[SML] Dummy load resistor?

[Dan Sheehan]

2.7 K or 3.3 K would be stock values (10% is plenty good enough).
A 3.3K on 120V will burn about 4.4W.  This is OK.

But where you need to stabilize the dimmer-and-LED-lamp
system is not at 120V RMS (@FULL),  but down at the low end.

Unlike tungsten lamps, which have ~ 10:1
tempco between 120V operating point and room temperature,
Resistors prefer to have a minimum tempco.
(gets expensive, and tricky, if very low tempco is required)

You could get a fistful of 3.3K's and stack them up
in parallel until you get enough to stabilize the system.




On Thu, May 3, 2018 at 1:03 PM, Bill Nelson via Stagecraft <
stagecraft at theatrical.net> wrote:

>
> > Thoughts?  What size resistor would be necessary to fake a few watts?
>
> I have just wrapped a small incandescent in aluminum foil. I don't know if
> it
> would work for an extended period without getting too hot.
>
> You can always parallel some lower wattage resistors to get a higher
> wattage.
> That would also lower the assembly resistance, which would be a good thing
> for
> soaking up the idle current.
>
> I think Radio Shack has some low value 5 watt resistors available.
>
> To figure out the minimum resistance you will need, use the formula:
> Wattage = Voltage^2/R.  Rearranging gives you R = Voltage^2/Wattage
>
> So if you want 10 watts of dissipation in the resistor(s) without
> overheating
> and have 120 volt dimmers:
>
> R = 120x120/10 = 1440 ohms. You could get that value by placing two roughly
> 2880 ohm 5 watt resistors in parallel.
>
> Four 2880 ohm 5 watt resistors in parallel would give you 20 watts
> capability
> and a 720 ohm resistance.
>
> That would give a dissipation of 120x120/720 = 20 watts.
>
> Bill
>
>
>
>
>
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-- 
...Dan Sheehan
Fixer of things that break
TD Walpole (MA) Footlighters
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