Very good tips David... also to note a good source for used caps in great condition here in the states is Telecom gear. The "rectifiers" as they call them use a nice cap and its usually over-sized on purpose by the manufacture for reliability needs. I bought a very clean unit for $3 U.S. and had four nice caps that have served me well.
Eric W9WLW On Oct 7, 2012 12:25 PM, "David Cutter" <d.cut...@ntlworld.com> wrote: > The car stereo situation is different in that the battery is charged from > a high frequency 3 phase supply ie the vehicle alternator. The ripple > frequency is quite high, from low kHz at tickover to 10s of kHz when you > are motoring. In either case it's a lot higher than the 120Hz ripple > frequency of your home charger, ie it's much longer between current bursts > injected into the battery. Your vehicle supply is voltage limited to > around 13.8V average and the peak of this voltage under normal conditions > is probably around 15V - 16V or so, though it can have considerable nasty > spikes on it during engine starting and when large solenoids pull in and > drop out. That makes a vehicle supply quite aggressive but not hard to > filter. Your home supply can have nasty spikes as well but more important > is the on-load, off-load and line voltage variations you can experience. > For this reason, you need a much higher voltage rating capacitor than you > might think at first sight. I would take a compromise on size and cost and > go for 25V minimum and feel fairly safe at 35V as big uF as you like. > Caution: when you first apply volts to your cap, it will suck an enormous > current, possibly enough to weld the open ends as they touch, so, I would > charge it up first with a modest resistor. > > Ideally, the place to put the cap is near the radio so it absorbs > fluctuations in resistive drop of the supply cables, but that is sometimes > inconvenient electrically and mechanically. > > David > G3UNA > > > ----- Original Message ----- From: "Eric Sluder" <eslude...@gmail.com> > To: <gold...@charter.net> > Cc: "elecraft list" <elecraft@mailman.qth.net> > Sent: Sunday, October 07, 2012 3:29 PM > Subject: Re: [Elecraft] Capicator Size for filtering across battery power > > > I typically use a high uF cap that is rated at 70-80 volts DC. My current >> installation utilizes a 44,000 uF cap and all is quiet for my DC power >> needs when running off of the battery fed by a charger. >> >> 73, >> Eric >> W9WLW >> On Oct 6, 2012 5:36 PM, <gold...@charter.net> wrote: >> >> >>> Gents, >>> >>> My setup uses four ()4 12v batteries in parallel for powering my K3 and >>> SGC powercube amp that I float with a battery maintainer. >>> >>> I believe that I have an RF problem with the power setup. I have put >>> chokes in the power leads to the equipment but at certain times I can >>> hear the ferrites buzzing with either the digital code being sent of >>> matching my voice with SSB. The chokes are clamp on types. I am not >>> observing any RF problems or reported problems on the air. But I think >>> that something is not right as of yet so I want to go after it to make >>> my shack even better. >>> >>> It has been suggested to me by a ham on the air that batteries just pass >>> this thru as they have no filtering capability. His suggestion is to >>> but a bit CAP across the batteries to kill this phenomenon. >>> >>> So my question as I am not an EE by education is how would I properly >>> pick a CAP size and would different materials that CAPS are made out of >>> make any difference. >>> >>> It would be easy to go out and get a large CAP like used on car stereo >>> systems but I want to have a better shot of fixing it right than just >>> hacking away. >>> >>> As always thanks in advance for your help. >>> >>> ~73 >>> Don >>> KD8NNU >>> FH#4107 >>> ______________________________**______________________________**__ >>> Elecraft mailing list >>> Home: >>> http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft> >>> Help: http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm> >>> Post: mailto:elecr...@mailman.qth.**net <Elecraft@mailman.qth.net> >>> >>> This list hosted by: http://www.qsl.net >>> Please help support this email list: http://www.qsl.net/donate.html >>> >>> ______________________________**______________________________**__ >> Elecraft mailing list >> Home: >> http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft> >> Help: http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm> >> Post: mailto:elecr...@mailman.qth.**net <Elecraft@mailman.qth.net> >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
