[SML] Dummy load resistor?

[Dan Sheehan]

 that tempco is why lamps almost always blow at the instant of switch-on,
you're hitting the cold R with full V with no ramp-up time
so inrush current is almost 10X operating current.

On Thu, May 3, 2018 at 8:11 PM, Dan Sheehan <dsheehan.sml at gmail.com> wrote:

> problem with heaters etc that aren't tungsten lamps...
>
> if they have the resistance of a cool lamp,
> as is needed  to stabilize the dimmer/LED combo at low level setting,
>
> they will have approx that same low R when the level goes to @FULL
> thus draw much more power...
> unlike a tungsten lamp filament which has almost 10X the cold R when @FULL.
>
> So looking at a 40W lamp example
> (which I've sometimes  found to be about the smallest-W
> lamp that will work for stability)
> that  lamp, heated @FULL, has about 360 ohms to draw 1/3 A,
> thus about 40 ohms cold.
>
> Replace that lamp with a 40 ohm Resistor [heater] for same stabilizing
> effect,
> it's still near 40 ohm @FULL, 120V on 40 ohm is 3A, that's 360 W.
>
> You would have to figure out how to handle 360 W of heat.
>
> If it's not going to be @FULL for a longtime,
> bury the 40W ballast lamp in a tin can or something.
> You can provide air flow and still block the light path,
> so it will be hot, but dark.
>
> The apparent complexity of the math
>  is inversely proportional
> to the level of beer remaining in the bottle.
>
> Currently enjoying a KONA (HI) product.
>
> --
> ...Dan Sheehan
> Fixer of things that break
> TD Walpole (MA) Footlighters
>
>


-- 
...Dan Sheehan
Fixer of things that break
TD Walpole (MA) Footlighters
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://theatrical.net/pipermail/stagecraft_theatrical.net/attachments/20180503/eac59997/attachment.html>