RailPro > RailPro Specific Help & Discussion
Keep Alive installation w/ Railpro
G8B4Life:
--- Quote from: Michael Larson on February 20, 2017, 09:46:13 PM ---I have to say, this makes me wonder why the new "negative" pin on the LM-3 is there?
--- End quote ---
I have to say I wonder as well. Given Rings statement on the LM-3
--- Quote ---A 'Negative' terminal is better for battery powered connection and will be more flexible to add a keep alive product.
--- End quote ---
why would you only go half way with the redesign of the LM board needed to bring these connections out to the user? Maybe Ring has some wizard circuitry up his sleeve that'll allow his KA's to be attached to the blue and negative wires.
Speaking of circuitry, Alan I'm constantly amazed with the homemade circuitry work you post on your blog and now here. Inspirational, helpful and I must say better "fire under the backside" tutorials than others I've seen out there.
- Tim
Alan:
Tim did not say what is the purpose of the negative pin although to be fair I did not specifically ask. His answers were the typical, vague, non-technical responses I have come to expect from him. No warranty, risk of fire, blah, blah, blah. The one nugget of information he did supply is that there is no LM over-current protection in a blue wire / ground pin capacitance application. Since that was the key piece of information I was seeking I stopped there. I make it a habit not to post email conversations publicly online but you aren't missing much. That really was the only juicy answer he provided. He did say he is aware some people are connecting KAs in this manner but quickly followed with another bout of no warranty, at your own risk, etc.
When you think about it the answer could not have been any different. The ground pin is immaterial. The root problem is huge capacitance on the Vcc rail at the load. Absolutely the worst place to put it in any electrical circuit.
One good use I can envision for the ground pin is to add a small non-lethal amount of capacitance. Just enough to keep the LEDs lit and the sound system from resetting when momentary loss of rail contact occurs but not so much as to fry the output transistors from a short circuit. Much like what other DCC sound decoders do with their external capacitor. This wouldn't do anything for the motor function but, as I understand it, momentary sound resetting is a common annoyance for some. It may fix that problem.
Tim isn't going to reveal granular design details. Nor should he. He has a business to protect. We can only speculate and deduce from basic electronics facts. We suspected, and Tim confirmed, the blue wire / ground pin is not a safe place to connect a motor KA. All this exercise did was confirm you guys are doing it the right way with your homemade KA circuits. At least on LM1, LM2, and LM3 units. Who knows what is in store for LM4s.
Alan:
--- Quote ---Maybe Ring has some wizard circuitry up his sleeve that'll allow his KA's to be attached to the blue and negative wires.
--- End quote ---
KA with built in current regulation - done.
Mark Gurries lists regulated/not-regulated on the web page Bill linked to earlier however, regulated in the DCC KA world means voltage regulation as noted in Mark's answer to question #4. We need current regulation. If I were a betting man my chips are on a RP KA product that has built in current regulation. Then blue wire/ground pin makes total sense. The addition of the ground pin may be laying the groundwork for such a device.
It is worthy to note our entire discussion revolves around protecting your LM. If you are confident you can install in such a manner that a short circuit will never occur inside the locomotive then putting a store-bought KA on the blue wire/ground pin will work. Essentially, a $70 gamble on your part. Tim Ring on the other hand knows people will make mistakes and the last thing he wants is more warranty costs or bad public image by not honoring warranty. When he receives a returned dead module he has no way of knowing that a KA killed the module. Hence, he is doing the logical thing by saying don't attach a KA.
William Brillinger:
@Alan
I just want to take a moment and publicly thank you Alan, for your invaluable contributions to this forum.
I hope I speak for everyone when I say I really appreciate your time and input here.
There are so many great people here and I am thankful for every one of them, but your efforts stand out as above and beyond.
Thank you.
Alan:
--- Quote ---I hope I speak for everyone when I say I really appreciate your time and input here.
--- End quote ---
Thanks Bill. It is fun playing RP detective trying to piece together the clues! They are just clues however. Being thrown into the conversation for little more than conversation's sake. If the thread helps someone build a better RP KA for themselves then so much the better. Glad to be a part of it.
Odd isn't it, for someone with no need whatsoever for KAs to get so engrossed in the subject? Clean your track dagnabbit!
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version