Keep Alive installation w/ Railpro

[Alan]

Your low voltage indication is no doubt the result of passing the track voltage through 3 additional diodes (one each direction in the bridge rectifier and another in the KA discharge line). Each diode drops 0.7V. Whatever your power supply voltage is, you can subtract 2.1V to arrive at what is actually getting to the module now.

Recall earlier I commented that an argument could be made if a KA is in one loco then it should be in all? You are experiencing why.

[William Brillinger]

Recall earlier I commented that an argument could be made if a KA is in one loco then it should be in all

Yup. And I will be adding them to my entire fleet for sure.
At which point I may look at increasing my track voltage by 2V.

[Alan]

Beware. Once you raise the track voltage then it may become dangerous to run a non-KA loco as you will be right at the upper limit of acceptable LM voltage. Your layout effectively becomes mandatory KA for any visiting railroaders.

You will have to put this on your train room door! 

[William Brillinger]

sigh.     

Thanks Alan, The voice of reality strikes again.

[William Brillinger]

I got out my meter, and I read 14.28V on my rails, both at the nearest point to the PWR-56 and also at the furthest reaches.

The LM-2S manual says the MAX is 18V.

If I would increase the voltage to ~16V it should be fine and should eliminate the warning condition.

The question is this: Where would I find a 16V DC PSU that is appropriate for the Job.
I wonder if there is an appropriate 1.5 or 2V step-up converter?

On the downside, the KA3 is rated for 12 to 16V input. That might be cutting it close.
**Actually it should be fine, since the KA3 is on the lower voltage side of Diodes.

[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.    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]

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.

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

$18 bucks and free shipping. How can you go wrong?

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

[Alan]

I can't think of a reason why anything should change. The eBay converter is rated higher than the RP PS. Current flow is still current flow.

[William Brillinger]

Alan,

What about using this up converted higher voltage with the AR's and other Ring Engineering components?
Do you see any issues there?

[TwinStar]

What is the net effect of lower voltage at the motor? Poor performance or just a lower top speed?

[William Brillinger]

The lower voltage is still in range of what the module wants to see.

I have my locos dialed back to 75% for top speed, so I have headroom if for some reason there was not enough power at the motor, but I don't see it being an issue.

[TwinStar]

Thanks Bill.