Re: LED Charge Indicator

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: robert heidlebaugh <rheidlebaugh@xxxxxxxxxxxxxx>

One word of caution. The NE2 neon lamp dose not stop glowing at no volts.
There may still be as much as 90 volts remaining when the lamp goes out.
   Robert   H
--


> From: "Tesla list" <tesla@xxxxxxxxxx>
> Date: Sun, 09 Oct 2005 15:11:44 -0600
> To: tesla@xxxxxxxxxx
> Subject: Re: LED Charge Indicator
> Resent-From: tesla@xxxxxxxxxx
> Resent-Date: Sun,  9 Oct 2005 15:11:51 -0600 (MDT)
>
> Original poster: Jan Wagner <jwagner@xxxxxxxxx>
>
> Tesla list wrote:
>
>> Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
>>
>> At 08:18 AM 10/9/2005, you wrote:
>>
>>> Original poster: Jan Wagner <jwagner@xxxxxxxxx>
>>>
>>> It's a bit "low tech" but you could use a neon glow tube (glimm
>>> lamp, guide light, ...). Just add multiple normal 1/4W 500Vmax
>>> carbon or metal foil resistor in series with the lamp, or just a
>>> single HV resistor, to keep the tube current down and below 1mA.
>>
>> 1mA and 20kV = 20W dissipation in that resistor...  Sure you want to
>> burn that much power?
>
> Well, as I said, keep the current below 1mA.
>
> For an actual value, you'll have to check the ratings of the
> particular glow tube that you're going to use (NE-2, for example).
> AFAIK most of these small tubes are rated for the order of 0.1mA
> (100uA), at which they'll glow brightly. So that'd be what, ~2W
> overall resistor dissipation at 20kV? Typically 0.01mA works, too,
> though probably with a dimmer glow.
>
> An untested idea: you could build your own optoisolator around a
> glowtube and a BPW77 visible light phototransistor. Add external
> supply, collector resistor, comparator (LM311, 50mA sink current
> capability), and a brighter indicator lamp (50mA rated <50V) or
> LED+series resistor if you insist ;-) Basically just a gimmick. The
> simple glow tube approach would be the more reliable one of these
> two, though probably not the most easily readable one.
>
> - Jan
>
>
>