Building a GP9 in Proto:48

[ednadolski]

Thanks Peteski,  I was presuming 12v Vs and 2.1v for Vf, but I don't have the spec for these LEDs so I will have to go measure one

Ed

[peteski]

Thanks Peteski,  I was presuming 12v Vs and 2.1v for Vf, but I don't have the spec for these LEDs so I will have to go measure one

Ed

1.7 - 2.1V is the usual Vf for LEDs other than white, blue and true-green which (due to a different chemistry) have Vf around 3V.

[glakedylan]

very exceptional modelling here!
I appreciate your level of skill and craftsmanship.
splendid!

BTW, what kind of body putty is it (the green type)
I am unfortunately not familiar with it?

thanks for sharing

respectfully
Gary

[Jesse6669]

Squadron Hobby green putty (item 9055) most likely.

[ednadolski]

Yep, you're right, squadron green.   I prefer to wet-sand it with 600 grit or higher.  Being softer than the surrounding plastic it can be easy to take off too much.

Ed

[ednadolski]

Looks like the 402 and 603 LEDs that I have will do 3v @ 20mA.  This is using the Ngineering N8021 LED tester which is a 20 mA constant current source.  The LEDs are pretty bright with 20 mA, so I am going to try with some resistors to see what they look like at 15 mA.

(Now for the hard part: trying to find what I need from the parts that I have on hand.)

Ed

[peteski]

Looks like the 402 and 603 LEDs that I have will do 3v @ 20mA.  This is using the Ngineering N8021 LED tester which is a 20 mA constant current source.  The LEDs are pretty bright with 20 mA, so I am going to try with some resistors to see what they look like at 15 mA.

(Now for the hard part: trying to find what I need from the parts that I have on hand.)

Ed

20mA through SMD white LEDs will make them really bright!  BTW, most 0603 and 0402 LEDs are designed for operating from 5 or 10 mA - 20 mA is probably the absolute maximum rating which should not be used for prolonged period of time.  If you have the technical specs for your LEDs, that should all be clearly stated.

[ednadolski]

I'm pretty sure the 603s are the sunny white from Richmond Controls which are rated 3v 20 mA.  (The 402s I don't have the info). But you're right, probably best not to operate them at that current.

Ed

[peteski]

I'm pretty sure the 603s are the sunny white from Richmond Controls which are rated 3v 20 mA.  (The 402s I don't have the info). But you're right, probably best not to operate them at that current.

Ed

Richmond Controls might be using the absolute maximum rating (not the best way to power up LEDs). But maybe they do sell LEDs which are more robust than the ones I use. 

Here is a sample data sheet for a 0402 white LED to give you an idea what I'm talking about: http://www.semicon.panasonic.co.jp/ds4/LNJ047X8ARA_E.pdf

You'll notice that only 10mA is the Absolute Maximum rated current.  While the LED should withstand that current, it is not a good design to use that high of a current. Then under Electro-Optical chart you'll see that all the ratings are based on 5mA current. That is the value the LED is designed to operate at.  While I know that this data sheet is not for your 0402 LEDS, the 0402 LEDs are delicate.

[ednadolski]

Update time.  I have been testing out the unit on some temporary track and found that the  motor and decoder were running rather hot after a few minutes of use.  Checking on DC I measured that the motor was drawing about 1.2 amps.  After consulting with some folks on the P:48 list who know about O scale drives, I ended up taking two steps.  First, I replaced the motor to a more powerful Pittman sold thru NWSL.  Second, I completely disassembled the drive train: trucks, towers and gearboxes. I cleaned up all the moving parts and re-assembled everything, being sure to include sufficient lube with some lite oil on all the moving surfaces. This significantly reduced the drag in the overall drive train, even tho initially it seemed to me that (from turning by hand) things were not actually all that bad.  Ah well, now I know what this kind of drive *should* be like!   .   After getting it all back together, I measured the current draw again and found it was reduced nearly by half.  Now the unit no longer runs hot, and I am in the process of finishing up the re-assembly for some additional testing and tuning.

I still have a few miscellaneous details to add (horn, speed recorder, all-weather window), then it is on to the weathering shop for this guy.   

Cheers,
Ed

[strummer]

Am looking forward to seeing it in action...what Pittman did you use as a replacement?

Mark in Oregon

[ednadolski]

Mark, I used the 8424, available thru NWSL:  http://shop.osorail.com/images/30621-9.jpg

It's pretty much a drop-in for the original Pittman.  The only thing I had to do was shorten the shafts, by carefully cutting them with a Dremel cutoff wheel.

Ed

[svedblen]

As a newbie in O I have looked at this thread again, with renewed interest. Great thread and a great build!!!

I'm wonderinga about the couplers you are using, which I understand are the Protocraft couplers. At least for the engine. But what about the tank car, does it also have Protocraft couplers? Do you have any experience with the San Juan operable couplers?

How about the coupler boxes? Did you handcraft those yourself or are you using anything ready-made?

[ednadolski]

The coupler pocket for the GP is the one that came with the RC kit, and it uses the Protocraft coupler.   For the hopper I scratchbuilt the pocket from styrene to accommodate the SJ coupler (SJ makes 2 variations - one that has a screw/pivot and one that has the bar/key.  I made the pocket for the latter).  I'm also working on a pocket made from etched metal & styrene, designed for the key-type SJ.  I want to find a way to make that work with the Protocraft coupler, which I think operates more reliably since it is made from cast brass.

Ed

[svedblen]

Thanks. Of course it is a hopper. I was apparantly not paying attention.
EDNX - your private carrier I guess