# Re-wiring Bachmann K-27, cooling fan question



## steam5 (Jun 22, 2008)

In another post I asked about the fan sucking the smoke back into the boiler of my K-27. The solution is turning the fan around.

http://www.mylargescale.com/Community/Forums/tabid/56/forumid/14/tpage/1/view/topic/postid/69995/Default.aspx#70516

It appears this is a cooling fan and probably should be kept. When I re-wire the loco (I currently plan to remove most of the electronics) I will remove the smoke unit, should I still keep the fan installed for cooling?

When I install the DCC decoder, how have others wired the cooling fan up? Parallel with the motor, or power it from a DCC function output?


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## Greg Elmassian (Jan 3, 2008)

I'd make it run full speed whenever the loco is "on" just because power on dcc is not usually a problem. I don't think paralleling with the motor is the best way, you can load the motor at lower voltages, and the fan might be going too slow. A function output that is on whenever the loco is moving might be ok, but would shut the fan off even if you just finished a very hard pull. 

Regards, Greg


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## StanleyAmes (Jan 3, 2008)

Posted By steam5 on 12/29/2008 9:09 PM
In another post I asked about the fan sucking the smoke back into the boiler of my K-27. The solution is turning the fan around.

http://www.mylargescale.com/Community/Forums/tabid/56/forumid/14/tpage/1/view/topic/postid/69995/Default.aspx#70516

It appears this is a cooling fan and probably should be kept. When I re-wire the loco (I currently plan to remove most of the electronics) I will remove the smoke unit, should I still keep the fan installed for cooling?

When I install the DCC decoder, how have others wired the cooling fan up? Parallel with the motor, or power it from a DCC function output?


I provided some suggestions to Bachmann when they developed the Ks electronics so I am familiar with whats inside and therefore may be able to help you with your modifications.

The K27s electronics are totally isolated from the tracks and the fan is powered from DC provided through the device plugged into the socket. The fan is likely very important if the motor is under load for extended periods but also likely not of much need for normal light running. 


If the noise of the fan is something you want to remove then I would suggest adding a low value thermistor attached directly to the motor. SInce most common thermistors are break rather then make in the presence of heat you would also need a relay so that if the motor heats up the fan turns on.

If you tell us what effects you would like to be different from the stock locomotive some of us may be able to suggest changes to the existing wiring to accomplish these changes.

Stan
http://www.tttrains.com/largescale/


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## Curmudgeon (Jan 11, 2008)

Posted By StanleyAmes on 12/30/2008 5:26 AM
Posted By steam5 on 12/29/2008 9:09 PM
In another post I asked about the fan sucking the smoke back into the boiler of my K-27. The solution is turning the fan around.

http://www.mylargescale.com/Community/Forums/tabid/56/forumid/14/tpage/1/view/topic/postid/69995/Default.aspx#70516

It appears this is a cooling fan and probably should be kept. When I re-wire the loco (I currently plan to remove most of the electronics) I will remove the smoke unit, should I still keep the fan installed for cooling?

When I install the DCC decoder, how have others wired the cooling fan up? Parallel with the motor, or power it from a DCC function output?


I provided some suggestions to Bachmann when they developed the Ks electronics so I am familiar with whats inside and therefore may be able to help you with your modifications.

The K27s electronics are totally isolated from the tracks and the fan is powered from DC provided through the device plugged into the socket. The fan is likely very important if the motor is under load for extended periods but also likely not of much need for normal light running. 


If the noise of the fan is something you want to remove then I would suggest adding a low value thermistor attached directly to the motor. SInce most common thermistors are break rather then make in the presence of heat you would also need a relay so that if the motor heats up the fan turns on.

If you tell us what effects you would like to be different from the stock locomotive some of us may be able to suggest changes to the existing wiring to accomplish these changes.

Stan
http://www.tttrains.com/largescale/



This is too good to not archive.
Plug and Pray, redux.


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## steam5 (Jun 22, 2008)

Greg, I agree about you point on paralleling the fan with the motor, it was just a simply nasty solution  But I do think there would be more electrical issues with that solution, due to different current draws.


Stan, The noise does not bother me; I don’t think I will hear it over the phoenix sound board when I install it. Where would you get the power from to power the fan? If you leave all the Bachmann electronics how does the fan behave under DCC operation?

I guess ideally I would like the fan to come on automatically when the motor starts to turn. I don’t think this behaviour can be programmed to a DCC function output?

