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Re: [TCML] Re: Dummy load for optimum cap size Experimentation

Hi Bart,

I had been using a Cadmium Sulfide photocell, which changes resistance as a
function of light.  I see that you're using a photovoltaic cell, with a
varying output voltage.  I just tried that.  With a voltage output, I can
fashion a much more effective R-C low-pass filter to smooth out the
variations.  I'm sure there's a way to use the CdS cell and build a LP
filter for that, but it's not jumping out at me.  With the Photovoltaic cell
and filter, it's still not rock-steady, but a about a hundred times better
than before.  Maybe if I play a bit more.  Thanks for the idea!

Regards, Gary Lau

On Sun, Aug 8, 2010 at 3:36 PM, bartb <bartb@xxxxxxxxxxxxxxxx> wrote:

> Hi Gary,
> Focusing on photocell:
> What type of photocell are you using? Is it one of those 1/2" circular
> photocells (zigzag line things)? I used something a bit different but cheap.
> Think I got it at Jameco years ago, but this is what I used along with the
> box and description mentioned previously.
> http://www.flickr.com/photos/bart-coils/4872360015/
> One thing I did have to do was to cover most of the area with black tape to
> remove ambient light as well as force only a  portion of the cells to react
> through the hole within the box that the 500W halogens were inside. I
> believe I also had to use minor lens filter (most anything will do) between
> cell and the light coming out of the hole.
> I'd be more than happy to send this to you if you like (no charge and don't
> even want it back). Just send address my way if you want to give it a try.
> Best regards,
> Bart
> Gary Lau wrote:
>> OK, back from vacation, time to start the experiments!  Igor???
>> I tried monitoring the lamp brightness using a photocell.  Previously I
>> just
>> applied Variac'ed AC to the bulbs to test the photocell response.  Today I
>> hooked up the actual spark gap and capacitor to an NST.  Just as I feared,
>> the chaotic gap behavior resulted in extremely erratic resistance
>> readings.
>> Useless.  I tried placing a big cap across the photocell terminals, but
>> that
>> didn't work.  Back to monitoring the bulb temperature with a thermocouple.
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