[simpits-tech] AC dimmers and transformers

[geneb]

On Mon, 27 Oct 2014, Matt Bailey wrote:

> On Mon, 27 Oct 2014 06:22:03 -0700 (PDT)
> geneb <geneb at deltasoft.com> wrote:
>
>> On Mon, 27 Oct 2014, Matt Bailey wrote:
>>
>>> Question: What sort of dimmer device is typically used in old
>>> business jets? Just a standard triac? I'm trying to figure out
>>> exactly what is in my Sabreliner.
>>>
>>> Second question: how tolerant are typical aircraft AC transformers
>>> and power regulators to variations in frequency? For instance, I
>>> have 115v/400hz coming off my inverter, but it breaks down to 5v AC
>>> for lighting (and 26v AC for other stuff). I'm wondering how
>>> critical it is to maintain the 400hz frequency.
>>
>> Matt, typically variable transformers are used for dimming - at least
>> that's what I've found.  If you're going to use the original variable
>> transformers, you'll need to feed them 400Hz.
>>
>
> That's what I was afraid of. Alright, time to break out some Arduinos
> and transistors. :)

I'm cheating.  I replaced all my big variable transformers with pots that 
will be used to adjust a pile of LM317 variable voltage regulators.  You 
can run a number of them in parallel to handle the high amp loads of those 
edge-lit panels.  Here's a site with a calculator that will help you find 
the optimal value for the pot needed to control the output:
http://www.reuk.co.uk/LM317-Voltage-Calculator.htm

For mine, I set the target output to 6v and R1 to 240.  That results in a 
calculated R2 value of 912, which is close enough to use a 1k pot.  Those 
values should result in a voltage range of about 1.5 - 5V.  It's a dead 
simple circuit to build as well - that page I reference above even shows a 
reference schematic that'll work perfectly.  Just feed it 12V in and 
you're golden. :)

g.


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