AC and Pwr Supply

AC and other line topics ------------------------------------------------------------------------------------------------------------ Date: Sun, 9 Nov 1997 08:02:09 +0500 From: "Chuck Rippel" <crippel@...> Subject: [R-390] Re: Help please GFI problem > Subject: Help please GFI problem > Chuck, you may have once posted suggestions to me or to the reflector > regarding the apparently naturally-ocurring leakage at the line filter > which then trips my GFI in my modern home. I wired in a nice 3-wire > grounded cord and plug to my 390A, and tripped the GFI in the bathroom > adjacent to the shack, taking out the power to the radio. Now, I just am > using a 2-pin adapter at the end of my 3-pin plug, so I've effectively > undone the update I installed. The 390 will not work in a GFI outlet. Wasn't made to pass UL in 1954. > Is there a simple fix to the radio? I'm getting all kinds of > theories from local (well-meaning) ham-friends, but would really > appreciate hearing from you on this. As always, thanks for all your > help. Would like the venerable old radio to be happy in the modern home, > with me the operator safe from annoying "tingles" or worse. I'd put on a 3 wire cord. I do on all the ones I restore. There is actually a military mod for it. It's kinda tricky to make sure you get the polarity right in the input filter tho. The black wire should attach to the terminal on the input network that is TO YOUR >RIGHT< as you face the REAR of the radio. White, or neutral is to the left. The ground lug goes on the screw which holds the protective cover over the input network. Hope that helps. ----------------------------------------------------------------------------------------------------- Date: Sun, 9 Nov 1997 08:35:40 -0500 From: Don Stepka <dts4@...> Subject: Re: [R-390] Re: Help please GFI problem The line filter has about .05-.1uF from each leg of the AC to ground. The primary purpose (i.e., the reason the caps are so large) is to prevent signals from leaking OUT of the 390. If this is not a problem (and it shouldn't be, unless you are trying to make sure a submarine can't target your house), then replace the filter with a .001 from just one leg to chassis. If you use a 3-wire cord (or polarized 2-wire), you can choose the neutral leg. ------------------------------------------------------------------------------------------------------------ Date: Wed, 12 Nov 1997 00:24:33 -0500 From: Don Stepka <dts4@...> Subject: Re: [R-390] Re: Help please GFI problem No magic. The root of the need for line-to-chassis caps is RF leakage. RF can leak into the radio on the power line, and it can leak out. If the line is not bypassed to chassis, crud on the power line (from motors, fluorescent lights, dimmers, etc.) gets into the radio and raises the interference level. The .001 uF value I recommended is the traditional value used by radio manufacturers for decades to solve this problem. The traditional approach bypasses only one side of the line because the capacitive coupling of the two phases in house wiring and in the radio's power cord is pretty good at HF, so the one bypass is sufficient to eliminate line-borne RF interference. The reactance of the .001 uF capacitor at 60 cps is around 3 M ohms, so even if it is connected from the hot side of the line to chassis you get only around 40 uA of ground leakage, not enough to trip most GFIs. (Of course, if it is connected from the neutral side of the line to chassis the ground leakage will be much lower.) In the old non-polarized, non- grounded plug days, the leakage current could potentially flow through the operator to ground from the chassis, and the .001 uf / 40 uA possible leakage current was chosen to limit the risk of shock. Those with VTVMs could measure the chassis potential and plug the radio in such that the neutral leg was the one bypassed to chassis. In these grounded-plug days, any leakage current flows through the ground wire and the GFI (if any). The 390 series radios were designed to be low-radiation devices so that their installations would not give themselves away to an enemy using direction-finding receivers, particularly in seagoing (i.e., low-background-noise) missions. This requirement called for better bypassing than the interference requirement above calls for, so the 390 series designs have both sides of the line bypassed to chassis with larger capacitors. This has two effects: because both sides of the line are bypassed, no matter which way you plug it in the chassis floats at half line voltage; and the leakage current is much higher (as much as several mA) -- high enough to trip GFIs with authority (you can easily draw sparks from the (ungrounded) chassis to ground). Since most of us have no reason to Tempest-certify our shacks, the .001 uF bypass on one power leg is the better choice for us. It does a perfectly good job of preventing line-borne RF interference without risking shock or GFI problems. The best technique is to install a 3-wire cord and bypass the neutral leg to chassis with the .001 uF capacitor, so the 60 cps ground leakage will be almost nil. Of course, the capacitor chosen should have a self-resonant frequency well above the high-frequency limit of the radio, and should withstand 120 VAC continuously with a large safety margin. 