Michael and all,
Loy's Toys used to sell a resistance selector box that took the muss and
fuss out of trying to calculate the correct resistor for lighting. Just
connect it in series with the power source and light. Starting with the
highest resistance, step down to the desired brilliance. As a safety measure,
you can connect a voltmeter across the bulb to make sure you're not
overpowering it. What's nice about the box is it's placarded showing the
resistance value in the test circuit. Not everyone is aware of the fact that
resistors rarely are available in the size that is mathematically calculated.
So, one has to go to the nearest higher value. Even at that, there is a
tolerance of 10% or 20% (4th color band) on Radio Shack resistors. Electronic
supply houses may carry a wider range of resistor values with 5% tolerance.
That being said, the bad news is Loy went out of business some months back.
However, Litchfield Station www.LitchfieldStation.com now carries a lot of
Loy's products. Give them a call and see if the resistance box is still
available. As I recall, it was reasonably priced. Warning: If testing with
LED's, make sure the polarity is correct! I'm drawing a blank at the moment,
but I think the cathode (-) is the longer lead on a LED. Don't anyone be
bashful about correcting me if I'm wrong! :-)
Gary Chudzinski
[EMAIL PROTECTED]
Re: lighting
Posted by: "meldridge2000" [EMAIL PROTECTED] meldridge2000
Fri Jan 4, 2008 9:20 am (PST)
If only life were so easy. I would guess a bulb rated at .030 amps
probably varies from .015 to .025 amps for full brightness. The
current rating is a maximum safe value. Resistors are cheap. Buy a set
of values from 330 to 1000 in intervals of roughly 100 ohms. Start
with the highest, work your way to the lowest. As soon as it's bright
enough, stop. Also, you can completely disregard the resistor
tolerance. Do not use 1/8 watt resistors, but they probably don't
stock those at Radio Shack anyway. 1/4 watt will be fine. Or, you
could skip all that and do what the decoder manual says.
-Michael Eldridge
--- In [email protected], Bill Roberts <[EMAIL PROTECTED]> wrote:
>
> Using [1], if the supply is 14 volts and you need just 1.5 to light
> your .030 amp bulb, then you need to drop 12.5 volts:
> (14 - 1.5) / .030
> This works out to about 417 ohms.
[Non-text portions of this message have been removed]
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