Andy,? I may have missed a couple of other observations but I would like to mention:

1) In situations with a lot of old fashioned 1/2 wave rectifiers or SCR voltage controls (arc furnaces, electroplating controls, certain PCs and the like) or in particular, simple light dimmers, there is a DC unbalance reflected back to the line transformer source.?? Line power transformers are likely to be running near saturation (it's an economic design choice.)?? The transformer is now non-linear and harmonic mixing will take place.? This effect even shows up in big substation links from ground currents such as Schumann resonances generating modulation side bands.

Another example.? I went to a customer site for a problem with our equipment.? They had racks of PCs being turned and off for the start and finish of test sequences.? The surge of too many adjacent test PCs simultaneously coming on coupled with too small wiring, led to PC power supply glitches affecting the test as each test start required the charging of the electrolytic capacitors in the step down power supplies.? A couple of cycles, but more than enough to cause trouble. The turning-on PCs ignored the glitch as they have have delay circuits built in and ignore their own disruptive effect, but already ON PCs were not happy.

Thinking back about the past, mercury vapor rectifiers were often in 1/2 wave configurations -- too expensive to wire up full wave rectifiers --
a 4:1 cost.

Your linear accelerator may have had a similar problem, needs for a lot of power on a pulse basis.? It may? even have been synchronized to the line as I believe some are to minimize line noise from data capture,

Regards,
Charles Patton

On Sunday 15 December 2024 12:13:34 am Andy via groups.io wrote:

But I believe there are more extreme cases where the mains 60 Hz waveform might have distortion around 25% or so.? And those are the kinds of waveforms you actually might want to look at on a 'scope.? 25% THD looks pretty bad.

There's a guy on YT that does a lot of videos on generators, and when he gets one fixed up and making power, he will load test it, which will also typically include hooking a meter and a scope (tablet style) to the output of the generator and seeing what the waveform looks like and how much distortion there is. I don't think I remember any of them being nearly as high as 25%, maybe half that at the most. The ones that were the best were the "inverter" types, which used some electronics to generate the output waveform. They were also the only ones that didn't have to run at a fixed speed, and were therefore more economical for light loads, but they were also the most expensive to fix, if there was any issue with the inverter circuitry.

Got a pile of UPSs to scrap out in the garage. Have any of you guys messed with those? Looked at waveforms, etc.? Schematics for them seems to be pretty scarce, I think I may have run across *one* in all the looking I've done for them. Most are 300VA, for whatever that's worth.

--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin

On Sunday 15 December 2024 10:41:37 am wn4isx via groups.io wrote:

Somehow I suspect it was easier/safer to couple RF onto the AC Mains at RF then to extract raw 60Hz plus harmonics. The BSR- X10? control system used carrier current. AC light dimmers often made them unusable.

If you think old style, magnetic ballast, florescent light were noisy, the modern ones with electronic ballasts are a whole new level of trashy noise.? Probably less harmonic distortion of the 60Hz, but a nightmare of RF EMI.

Yes.

When I last had my bench set up, at my former residence, I had a couple of 4 foot flourescent fixtures hanging over it. They caused a great deal of radiated "stuff" that showed up on my scope, typically around 40 KHz or so. I'm guessing that had something to do with the electronic ballasts in those fixtures...

--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin

开云体育

Another aspect of EMI and ESD to be aware of with fluorescent fixtures. The unshielded tube is like a big long (multi-foot) antenna with a gas arc inside radiating. Even with inductive ballasts, the EMI is there, but more important, if you're interested in high-impedance measurements such as triboelectric charging, you now have 110 V, 60 Hz (USA mains), or 220 V, 50/60 (European, Asian or industrial lighting in the USA) mains a few feet above your experiment. Due to capacitance effects the voltage will probably be divided between ground and the lamp, putting your experiment in a somewhat lower field, but still multiple volts. I used to use a bench with a copper plate surface for EMI work. The voltage divider effect is better controlled, but still has to be considered.

On Sunday 15 December 2024 03:12:22 pm wn4isx via groups.io wrote:

I was given some LED replacements for 4 foot florescents. They were defective from the factory, I carefully disassembled them, removed the stock SMPS, added a simple full capacitor feeding a wave bridge to drive the LEDs. I picked a capacitor whose capacitive reactance made the LEDs bright enough but they didn't get warm. 4 of them are roughly equal to 2 real florescents with no EMI. I bypassed all 4 diodes with low value caps.

Yea a lot of trouble but I was bored and my mobility was somewhat limited this summer.

I looked at those, briefly. IIRC you had to rewire the fixture to remove the ballast from the circuit. Those fixtures I mentioned came with bulbs that were rather mediocre, so I went shopping and saw some "high output" bulbs and ended up getting those, and that's what's in the fixtures now. Those LED replacements were around $20/bulb at the time, which struck me as a bit much. In the meantime I had picked up a 2-pack of reflector style bulbs to replace an outside light where I used to live, and one of those over my current work table gives plenty of light in there.

I've been fairly impressed with a lot of what I'm seeing out there using LEDs, not so much the regular light bulb styles but stuff that was designed for LEDs to start with. I bought a 10-pack of 10W LEDs a while back, and built a few lamps, using some little modules with 3 trimpots on them. I think that they were originally intended for battery charging, as one of those trimmers is irrelevant to my use. One is installed over my lady's desk, to replace the small incandescent fixture after she burned her arm on it, one is over my desk, and one over my radio gear. The two trimpots set the voltage and current. The LEDs I got are 3 chains of 3 in series (other ones put 'em all in series) so I set the voltage for around 10V maximum, and then set the max current to something like 300mA, meaning they're dissipating about 3W. Which gives plenty of light, and being 10W parts, they oughta last a good long time.

For some reason when I plug a small wall wart in for my desk light it pulsates several times before it settles down. So the one I'm using is an older one, with a regular transformer and bridge rectifier. Hers works fine on a switcher. I never did investigate why it did that, probably something to do with the design of the particular switcher I was trying to use. Having several large boxes of wall warts, I have plenty to choose from.

I'd like to come up with some simple circuit that would limit the output voltage and more importantly the current to drive these LEDs with, since I still have a bunch of them around...

--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin

On Monday 16 December 2024 02:18:56 pm wn4isx via groups.io wrote:

OK this is as crude as it gets...

That's the basic capacitive dropper circuit that Big Clive bumps into in a great many places. Maybe I should have specified operating from a 12VDC source...


--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin