• Electrical Engineering V2
    5,003 replies, posted
So, I dug up this 5 watt fm transmitter I have, and tested it. The thing is, it doesn't emit a carrier on one frequency, however, it fucks up the whole 3meter band to noise, I can't hear any other radiostation any more when I turn this thing on, and I have absolutely no clue what's wrong with it. Ideas?
[QUOTE=Chezburger;41249664]So, I dug up this 5 watt fm transmitter I have, and tested it. The thing is, it doesn't emit a carrier on one frequency, however, it fucks up the whole 3meter band to noise, I can't hear any other radiostation any more when I turn this thing on, and I have absolutely no clue what's wrong with it. Ideas?[/QUOTE] It sounds like it's broken, open her up and post pictures. If it's a discrete transmitter it should be fairly easy to fix.
[QUOTE=nuttyboffin;41249291]That is often the cheapest method of getting wire, buying large multi core cable, irritating as hell however...[/QUOTE] Hobos can get you the best deals. Just don't ask where they got it from.
Just reporting back to say that the installation of the replacement capacitors in my monitor went swimmingly and I am currently using it as my primary monitor, It's like a brand new monitor for a fraction of the price of buying a new one. I can see how you guys can get addicted to this stuff!
If I short a capacitor it loses its charge, right?
[QUOTE=SEKCobra;41267646]If I short a capacitor it loses its charge, right?[/QUOTE] Yes, it can however rebuild some of it's charge after being shorted.
Chryseus, I finally got around to looking at those books you found for me. Thank you very much, it's exactly what I was looking for!
[QUOTE=ddrl46;41267758]Yes, it can however rebuild some of it's charge after being shorted.[/QUOTE] With large capacitors (or any capacitor for good safety practice) you should keep the terminals shorted at all times, i recently got shocked from a bag of 330v caps, i hadnt opened them in a year!
[QUOTE=nuttyboffin;41270952]With large capacitors (or any capacitor for good safety practice) you should keep the terminals shorted at all times, i recently got shocked from a bag of 330v caps, i hadnt opened them in a year![/QUOTE] That's impressive, I'd thought that the leakage would discharge them in a much shorter time. Edit: Actually I suspect that an electric field has charged it or something, it sounds improbable to me that a cap should have held it's charge for 1+ years.
That's some very decent cap then isn't it.
Most modern electrolytic caps that are good have a leakage under 1uA, sometimes as low as 100nA.
[QUOTE=BuG;41271215]That's impressive, I'd thought that the leakage would discharge them in a much shorter time. Edit: Actually I suspect that an electric field has charged it or something, it sounds improbable to me that a cap should have held it's charge for 1+ years.[/QUOTE] The caps i have wernt acctually in a bag, more like a box, cause each of them are about 4700uf xD oh, and they were 400v not 330v. the big thing you need to watch out for is capacitor memory, where once you dischage them, they regain some of their charge. thats got me a few times, so i always keep the larger ones shorted now.
[QUOTE=nuttyboffin;41278240]The caps i have wernt acctually in a bag, more like a box, cause each of them are about 4700uf xD oh, and they were 400v not 330v. the big thing you need to watch out for is capacitor memory, where once you dischage them, they regain some of their charge. thats got me a few times, so i always keep the larger ones shorted now.[/QUOTE] Speaking of which, I found my box-o-caps the other day... Including the 160,000 uF 40V one I found somewhere. :v:
[QUOTE=Zero-Point;41282722]Including the 160,000 uF 40V one I found somewhere. :v:[/QUOTE] Make a spot welder
[QUOTE=Chryseus;41278078]Most modern electrolytic caps that are good have a leakage under 1uA, sometimes as low as 100nA.[/QUOTE] [QUOTE=nuttyboffin;41278240]The caps i have wernt acctually in a bag, more like a box, cause each of them are about 4700uf xD oh, and they were 400v not 330v. the big thing you need to watch out for is capacitor memory, where once you dischage them, they regain some of their charge. thats got me a few times, so i always keep the larger ones shorted now.[/QUOTE] i(t) = C*dv/dt <=> i(t)/C = dv/dt 100nA/4700uF = 0.02128uV/ms 0.02128uV/ms * 31536000000ms (1 year) = 671.09V. So unless I fucked up somewhere, a capacitor with 100nA leakage and 47000 uF capacitance should loose 671V per year due to that leakage. [I]The plot thickens.[/I]
Is the leakage really a constant current? It should be proportional to the current voltage/charge, making it a differential. [editline]edit[/editline] [URL="http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.html"][sup]U = U_0 * e^(-t/(RC))[/sup][/URL] The discharge rating could be for the maximum voltage.