1000 V disk ceramics are a good choice. Don ----------------------------------------------------------------------------------------------------------- From: Walter Dail <dail@...> Date: Mon Jan 12, 1998 5:39 am Subject: [R-390] FL-101 AC Input Filter In my Amelco R-390A, I am finding that I am having excessive AC leakage to ground(very unsafe!). Anyway, I suspect the AC input filter FL-101 has bad caps. Since this is a sealed unit, I guess I should remove it totally from the circuit. I was wondering if anyone else has had this problem, and what did you do to solve it. I really hate taking parts out of my radio, since I want it to be EXACTLY like the factory built it, but I have to be safe too. Any suggestions? ------------------------------------------------------------------------------------------------ From: "Dr. Gerald N. Johnson, P.E." <geraldj@...> Date: Mon Jan 12, 1998 7:48 am Subject: Re: [R-390] FL-101 AC Input Filter The original caps are probably large enough to cause what today is excess leakage. Most radios of the 50s and 60s had .01 to .05 mf from each side of the line to the chassis. Enough to cause a shock when the radio wasn't grounded. Add a little leakage from rotten caps and things get lively. Unless this "excess" leakage is tripping the GFI in the power line and you don't have the chassis grounded, the power line should eventually fry the bad cap, hopefully open. Then you won't have such a problem. But any radio of that vintage without a ground on the chassis will tickle. ---------------------------------------------------------------------------------------------------- From: "Dr. Gerald N. Johnson, P.E." <geraldj@...> Date: Tue Jan 13, 1998 7:24 am Subject: Re: [R-390] FL-101 Input Filter Comments Strictly speaking, Walter, the current to ground through the bypass capacitors is NOT power but purely reactive current (e.g. 90° out of phase with the applied voltage) and doesn't make the KWH meter move. So there's only a tiny waste of power from the losses in the series resistance of the current in the power wires. And that's barely detectable but NOT registered on the KWH meter either. ----------------------------------------------------------------------------------------------------------- Date: Sun, 23 May 1999 12:44:00 -0500 From: "Dr. Gerald N. Johnson, P.E." <[email protected]> Subject: Re: [R-390] FAQ Page Updates Al, I agree with the concept but I object to your circuit... First you raise the receiver neutral line away from ground. That means there's 12 volts to ground on the neutral even with the receiver power switch off. That's NOT good. Then you have full elevated line voltage on the transformer primary, that's inefficient wasting more power in core losses than needed. It would be safer and more efficient to connect the transformer secondary on the high line input side of the transformer so you lower the voltage on the transformer primary and so lower its energy wasted in core saturation (precisely what you are trying to do for the R-390) and you maintain the neutral wire unbroken... In your picture, spin your transformer and windings (including pri/sec labels but not voltage labels) 180∞. Its best to experiment with the connections to get the polarity correct in this manner. Connect a lead from the transformer secondary to the high side of the transformer primary and apply voltage (6 to 125) to the transformer primary. Check the voltage from the open end of the secondary to the low side of the transformer primary. If its less than the applied voltage, swap the secondary leads (with power off). If its greater, its correct. Then for use, apply the high line voltage (127 or so) to the series connection of the two windings, and connect the receiver load across the original primary alone. Besides filament transformers there are transformers made with 12/24 or 16/32 secondaries and 120/240 volt primaries specifically for the purpose. Weekend before last, I did that with a 45 KVA 3 phase 480/208 transformer to let it run cold with 250 three phase applied to what had been the 208 volt winding to supply power for a LARGE 440 volt planer in a wood working shop.

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