Improved llight intensity on BLI P70's

[Lemosteam]

Replaced the four 221 resistors with 5111 SMD.  I suppose one could go evenhiger, but I was happy with this new intensity:


Before:


After:


Side by side:

[jdcolombo]

MUCH better!

John C.

[greenwizard88]

Beautiful. That is what they should ha s looked like to begin with!

Are all SMD resistors the same size? If not, what size are these? I've never worked with smds before, is it hard to do?

[Lemosteam]

Beautiful. That is what they should ha s looked like to begin with!

Are all SMD resistors the same size? If not, what size are these? I've never worked with smds before, is it hard to do?

@greenwizard88 , no the hardest part is getting the originals off. I just wedged an exacto under ad twisted away from the side I was unsoldering. Then a pair of pliers to pull the old one off while de soldering the other side. Work toward the end of the car.

These are 1206 (CORRECTED) size. A tiny dab of flux on the solder pads will hold it in place until you are ready to solder, then use a toothpick to hold it down when you touch the joint with the iron on each side. This time work away from the end of the car.

[peteski]

Beautiful. That is what they should ha s looked like to begin with!

Are all SMD resistors the same size? If not, what size are these? I've never worked with smds before, is it hard to do?

Like John, to unsolder the SMD resistors I add extra solder and paste flux to both pads, then alternately heat up the pads until both stay liquid, then using the soldering iron's tip I push the resistor off the pads.  This is all done rather quickly so the solder stays in a liquid state.  But Joe D has found another very interesting and clever way to remove SMD components.  I have to order some of that stuff!  See https://www.therailwire.net/forum/index.php?topic=48559.0

Resistors have physical size and resistance value.  Physical size of these is 1206 (footprint is 0.120" x 0.060") and the original resistors were marked "221" which resolves to 220 ohms.  The resistors John used are "5111" which resolves to 5.11k ohms (or 5110 ohms).  Those are what is called "precision" (1% tolerance) resistors - not sure why John used those instead of the standard 5% tolerance resistors (which would be marked "511").  Either will work.

The value of those resistors will determine the LED brightness.  Each resistor controls brightness of each LED on the strip.  You might experiment with other values too (to better suit your taste.  Anything between 220 ohm (nuclear blast brightness) to 10 or 20k ohms (very dim) will work.

I'm in a process of creating a similar write-up for reducing the brightness of these LEDs, but it is not ready yet.  Mine will have 2 options. One is to  use a single fixed value resistor, or the 2nd option will be to use adjustable resistor (trimmer potentiometer) to adjust the brightness.

Due to to the way the factory circuit is designed, John's modification does not prolong the time the "keep-alive" cap will keep these LEDs lit during track power dropouts.  My circuits modifications will greatly increase the time the LEDs will stay lit during power dropouts.

[thomasjmdavis]

Resistors have physical size and resistance value.  Physical size of these is 1206 (footprint is 0.120" x 0.060") and the original resistors were marked "221" which resolves to 220 ohms.  The resistors John used are "5111" which resolves to 5.11k ohms (or 5110 ohms).  Those are what is called "precision" (1% tolerance) resistors - not sure why John used those instead of the standard 5% tolerance resistors (which would be marked "511").  Either will work.

With all due respect, shouldn't that read "(which are marked "512")"?  511 would be 510 ohms, not 5.1 k ohms.  Or is my handy calculator for these things off base? (I did check)

[peteski]

With all due respect, shouldn't that read "(which are marked "512")"?  511 would be 510 ohms, not 5.1 k ohms.  Or is my handy calculator for these things off base? (I did check)

Well, you are not off base, but John's resistors are not standard 5% SMD resistors (which use 3-digit resistance codes).

They use 4-digit code which indicates they are precision (1% tolerance) resistors.  In that code, the first 3 digits are the first 3 digits of the resistor value, then the last digit is multiplier (or how many zeros to add to the first 3 digits).  so 5111 is 511 plus one zero, or 5110 ohms, or 5.11k ohms.  Like I mentioned, not sure why John used those resistors. The 5% resistors are much more widely used.

The original resistor was a standard 5% resistor. "221" was 220 ohms.

The 4-digit codes are briefly mentioned in https://www.hobby-hour.com/electronics/smdcalc.php

[Lemosteam]

When you and I first started on th polar express I bought an assortment kit from Digikey with several values of ten unit strips. Those came iin the set and .i just used what I had.

[peteski]

You must have picked up a kit of 1% tolerance resistors.  Nothing wrong with that, but it is unusual to see these used for model railroad applications (or most consumer-grade electronic devices) where you would usually  find the most popular 5% tolerance resistors.  Those 1%  resistors probably ended up costing few cents more, but again, not anything outrageous.