crochambeau
Active member
I believe I have a part built for 400 hz operation.
Okay, here's the back story: I'm building a very simple variable DC power supply for a weirdo project I am building. I know it's going to be noisy, that's part of the charm.
Power supply consists of AC mains, switch, fuse, variable autotransformer, 120 to 24 volt step down transformer, full wave rectification & a cap (3300 @ 35v).
So, the cap is old and I figure I may as well burn it in slowly. There's a little electrical buzz coming from the variac (actually a Standard Electrical Products Adjust-A-Volt, but variac is easier to type), but nothing major and no cause for alarm. About half way through the travel my nose/gut tells me it's time to temperature check everything. Remove mains connection and feel around. Everything is nice and cool until I get to the variac.
It's uncomfortably warm enough to conclude that long term use is not going to work out for me. I run through the standard stupidity checks and everything seems OK. No shorts, wiring looks good. Then it dawns on me, I think the variac was harvested from some mil spec survey equipment which was built for 400 hz AC.
Naturally, the part in question has no labelling, so I'm reaching a little bit. My cheap inductance meter operates at higher frequency, so I don't think it's measurement is conclusive. The more I think about it, the more sense it makes, perhaps 60 hz was working on cooking the winding and there's simply no way to safely deploy this part in 120 volt 60 hz mains?
So. My options now seem reduced to wiring up the variac in the 24 volt AC portion of the secondary, which also "suffers" from low frequency but at a fifth of the voltage, or just using the part as a variable inductor for passive EQ.
Would 24 volts at 60hz be that much safer, or is it six of one half dozen of another?
Okay, here's the back story: I'm building a very simple variable DC power supply for a weirdo project I am building. I know it's going to be noisy, that's part of the charm.
Power supply consists of AC mains, switch, fuse, variable autotransformer, 120 to 24 volt step down transformer, full wave rectification & a cap (3300 @ 35v).
So, the cap is old and I figure I may as well burn it in slowly. There's a little electrical buzz coming from the variac (actually a Standard Electrical Products Adjust-A-Volt, but variac is easier to type), but nothing major and no cause for alarm. About half way through the travel my nose/gut tells me it's time to temperature check everything. Remove mains connection and feel around. Everything is nice and cool until I get to the variac.
It's uncomfortably warm enough to conclude that long term use is not going to work out for me. I run through the standard stupidity checks and everything seems OK. No shorts, wiring looks good. Then it dawns on me, I think the variac was harvested from some mil spec survey equipment which was built for 400 hz AC.
Naturally, the part in question has no labelling, so I'm reaching a little bit. My cheap inductance meter operates at higher frequency, so I don't think it's measurement is conclusive. The more I think about it, the more sense it makes, perhaps 60 hz was working on cooking the winding and there's simply no way to safely deploy this part in 120 volt 60 hz mains?
So. My options now seem reduced to wiring up the variac in the 24 volt AC portion of the secondary, which also "suffers" from low frequency but at a fifth of the voltage, or just using the part as a variable inductor for passive EQ.
Would 24 volts at 60hz be that much safer, or is it six of one half dozen of another?