Chassis headlight electrical connection, DCC

[Scottl]

I hardwired a Lokpilot v4.0 micro today in a Kato SD40-2 that I have converted to a 8-40CM with the Briggs kit.  So far so good, the motor runs well and all makes sense.

For the headlight, there is only a single lead from the decoder (yellow wire) and one for the rear light.  The manual indicates the light circuits should be completed by attachment to the Loco chassis.  From what I understand, the metal chassis is isolated and there is no current flow in it.  Should I still connect the headlight to it, or is there another way to do this?  The manual, while very thorough, is silent on this issue.

Thanks in advance.

[jdcolombo]

Hi Scotti.

Photo?  What you've described honestly makes no sense to me.

First, the chassis is not isolated.  The trucks on the Kato contact phosphor-bronze pickup strips that are attached to the chassis.  Each side of the chassis is "live" providing electrical conductivity to the rail on that side.

Second, if you "hard wired" a LokPilot, then it had a white wire and a yellow wire at a minimum.  If you are using a six-pin plug version, then there is no blue wire.  The blue wire is usually the function common (e.g., the positive connection to lights).  The white wire is the headlight, the yellow wire is the rear light.  If you do no have a blue wire then you have to wire the positive side of the LED (I'm assuming you are using LED lighting) to the chassis.  The negative side of the LED is wired to white (headlight) or yellow (rear light) with a 1K dropping resistor to avoid burning out the LED.

If you post a photo of what you have done, maybe I can provide better information for you.

John C.

[RBrodzinsky]

The blue wire should be used for the positive feed of the LEDs. If your decoder doesn't have one (was it six pin version), you can add it to the decoder easily. The common is the pad at the edge of the board, next to the yellow and white wires.

[jdcolombo]

The blue wire should be used for the positive feed of the LEDs. If your decoder doesn't have one (was it six pin version), you can add it to the decoder easily. The common is the pad at the edge of the board, next to the yellow and white wires.

Yes, Rick is right, and it really is much better practice to use the blue wire and not use a chassis connection for lighting.  Blue wire to positive side of LED (both front and rear; take a scrap piece of wire to connect the two positive sides of the LEDs); white wire to negative of headlight (with dropping resistor; don't forget the resistor), yellow to negative of rear light (with dropping resistor).

John C.

[peteski]

Manufacturers of the 6-pin plug-n-play decoders, or other decoders which do not have the decoder's positive lead (blue wire) present instruct the modeler to wire the positive side of a function device (like a bulb or LED) to either of the rail pickups.  Because the DCC voltage flips polarity many times a second that method does provide a positive potential to the function device roughly 50% of the time.  This gives acceptable result with incandescent bulbs, but not so good with LEDs.

I suspect that the blue-wire-less headlight install is the reason the instructions direct him to wire the positive side of the headlight to the chassis (which they assume is part of the electric pickup circuit from the rails). They don't specify which side of the chassis because either side will work.  But the Kato loco Scott is working on has an electrically isolated single-piece metal chassis. Hooking up the headlight as instructed in the manual would not work.

So, as other have mentioned, do not hook up anything to the chassis. Look over the decoder's manual and find where the blue wire would be attached and hook up the positive side of your headlight there.  If not shown in the decoder manual, we can help you in locating the place on the decoder where the blue wire should be.

[Scottl]

OK, thanks everyone.  There is (or was) a blue wire that I can use.  The manual is not very clear on what the wire was for but now I understand.

I removed the Kato chassis powering strips as the new trucks that assembled from the kit did not reliably rub and provide power. I hard wired power leads to the power pickup on both sides of the truck.  So my chassis has no power going through it, I simply bypassed this with the hard wiring.

[peteski]

OK, thanks everyone.  There is (or was) a blue wire that I can use.  The manual is not very clear on what the wire was for but now I understand.

I removed the Kato chassis powering strips as the new trucks that assembled from the kit did not reliably rub and provide power. I hard wired power leads to the power pickup on both sides of the truck.  So my chassis has no power going through it, I simply bypassed this with the hard wiring.

Oh, I thought your loco had one of the new screw-less chassis designs with shock-absorber truck suspension.  But regardless, what you did will work fine.  However I;m surprised that you had problems with the standard Kato truck-to-chassis pickups strips. Those are usually very reliable. For even more reliability I usually polish the area of the strips where the truck's nubs contact it, then I also polish the tips of those nubs.  I don't much care for hard-wiring the trucks on locomotives.

[Scottl]

This kit relocated the tabs that stuck up to make contact with the strips and I found the contact was not great.  I could have bent the contacts but I figured I would try hard wiring to see if it helped things.  It definitely worked and the Lokpilot decoder works very well.  I'm starting to get sold on these, but the lack of a drop in version is a pain.

[RBrodzinsky]

Oops, I posted where the blue wire (common) pad was on the LokSound. On the LokPilot, the pad is on the back of the decoder. It is in the middle of the edge with pads, the first pad after the small component. See Figure 2 in the LokPilot PDF from the ESU site

[craigolio1]

The kit Scott is building uses the original SD40-2 chassis and has replacement trucks that use the Kato wheels and gears. The new trucks don't realiably contact the pick up strips , as he mentioned, and thus his need to hard wire them.

Scott I'm excited to see one of these running. I think I over tweaked my trucks and may have created shelf queens. We'll see.

Craig

[peteski]

Ah, so those trucks are resin cast from Briggs?  Now  that makes sense.

[craigolio1]

Yes sir. Peteski we should both be sleeping.

[peteski]

Yes sir. Peteski we should both be sleeping.

LOL, I don't think my manager would like me to do that - I'm at work. 

[craigolio1]

Oh yeah. Me too.

[Scottl]

@craigolio1 mine runs pretty well, but the gear noise is a bit loud.  It needs to run a bit and wear in, I think. I found the drop in TCS decoder interfered with the shell so I went with the Lokpilot.  I don't regret it, it starts on speed step 1 and moves smoothly (albeit with a healthy grind effect!).