LM-2S with a K-A, but no Bridge Rectifier??

[CPRail]

Hey Gang,

The old man was doing an install a couple of days ago while I was busy trouble shooting one of his other locos. I was vaguely following his actions as it was his first ever hard wire and he was installing a K-A.

Oddly enough he was using an LM-2S, not a 3S and hooked up the K-A as you do with a 3S (i.e. without a bridge rectifier and across the 9 & 6 pin plugs). It worked fine!

Before he rips it apart to install the bridge rectifier, is there something that has changed so you don't need a bridge rectifier?

[William Brillinger]

When you say, "It Works" - do you mean the the KA is functioning properly?

That yellow wire is labelled as an Input on the LM-2S wiring diagram.

I don't know if Tim made any actual changes when it was repurposed and labelled "negative" for the LM-3S. You might want to contact him directly to find out.

[KPack]

I'd love to get some clarification on this as well.  I'm getting ready to do an install and just realized I'm out of bridge rectifiers.  And I'm using up my last LM-2S, so I would love to just hook up the KA without having to wire in an extra component.

[CPRail]

I honestly can't remember if it did all the K-A magic once off the rails, but I'll confirm tonight and let you gents know tomorrow.

[drisdon]

Kpack
Bill has the keep alives and bridge rectifiers in stock, all with free shipping!   

I too will soon, once the painting and decaling is complete, be doing LM-3S installs with keep alives in three Genesis GP38-2's (CSX each in a different paint scheme), one Genesis GP40-2 (CSX) this one gets a LM-2S, one Atlas B23-7 (CSX Family Lines), and one Atlas GP40 (CSX B&O Painted).

Dan Risdon

[KPack]

Kpack
Bill has the keep alives and bridge rectifiers in stock, all with free shipping!   

I too will soon, once the painting and decaling is complete, be doing LM-3S installs with keep alives in three Genesis GP38-2's (CSX each in a different paint scheme), one Genesis GP40-2 (CSX) this one gets a LM-2S, one Atlas B23-7 (CSX Family Lines), and one Atlas GP40 (CSX B&O Painted).

Dan Risdon

The problem is that this is the last locomotive I have to do an install on for a while.  I likely will not need another for at least a year.  And I already have everything (LM-2S, KA, harness) except for the bridge rectifier.  It'd be so much easier to just install without it.

[William Brillinger]

Kevin, I'll send you a bridge rectifier no charge. I only have a few left now.

[CPRail]

Here are the results of last night's testing:

While the engine control and sounds are fine, as soon as you take the loco off the track, everything shuts off. Just like if there is no K-A installed at all.

So, hooking a K-A up LM-3S style to a LM-2S doesn't work. No idea if it works if you hook up a K-A the proper way but without a Bridge Rectifier.

Guess the old man will have to rip it apart and redo it!

[William Brillinger]

No idea if it works if you hook up a K-A the proper way but without a Bridge Rectifier.

If you connect a KA to the power leads, outside of the LM-2, without the bridge rectifier, it will explode.

[CPRail]

Duly noted...

I have no desire to rename my layout the Chernobyl Central...

[G8B4Life]

without the bridge rectifier, it will explode.

Only if the polarity changes, which if you have any kind of reversing loop (or power it with DCC) it will. On a simple oval of DC track it wouldn't explode. More to the point though without the bridge rectifier it's kind of pointless anyway; without the bridge rectifier you'd be letting all that stored energy flow back down the track as well in a power interruption. The bridge rectifier prevents that so the LM gets all the juice.

- Tim

[William Brillinger]

Only if the polarity changes, which if you have any kind of reversing loop (or power it with DCC) it will.

or putting it on the track backwards.

[G8B4Life]

OR PUT IT ON THE TRACK BACKWARDS.

Why are you shouting at me? I was simply pointing out that not every use case would result in a KA explosion, the majority yes, every no.

Yes, putting the loco on the track backwards would also change the polarity to the KA and cause the KA to explode.

- Tim

[William Brillinger]

sorry, not meaning to shout.

Simply emphasizing that not using the Bridge Rectifier will cause it to explode. It's guaranteed to fail, even if you get lucky and apply power to it in the one way that it might survive, next time it goes on the tracks, it probably won't be the same.

[Alan]

The KA may be internally diode protected against reverse polarity. Hooked up backwards or placed on reverse polarity rails may simply cause the KA to not work rather than explode. Diode protection is prudent for the manufacturer given our litigious society.