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RE: [TCML] RF Ground and Brass
Hi Bart,
I don't believe that I have misinterpreted Terry's measurement. His measurement is consistent with mine, based on the current through my light bulb. His post is at http://www.pupman.com/listarchives/2000/July/msg00478.html and is very clear:
> The secondary RMS current is around 350mA for a 15/60 coil. At least it
>is for my big LTR coil but say 100-400mA should cover them all...
I can't check the paper he wrote just now (a firewall issue at work); I'll look at that this evening. If you're looking at waveforms, maybe you're talking about peak currents? Different storey there!
Critical to this discussion are the answers to my questions of your measurements -
1) What size/power the coil are you talking about? and
2) Are you talking about peak current or RMS current?
> As of recent, I've been looking to predict secondary base current as it
> is directly related to output potential (something I'm looking to add in
> Javatc)
Is RMS base current correlated with output potential? In a given coil, if you always had the same size bangs, the output potential would be the same from bang to bang regardless of BPS, but if you double the BPS, you would double (I think??? Certainly increase...) the RMS base current.
> Ibase(rms) = (Transformer rms output voltage x
> sqrt(Sec_Les/Pri_Ldc))/Sec_Reactance
> I've also checked the above equation against Ibase(rms) = 0.707 * (sqrt(
> 2 * E_bang / Lee)) and it seems to follow well.
This sounds wrong to me. Since you are talking about RMS current, the bang duty cycle or BPS directly affects RMS current, but doesn't appear in your equations.
Regards, Gary Lau
MA, USA
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of bartb
> Sent: Wednesday, March 05, 2008 9:29 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] RF Ground and Brass
>
> Hi Gary,
>
> I've measured (although along time ago), but Terry has also measured
> several amps (about 10A on one known test coil). I'm not sure why your
> thinking 350mA (maybe just a misinterpretation).
>
> Here's a document Terry put together. Go down to the area titled "Top
> Terminal Voltage and Secondary Base Current". You'll see the waveforms.
> http://hot-streamer.com/TeslaCoils/MyPapers/modact/modact.html
>
> As of recent, I've been looking to predict secondary base current as it
> is directly related to output potential (something I'm looking to add in
> Javatc). I am currently equating base current (without losses) as:
> Ibase(rms) = (Transformer rms output voltage x
> sqrt(Sec_Les/Pri_Ldc))/Sec_Reactance
> I've also checked the above equation against Ibase(rms) = 0.707 * (sqrt(
> 2 * E_bang / Lee)) and it seems to follow well. I'm just playing with
> these numbers as this point.
>
> My reason is to pull in the current and voltage profiles along the
> length of the coil and have the program perform the length conversion
> for the user. Fantc does this now, but uses a 1A default. The user if
> desired could take that data and convert to the actual length segments,
> measure base current, and scale both current and voltage accordingly
> (that was the idea behind the profile graphs). I'm trying to get Javatc
> to do all this automatically (for a prediction). I have it running fine
> on a test program, but I need to make many base current measurements to
> verify prediction to measurement before I even think about including it.
> But, my output voltages are much closer to reality which is a "feel
> good" for me. Even if most are not interested in this type of data about
> their coil, the base current itself could come in handy simply in wire
> size requirements.
>
> Take care,
> Bart
>
> Lau, Gary wrote:
> > Hi Bart,
> >
> > I'm curious how you came to noting several Amps of secondary base current. On
> what size/power coil? Are you talking about peak or RMS Amps? On my 15/60-
> powered coil, I once placed a small flashlight bulb in line with the secondary base,
> and I think it only registered a modest glow (though my recollection is also dim). I
> recall that Terry Fritz (in a post dated 7-21-2000) had measured his base current,
> also with a 15/60 NST, as 350mA RMS.
> >
> > Regards, Gary Lau
> > MA, USA
> >
> >
> >> -----Original Message-----
> >> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> >> Behalf Of bartb
> >> Sent: Tuesday, March 04, 2008 10:03 PM
> >> To: Tesla Coil Mailing List
> >> Subject: Re: [TCML] RF Ground and Brass
> >>
> >> Hi Gary,
> >>
> >> There can be several amps on the secondary base current to ground (much
> >> higher than the currents in the secondary which diminish over length)
> >> and in some coils too high for 18 awg if it was a continuous current.
> >> However, this current is time dependent, so I agree that smaller wire
> >> size can be used.
> >>
> >> I run 18 awg hv wire from the base to a terminal point (about 12"
> >> length). From the terminal point to RF ground I use 6 awg high strand,
> >> about 1 meter length. I haven't noticed the 18 awg getting warm, so I'm
> >> sure the small length from base to terminal is fine. Like everything
> >> else, if after running, a coiler finds the base current wire warm, then
> >> it's time to go bigger (thermal losses are never good). But if it's at
> >> ambient temp then "all is good".
> >>
> >> BTW Gary, I received my fiber optic cable and voltage converters today.
> >> So hopefully I can get this bps measurement going soon. Just need to
> >> proto up a simple circuit and I should be off and running (hoping for
> >> this weekend).
