# Bachmann K-27 chuff timer wiring.



## Josef Rieder (Jan 18, 2008)

Does anyone know which wires feed into the tender plug from the optical chuff timers. Chuff is going timed the old fashioned way: with reed switches and magnets. I might try to splice into the circuits that run from the timers to the board in the tender that way I won't have to run an extra wire from the loco to the tender. Has anyone tried/considered this?


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## bobgrosh (Jan 2, 2008)

The two outputs leave PCB05 (bottom board the motor connects to inside the boiler) and go to PCB02 (top board inside the boiler) on blue and orange wires. 

You can cut the blue and orange wires near the plug on PCB05 and connect the reed switch to the wires feeding the top board. 

Inside the tender you will find these two wires on opposite ends of JP1 Remove JP1 to gain access to whatever you connect to the blue and orange in the boiler.


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## jimtyp (Jan 2, 2008)

Bob, is the board in the boiler easy to get at? What needs to be removed to access it?


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## bobgrosh (Jan 2, 2008)

(1 and 2) Remove two screws under the cab 

(3) Pull off the front dome and remove the single screw under it 

(4) Remove the small screw in the reversing linkage. Where? Reach inside th cab, lift up on that big lever where the engineers right hand is, and you can move the lever forward and back. the lever extends through the cab floor. follow the moving part forward along the right side of the loco to about the middle of the loco. There, you will find a tiny screw loosely attaching it to a lever that moves some of the valve mechanism. That's the screw. 

Those are the four screws Bachmann says to remove. I STRONGLY advise you to remove 4 more. 
(5 through 8) Remove the four screws that hold the two boiler braces. These are the two rods that connect the front of the smoke box to the cow catcher. Then rotate the two rods upward and pull them out of the sides of the smoke box. 

Finally, remove the front of the smoke box, not just the door on the smoke box front, but the entire plate the door hinges on. Look inside and notice that there is a* LARGE LIP* on the cross-head then protrudes forward and holds the smoke box down. 

Now, working from the rear, lift up on the cab and rotate the cab and boiler assembly about 20 degrees, then slide the cab and boiler forward to disengage the *LARGE LIP * from the inside of the smoke box rear. 

When reassembling, the hardest part is getting the large lip engaged up and over the bottom rear edge of the smoke box. While you don't need to remove the smoke box front to take the loco apart, you will need to remove it to put it back together. (Just ask Tony) I recommend removing the front and looking at the large lip prior to removing the boiler, just so you will know what you need to accomplish when putting the loco back together. 

Believe it or not, It only takes a minute or two to remove or install the boiler.


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## jimtyp (Jan 2, 2008)

Thanks Bob! And thanks Josef for asking the question


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## jimtyp (Jan 2, 2008)

Bob, I do have another question about the B' K-27 Chuff. I've noticed with my P5 using the optical chuff that the chuff starts missing about 40% of full throttle and eventually cuts out all together. Are you using the optical chuff and if so do you see this also?


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## TonyWalsham (Jan 2, 2008)

Jim, 
The K-27 has the wrong gear ratio. 
It is about 15:1 instead of the planned 30:1. This means it runs twice as fast as intended. 
Maximum speed is about right on 14.4 volts of batteries. 
I have no chuff definition problems with the K-27 running at full speed on 14.4 volt batteries. 

What voltage are you powering the controller with? 
If you run higher voltages the chuff will be trying to signal at a speed faster than is needed and this will tend to blend in. 
The P5 can be programmed to read the chuff signal either + or -. 
As yet I have not tried using the + output but I will soon. 
On the RCS battery powered PnP-3 R/C pcb I have smoothed the signal with a .1µf cap and then inverted the signal with an open collector tranistor to get - output. The RCS PnP-3 pcb has a selector for either + or -.


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## jimtyp (Jan 2, 2008)

Tony, I'm running about 21 - 22v. There was an article in Model Railroad News that stated the Scale mph was 31 at 22v at full throttle on flat track. I have not verified this. There is a blurb on the Blackstone site that says the K-27 could get up to 45mph (based on what old-timers stated:  reference ). My understanding is they typically ran at 20 - 25 mph, which according to the article in MRN would be about 50% of full throttle at 22v (23 scale mph). I prefer to run models similar to prototype speeds, but if I try and run at this speed the chuff cuts out, it starts cutting out about 40% of full throttle at 22v. 

If i could get the chuff to not cut out at even 50% of full throttle at 22v I would be happy with that speed  I can always go back to magnets but I'd still like to get the optical chuff working if possible, but I'm getting close to giving up on it. I see where others have had this same problem so I don't think my K-27 or P5 are defective. 

