[TR] Converting TR6 rheostat to LED use

[ptegler at verizon.net]

gains you get from LEDs lost to heat in the 317???  he he
oh...so you're saying our LBC's are energy efficient to begin with?  ha hah
seriously though.... the bulk of people going to LEDs are doing so to be able to see their gauges at night.
I'll lay dollars to donuts most people will barely dim them to begin with   :-)
the 317 route might cost you $6-$8 while the pwm dimmer will be 2x-3x that and the led bulbs they'll buy from Moss and etc
will cost 16x the dimmer ckt.
it's all relative.
For reference.... look up Lionel Train (yes toy train) E10 LED lamps
sencart.com.... $3.29  for x2 9LED bubs that fit the sockets
even 1157s eetc are only $4-$6

 

ptegler at verizon.net

 

 

-----Original Message-----
From: John Innis <jdinnis at gmail.com>
To: Paul Tegler <ptegler at verizon.net>
Cc: Truiumphs <triumphs at autox.team.net>
Sent: Thu, Feb 22, 2018 8:49 am
Subject: Re: [TR] Converting TR6 rheostat to LED use



I LM317 is a voltage regulator.  You CAN use it as you describe, basically with a series resistor to sink the excess voltage and therefore indirectly adjust drive current.  But I find this approach to have a very poor dimming curve.  The PWM dimming solution gives you a much better control, especially at the dim end of the curve.  The other issue with the LM317 is that it is not very efficient.  All the gains you get from going to LEDs are essentially going to be lost as heat from the regulator.



On Wed, Feb 21, 2018 at 4:50 PM, Paul Tegler <ptegler at verizon.net> wrote:

Randal corrected my 'incomplete' response (tnx)
see below

all my LBC's have LED's in the dash
since they draw much less current than normal bulbs all you need is a
simple LM317 regulator,
one 5K pot and one 240 ohm resistor

It will be 'warn to the touch, but no more than the old bulbs would be warm

look up the spec sheet for am LM317. truly dirt simple...doesn't need and diodes or caps

ptegler

Paul Tegler ptegler at verizon.net www.teglerizer.com


On 2/21/2018 12:35 PM, Randall wrote:



One note of caution.  Read the instructions that come with a PWM dimmer
carefully.  Some require that the LED's connected to them are NOT

grounded.

This can be a real pain the butt for LBC's where everything is metal and
all the metal is grounded.

Which is exactly why I would say the one you linked to is Not Suitable.

As usual, Amazon won't tell you little things like whether you can use it or
not; but the information is on the seller's web site:

"As with pretty much all dimmer switches, the ground side is switched rather
than the positive side. So you must hookup the output ground wire to your
LEDs."

https://www.oznium.com/led-dimmer-knob

-- Randall



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