MTH Smoking Tank Car smoke unit questions and.......how to install bridge rectifiers to control voltage and speed in Williams engines

You won't want to put more than about 6-7 volts or so on that 8 ohm smoke unit.  I'd stick with the bridge rectifier, and if the DC-DC converter doesn't have a very large capacitor on the input side, you'll need to add one.  The biggest I've seen is around a 220uf, that won't cut it for supplying close to an amp from the DC-DC supply, add a 1000uf 35V cap as a "helper".  Remember, the output voltage has to be totally isolated from frame ground, with a bridge rectifier, you do NOT have a common ground.

If the smoking tank car smoke units are from the first issue of the MTH smoking tank cars, I would not use them. MTH recalled the first issue of the cars because the smoke units would overheat and catch fire. They have recently reissued the smoking tank cars with updated smoke units. 

Vic,

How old are the "first issue" units?  Were they recalled because the smoke unit burned or.....the board itself? If it was the board, I would think the buck converter is far more robust.

John,

I'll check the cap on the buck converter. A couple of questions......if the unit is not "totally isolated" how would you know? Short? Fire?     

Actually, the "first issue" you speak of was only a couple years ago.  MTH has made smoking tank cars well before that problem release, I've had a couple for years.

John,

I've got a buck with a 6 amp diode connected to a Lionel 8057 in a factory building and a dummy engine. Been there for a number of years. Should I remove the diode and replace it with a bridge?

Roger

Don't fix stuff that ain't broke.

If it's doing the job for that long, I'd just leave it alone.  If it's the 8 ohm MTH smoke unit on 18V AC with a diode, I'm surprised it's lasted that long as that would be dissipating north of 10 watts, way too much for a smoke unit as a rule.  It should also smoke a LOT with that kind of power!.

John,

No.....I've never used those tank car units for anything other than the tank cars. The two I'm referring to are 8057 Lionels

Roger

I bought the car about 3 or 4 years ago and it was recalled shortly after I bought it. I just bought a new one from their latest issue. 

ROGER1 posted:

John,

No.....I've never used those tank car units for anything other than the tank cars. The two I'm referring to are 8057 Lionels

Roger

The Lionel units work fine with a diode, they come with a 27 ohm resistor stock, and in a TMCC locomotive they're powered by half-wave track power, same as you are doing with the diode.

ROGER1 posted:

...But in my parts box I've got two Smoking Tank Car units and one circuit board. They are much smaller and still produce decent smoke and while I considered them for this application, I think I might use them for a smaller engine. 

Here's what I would like to know about them. I tested the board this afternoon to see what the output is on it. I clipped it to track voltage and the two + outputs on it both showed 5.67V DC. I'm not thrilled about that little board. I've had a couple burn out in the tank car and this was a spare. If I use these smoke units I'd like to use something beefier as a board. I've got a bunch of DC-DC buck converters I'd rather use for this (I've had real good luck with them). I'm thinking that I would put a 3amp diode in front of it and then set the output to around 5.7V and (as with the original little board) control the fan and the smoke element with that voltage. The element in the smoke unit tests out at 8 ohms. I'm guessing that's why the voltage to it is so low. Two questions......can I get away with the diode rather than a bridge rectifier?  And what would be the max safe voltage I could send to the unit?  5.7 or will it accept more?  .

Have your questions been answered? 

In your original post you said the board puts out 5.67V DC on both outputs.  Is the board as shown above from the MTH smoking tank car instructions?  And by both outputs you mean the 2-wires to the fan motor and the separate 2-wires to the smoke heater element are both 5.67V DC?  I don't have one of these boards but since both outputs measured identical voltages are the fan and heater voltages coming from the same regulator circuit?  

So now you're proposing to replace the MTH board with a DC-to-DC buck regulator.  To be clear, which style of "buck" regulator do you have?  Does it say LM317 or LM2596?

Hi Stan,

I'll get back to you on the buck.  Have to dig one out (if I had to guess, I'm thinking 2596).  As for the wires......there are two reds coming out of + on the board and 2 blacks on the other side. I metered one red and one black and the other red and the other black. Both readings were the same. Both of those units have been out of sight, out of mind in my parts bins and since I've been doing a smoke unit mod, I dug them out and thought maybe I could use them for future projects. But not if they'll burst into flames. 

Roger

Yep......2596 with a 220 cap on it.     As indicated above, I've used those on two occasions with a 6amp diode in front of it connected to 8057 units. I thought maybe I could do the same with these little MTH units and dial down the voltage.

Roger

As described in this thread (with dramatic video), the flames are from the heater unit itself - as opposed to from the circuit board.  Here's the recall notice.  I don't remember anyone identifying the specific component(s) on the circuit board that caused the excessive heating - but the point is you're replacing the circuit board anyway with your buck converter.  As I see it, the take away is do not to set the output voltage too high.