> >>
> >> Take care,
> >> Bart
> >>
> >> Lau, Gary wrote:
> >>
> >>> Hi Scott,
> >>>
> >>> I think folks often go overboard with unnecessarily large RF ground cables and
> >>>
> >> connections. It's important to remember that the actual RMS current in these
> >> conductors is very small. It may be useful to use a fat conductor for portions
> that
> >> are very long, as a means of minimizing conductor inductance, but I'm not even
> >> sure that this is critically important. Minimizing the total conductor length to the
> >> ground rod(s) is probably the most useful point. But for a couple feet or less
> from
> >> the secondary base to a central tie-point, it's pointless to use anything heavier
> than
> >> simple stranded #14 or #18AWG - it only needs to be heavy enough to not be
> >> fragile. Same with the connection to the NST, Terry filter, and strike rail. I don't
> >> think copper vs. brass makes any difference for the ground connection, but
> since
> >> wire is typically copper, I would use that.
> >>
> >>> The secondary base connection method advocated in the COILBUILD
> documents
> >>>
> >> is silly. These are very old documents and in need of revision. Trying to secure
> a
> >> copper strap ground conductor to a copper plate, both subject to surface
> oxidation,
> >> with a rubber band, sounds like a very poor and unreliable connection. I use a
> 1/4-
> >> 20 screw connection to each end of the secondary, as both a mechanical and
> >> electrical connection. See http://www.laushaus.com/tesla/secondary.htm If you
> >> don't have access to press-fit threaded inserts, there are other ways using
> common
> >> hardware.
> >>
> >>> Your EMI filter hookup sounds correct. My thoughts on the topic are at
> >>>
> >> http://www.laushaus.com/tesla/emifilter.htm.
> >>
> >>> As for surge protectors in a power strip, I've always wondered whether they
> are
> >>>
> >> attempting to protect against differential (hot to neutral) spikes, or common
> mode
> >> (ground to hot & neutral) spikes. IMO, common-mode spikes are more likely, so
> >> I've added a couple of MOV's inside of my Variac case from hot & neutral to
> >> ground.
> >>
> >>> Regards, Gary Lau
> >>> MA, USA
> >>>
> >>>
> >>>
> >>>> -----Original Message-----
> >>>> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> >>>> Behalf Of Scott
> >>>> Sent: Sunday, March 02, 2008 7:49 PM
> >>>> To: tesla@xxxxxxxxxx
> >>>> Subject: [TCML] RF Ground and Brass
> >>>>
> >>>> Hi all,
> >>>>
> >>>> I hate to touch on two topics that are so widely discussed here, but I have
> >>>> a question that kind of falls into a gray area.
> >>>>
> >>>> First off, I'm on the last stage of my coils construction, the
> >>>> grounding. This topic has been fought over many times on the list (I just
> >>>> spent 2.5 hours reading over all the entries about RF ground) and have
> >>>> decided on the following scheme:
> >>>>
> >>>> Connections to RF ground:
> >>>> --Secondary Coil, follwing these insuctions :
> >>>> http://www.pupman.com/howto/COILBLD3.GIF
> >>>> --NST case
> >>>> --Strike Rail
> >>>> --"RF Power Ground" line coming out of Terry Filter. (The "NST Ground" line
> >>>> coming out of the Terry Filter will go into the NST case I guess...refer to
> >>>> the Terry Filter diagram to see the lines I'm refering too ;) )
> >>>>
> >>>> Now the Mains supply will go like this:
> >>>> 1.) A power strip with a surge protector will plug into a wall outlet
> >>>> 2.) From the surge protector, a cable will go into a EMI Filter, from Tesla
> >>>> Stuff:
> >>>> http://cgi.ebay.com/RFI-EMI-Tesla-Filter-2-x-20-Amps-115-
> >>>>
> >>>>
> >>
> 250vac_W0QQitemZ140211303737QQihZ004QQcategoryZ7288QQssPageName
> >>
> >>>> ZWDVWQQrdZ1QQcmdZViewItem#ebayphotohosting
> >>>> The side with the 3 terminals will be hooked up to the output from the surge
> >>>> protector, with the center terminal being the ground.
> >>>> 3.) The side of the EMI filter with 2 terminals will run into the NST's hot
> >>>> and neutral inputs.
> >>>>
> >>>> Simple Enough right?
> >>>>
> >>>> Now the RF ground itself will be right next to the coil: outside, 4 steel
> >>>> spikes hammered 3 feet into the Earth.
> >>>>
> >>>> Now here's my question:
> >>>> I have this ribbon coming off the secondary coil and 10 AWG wire coming
> from
> >>>> the NST case and strike rail, how do I actually connect them all together to
> >>>> the physical RF spikes? I was just gonna solder the ribbon to the spikes,
> >>>> and then thread the other wires through a hole in them.
> >>>>
> >>>> And a second question:
> >>>> For the metal grounding ribbon coming off the secondary, does it need to
> >>>> copper for sure? I wanted to use brass instead. At my hardware store,
> >>>> brass is 1/4 the cost of copper and available in more thickness's. And does
> >>>> the ribbon need to go all the way from the secondary base to ground
> >>>> spike? It would be 3 feet of ribbon that way even is the coil is right next
> >>>> to the RF ground!
> >>>>
> >>>> Also, the grounding on the Terry Filter seemed a little weird too, maybe
> >>>> someone could confirm could I'm doing it right as described.
> >>>>
> >>>> Sorry for the massive post again, but I have been piecing together this
> >>>> problem for the better part of the day, and would like some loose ends tided
> >>>> up.
> >>>>
> >>>> Thanks for all responses!
> >>>>
> >>>>
> >>> _______________________________________________
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> >>>
> >>>
> >>>
> >>>
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> >>
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