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From: Roger Hayter <roger@hayter.org>
Newsgroups: sci.electronics.repair
Subject: Re: Voltage halver.
Date: 3 Apr 2024 21:09:25 GMT
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On 3 Apr 2024 at 21:40:27 BST, "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"?

Also, an electric fire element is going to be about 30ohms in North America,
and since you want fractions of 2ohms adjustment over 1 to 3 turns is going to
be somewhat fiddly.

-- 
Roger Hayter