Note that as GRJ recommends, the 220uF should be on the INPUT or IN+ of the buck module.  Some of the LM2596 modules have only a 100uF on the IN+ side.  Most modules have 220uF on the OUTPUT or OUT+ side but that's less relevant for the matter at hand.

As GRJ says, no point fixing something that ain't broken, but if starting from scratch I'd go with a bridge rectifier - seeing as they are only 10 cents.

A bridge may actually be easier to install as I'm not sure the fat wire lead of a 6A diode fits into the IN+ hole of the buck module?  Yes, kind of a trivial point.  Another is if a single-diode (vs. a bridge) means you need to add an additional capacitor, I'd choose a 10 cent bridge vs. a capacitor.  In my experience these electrolytic capacitors have a higher failure rate than diodes/bridge-rectifiers in an apples-apples situation.  The bridge rectifier also draws power equally from both sides of the AC transformer output which is arguably a more desirable operating mode for a transformer.

John is right on the tank cars with the problems. 

It was specifically the NASA and Air Products versions that had the issue and were recalled and recently re-made with new boards due to the recall. (The replacement NASA car and replacement Air Products car were in the 2016 RTR catalog)

The ones with the faulty boards were by no means the 1st issue smoking tank cars, they just had a production flaw that left the possibility of what is shown in the video on the other thread.  (Even the recall one was the second NASA smoking tank car, the first came out in 2010).

I'm not 100% sure it was the first smoking tank car ever (I think it was), but there was a TCA convention car MTH made - the  "Hot Salsa" smoking Tank Car (unfortunately no pic in the link) that was the first one I had.

-Dave

My thread is taking a VERY interesting and disturbing turn.  I have 3 smoking tank cars......Isaly, NASA and an apple car. I don't recall ever getting a recall notification. I'm going to contact MTH and find out if my cars should have been gigged by the recall. 

Roger

ROGER1 posted:

My thread is taking a VERY interesting and disturbing turn.  I have 3 smoking tank cars......Isaly, NASA and an apple car. I don't recall ever getting a recall notification. I'm going to contact MTH and find out if my cars should have been gigged by the recall. 

Roger

The ONLY 2 cars recalled were the NASA and Air Products versions I linked to above.

Check those vs. your catalog numbers and you will know.  The MTH page for each car clearly states the recall cars should be returned to your dealer.

{edit: I also found the original thread posted here on OGR.  See Link.}

As to being automatically notified by MTH, I don't know how that went.  I read about the problem here, but I have no idea if MTH sent notices out to people who register their items by sending in warranty cards or registering on-line since I generally do neither.

-Dave

John,

Just finished this project.....or so I thought. Put the Lionel smoke unit in, put anERR railsounds board in,a full size Fat Boy,LED headlight, lead ballast, and the reed switch worked great.  But there's a problem.  This Williams engine pulls a ton at 10V.  Not enough volts for the smoke unit. Normally I'd wire in series but not with a single motor. What are my options?   Diodes?  Last time I fiddled with that it got too hot for my comfort  Ideas?

Roger

Well, I'm far from the ideal guy to fix conventional running issues, I'm a 99.9% command kind of guy.  However, I'd pick up several 6A bridge rectifiers and wire them as diode pairs that will drop the voltage to the motor a few volts.  If two don't do it, add another one.  A 6A bridge rectifier won't get very hot running a motor.

eBay: 282352936494, $1.40 for five of them shipped.

Here's a pair of bridges wired to drop AC voltage.  Just add more bridges to drop more voltage.

John,

A couple of questions about the bridges. How many volts will 2 bridges drop the voltage? 3?    Second.....in your wiring diagram, each positive seems to be wired to its own negative.  Shouldn't they be wired to the motor?    And thanks for your help. 

Roger

Roger, trust me on the wiring, it's correct.   The +/- really does connect together.  Look at the diode configuration, the way they're connected is really two pairs of back-to-back diodes for each bridge, that will pass AC and drop about 1.5 volts.

Each bridge drops the voltage about 1.5 volts, give or take a couple of tenths.

I totally trust you, John, but my electronics background is not the best. What I was confused about was that a bridge generally has AC in and then DC out. In this diagram, it seems as though there is AC in on one side and AC out on the other side. So the voltage (AC) is being dropped, but remains AC on the output. Is that correct?     If so, I'm thinking that this would have to be put in place in front of the reverse unit and not the motor because the motor gets DC.   If I'm wrong, feel free to blast me. LOL

Roger

I have 2 bridges downstairs. Going to alligator clip them together and see how it shakes out.

Ok......I totally understand now. Went down and clipped the two bridges together and sure enough......AC in, AC out. That's what I was confused about as I've always used these things (diodes and bridges) to convert AC to DC. I used a bulb as a "load" and it dimmed considerably after one bridge was connected and then 2. These were 4 amp bridges, so I will order 6 amp ones and try it out. I'm thinking that I should connect them in where the tether brings the AC from the rollers to the reverse board. I had tapped in there to power the ERR board. 

