Swapping resistors in old TMCC fan driven smoke units.

I’d stay with the 22

The coated resistors do not work well unless coating removed.  I recently upgraded a Weaver mechanical smoke unit with TMCC.  Know what resistor it had in it?  16 ohms.  The triac on the R2LC has a high current rating and 16 ohms divided by a full 18VAC (which the resistor will not see) is less then 1 amp.  What the risk will be is the 16 ohm element does not last as long.  G

https://media.digikey.com/pdf/...2N6071A_B_Series.pdf

GRJ has proven track record pertaining to the 20 ohm resister. Take his warning or you’ll be buying a new smoke unit board.

romiller49 posted:

GRJ has proven track record pertaining to the 20 ohm resister. Take his warning or you’ll be buying a new smoke unit board.

It's worth the risk!!! 

Let me explain before everyone freaks out!!! I typically run it a few minutes with the smoke on and then shut it off. It's not like it's on for hours on end. 

I did some bench tests with 16 ohm resistors, and at 18 VAC on the track, the triac achieved a 90-95C temperature, too hot for me to be comfortable with it in an enclosed space.  With the 20 ohm resistor, I was back to 70-75C, a temperature that didn't concern me nearly as much.  The operating range for the triac is -40C to +110C.  I've also replaced several triacs that I used 16 ohm resistors with before I did a little more research and decided that was a bit too "stiff" for the smoke triac.

Remember, while the triac is a 4 amp rated triac, that's with a proper heatsink!  The junction to ambient thermal resistance is 75°C/W, but the junction to case thermal resistance is 3.5°C/W.  So, with a good heatsink, the triac can indeed handle a lot of current.

I bought a handfull of 20 ohm resistors from Digi-Key :

NKN200JT-73-20R, Description; RES 20 OHM 2W 5% AXIAL

Checking them with the mutimeter, they are all at about 22.5 ohms. Is this typical??

Jeff T posted:

I bought a handfull of 20 ohm resistors from Digi-Key :

NKN200JT-73-20R, Description; RES 20 OHM 2W 5% AXIAL

Checking them with the mutimeter, they are all at about 22.5 ohms. Is this typical??

 

5% is one ohm. I would say that your meter might be off another 5% or more.

cjack posted:

Jeff T posted:

I bought a handfull of 20 ohm resistors from Digi-Key :

NKN200JT-73-20R, Description; RES 20 OHM 2W 5% AXIAL

Checking them with the mutimeter, they are all at about 22.5 ohms. Is this typical??

 

5% is one ohm. I would say that your meter might be off another 5% or more.

Everything I have ever checked has been spot on, I think the batch I have is off.

Well then I would say it's not typical in my experience.

I'd suspect the meter.  I keep a few .1% resistors around to check calibration, you'd be surprised how far low ohm readings can be.  At 20 ohms, even test lead resistance or contact resistance makes a big difference.

Lionel uses 3 watt resistors and IMHO they dissipate too much of the heat.

I use a 1 watt resistors for replacement in locos that are weak smokers.
I use a Mouser 594-AC01W30R00J  "Vishay" series ceramic wire wound resistor that I remove the ceramic coating.

The are available in several resistance values to suit various smoke units.

You can actually can go to a slightly higher resistance which is easier on the regulators.

Another tip is to use rock wool for the replacement packing. It is available in packages sold as seed starting medium. It does not burn, is cheap and works extremely well.

Carl

I tried rock wool, but it's a real PITA to deal with, it will give you little needles all over your fingers trying to handle it!

I use the 2W 20 ohm resistors.  As far as all the resistors measuring 22.5 ohms, the fact that they're consistent tells me that they're either mis-marked (pretty unlikely), or your meter is off.

gunrunnerjohn posted:

I did some bench tests with 16 ohm resistors, and at 18 VAC on the track, the triac achieved a 90-95C temperature, too hot for me to be comfortable with it in an enclosed space.  With the 20 ohm resistor, I was back to 70-75C, a temperature that didn't concern me nearly as much.  The operating range for the triac is -40C to +110C.  I've also replaced several triacs that I used 16 ohm resistors with before I did a little more research and decided that was a bit too "stiff" for the smoke triac.

Remember, while the triac is a 4 amp rated triac, that's with a proper heatsink!  The junction to ambient thermal resistance is 75°C/W, but the junction to case thermal resistance is 3.5°C/W.  So, with a good heatsink, the triac can indeed handle a lot of current.

Was that command mode or conventional?
in command mode you have half sinewave so effective voltage at 18VAXC track is about 12 or less, less per some of your own post way back when.  SO that is really going to be reasonable current around .6a and power.

