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Keep Alive installation w/ Railpro

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Alan:
You need to measure the track voltage (at both points as before) while the system is under heavy load (several locos with lots of cars) and under no load. Then you will know the lower and upper voltage range your layout will experience.

No, forget about a "converter". There are DC-DC converters (called buck converters) but they are pricey for units that can manage the 4 amp output of a power brick. Easily close to $100.

Do I look smug? I feel smug.  ;D  Bill, you need the same power supply I use - a 15V cheapie switch mode. They have an adjustment potentiometer on the circuit board that has about a 4 volt swing - 2V above and 2V below. A 15V switch mode power supply therefore can be anything from a 13V to a 17V unit. Mine are set at 16.9V to deliver 14.8V to the rails after the 3 diode drop in my occupancy detectors.

$18 bucks and free shipping. How can you go wrong? http://www.ebay.com/itm/RS-75-15-Mean-Well-Power-Supply-15V-5A-/122011245930?hash=item1c686fdd6a:g:9HkAAOSwnFZXWhje

The KA is on the far side of your bridge rectifier (2 diode path) so it will always be 1.4V below track voltage. The 3rd diode is after the KA but before the LM. The LM is the only component seeing the full 2.1V drop.

William Brillinger:

--- Quote ---The KA is on the far side of your bridge rectifier (2 diode path) so it will always be 1.4V below track voltage. The 3rd diode is after the KA but before the LM. The LM is the only component seeing the full 2.1V drop.
--- End quote ---

That's what I meant, but thanks for the full detail version.


--- Quote ---$18 bucks and free shipping. How can you go wrong?
--- End quote ---

I'ma do that.

Alan:
I need to correct an earlier statement of mine. The LM only experiences the additional 0.7V drop of the KA's internal diode when track power is missing and the LM is running on KA discharge. The KA diode is not in series with the LM when track power is available. So, the LM will be driven by either power supply voltage minus 1.4V or supply voltage minus 2.1V depending on whether track power is available or not.

The relevance is a 0.7V swing is built into the homemade LM / KA arrangement. Important? I doubt it. Just know that it is there.

Alan:
HOLD THE PRESSES!!!!

Bill, check this out. An inexpensive solution for your power supply issue: http://www.ebay.com/itm/150W-DC-DC-Boost-Converter-10-32V-to-12-35V-6A-Step-Up-Power-Supply-Module-Board/132053796647?rt=nc&_soffid=5023882200&_soffType=OrderSubTotalOffer&_trksid=p5731.m3795

William Brillinger:
That's interesting.

I wonder if the short circuit protection on the PWR56 side would be affected by using this?

- Bill

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