RailPro > RailPro Specific Help & Discussion
Keep Alive installation w/ Railpro
Alan:
I see you guys are all using big flat pack (GB case style) rectifiers. If you are cramped for space there are much smaller rectifiers available. For example, here is a SMD unit that would fit anywhere: http://www.mouser.com/ProductDetail/Bourns/CD-HD201/?qs=sGAEpiMZZMtQ8nqTKtFS%2fLRuoW8XJyK4EtCzdLtg3ZgpcRnkNzl%252bKw%3d%3d. Just solder wires to the SMD pads. Or you might consider the round RC case style units which are typically more compact than GB style.
Another consideration is the forward voltage drop. Typically, it is 1.4V for a common bridge rectifier. Units with lower drop are readily available. The rectifier in my link above only has a 750mV drop. For use with an LM, the lower the forward voltage the better. Lower forward voltages will reduce the, what Kevin calls additional oomph to get started, effect.
You can filter by both forward voltage and case style on most electronics suppliers web sites. Here is the Mouser filter:
KPack:
--- Quote ---...what Kevin calls additional oomph to get started...
--- End quote ---
That's a scientific term right there. Perhaps I should trademark that?
Thanks for the link to the SMD rectifier. I had wondered if there was something like that out there. I'm all about SMD components....ever since I made the switch to SMD resistors and I realized how much space it free'd up. If I was really organized I could etch a small board and solder on all the resistors I need and the bridge recitifier, then just solder the wires to the board. Much cleaner. But etching is nasty stuff and takes a good amount of work from what I understand.
-Kevin
Alan:
--- Quote ---But etching is nasty stuff and takes a good amount of work from what I understand.
--- End quote ---
Not true. Very easy to do. Check out this post: http://www.lkorailroad.com/control-panels-part-vii/ You see I use an old lamp, kitty litter pans, and a picture frame. Not exactly hi-tech but works great.
You may be thinking about the old negative resist process. Yeah, it was a PIA. Required an expensive UV bulb and was very finicky. In my younger days I made more junk boards than I did good boards using the negative resist process. Then positive resist came on the market. What a godsend. Made circuit board creation Fisher-Price simple. MG Chemicals is the dominant US supplier of positive resist materials: http://www.mgchemicals.com/products/prototyping-and-circuit-repair/presensitized-boards/positive-presensitized-600-series
The most challenging part of the process is not the etching of the boards. Etching is easy. The possibly challenging part is creating the circuit artwork. But for the relatively simple circuits needed for loco installation that shouldn't be a problem. The key is to draw with vector art, not raster art. I use Adobe Illustrator however it is an expensive program if you don't already own it. Inkscape is a free vector art program that would work great for circuit art. You could even use the Draw objects in MS Office PowerPoint if you wanted to. They are vector.
Print the art at 1:1 on an inkjet transparency and you are ready to go. 25 minutes later you will have a ready-for-solder circuit board.
Here are some examples of homemade circuit boards used on my railroad - power district circuit breakers and occupancy detectors.
Alan:
Swapped emails with Tim Ring today. It is confirmed you should NOT connect a keep-alive to the ground pin and the blue wire of a LM3. Our assumptions were correct. The blue wire is south of the current limiting circuitry of the LM meaning an accidental short of an output could lead to the keep-alive blowing a huge wad of current through the LM. Not good.
The keep-alives you guys are building is the way to go with RP. Or, clean your track. :P
melarson:
--- Quote from: Alan on February 20, 2017, 07:17:43 PM ---It is confirmed you should NOT connect a keep-alive to the ground pin and the blue wire of a LM3.
--- End quote ---
I have to say, this makes me wonder why the new "negative" pin on the LM-3 is there? If not for keep-alives (and I assume also batteries), then what? It is astonishing to me that Tim would make such a connection available that is apparently so dangerous if miss-used. Did he say what the purpose of the negative lead is supposed to be?
Michael
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