Should work

I can't see any electrical reason why this wouldn't work.

Polarity change

By adding the bridge rectifier, the polarity going into the rail pro module will always be as you show in the chart.  When before you add it the polarity will switch when you rotate the engine 180 degrees.  How is the module going to deal with this? 

I Believe.....

.......The directionality is not polarity dependent. Just like DCC. The direction is controlled by the chip not the track polarity.

Yep

Sure, why not. Essentially the basic circuit for any AC to DC power supply. The rectifier and cap may throw off the calibration of the track voltage feedback to the controller but that is of no real importance.

Feeling like I'm on the right track...

Can someone suggest what specs I should be looking for in a diode bridge for this applications?

amperage

Greater amperage rating than module's maximum load rating. I believe the modules are 800ma continuous and 2A stall. So, a 2A bridge.

ummm

< friendly jab>

Bet you wish you had run a few more wires to those turnouts now, huh? A few wires and done forever. You will be installing bridges and caps every time you get a powered piece of of rolling stock. And you thought I was nuts with all my wiring. Well, you are probably right but there won't be any stalling on my railroad!

< /friendly jab>

did I ?

I don't think you're nuts. at least not any more than the rest of us. 

26 cents

http://www.mouser.com/ProductDetail/Shindengen/S1ZB80-7062/?qs=sGAEpiMZZMtQ8nqTKtFS%2fC1PHfFfWWLnL4AuMCc7Arc%3d

10 cents

http://www.ebay.com/itm/50-Pieces-DB106G-1A-800PIV-Bridge-Rectifier-/271819528270?pt=LH_DefaultDomain_0&hash=item3f49b4d84e

50 cents, arrives sooner and is in stock...

50 cents each after shipping...

http://www.ebay.com/itm/Qty-10-pcs-DF04S-DF04-SMD-Bridge-Rectifier-Surface-Mount-1A-400V-US-SHIP-/291421392518?pt=LH_DefaultDomain_0&hash=item43da118e86

Anything wrong with these specs?
DF04 SMD Bridge Rectifier Surface Mount ~ 1A 400V
http://www.vishay.com/docs/88573/dfs.pdf

Nope

Looks fine.

Current?

I noticed that Alan suggested a 2A bridge in an earlier post but the part you spec is rated at 1A I believe.

Just pointing this out in case it matters in the end?

Continuous

Continuous is 1A. Ring module is 800mA continuous. All good. Bill's component choice has a surge rating far above his power supply's output.

The only way he might get into trouble is operating a heavy draw loco (blue box) for an extended period of time. Something pulling an amp and a half or so. I think the Ring module overheat shutdown will take over before the diode vaporizes. The 2A recommendation was for some headroom.

the 2A diode bridge...

the 2A diode bridge is so much larger. I think these will be good.

Bridge Rectifiers

But I thought that LM-2's were not supposed to have these problems?

The rectifiers Alan referenced are less expensive, but only get you to 800 mA or 1 A which do not provide adequate design / operational margins. Also these DIP and Surface Mount packages complicate the wiring. Yes they are more expensive (~$0.60), but WOG packaged devices with rating of 1.5 A and 2.0 A devices are available. These devices provide adequate margins and should be easier to wire.

General Mouser Search:

http://www.mouser.com/Semiconductors/Discrete-Semiconductors/Diodes-Rectifiers/Bridge-Rectifiers/_/N-ax1mf?P=1z0wap7Z1z0w1kiZ1z0w4nyZ1z0waqpZ1z0sx1fZ1z0warfZ1z0z63xZ1z0xs5h

2.0 A Device:

  610-CBR2-060

Let us know how the RailPro receivers work with the Keep Alives, and I will think about risking one to determine where to wire in a KeepAlive (unless you would like to volunteer one of yours).

One ring to rule them all

They don't. Bill's track wiring does!

Parts ordered...

2 KA1's from YankeeDabbler (on ebay)

and 10 Little diode bridges to rectify the situation!

...I'll let you know how it goes.

I think this...

could be one of the reasons I want to have powered frogs and will use slide switches to change frog polarity when turnouts are thrown.  Fewer dead spots in the track work.  I gather that's what Alan is referring to in Bill's wiring?

Bill, Be Aware

Of what your supply voltage is to the track. You will drop the supply to the module by 1.4 volts with a bridge. Below about 12v DC the supply to the module starts getting "iffy" and you may trigger a low voltage warning.

I've been using RailPro about 2-3 months now and have thought about a KA type circuit as well. Non-polarized caps would be another solution, but I don't think they make them large enough (mfd - wise) to be useful, otherwise they would have already been used for DCC.

Adding track sliders is another way to improve pickup.

If you have never had the nerve to look inside an LM2(S) module have a peek. I think I have figured out where a KA would connect, but soldering wires there would be MOST difficult.

The bridge circuit is probably the best choice unless Tim chooses to use the unused "input wires" to this purpose in future versions of the LM.

I look forward to hearing how it works. Theoretically it should be OK.

Espee over Donner

I did...

I opened up one of my LM2-S modules and decided it was way to crowded for me to add a KA to it that way.

Note to everyone with RailPro: Email Tim and ask him to add Keep Alive support to the modules.

Just for info

What is the turnout issue, Dead frog? Are all the engines having problems with all the turnouts?  

If it's wiring, why not redo a couple to verify that the problem goes away?  Of course, you may want KA for other durability issues.  It seems to be a game changer solution for robust operation.

Are we dealing with a rights issue here?  I'm sure TCS would sell KA's to the Rail pro people, but that would impact the module price point.  

The turnouts are...

Peco Insulfrogs. Mostly the 1980's/90/s design, not the newest ones.

My Kato SD40-2's like to stall on them sometimes, but not consistently.
I've rebuilt the trucks to include wipers from the wheels wired into the decoder.

9 out of 10 times it's fine and then all of a sudden, usually when in pairs, one or both of the units stall on turnouts. and then it's fine again.

Totally ruins the experience for me. Maybe I need to break out my Graphite!

ARRRGGGgggggg!

So I just spent 35 minutes running over my trouble spot with my trouble spot susceptible locomotives... with no problems. Why no problems? well, I hit the rails for 2ft in each direction with a light dose of graphite and could nno longer replicate the problem... 

sigh.

(I'll find out tomorrow if it was just a fluke. More testing ahead!)