatly, therefore the current is constant, and if a voltage spike were to appear on the incoming AC, because the transformer is in saturation the spike is not passed through from pri. to sec. Therefore the sec. voltage is constant.
Some types have sine wave out and some squarewave, depending on the design.
Al.

[KaptainKarst]

Thanks for the response.

Do you think that it will be okay to operate without the cap and utilize the 52Volts off of the secondary as is?

[Al_The_Man]

I have never tried that, but If you do attempt it and your current is not that high it might work, I would see what happens to the voltage at different loads.
Al.