Thanks so much for doing this posting. I too have several older fan driven smoke unit steam engines that I wanted to have the synchronized puffing feature since the TAS chuff n' puff boards became unavailable.  Your posting has made that want of mine possible.

I will point out that this mod ends up connecting the fan lead directly to the chuff input of the locomotive electronics.  There have been at least two posts of folks that did this exact mod and ended up cooking the RailSounds board chuff input.

 

This input should really be buffered so that the spikes from stopping the motor are not fed back into the RailSounds chuff input.

 

Just sayin'...

 

Have failures been reported if the chuff switch is connected to the R2LC also or just if connected to the audio board?

 

Pete

What value diode is recommended for this mod? Where and in what direction should it be installed to adequately protect the sound board? Your reply is most appreciated.

Marty and John thank you for your advice. It is well taken and most appreciated.

Can this be done with ERR upgrade kits?  

 

Thanks, 

John

John: Thanks for the heads up.

 

Bob: Thanks for the tip on the diode I will install one on Monday.

 

wmswen: The end with the stripe would face the smoke unit. Any 4000 series diode should work fine.

 

After seeing the result I will not go back to that steady stream of smoke. The puffing just looks so good.

 

As with all modifications you always attempt at your own risk.

If the diode is placed with stripe facing the smoke unit and is in line with the ground wire from the cherry switch if will block the current return to ground and the fan won't work.

 

Isn't it better to place it in between the cherry switch and the R2LC chuff input with stripe facing the cherry switch?  This would prevent any positive voltage spike from making it to the R2LC input.   G 

Configured that way, the diode won't prevent any negative spike from reaching the board.  The collapsing field of the motor being switched off can induce spikes of either polarity into the board.

 

If you really want to fool around with this mod, the best protection would be a diode from 5V with the anode connected to the chuff input, and another diode to ground with the cathode facing the chuff input.  This will clamp spikes of either polarity.

 

I personally don't recommend this connection anyway, but if you must, I'd at least protect the input from transients.

I may be thinking too simplistically here, but wouldn't using a transistor to switch the power to the motor be a better way?

You're thinking correctly, that's how I do it.

 

ERR's Puff N Chuff circuit addresses this. Currently working on improvements to this.

 

Pete

I'm also working at building a unit similar to the Puff-N-Chuff to buffer the motor drive.  I also want to add running the smoke at idle with a lower voltage on the motor when chuffs are no longer coming in for a couple of seconds.  This is how Legacy and MTH manage the smoke when the locomotive stops, it also keeps the smoke resistor from cooking the wick. 

 

Since no chuffs indicates the locomotive is stopped, I'll also add the ability to turn on the cab lights and manage the headlight for Rule 17 lighting.

 

I'm thinking of a fixed interval of fan motor for each chuff, and when the intervals converge at high speed, the fan run continuously.

 

I guess I am confused.  The R2LC Chuff input sits high and goes to ground to activate a chuff.  Not quite sure what the diode from 5V is doing.  Also not sure if the DC motor can generate a negative spike, but if it did wouldn't it just be a stronger chuff signal.   G

Inductive sources, such as the motor, can generate spikes far in excess of what the inputs to the board are rated for.  This happens when the power is suddenly removed and the magnetic field collapses in the motor.  The diode to 5V is a low impedance path to shunt any voltages harmlessly away from the input.  This is a pretty standard way of protecting a digital input from excess voltage spikes.

 

Let me look up a reference for you, since apparently you don't believe me.

 

Protecting Inputs in Digital Electronics

When you build it I will come.

Put me in line as a beta tester. Also put me down to purchase 6 units. All my K-line puffer units would then be converted to fan driven.

 

One observation, I have 2 Lionel units with the constant fan the one I modified and one that is not. I have noticed at high speed the constant unit just puts out a stream of smoke. The one that is modified even with the short off period causes the smoke to swirl. This swirling action is a nice visual effect.

If you get the chuffs close enough together, then they will merge.  However, that may only happen at highball speeds, I suspect that for most speeds you will still have discrete chuffing.  Of course, I'll also be able to tinker with the length of the chuff to get the best effect on whatever my test subjects are.

 

Until I have a working unit, I won't know how long a motor run will make sense to get good looking smoke puffs.

 

I also have quite a few steamers that don't have the ability to run the fan when stopped, I'd like to be able to add that.  The cab lights and Rule 17 lighting are just icing on the cake.