LIONEL 6-84470 - 27ohm smoke resistor in place of 8ohm - BAD IDEA??

Questions:

1) Were the original 8 Ohm resistors wired in series or parallel?

2) What are the wattage ratings on the 8, 16, and 27 Ohm resistors?

That unit has heat sensing thermistors. Its possible the thermistors being to far from the resistors is what caused the overheating. 27 ohm will barely produce any smoke and may in fact generate an error.

Pete

Pete, thank you for that reminder.  I think this recent thread covered this issue really well.

Link: New Lionel smoke units over heating

Bad idea, the smoke circuit is designed around the 8 ohm resistor.  The 27 ohm won't give you much (if any) smoke.

I'm confused about the dual smoke resistor, each of those resistors is powered individually by a different control circuit.  If they're overheating, there's a reason.  Tinkering with the values of the resistors is not the way to solve it.

Make sure the resistors and thermistors are firmly in contact with the wick material, but not totally buried in it.  Also, in the picture of the smoke unit board in the Lionel parts listing, the thermistors are too far from the resistors, they should be between 1/8" to 3/16" from the smoke resistor.

@gunrunnerjohn posted:

Bad idea, the smoke circuit is designed around the 8 ohm resistor.  The 27 ohm won't give you much (if any) smoke.

I'm confused about the dual smoke resistor, each of those resistors is powered individually by a different control circuit.  If they're overheating, there's a reason.  Tinkering with the values of the resistors is not the way to solve it.

Make sure the resistors and thermistors are firmly in contact with the wick material, but not totally buried in it.  Also, in the picture of the smoke unit board in the Lionel parts listing, the thermistors are too far from the resistors, they should be between 1/8" to 3/16" from the smoke resistor.

OK. If John says don’t do it - I ain’t doin’ it.

Thanks guys!

*Under the circumstances - I will have to pull an 8ohm off another good engine of mine to get this customer repair done in a timely manner, then order the part and wait for it to go back into my own piece. Not the plan B I was hoping for but, oh well. Better than no option.

Order the Yageo SQP500JB-8R2 from Digikey.  Clamp it diagonally in a vice on the corners indicated and slowly tighten.  The square ceramic will crack off and you'll have a perfect 8.2 ohm smoke resistor.  You can have these in a couple of days.  Use safety glasses, the pieces sometimes fly quite a ways.

These 8-ohm resistors are getting harder to find.  Glad this thread came up on the search and I plan to try the vise treatment suggested above.

I thought it would be good to give this thread the light of day and also the point of how close the thermistors should be to the resistor.  My guess is that may have played a part in why mine failed. 

@gunrunnerjohn posted:

Bad idea, the smoke circuit is designed around the 8 ohm resistor.  The 27 ohm won't give you much (if any) smoke.

I'm confused about the dual smoke resistor, each of those resistors is powered individually by a different control circuit.  If they're overheating, there's a reason.  Tinkering with the values of the resistors is not the way to solve it.

Make sure the resistors and thermistors are firmly in contact with the wick material, but not totally buried in it.  Also, in the picture of the smoke unit board in the Lionel parts listing, the thermistors are too far from the resistors, they should be between 1/8" to 3/16" from the smoke resistor.

It's how I get all my smoke resistors nowadays.

@gunrunnerjohn posted:

Order the Yageo SQP500JB-8R2 from Digikey.  Clamp it diagonally in a vice on the corners indicated and slowly tighten.  The square ceramic will crack off and you'll have a perfect 8.2 ohm smoke resistor.  You can have these in a couple of days.  Use safety glasses, the pieces sometimes fly quite a ways.

I also found them on Amazon without the up charge. Great minds find simple solutions

@ThatGuy posted:

I also found them on Amazon without the up charge. Great minds find simple solutions

Up charge?  What's that?

I find for this kind of component, I almost always do better on places like Digikey or Mouser.  Also note, I pick that specific brand for a reason, my experience is that some of them I've tried did not have suitable internal resistors to be smoke resistors.

For instance, I found this particular part on Amazon for a reasonable price, but I got the same part (at least the exact same markings) from Aliexpress for true peanuts.  However, it turned out that the internal resistor didn't work out as a smoke resistor, it was too small.

@gunrunnerjohn posted:

Up charge?  What's that?

I find for this kind of component, I almost always do better on places like Digikey or Mouser.  Also note, I pick that specific brand for a reason, my experience is that some of them I've tried did not have suitable internal resistors to be smoke resistors.

For instance, I found this particular part on Amazon for a reasonable price, but I got the same part (at least the exact same markings) from Aliexpress for true peanuts.  However, it turned out that the internal resistor didn't work out as a smoke resistor, it was too small.

When I bought them a few time with some other things there was duty charge? So I just looked elsewhere.

@ThatGuy posted:

When I bought them a few time with some other things there was duty charge? So I just looked elsewhere.

I buy stuff from Digikey all the time.  Big deal, for 25 resistors, the tariff was four cents each!  And I got the exact product I needed and know it'll work in my application.

GRJ....The Legacy conversion I am working on has a PS 1 smoke unit. The RCMC that I am using has a five pin connector with an additional pin for the thermister. I have not yet opened the smoke unit to see if I can add a lead for the thermister. I saw a post from you that mentioned "spoofing " the controller with a resistor. Have you or anyone modified a PS 1 smoke unit for Legacy? If a termister was added the Part number would be helpful. Thanks for the 8 ohm resistor part number. I use the 20 ohm version of that part with TMCC.

Richard

Richard, you can add a 4.7k 1/8w resistor across pins #3 and #5 of the RCMC smoke connection and that will keep the RCMC smoke monitoring software happy.  I don't try to add in the thermistor, that would be a much bigger deal, and pointless IMO.

Thanks John. Added to my build notes on this project.

Richard

@gunrunnerjohn posted:

I buy stuff from Digikey all the time.  Big deal, for 25 resistors, the tariff was four cents each!  And I got the exact product I needed and know it'll work in my application.

Ok, I bought 25 TOS’s and had a 10 charge. It is what it is, I find the same items elsewhere with free shipping and no delays whatever works for you

What's a TOS?