Will the ERR board be ok running on the reduced voltage as well? If not, I could simply connect these bridges downstream from where the ERR is hooked in.

Am I correct in what I wrote?

The 4 amp bridges are probably plenty, I just was going for a robust solution since the price was so insignificant.

Are you running conventional or command?  For conventional, which is what I thought we were dealing with, put the bridges in one of the motor leads.  We want to drop the power to the motor and let everything else run on full track power.

John,

In all I've read on here, I've never seen this option. As I mentioned, I have a number of engines that over the years I've series wired them.  And I have tried the diode pair method (once.....got too hot). This seems like the best solution. Smaller than the diode string with greater voltage reduction and it doesn't come with the disadvantage (of series) of the effect of wheel slip on the motors. Really looking forward to trying this.  Any downsides to it?

As for the connection.....I'd rather put it in the tender if I can. I localized the track voltage IN from the rollers in the tether. The tether has 4 wires in it. Are the other two wires the voltage OUT to the motor (from the reverse board)?

I will go with 6amps as I am due for a DigiKey order anyway.

Roger

There's no real downside to using diodes to drop the voltage, it's done all the time.  Using one bridge rectifier is exactly the same electrically as using four diodes, just a bunch of the wiring is already done for you. As far as the diodes getting hot, my guess is you used smaller diodes.  If you're using even 4 amp diodes in series with a motor or dual motors in a single engine, it's pretty hard to believe they'd overheat.  That would imply the motor is drawing way more current than is usual for a single engine!.

I'm amazed you haven't read about using bridge rectifiers to do this, it's also been discussed here multiple times.  Usually, you want them directly in the motor leads as that's the part you want the reduced voltage going to.  That runs all the electronics and smoke on the higher voltage, usually the desired effect.  Remember, the current to the motor flows both ways, depending on which direction you are going, hence the need for the "A/C" solution.

As far as the source for the bridges, I'm not sure why you reject the eBay: 282352936494 option for $1.40, it's a US seller so you'll get them pretty quickly and they're dirt cheap!  The cheapest similar one on Digikey is GBU6G-BPMS-ND at 88 cents each.  However, it's your money...

I don't know why I hadn't seen this discussion. After trying the diode chain, I got cold feet with it. I used 6 amp diodes on it and it got hot. People on the thread at the time were a bit incredulous. But I couldn't figure out what was wrong with it, so I took it out. 

I placed the order with Digi-Key because that item number came up as China origin (not US). 

As for the connection. In the engine, I had removed the 6V regulator which was connected directly to the rollers. It controlled the Seuthe and headlight bulb. I now have the wires from that roller going to the Lionel smoke and my LED headlight (for full track power), so I assumed that the only power going back in to the engine was for the motor. So........I tapped in to the wires (in the wire nuts) in the tender bringing  AC to the reverse unit (to power the ERR board). So.......wouldn't the ERR receive full track power and the motor get reduced voltage if I connected the diodes to the reverse board, power to the motor? If not, I'll tap into the motor leads in the engine. I wanted to avoid that as I had added ballast to the engine (under the drive shaft and also in the space between the gear box and smoke unit. I think I'd have to take one of those out to fit the rectifiers in there. I will if there's no way to do it properly in the tender.

And one other thing.......I'm assuming that the motor is running off DC and it gets the DC from the reverse board rectification. If I tap into the motor leads in the engine and connect the rectifiers there, wouldn't that mean the motor was being fed AC?

Roger, rectifiers don't change DC to AC, wouldn't it be grand if it were that simple!

The diodes simply provide a voltage drop wherever they are in the circuit.  The back to back diodes allow you to run the motor in either direction as a single diode would block all current in one direction.  For DC, only one of the diodes in each pair will be conducting, dependent on the polarity of the current flow.

You're going to have to exhibit a little trust that I know what I'm talking about here.

John,

I apologize if it appears I'm not trusting you (which I totally do). My goal is always to try and understand the underlying principles of what I put into my engines. It would be easy for me to just pop stuff in there and be good to go. After a lifetime as a  former high school science teacher it was always important to me to understand the principles I was teaching in order to be as effective as possible. So, I thank you for your patience as I work these things out in my head. It's much easier that way when I'm  helping friends out with projects and I can explain to them how it actually works.    My mistake here was thinking that diodes always change AC to DC. But I understand that wiring diagram now in terms of the output being AC. 

Earlier you mentioned you are using DC-to-DC "buck" regulator module to control voltage to the smoke unit.  Now it appears you are trying to drop voltage to a DC motor so that the smoke unit gets more voltage??

