The AM Forum

I'm building an unregulated power supply using a transformer as a voltage doubler.  The power transformer has a secondary of 45 volts at 17 amps.  I'd like to limit the current inrush during power up and I happen to have a really big ballast transformer (see picture).

Could I use the secondary of the ballast transformer as an inductive filter for the power supply?  Resistance starts out at around 2 ohms and settles down to 0.3 ohms.

Jon

If you are going to draw more than about 5 amps in your power supply it wont cut it.

Did you measure the inductance of the secondary?



Phil

It would at times draw more than 5 amps, so, yeah...

I didn't measure the inductance since I don't have a meter.  I need to invest in one since they're pretty cheap.

I'll just use some sort of timed soft start circuit.  I'm going to Vegas again for a couple days (I know, weird), so I'll think of something.  I'm taking the laptop this time.  No evil, scary books and calculators.

Jon

cheap inductance checker.

will it make a difference if the inductor saturates at >5A as long as the windings don't overheat? It'll already have done its job? I don't know your circuit.

Excuse the napkin, it’s the only paper at the moment.

True about the saturation. I only need inductive resistance for a few seconds. The coil windings are big enough to handle the current.

Jon

Yeah, that’s not going to work in a voltage doubler. I’d need something purely resistive in this case.

I’ll just do a resistor in the primary and then short it after a few seconds. It’s not thrilling, but it works.

Jon

Ur running an 800w PS.
You'll want a fairly hefty relay, and fairly hefty power resistor in series.
Something around 10ohms +/- will do the trick. About 50watts - the less time you have it in series the lower
the wattage needed.
The Chinese on epay sell these little adjustable timer modules with a relay for a buck... :D

What's it gonna run?

                             _-_-

I hate to say it, but I’ve changed my mind on what to build. I had planned on building a PWM for a class E rig, but instead I’m building another E transmitter. I already have the Heising modulator for it completed.

This transmitter will be 100 watts carrier for 40 meters using two FETs in parallel. It’s just like my current 40 meter, single FET rig except I’m just adding another FET.

My coworker is painting the cabinet for me. I picked it up at the last hamfest, and it is absolutely the perfect chassis for the project.

Jon

So, a class H modulator then?? Or?

Modified Heising with an external solid state audio amp.