Dale Botkin wrote...

>They're 8W bulbs, little wussy thangs.

"Wussy" is right.  I'm sure the bugs will have no difficulty finding
them, but are you going to be able to see OK with those little things? =20

The data I have so far indicates that this inrush current issue is
perhaps being overstated a bit.

My 1968 edition of the Motorola Power Circuits Handbook (written back
when TRIACs were apparently still "rocket science") has a good
discussion on solid-state relay design and in one subchapter about
soft-start circuits for lamps, goes into some detail on inrush current.

They measured current versus time for a 500W 120V tungsten lamp with a
triac triggered right at the peak of the line voltage waveform, and
found the inrush current decayed by 60% within two line cycles of
turn-on.  In another test, with 120V DC applied, the inrush decayed from
its initial 60A down to 30A in about 5 milliseconds.

Now those results are for 4 amp filaments, about 6 times more massive
than the ones in your yard lamps which are rated at just under 700 mA.
So I would expect the current to decay quite a bit faster in your case.


And if that's so, inrush may well be a only a minor issue here.

>The transformer supplying power to this whole thing is rated at 121W
>according to the label, if that makes a difference to you.

I don't think it does, other than presenting a small additional
impedance in series with the lamps and the MOSFET switch.  If it has any
effect, it will be in the direction of alleviating--albeit slightly--the
inrush current problem if one exists.

>This is actually an interesting question, I'm going to dig around=20
>myself and see if I can figure this one out.

I've been an engineer for nearly a quarter-century and was a technician
for more than a decade before getting my degree; and I've been an
electronics hobbyist for almost 45 years.  So you would think by now I'd
be well past the point where I could get absolutely fascinated by dumb
stuff like "What do light bulbs **REALLY** do?"

But I'm not.  And that scares me...

Dave

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