My power supply is switchable and if I run 16v I can't get near what my locos run at 22v. So I'm sure those running at 14.4v would not see the problem even at full throttle. 
I have the P5 connected using an NPN transistor, as that is what Pheonix says to use. Some say it is not needed, but when I called Phoenix (John) they said it is required for the P5 but not the 2K2. So I have not tried the install without one. Phoenix said they would send me a 2K2 to test to see if I have the same issue with that card, but I'm still waiting after 2 weeks. 

I also tried a 0.1 capacitor. It helped very minimally in my case. Another theory is that since I run DCC that mabye it has some extra noise that battery or DC folks do not see? 

I think you have done a great job with the RCS system, and as others have noted, I believe yours is the only true Plug-n-Play install for the K-27. Well done!


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## Josef Rieder (Jan 18, 2008)

Well guys, it looks like I opened up a good can of worms here. I figured you would have to take the boiler apart to access the board in there. That shouldn't be to bad given the exploded diagrams they give you with the loco. If this becomes to troublesome, I may just end up installing my own connection between the loco and tender. Good hunting!


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## TonyWalsham (Jan 2, 2008)

Jim. 
I can't comment about a DCC decoder having an incompatible ground with the K-27 wiring ground. I have no experience with DCC decoders. 

What I can tell you is that the K-27 ground is the same right throughout the loco. I power the Bachmann board + & - through a diode from the battery power supply. This means the ground is common for the loco, RCS/EVO control system and the Sound system I choose to use. I too have used the Phoenix P5 + P5T and have absolutely no issues with the chuff timers being filtered, a decision I arrived at from a recommendation by Phoenix and my own personal testing. I had to use the .1 µf mono cap. This filtered signal then drives the base of an NPN open collector transistor I have on the RCS pcb. I set the trigger up so that by moving a small headshunt the operator can select either a filtered + chuff or an inverted - chuff. Further, the options give me the flexibility of also catering for any change in future chuff timing to a - signal. I just bypass the transistor. 
I will get around to testing the P5 with a + chuff soon. Probably next week when I hope to get another shipment of Phoenix sound systems delivered.


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## jimtyp (Jan 2, 2008)

Tony, would your circuit/socket work with track power? If so I'd be interested.


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## Greg Elmassian (Jan 3, 2008)

Most DCC decoders have a full wave bridge to power themselves from the track, which is sort of AC or is AC depending on your interpretation. 

That means you can have at least one diode "between" the DCC decoder's ground and the bachmann circuit board ground. There is the source of ground problems, which may affect things like the chuff being fed to the decoder. 

It depends on the decoder. If you have problems, you could power the chuff circuit from the decoder GND and UNREG pins (the power "output" from the DCC decoder). 

Regards, Greg 

p.s. it sounds like Tony has NO diode between the ground in his circuitry and the ground of the Bachmann.


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## jimtyp (Jan 2, 2008)

I'm not sure if the problem is I'm using a decoder that does not have a ground, NCE D408-SR? I don't know enough about electronics to figure it out. But I know you guys know a lot (Bob, Tony, Greg and others). So i was hoping one of you would figure it out for me  

If the ground is important then I would have to switch to another decoder that has a ground. Or can I use the ground on the dummy socket some how? 

However, I'm not sure why folks think the ground is important? If it were then why would the P5 work at all? If the P5 works up to 40% of full throttle at 22v then why would a grounding issue cause a problem at that point? 

I would be interested if ANYONE said they had their B' K-27 running on DCC at around 22v was using the optical chuff successfully at full throttle or even close to it. If so I'd like to know which decoder and which sound system. 

I really think it's because the optical chuff trigger is too short at higher speeds.


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## TonyWalsham (Jan 2, 2008)

Posted By jimtyp on 04/03/2008 9:16 AM
Tony, would your circuit/socket work with track power? If so I'd be interested.





Hi Jim the RCS/EVO PnP-3 is designed for battery power only. 
It could be made to work on a constant track voltage by the addition of a bridge rectifier and suitable filtering, but not by me. 

Greg. 
You are correct. 
The grounds of the Bachmann, RCS and sound system are all simply tied together. 
There is a diode in the + line from the batteries for polarity protection.


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## TonyWalsham (Jan 2, 2008)

I have now had the chance to test the P5 using the + signal from the K-27 chuff timer. 
I can confirm the chuff signal set to + does *NOT* work with the P5 even with battery R/C. 
Back to a - signal only.


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