Trains America Smoke Units

[RR Redneck]

I have been wanting to try these babies out, but havn't had the guts to get out my tools. Thanks for the info y'all.

[lionelsoni]

Well, I worked it out:  For small voltage reductions, the bridge rectifier dissipates almost twice the power of the resistor.  At about 2/3 the RMS voltage, they are equal.  At about 40 percent voltage, the rectifier dissipates half the power of the resistor and continues to get better down to zero voltage.

[laz 57]

Thanks GIZ,

   JELECTRIC has a few of the bridge rectifiers that he is going to send me.  Thanks again for this info.  I'll let you know how it turns out.

laz57

[ChiefEagles]

LAZ, I ended up using only 3.  Probably 2 for a steam loco.  As for heat, I can touch them and not get burned.  In fact I used them [3] wrapped in electrical tape in an engine that had problems with the smoke protion of the TMCC board.  They are packed tightly in with two boards inside a shell.  No problem for two years now.    

[luther_stanton]

I think that the total heat generated would be the same as you are dropping the same voltage at the same current in either case.  Since the power disspated (in the form of heat) is the product of the current and the voltage, the net result is the same.  It may "seem" to be less with the rectifiers as there is significantly more surface area.

Although I have never seen a rectifier used to step down voltage in this manner, it is an interesting approach.  I have typically seen / used them to rectify AC into DC (most common), filter,  prevent conduction in a specific direction or provide protection with inductive loads.

In a situation where you have a steady current source, as Bob mentioned, I think the resistor is a better approach.  While there are ways of stabilizing a voltage divider circuit with varied loads, in that scenario I might try the rectifier / diode approach.  Nice to have in the "bag of tricks".

I also liked the example of the 1 ohm resistor.  I thought about it afterwards - and again as Bob stated, if you only have a volt meter, it gets the job done. Neat.

- Luther

[lionelsoni]

The bridge rectifier also dissipates heat.  It has a voltage across it and a current through it; so its instantaneous power dissipation is the product of the two.  Whether it is more or less power than with a resistor is a complicated problem to calculate and depends or the voltages, currents, and the nature of the load.  I would guess that the resistor and bridge rectifier are comparable in terms of power dissipation.

[laz 57]

Using the resistor will also build up heat some where else, no?  So will it not be better to go the way of the bridge rectifier?

laz57

[lionelsoni]

The reason I suggested the series resistor method for calculating the current is that AC ammeters are not that common.  The 1-ohm value was just an example.  If the current is as low as Luther's 200-milliampere example, you would find it difficult to measure the tiny voltage that would result and would have to try again with a larger resistance.  Again, the resistance value would not matter as long as you know what it is so that you could calculate the current by dividing voltage by resistance.

A resistor might well be smaller than the bridge rectifiers.  But Frank's rectifiers are much heftier than the 1.4-ampere ones that I suggested for a smoke generator, which are about the size of an aspirin tablet.

[luther_stanton]

Aside from trial and error, a way to calculate the resistance needed is to put some known resistance, say 1 ohm, in series with the smoke unit and then power it from an adjustable (sine-wave, not CW80) transformer, set for the smoke performance that you want.  Measure the voltage across this test resistor, divide that by the resistance, and you have the current.  Then measure the voltage across the smoke unit and subtract that from the track voltage to get the voltage drop needed.  Divide the voltage drop by the current that you already calculated, and that is the resistance that you need to use.

If you have an ammeter you will not need the 1 ohm resistor.  You can simply hook the smoke unit direct to the power source and adjust as described.  Measure the voltage across the load  and then put the ammeter in series to determine the load current. 

Then as Bob recommends, the voltage drop needed by the resistor (resistor voltage) will be track voltage - smoke unit voltage.  The resistance is computed as resistor voltage / load current (round up) and the power rating for the resistor will be resistor voltage x load current.

Example:

The smoke unit runs at 14V and track voltage is 18V.  The smoke unit pulls 200mA while running (I made these number up!).  The resistor voltage drop needed will be 4 volts at 200mA, which is 20 ohms, the power rating needs to be 0.8 watts.  A 1W resistor would work, but a higher rating will allow better heat dissipation.

