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I installed a TCS WOW 501 decoder for steam and this MTH smoke unit https://mthtrains.com/aa-2100002 . However, when I set the CV for the smoke unit voltage to the lowest setting the decoder allows (setting 1 on a scale of 1-30), it still overheats the coil. I can't use a larger smoke unit because of the space limitations (I am an S scaler), so I am wondering if there is another solution such as putting a resistor in line with the hot wire that powers the coil.

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With S Scale smoke units I usually turn them off and on with a relay off the decoder instead of the smoke unit off the decoder.  Much less amperage draw on the decoder.  You can then power the smoke unit with either track voltage or reduce it using a linear or switching (cooler) voltage regulator of either fixed or variable nature.  If you make it such that the relay is NC then you'll also need a hardwired switch to isolate the smoke element for Programming Track decoder programming or the smoke element will appear as a short and prevent CV programming.  If you prefer the relay NO, then no need for the hardwired smoke on/off switch.  

Dave

 

GGG posted:

No.  What is the recommendation of the decoder manufacture for smoke unit rating?  WHat voltage does it send to smoke unit?  MTH single smoke element resistors are 8ohm.  You need to change it up to a 16 ohm or maybe even more 22-27ohm depending on what the decoder does.  G

Thanks. I have posed these questions to TCS, and I'll see what they say. Their documentation had none of these answers so I knew I was flying a bit blind when I tried the AA2100002 with it, especially since MTH provides no documentation on this unit. But I thought it would be safe to set the decoder at the lowest voltage setting. If I do need to use a higher resistance heating element to fit in this unit, is that something MTH sells?

What's the lead pair off the 501 you're using for smoke unit control rated at in terms of mA/Amps?  The 501 is a 5A decoder, which is plenty beefy overall, but what matters is the rating of the extension from it that you're using for smoke.  Many decoder leads are rated at 130mA (ergo the use of a relay instead of direct connect to the smoke element).  I couldn't find a spec sheet or user manual for the 501 on TCS web site, unlike Soundtraxx for example which have all their manuals onsite for pdf download.  But maybe I just missed that.  Good luck.  Let us know what TCS has to say.  

Simple solution, just change the value of the smoke resistor.  I've used this in TMCC upgrades, and I remove the 8 ohm resistor and change it for a 22 ohm resistor.  This is the value for TMCC applications, I'd have to know more about your DCC output voltage/current to recommend a value for the resistor.

I buy my resistors on Digikey, you need to match the physical size of the resistor to the one in that unit.  You need around 5-6 watts of power dissipation in the smoke unit to generate decent smoke, that's a number to keep in mind sizing the resistor.

Chuck K posted:
GGG posted:

No.  What is the recommendation of the decoder manufacture for smoke unit rating?  WHat voltage does it send to smoke unit?  MTH single smoke element resistors are 8ohm.  You need to change it up to a 16 ohm or maybe even more 22-27ohm depending on what the decoder does.  G

Thanks. I have posed these questions to TCS, and I'll see what they say. Their documentation had none of these answers so I knew I was flying a bit blind when I tried the AA2100002 with it, especially since MTH provides no documentation on this unit. But I thought it would be safe to set the decoder at the lowest voltage setting. If I do need to use a higher resistance heating element to fit in this unit, is that something MTH sells?

MTH unit are know to the tech because they you basically the same set up for all PS-2 and 3.  Large are 2 16 ohms in parallel for effective 8ohms.  Single small unit use single 8 ohm.  HO has some variations but much the same.  So as John said you go to digi-key.  Just make sure you have the element length/dia about right to fit without grounding to side of case.  G

Very helpful guys. TCS tells me that the lowest CV setting should yield 1-2 V.  I'll hopefully get a chance to test the output voltage from the decoder this week, but they suspect that screw terminal has shorted given my description. They told me how to program another screw terminal to control the smoke coil.

John, is the kind of resistor you are talking about...

https://www.digikey.com/produc...CB5JB18R0-ND/1740799

I found on my TCS501 board that the hole in the board to mount onto whatever stud / mount / bubble gum that you use to mount the board...the hole is very close to the smoke output terminals.  I originally used a #8 pan head phillips screw, but the head stuck out high enough to make it really hard to get those smoke leads into the board.  When I pulled the mounting screw, I actually noticed that one of my smoke lead wires had frayed as I was inserting it, and a little part of the frayed wire actually wedged itself into the mount screw.

I hadn't applied power at that point, but if I had there's a good chance that the lead would have connected to ground.  As I understand the TCS board, they don't actually regulate the voltage on the light / smoke outputs.  They just pulse full battery voltage (minus I think 1.7 volts for some internal diodes and whatever) to achieve an equivalent voltage. And they do so by pulsing the ground.  So if that lead was grounded to frame, regardless of what setting was in the programming, the smoke coils would have had full battery voltage 100% of the time.

I was lucky enough to catch before I turned it on.  That screw is really tough to navigate around.  In the end though, it works great!

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