[QUOTE=Tamschi;41285330]Is the leakage really a constant current? It should be proportional to the current voltage/charge, making it a differential. [editline]edit[/editline] [URL="http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.html"][sup]U = U_0 * e^(-t/(RC))[/sup][/URL] The discharge rating could be for the maximum voltage.[/QUOTE] You got a point. If we say that the only loss is through the ohmic loss of the dielectric, which I don't think is the case, but if we just say it is, 400V/100nA = 4Gohm's. That gives us an RC time constant of 18800000s or 217,6 days. If you start out at 400V, you could get zapped after 365 days, if we consider >50V as a zap. Interesting. :eng101:
Ive always wanted to get hold of some of the big pulsecaps like these: [url]http://www.ebay.co.uk/itm/GENERAL-ATOMICS-MAXWELL-ENERGY-DISCHARGE-CAPACITOR-/221247472182?pt=LH_DefaultDomain_0&hash=item3383608236[/url] Probably use them to make a coin shrinker or try and make the worlds most powerful coilgun.
[QUOTE=Chryseus;41284685]Make a spot welder[/QUOTE] With 40V?
160mF is a lot of capacitance, at 40V the total charge stored is 6.4 coulombs, more than enough to be used as a spot welder.
[QUOTE=Chryseus;41287217]160mF is a lot of capacitance, at 40V the total charge stored is 6.4 coulombs, more than enough to be used as a spot welder.[/QUOTE] Shame I don't really have any use for a spot-welder at this point in time then. Also my memory failed me, it's only 78,000 uF. But the capacity is rated -10% + 75%. :v: [img]http://img441.imageshack.us/img441/685/ocat.jpg[/img]
fuck [editline]3rd July 2013[/editline] it's so big
[img]http://classified.ndntp.com/Images/2011/12000ufb.JPG[/img] i got 2 of these on the way, 450v 12000uf Charge Q = 5.4 Coulombs Energy E = 1215 Joules each gonna use them as smoothing for my H-Bridge of 600A 1200V IGBT bricks: [img]https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcRXR8Z1f-rAeAxy3wGL7G3uBUWDOIB_pFb45DOA7_2YDUZI-b313w[/img] But first... need to find a heatsink large enough for them + 4 100A diodes XD [editline]3rd July 2013[/editline] [QUOTE=Zero-Point;41300093]Shame I don't really have any use for a spot-welder at this point in time then. Also my memory failed me, it's only 78,000 uF. But the capacity is rated -10% + 75%. :v:[/QUOTE] That is the worst tolerance i have ever seen on a actual product....
[QUOTE=nuttyboffin;41302168][img]http://classified.ndntp.com/Images/2011/12000ufb.JPG[/img] i got 2 of these on the way, 450v 12000uf Charge Q = 5.4 Coulombs Energy E = 1215 Joules each gonna use them as smoothing for my H-Bridge of 600A 1200V IGBT bricks: [img]https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcRXR8Z1f-rAeAxy3wGL7G3uBUWDOIB_pFb45DOA7_2YDUZI-b313w[/img] But first... need to find a heatsink large enough for them + 4 100A diodes XD [editline]3rd July 2013[/editline] That is the worst tolerance i have ever seen on a actual product....[/QUOTE] Strange, mine's a lower capacity and voltage but appears larger. Must be because it's so old. [img]http://img838.imageshack.us/img838/3505/mlf2.jpg[/img]
its probibly because it needs much more for its capacitance, voltage only means really it needs a higher dialectric. i think.... xD
[QUOTE=nuttyboffin;41302168][img]http://classified.ndntp.com/Images/2011/12000ufb.JPG[/img] i got 2 of these on the way, 450v 12000uf Charge Q = 5.4 Coulombs Energy E = 1215 Joules each gonna use them as smoothing for my H-Bridge of 600A 1200V IGBT bricks: [img]https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcRXR8Z1f-rAeAxy3wGL7G3uBUWDOIB_pFb45DOA7_2YDUZI-b313w[/img] But first... need to find a heatsink large enough for them + 4 100A diodes XD [editline]3rd July 2013[/editline] That is the worst tolerance i have ever seen on a actual product....[/QUOTE] Jesus christ, what are you building? A motor controller for a train?
im either gonna use it for a GIANT teslacoil OR most likely a Inverter for a 10Kw+ Ferrite transformer to give me like 10Kv out @ 1A then use a doubler or trippler to get 20Kv or 30Kv not sure why.... Oh Well! il figure out what to do with it later... Edited: Spelling Mistakes.
I don't know what to use this for besides killing people. [IMG]http://i11.photobucket.com/albums/a166/ballsandy/CRW_8732.jpg[/IMG]
Well it seems spot welders have been in the news lately :v:
[QUOTE=pentium;41322256]I don't know what to use this for besides killing people. [IMG]http://i11.photobucket.com/albums/a166/ballsandy/CRW_8732.jpg[/IMG][/QUOTE] cut the wires off for connectors, mabye find some pipe it fits into, then use it as ammo for a spud cannon!
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