Inrush Current Limiting (was) Dual voltage mod for projector lamp

[Guy Dragoo]

You may want to try the inrush current limiter components (Inrush Current
Limiters...basically a NTC thermister).  These simple devices go inline of
the line voltage and provide a slower turn on.
This brings up an interesting point for an inrush current limiting thread.
I have been looking for a slow turn on device (other than current limiting
thermisters which come on pretty quick and don't do any good if already
heated up).
This would be a good add in for the many tube rigs that are either converted
to solid state rectifiers or just to add a gentle start up to some of those
valuable old tubes and capacitors.
Does anyone have any schematics, information, or insight  regarding such a
beast?
73
Guy AC5HL

-----Original Message-----
From: Richard Post [mailto:post at OUVAXA.CATS.OHIOU.EDU]
Sent: Monday, October 04, 1999 11:47 AM
To: BOATANCHORS at LISTSERV.TEMPE.GOV
Subject: OT: Dual voltage mod for projector lamp



Robert,


One option that will increase the life of a 120 volt bulb is to wire a diode
in series with it. That drops the RMS heating equivalent to 85 volts. (120
divided by square root of 2) A simple switch can be used to short the diode
for full voltage to the lamp. A time-delay relay or triac can do the timing
for you but the 85 volts equivalent may be enough for some viewing. As I
recall, but it's been a long time ago, the Pageant uses a 120 volt lamp. If
not, forget this solution. A projection lamp rated at 85 volts already uses
this method.


Practically all modern overhead projectors use this diode solution
permanently so that longer-lasting heavier filament lamps (rated at 85
volts) can be connected cheaply.


BA radio tie-in: This is a partial solution to replacing the series-dropping
resistance-line-cord of the 1930s and 40s. The diode generates little or no
heat and, together with a smaller resistor in series with the filament
string, can be used to replace the rather dangerous and unobtanium
resistance line cord or a ballast tube.


Rich

Boatanchor Pix website - KB8TAD

http://oak.cats.ohiou.edu/~postr/bapix/



>Date: Sat, 02 Oct 1999 16:51:33 -0500

>From: "Robert M. Bratcher Jr." <bratcher at PDQ.NET>

>Subject: OT: Dual voltage mod for projector lamp

>Sender: Boat Anchor Owners and Collectors List
<BOATANCHORS at LISTSERV.TEMPE.GOV>

>X-Sender: bratcher at pop.pdq.net

>To: BOATANCHORS at LISTSERV.TEMPE.GOV

>Reply-to: "Robert M. Bratcher Jr." <bratcher at PDQ.NET>

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>Comments: To: 16mmfilm at onelist.com

>Comments: cc: fcls at flash.net, glowbugs at piobaire.mines.uidaho.edu,

> boatanchors at qth.net

>

>Does anybody know where I could find a solid state schematic for a dual

>voltage supply that would give about 30v for perhaps 5 seconds then the

>full 120v? Or how to make one? I'd like to extend the life of my projector

>bulbs. Sure they go out after about 25 hours but I would love to double or

>triple that life. For those of you not on the 2 film collector lists bulbs

>cost around $23 apiece.

>

>If your not on the film lists then please respond directly to me. The

>16mmfilm &fcls users can just reply to the list if they wish.

>Thanks very much. I'd like to install something like this in my Kodak
Pageant.

>

>bratcher at pdq.net

>Robert M. Bratcher Jr.

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