RC Snubber Network for Power Supply Input Choke

[W2XR]

Guys,

I am looking to include an RC snubber network across the input swinging choke of my high-voltage choke-input power supply.

The choke is a 5-25 Hy. @ 1.2 amp swinging choke, followed by 32 mfd of filtering/energy storage. The rectifier network is a full-wave center-tapped configuration using silicon rectifier stacks.

The purpose of the desired snubber is to dampen the possible transient that could be developed by the swinging choke upon turn-off off the of high voltage; I am concerned that the collapsing field within the choke could develop a transient voltage high enough to damage the rectifier stack.

My idea of the snubber network is to use a 3000 ohm resistor in series with a .002 uf. @ 8000 VDC plastic capacitor. The 3000 ohm value is essentially equal to the total load impedance presented to the power supply. This network would be connected across the two terminals of the swinging choke.

Am I on track here with the necessity of including this network within the PSU? Are these RC values I have selected suffiicient for the intended application?

Any thoughts here would be really appreciated!

Thanks & 73,

Bruce, WA2OGS

[WA1GFZ]

Bruce,
Cap may be a little small. I would also do a spark gap. Go to linear Tech and download simulation software and simulate it. It is free. Also works well.
E=Ldi/dt into I=Cdv/dt for starters makes me think the cap could be larger for the current through the resistor limiting current.  3000 sounds good for the resistor since 100 ohms is a common value for line voltages.

[W2XR]

Hi Frank,

Long time, no talk (or QSO)!!! Hope you are doing well, and tks for the reply!

I am getting the 2x 4-400A by 2x 833As rig ready to hit the air very soon now. Antenna should be back up by the 4th of July.

Just kind of gilding the lilly in the rig now, in terms of protecting the larger magnetics, as well as the silicon rectifier stacks. I will calculate the value of C required, based upon this software. I can easily add the ball gap across the swinging (and smoothing) chokes for further protection.

So, what have you been up to lately? Have'nt seen you in a few years since the last Hosstraders I attended.

Best 73,

Bruce, WA2OGS

[Steve - WB3HUZ]

The snubber network on one of my HV supplies (2500V 1.5A) is on the input side of the filter choke. It's a 1uF/5kV glass cap in series with a 5k/100W resistor to ground.

[W2XR]

Hi Steve,

Tks for the info.

The 1 uf cap sounds large, to me at least. The reactance at 120 Hz is significant enough that it is always passing ripple voltage thru the resistor to ground, and possibly acting as a capacitor input filter.

To clarify, is this network connected at the input of the swinging choke directly to ground? How did you derive the values of R & C? And are you using a spark gap across the swinging choke winding?

73,

Bruce, WA2OGS

[Steve - WB3HUZ]

Yes, directly to ground. It's a commercial supply. It's most certainly different than anything I've seen before.