Re: Voltage halver.

Roger Hayter <roger@hayter.org> wrote:

On 3 Apr 2024 at 21:29:19 BST, "Liz Tuddenham" <Liz Tuddenham> wrote:
 

<peter@easthope.ca> wrote:
 

A variable power adapter is required to drive a 6 V, 30 W incandescent
bulb in a microscope.
 
Similar to the 3-12 V 5 A adapter here.
https://www.ebay.ca/itm/305207182573
An adapter providing 1.5-6 V output would be better but I haven't
found one.
 
Rather than limit the adjustment to 6 V, I think of halving the
output.  An integrated circuit in a 4 port package is conceivable.
https://www.youtube.com/watch?v=VJfqBQ2ybpk
 
Does the marketplace offer a solution?
Another idea?

 
A 6v transformer and an adjustable resistor made from an old electric
fire bar and two jubilee clips?

 
I thought of that, but it is not very useful to adjust while looking down the
microscope and I wondered if AC might affect microphotography.  Have you seen
the price of 30W WW pots or "rheostats"?

I hadn't, but I expect they would be expensive..  By comparison, making
big power resistors is surprisingly cheap -- I had to make some for a
5kW organ blower starter, so I had some slate bars cut for me by a
monumental mason and wound them by hand (with tappings).   The total
cost was surprisingly low.

I don't see how AC wold be a problem with microphotography unless you
were worried about ripple in the light output.  Low voltage lamps like
that heve a short thick filament with high thermal inertia, so they were
often used as the exciter lamp for for sound film reproduction.  Any
ripple would have generated a 100c/s hum, but there has been very little
sign of that on the vintage projectors I have worked on.


--
~ Liz Tuddenham ~
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www.poppyrecords.co.uk