Benesesso Posted May 8, 2004 Share Posted May 8, 2004 Finally got around to copying some old VHS tapes to DVDs. Noticed what appeared to be some periods of AC line noise. Hmm, sounds like the problem a small fish-tank heater caused on our radios and TV when I was about 16 years old. Soldered a small capacitor across the AC power line to the heater-end of problem. Mother thought I was a genius. Fast forward to this AM. Dug through my very limited supply of electronic junk to find a few small caps. Looked up on the internet to get some idea of what value to use. Found articles recommending everything from 0.1 uF to 300 uF for the whole house. Dang! Decided to try a 22 uF cap. that had a nice high rating of 350 volts. It *was* an electrolytic, but since I really don't know the difference about them I thought it would work fine. Remember guys telling me that AC Hz is "so low it acts like DC with a cap". Great, and since I use a transformer to step the 220V of Italy down to 110, I figured I'd put it across the 220V side--no sense in letting any noise get into the 2500 watt trans., right? PLUS, it's only 50 Hz over here, so that much closer to DC. Thought about using my larger 47 uF cap., but decided to try the smaller one first. Hooked it up and plugged the trans. in. POW!!! Lots of smoke too--all in the first second! As per the song, "Baby, What a Big Surprise"! Cap.was still too hot to touch after 2 minutes. Nowthen, where did this former genius go wrong? I don't suppose it was just a bad cap.(yes, I hear the laughter). Benesesso Quote Link to comment Share on other sites More sharing options...
Malcolm Posted May 8, 2004 Share Posted May 8, 2004 1. Apparently your mother was wrong about you. 2. You did not do your research. 3. If you keep doing the same, we will probably be reading about you. Just a few additional comments... That big step down transformer is probably doing an excellent job of filtering your mains all by itself. That 220V in Italy is RMS. It is around 311V peak to peak, kind of close to the DC working voltage rating of your capacitor. Regardless of voltage, the ripple current through that capacitor probably far exceeded its rating. Electrolytics are generally a bad choice for this kind of service. The capacitor you used is not rated for the line-to-line application you used it in. Capacitors placed across the line are supposed to be X rated (no pun), primarily to protect you when they do what yours did. There are probably already .1 uF caps or something similar across the inputs in your equipment. Why don't you just get a good filtered power strip? It would be simpler and cheaper than completing a basic electronics course, which is what you need. Quote Link to comment Share on other sites More sharing options...
Benesesso Posted May 9, 2004 Author Share Posted May 9, 2004 Thanks for the reply. Guess I should have paid more attention in the "basic electronics course" I took a long time ago, as I don't recall the teacher saying a whole lot about electrolytics except that they "go bad" often. Didn't think I'd ever need an advanced electronics course as I concentrated on metallurgy, mechanics and acoustics. Guess I'll have to hunt down that teacher and make him listen to some Bo$e noise for a couple of hours. Quote Link to comment Share on other sites More sharing options...
3dzapper Posted May 9, 2004 Share Posted May 9, 2004 Benesesso, Try a pair of mylar 600V 0.1mF caps from each the two hot wires to the ground lug. In all probability the cap you used saw 622V, if it was a polarized electrolytic,(-311V to +311V swing per cycle) By using two caps you halve the potential seen be each one and will shunt HF hash to earth instead of the other side of the line. I use 400V caps in my filter for the 125V AC here in the USA. Noise in power transmission lines is only going to get worse as more and more power companies use their transmission lines to transmit data. And now internet connections via power lines are starting to appear. Rick Quote Link to comment Share on other sites More sharing options...
gerbache Posted May 12, 2004 Share Posted May 12, 2004 They're making home networking solutions now which use the AC power lines of the house as a cheap, easy way to connect all the machines. The way I see it, yeah, it's a really simple way to get the problem solved, but there's enough noise on the line without me adding to it. Speaking of noise, I have a light in my new apartment right now that has been going nuts, looking like the voltage is fluctuating WAY up and down. Off to go see if I can find the cause for this one... Quote Link to comment Share on other sites More sharing options...
Benesesso Posted May 13, 2004 Author Share Posted May 13, 2004 Rick, Thanks for the info--I had no idea the voltages were that high. Quote Link to comment Share on other sites More sharing options...
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