27 ohm resistor not working?

What sort of smoke volume are you getting when it's working?

mostly the 27 ohm resistor does not get hot enough to make much smoke. I am kind of surprised that you are burning them out. 

Rod

Just curious why you are running two zw's in parallel?

what track voltage are you running?

Rod

Parallel ZW's increase amperage available, not voltage.

For your smoke unit, upgrade it to a pill type heating element and gain the flexibility of using pills or fluids, and not have to worry about keeping it full all the time.

I can't imagine how you're burning out the 27 ohm resistors and not the 8 ohm ones!

An 8 ohm resistor with 18 volts across it would dissipate 40 watts!  Not only would that produce prodigious amounts of smoke, it would itself go up in smoke in short order!

The 27 ohm resistor with 18 volts across it would only dissipate 12 watts, less than a third of the power you're pumping into the 8 ohm one.  It's still way over the rating of 2-3 watts for the typical smoke resistor, but nothing like the lower value resistor.

I have to believe there's something else in play here.

Maybe you are using a resistor that is too small.....rated wattage wise?

Most smoke resistors are 2 or 3 watt, they are undersized so they'll get how enough to make vapor.  However, typically, they want to dissipate around 5-6 watts in the smoke chamber, not 12 or 40!

The less the wattage, the hotter the resistor will get but the lifetime goes down. If he was using a lower wattage resistor it would explain the short life but not the lack of smoke unless it was burning out immediately like a fuse.

Pete

Actually, carbon or comp resistors don't take the heat like wirewound, which is why the WW ones are used.

I've seen an 8 ohm resistor with track power, it was impressive for about 20 seconds!  The smoke regulator shorted in a Legacy locomotive on the club layout, it looked like the engine was on fire!   Before we got the track power turned off, the resistor was toast!  I've used many 20 ohm resistors on the TMCC output, which is half-wave track power, so the effective heating power is around 9 volts.  They smoke good and I've yet to kill one, and some of the folks that got them run smoke all the time.  However, that's a 3 watt resistor with around 4.5 watts into it.  Legacy runs the 8 ohm resistors at 6 volts with the smoke regulator, so that's also 4.5 watts.  The MTH smoke unit has two 16 ohm resistors running from pulsed DC that has an average voltage of 6 volts, same thing.

For running off command track voltage at 18 volts, I'd be looking at a resistor at least 55-60 ohms.  60 ohms at 18 volts is 5.4 watts, plenty to drive the smoke unit.

Nick, what engine are we talking about here? If its a command engine the track voltage might be 18 volts but the resistor should be connected to the R2LC which drives it with ~12 volts. If its a conventional engine, they typically use 27 or 28 ohm resistors but you rarely run those engines at 18 volts (100+MPH??). 8-12v is more typical.

Pete

I was keying on the "track power" comment.  As I said, driving it from the R2LC you can go as low as 20 watts and have good results and no cooked resistors.

If it's running conventional, the 27 ohm is normally the one used, though I've found some of the new stuff has 30 or more.

Are you sure the smoke unit is directly connected to the track voltage?  Does the smoke run all the time track power is on?

That explains it. If you have another wire in the tether that would work. Alternately you could find a higher value resistor if you wanted to run off track power. Buying one or two could get expensive with shipping though either from Lionel or a third party. The tether option would be the easiest to implement.

Pete

It's cheap to get the resistors from Digikey, and shipping is only a couple of bucks. 

Here's a suitable 56 ohm resistor.  I take the powdered ceramic coating off them with a Dremel wire wheel, but it'll work without doing that as well.

43 cents in quantity one: http://www.digikey.com/product...6R/56AECT-ND/2059166

I can't, for the life of me, understand how you got an 8 ohm resistor to work for more than 15 seconds!

What TMCC package was used to convert it?  We can help you connect it to the proper place.

If you want to keep it the way it is, use the 27 ohm resistor and just put a diode in series with the smoke unit power, problem solved.

I was thinking if another wire were available in the tether that would be the best choice but if not and resistors can be had for a few bucks then go that route. I would order a few different values from say 40 -60 ohms in case you are not satisfied with one or the other. Adding an external wire to the tether would be a pain to connect and disconnect all the time and further ruin the appearance.

Pete

If you're connecting it to the smoke output of the TMCC package, you don't need a diode.  That was only if you were connecting it to the track voltage directly.  In effect, that would give you exactly what the TMCC connection gives you, half wave rectified track power.

Edit: correct typo

Make that a diode.

Hi John,

I am interested in trying out the 20 ohm resistor on a TMCC smoke unit.  Is there any particular one you prefer using?  Such as a part number from Digikey, Jameco, etc.

This is one that works well for me: NKN200JT-73-20R

Here's another choice that also works fine, but it's a bit more expensive: UB3C-20RF1

For either of these, I use the Dremel wire wheel to remove the powdered ceramic coating, that allows the smoke unit to start functioning faster when you apply the power. 

There are a host of various values available on Digikey, and they're all pretty inexpensive.

John,

Thanks.  I'll give them a try.