In conventional mode you really are not going to get voltage up that high.  But to each his own.  But a weaver unit has a 16 ohm resistor.  G

It was command mode, gets too how for me, regardless of what Weaver uses.

Send it to John to get it done.  Your locomotive came with a 27 ohm resistor.  Why not put in a new one with the rope (Reaganized) whicking.   I have seen many people who like to read posts try things and get themselves in over their head.  Remember, TMCC is not going to smoke like Legacy.  It is what it is.

Unless you have the equipment and know how that John has, do it stock with new parts.  I tell every self thought repair person not to mess with crazy items for wicking.  The standard today is the 8 inch wicking (691SMKP008)  that has been shreaded (Reganized) with a new resistor.  Stay clear from other items and by no means use pink fiberglass insulation.   I am talking for Lionel trains not MTH.

Marty Fitzhenry posted:

Send it to John to get it done.  Your locomotive came with a 27 ohm resistor.  Why not put in a new one with the rope (Reaganized) whicking.   I have seen many people who like to read posts try things and get themselves in over their head.  Remember, TMCC is not going to smoke like Legacy.  It is what it is.

Unless you have the equipment and know how that John has, do it stock with new parts.  I tell every self thought repair person not to mess with crazy items for wicking.  The standard today is the 8 inch wicking (691SMKP008)  that has been shreaded (Reganized) with a new resistor.  Stay clear from other items and by no means use pink fiberglass insulation.   I am talking for Lionel trains not MTH.

Marty, changing resistors and wicking is something I do with confidence these days. Understanding how low I can go with the resistor is where I get in trouble. While I do want it to smoke, I don't want to burn up the electronics!!

Already have the wicking and using that scientific method Mike Reagan showed in his old Lionel video! 

If your loc had the original 27 ohm ceramic resistor, it was known to be a bad smoker. The new 27 ohm resistors from Lionel work much better. I have replace all my resistors with the new 27 ohm ones. My locs all smoke very well.

Joe Fermani posted:

If your loc had the original 27 ohm ceramic resistor, it was known to be a bad smoker. The new 27 ohm resistors from Lionel work much better. I have replace all my resistors with the new 27 ohm ones. My locs all smoke very well.

Thanks Joe. The new 27 ohm looks much like the MTH resistor. Now to find a source other than Lionel. That $10 shipping is a killer on small parts.

I have thought that in the past about the comparison of parts cost to shipping cost. But now I try to look at it as supporting the fantastic (usually) Lionel parts system.

cjack posted:

I have thought that in the past about the comparison of parts cost to shipping cost. But now I try to look at it as supporting the fantastic (usually) Lionel parts system.

Certainly your option. 

Ten bucks a problem,  wow.

Marty Fitzhenry posted:

Ten bucks a problem,  wow.

No it's not. But when there are sources like Mouser and Digi-Key that charge less for the resistor and shipping...

I was wondering if Mouser or Digikey (both of which I buy from frequently) have the wirewound, exposed wire, resistors. They make the best smoke, better than the ones molded with ceramic coating.

They are not common for regular circuit board use. One thing, I think the square power resistors have just a shell around them and might be easier to remove than grinding off a ceramic coating. Maybe some of the bigger smooth round ones as well.

If you find some bare wirewound on Mouser or Digikey, let us know. Thanks.

I have looked for exposed wire resistors from all of the main distributors with no luck. Using a wire wheel works on the ones with a thin ceramic coating. I have a bench mounted wire wheel turning relatively slowly. The rectangular resistors are very easy to clean off the ceramic but I have yet to find any rated under 5 watts.

Back to Jeff's question, if your fan unit has a 27 ohm resistor its likely connected to the R2LC, not the track and not an AC regulator. In that case just use a 20 or 22 ohm resistor as John recommends. I use 22 but then I am not that much into smoke.

Pete

I have searched, a little, to find the uncoated resistors as well with no luck. As GRJ advises, carefully with a soft wire brush on a Dremel works for me to remove the coating. I put 20's in the units in place of the 27's and the smoke volume went up. Nothing like the old unit I had with the MTH 16 ohm resistor, but again I'll defer to GRJ and stay safe.  

You can use the 5W wire-wound square resistors, you simply crush them in a vice and out comes a nice wire-wound resistor.  The ceramic coated ones you use the Dremel as Jeff mentions.

I use these coated resistors that are rated at 3 watts and have 22 and 25 ohm ones. When they do heat up after about a minutes time, they smoke quite well. I got these many years ago from a friend who was the repair guy at Millburn Trains.

Everyone can use what they want.   Enjoy.