Re: RC filter resistor

["David W" <Dav_W926-at-xxxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

You are all talking about 50 ohms, 100ohms, etc. But I thought that a filter
resister for a TC system needed to be about a couple kilo ohms.  That's a
lot more than a light bulb.



----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, November 05, 2000 2:47 PM
Subject: Re: RC filter resistor


> Original poster: "Jim Lux" <jimlux-at-jpl.nasa.gov>
>
> A 100W light bulb, when hot, is roughly a 100 ohm resistor.  Sure, it
would
> work, but here are the practical problems:
> 1) The resistance varies a LOT from cold to hot. Very low when cold
> relative to the hot temperature. Standard 300W halogen bulb (nominally
> around 48 ohms when hot is about 3.5 ohms when cold.
>
> 2) Breakdown voltage. A standard 100W bulb and socket isn't going to hold
> off the high voltage real well because the clearances are kind of close
> (look how close the wires are inside the bulb.  In theory, the resistor
> potentially needs to take the full supply voltage at some point in the
> cycle.
>
> That said, something like a 150W halogen bulb or 300W halogen bulb might
> not be a bad idea.  They are long enough that breakdown voltage isn't an
> issue, and if you size it for the cold resistance, then you might have a
> winner. If you have a 30 mA NST, the bulb's not even going to get warm
> (considering normal operating current is around 2.5A for a 300W bulb).
> OTOH, there might be easier ways to get a 3 ohm resistor (like a fairly
> short length of nichrome wire).
>
> Scavenging an old toaster or electric heater might be a way to get
nichrome
> cheap, if you don't just buy it.
>
>
>
> ----------
> > From: Tesla list <tesla-at-pupman-dot-com>
> > To: tesla-at-pupman-dot-com
> > Subject: RC filter resistor
> > Date: Sunday, November 05, 2000 8:26 AM
> >
> > Original poster: "acmnovak" <acmnovak-at-email.msn-dot-com>
> >
> > Could a light bulb (>100 watts) be used as a power resistor in a RC
> filter?
> > They are made for heat and are redily avaiable most everywhere...
> > The fact that power resistors heat up and are not easy to find in the
> right
> > values really kinda makes me wanna avoid the whole RC filter situation.
> A
> > filter composed of two 100 watt lightbulbs, a safety gap, and a bypass
> cap
> > would be a cheap and easy way for one to protect a hard to
find/expensive
> > xformer..
> > Thanks
> >     -Michael
> >
> >
> >
> >
> >
>
>
>
>