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Re: [APD] Re: incandescent-replacement type fixtures -- or -

Scott's advice is right on.

Gas discharges are funny things, electrically. One of my associates at Stanford University got fascinated by the little NE-2 neon bulbs we used for panel indicators, in those days. He measured the incremental inductance, when one was running, as 1 Henry! That normally would take a 500 lb coil of wire and core.

Switching a current flowing in such a reactance might cause far, far higher voltages than Scott even predicted. Bottom line, from and old EE, is don't try to switch the flow in wires hooked to the tube. It is a *lot* bigger than a little NE-2 and the results are not likely to be satisfactory. Switch the incoming power line.


PS. You won't find an ac capacitor that will withstand that service, either.

Message: 1
Date: Wed, 3 Mar 2004 08:33:13 -0800 (PST)
From: "S. Hieber" <shieber at yahoo_com>
Subject: Re: [APD] Re: incandescent-replacement type fixtures -- or -
	living	with an ON/ON switch
To: aquatic plants digest <aquatic-plants at actwin_com>

The right value capacitor across the switch terminals can
prevent momentary arcing that's due to the switch contacts
almost touching during part of the switching cycle. They
highrer the voltage the wider the gap the arc can reach
across. What value capacitor will prevent the arcing on the
output, high voltage side, depends on the ballast and bulb
operating characteristics. Maybe one of the EEs can help
you there.

But there is another issue. If you're putting the switch on
the output side of the ballast, the side connected to the
lamps, then a 125V-rated switch is not adequate and
probably not safe. Your ballast and bulb probably run with
something more like 600 -- 800 volts across the output side
of the ballast, depending on the bulb and ballast
combination. If the ballast is instant start, the initial
strike voltage is even higher than the running voltage.
Much electrical stuff from the hardware store is rated for
600V, which isn't really enough either. So first thing you
need is a switch designed to handle that kind of voltage
and then some more for a safety margin -- probably 1000V.

Whether the Ballasts are remote mounted or not shouldn't
affect whether the on/off switch arcs *if* the switch is on
the input side of the ballast.  I'd rather have my switches
on the input wires and run the wires to where I want a
switch than put the swtich on the wires that are closest --
I'd rather not fiddle with the high voltage if I don't have
to and I only have to intall the wires once.

Scott H.
--- BAshcraft at BrashearLP_com wrote:

> Date: Tue, 2 Mar 2004 13:57:47 -0800 (PST)

Could you expand on "dropping a capacitor on the switch".
My ballasts are remote mounted, but I'd like to be able to turn the lamps
off with switches in the hood.

I've tried it, and the switch contacts do indeed continue
arcing. I was using a switch rated for 6 amps at 125v.

===== S. Hieber

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