If this is the situation, an option is to replace the "buck" regulator module which only lowers the voltage with a so-called "buck-boost" regulator module which has the ability to both lower or raise the incoming voltage to the desired smoke control voltage. 

Using diodes or bridge rectifiers to lower the DC motor voltage will work of course...but if dropping several volts while pulling several Amps it can be somewhat wasteful in terms of power consumption.

Stan,

Thanks for responding. At the beginning of this project, I assembled together the smoke units I had on hand as well as picking up a Lionel 8057 and an MTH PS1 unit. The ones I had on hand were the tank car units. I planned to use the one that fit the best and made the most smoke. The PS1 unit produced crazy smoke but was way too large to fit. I ended up using the 8057, but has asked some questions about the tank car units in anticipation of future projects that required a smaller unit.    That being said, I installed the 8057 (with a set of interlocking brass tubes that would reach the stack) and fashioned a "smoke gasket" at the top out of a felt chair leg pad (see enclosed photo). 

I removed the 6V regulator at the front of the engine and wired the smoke unit and my headlight LED straight to roller AC.  The buck converter would have been used for the tank car units had I used one. 

The problem I found after I finally fired this thing up last night was typical Williams. It runs on such low voltage that the smoke unit barely worked. John has been helping me out here with his bridge rectifier pair system. I've used series wiring on other engines (dual motor) and tried diode pairs. This method seems GREAT.  I just wired up some rectifiers I had on hand (I ordered larger ones to come next week) and tested it in my setup. Very pleased. It's knocking down the voltage to the motor and is not affecting the voltage to smoke, sounds or LED. Those are all running off straight track power. 

This stuff is fascinating, but I was having a bit of trouble trying to figure out how it actually worked. I had some incorrect preconceived notionswhich were creating some confusion.

Roger

Stan, if the motor is drawing amps, he needs to find out what's wrong with the locomotive.

I think I understand now - you are directly powering the smoke unit with AC track voltage - no regulator to the smoke unit.

Anyway, it appears you have a working solution once you get your parts... but in the interest of power management (saving energy), two options for others pondering a similar situation are:

1) place the diode/bridge dropping parts between the reversing unit and the DC motor. I realize you have no space in the engine chassis with the ballast you've added so this does not apply to you.  The idea being that this only drops the voltage to the DC motor while making full track voltage available to the other electronics (lights, sounds, etc.).  In some situations this can save several Watts of power.

2) change the heater resistors in the smoke unit.  I'm not familiar with the resistor values (Ohms) of your smoke unit but installing lower value resistors would producing more smoke for the same AC track voltage.  The idea is the power wasted by the diodes dropping motor voltage will be in the several Watts range.  Why not put those Watts to use in the smoke unit to heat up the resistors that generate heat/smoke rather than to heat up diodes/bridges which just warms up the engine chassis?!  

Stan, I did suggest putting the diodes in the motor leads, that's the logical place for them.

There's a happy medium with the smoke resistor.  If you put lower value resistors in, you risk too much heat in the smoke unit when you have higher track voltages, say running with a load or faster.  The buck/boost regulator would be a worthwhile solution as it would keep a constant voltage on the smoke unit.  Truthfully, you could get away with a buck regulator and a 6 ohm resistor, by the time you got the voltage low enough not to supply the 5 volts or so, you'd be stopped anyway.

Stan,

That boost/buck converter you posted has me intrigued. I may order one to play around with. I'm assuming this is a DC-DC converter and will require a diode or bridge out in front of it. Correct?

Second question: I ordered extra bridges for some other Williams engines I've got series wired. They are all dual motored diesels. So.......I'm thinking I would require a separate bridge pair for each motor. Correct? 

Roger

Yes, it requires a diode bridge, and you'll also have to add bulk capacitance as well, especially for low input voltages.  The more current the power supply draws, the more bulk capacitance you need for the rectified AC filtering.

You only require one set of bridge rectifiers for all the motors in a locomotive, no need to have two sets.

Thanks, John.     I'll be back to you after I get one of these and find a use for it. To find out how big a capacitor I'd need to wire in. 

2 questions on the bridge pairs........The reverse board on the dual motored diesels has separate outputs for the leads on the two motors. What would I connect the bridge pair to?       Second......if I were to decide to add a third bridge to the setup (I'll decide that after they arrive), how much more heat would I be dealing with?  As this tender is die cast, I'm not really concerned about it, but in the case of a diesel shell.....maybe. 

Roger

Here is one of the old threads I referenced........https://ogrforum.com/topic/diode-strings-vs-series-wiring........no mention of the rectifier pairs. I'm really impressed with this idea so far. We'll see how it shakes out when I do my final connect.

As for my previous question about where to connect the rectifiers in a dual motor engine........I think it's done the same as the diode chains.....cutting the 2 yellow motor wires and connecting 2 of them  to one end and the other two connected to the far end.