If (motorTurning = true){
Fan = ON}

Else{
Fan = OFF}


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## StanleyAmes (Jan 3, 2008)

Posted By steam5 on 12/30/2008 6:22 PM
Greg, I agree about you point on paralleling the fan with the motor, it was just a simply nasty solution  But I do think there would be more electrical issues with that solution, due to different current draws.


Stan, The noise does not bother me; I don’t think I will hear it over the phoenix sound board when I install it. Where would you get the power from to power the fan? If you leave all the Bachmann electronics how does the fan behave under DCC operation?

I guess ideally I would like the fan to come on automatically when the motor starts to turn. I don’t think this behaviour can be programmed to a DCC function output?

If (motorTurning = true){
Fan = ON}

Else{
Fan = OFF}


At worst the fan sounds like an electrical steam generator and is masked by the phoenix sound. Unless you have a specific change you wish to make I would leave the electronics as they are. The locomotive's electronics need DC to operate. This DC is normally provided by whatever you choose to plug into the socket. So if Power on/ Fan on. There is no connection between the fan and the motor. 

You can switch on and off the internal electronics (including the fan) by hooking up the locomotive's "-" wire to a function output. You can use the same function output to turn on and off the sound so that when the locomotive is not in service everything is off and when you want to fire it up you turn on the elecronics and sound.(which includes the fan)

To do what you desire (connecting the fan operations to the motors operation) you would need a mechanical or electrical sensor on the motor that would connect the - line when turning. 

I think either leaving it as it is or using the function control of the "-" line is a simpler solution.

The downside of using a function is that most current decoders (including the phoenix) only support F1-F12 and you quickly consume all 12. As the manufacturers start supporting all 27 functions this option becomes much more viable.

Stan
http://www.tttrains.com/largescale/


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## Greg Elmassian (Jan 3, 2008)

I don't know what the current draw of the fan is. If it's low enough to run from a function output, then you can pick a function and map it to something that is "on" in forward and reverse. I suspect if that was hard to find, 2 outputs, one on in forward and one on in reverse, combined with a coupler of diodes would do the trick. (sort of like if either the headlight was on or the backup light was on the motor was going)... in this way, you might find a way to do what you want. 

If the fan draws too much, then a small relay would do the trick. 

This method does not use a function button, only a function output, which many decoders have plenty of. 

Regards, Greg


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## steam5 (Jun 22, 2008)

Happy New Year

Stan my reasoning for re wiring the loco is I find myself changing items and it has always been easier for me to just start from scratch. I use this philosophy for all my HO installations, and I carried it to my first large scale installation (Spectrum 2-8-0) and it worked, the K will be my second.

Please don’t be offended, as I do it to nearly all my locos. I feel bad when I re build things, as someone put a lot of effort into it.

Greg that’s exactly what I was thinking. If I map an output to F0 (head light) the fan will run whenever the head light on. Not exactly what I want but it’s a compromise, it will keep it compliant with the KISS method, a temperature controlled unit would be nice, but it’s not KISS.

The Lenz Maxi can handle 1A for the total of all function outputs. If I go over this limit I think I will use one of the switches present in the front of the boiler, some will be free as I plan to by pass some. And to power it I will just make a simply bridge rectifier to get DC and filter it with a regulator and capacitors, I may be able to utilise the Bachman circuit, but I won’t know until I see what it is.


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## Greg Elmassian (Jan 3, 2008)

Wire the decoder common to the fan positive 
wire the fan negative to 2 diodes, the connection point would be 3 wires, the fan, and the cathodes of 2 diodes. 

Now take one of the diodes (anode) and connect to the F0 output, and the other to the output for the backup light. 

Now the fan runs whenever the loco is in forward or reverse. 

Regards, Greg


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## steam5 (Jun 22, 2008)

Now all I have to do is wait for the Aussie dollar to become a bit better, order a few bits and set aside a weekend to perform the open heart surgery! I look forward to it!

Since becoming a member here I have read so much about the K, it almost put me of buying one. The guy I purchased her from discovered Accucraft so the K was left in the shed, but I’m going to give her a chance, and see what I can make of her. 

I’ll be optimistic.


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## steam5 (Jun 22, 2008)

Just thought I’d tell people what I have done with the fan. 

Over the weekend I re wired the entire locomotive; all the Bachmann circuitry was removed. It all went well and the K is back running with improved properties. 

Currently the fan is powered from an output on the decoder which can be turned on and off with function 4. I need to finalise what outputs and functions do what later. 

The next part will be to install the Phoenix sound board.


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