Using a single resistor will take up a lot less space than the 4 or so bridge rectifiers you would have needed - and will be a bit less costs as well.

[laz 57]

Thanks BOB and CHIEF.

I'll do calculations tonite and let YUZ GIZ know what resistor I need.  Seems to be the easier way to go with this one being I just want to drop it 4 volts.

Thanks again.

laz57

[lionelsoni]

Yes, you can use a resistor; and, for a case like this where the load current is constant, a resistor is practical.  The resistance will depend on the current that the load draws at the reduced voltage; so you can't count on 4 volts for 4 ohms unless you know that the current will be 1 ampere.

Aside from trial and error, a way to calculate the resistance needed is to put some known resistance, say 1 ohm, in series with the smoke unit and then power it from an adjustable (sine-wave, not CW80) transformer, set for the smoke performance that you want.  Measure the voltage across this test resistor, divide that by the resistance, and you have the current.  Then measure the voltage across the smoke unit and subtract that from the track voltage to get the voltage drop needed.  Divide the voltage drop by the current that you already calculated, and that is the resistance that you need to use.

To get the power rating for the dropping resistor, multiply the voltage drop by the current.  Then get a resistor with about double that rating, so that it will run cooler.

[ChiefEagles]

Soldered together

In series

Hooked to smoke unit and tested [see the two "hot" wires connected together]

As it ended up, only needed three to reduce the voltage for diesel.  If you want more smoke, take one away, less smoke, add one.  Hope this helps. 

[laz 57]

Thanks BOB,

Can I just get a 4 ohm resistor and wire it in series to reduce the voltage by 4 volts?

laz57

[luther_stanton]

Connect the + and - pins together.  Then use the other two pins to wire the rectifier module in series with the load.  You can use multiple rectifier modules in series to get the voltage as low as you need.  Radio Shack's 276-1152 1.4-ampere 100-volt part for $1.49 is a good choice for a smoke unit.

Bob (lionelsoni),

So this will give you a 1.2V drop (0.6v x 2) per rectifier, correct?  At 17V you are looking at 7% drop.  With the amount of "modified bridge rectifiers"  needed to drop down to say 10 volts, would it not be more economical, in both cost and space to use some 1W resistors and create a simple voltage divider?

- Luther

[lionelsoni]

The bridge rectifier is a way to get 4 diodes in a single package to put in series with the load to reduce the voltage.  It is not actually used as a rectifier in this case.

Connect the + and - pins together.  Then use the other two pins to wire the rectifier module in series with the load.  You can use multiple rectifier modules in series to get the voltage as low as you need.  Radio Shack's 276-1152 1.4-ampere 100-volt part for $1.49 is a good choice for a smoke unit.

If you find that you need finer adjustment, you can use half of a rectifier module by connecting to the (wired together) + and - pins and either or both of the other two pins.

[laz 57]

CHIEF what do I need to build the bridge rectifier?  Do I get it at radio shack?   Thanks for the tip.

laz57

[ChiefEagles]

Hope it does not burn up element too quick.  The GIZ should know.  If it gets too hot, you can build a bridge rectifier and reduce voltage.  That is what I did for a unit I put in a dummy.  Also, it was diesel so you don't want lots of smoke or it looks like you need a rebuild.

[laz 57]

Well I called DA GIZ from TAS yesterday about my turbo smoke unit and they told me that it won't work with the existing board that is in the Mohawk.  But that I could work it off the pickup rollers and to put a switch in it to shut of the smoke when on a siding.  Did the hook up and all works great, LOTS O SMOKE.  Going to get another one in April at YORK.

CHIEF you were  right about running it off the track power.

laz57

[laz 57]

CHIEF,  I only have the three wires.  I don't follow you on the double up part.  Please explain further.

CHIEF this is made to run in command off of 18 v.

Thanks,

laz57

[ChiefEagles]

LAZ, double up the wires.  The wire that is making it run in forward [hot] put the other wire [hot] to it too.  That is how I have powered up the added smoke units that I have done.  Both "hots" need to be powered.  Not sure what power source you are using.  Remember, direct track power in command [18V] is too much for most smoke units.  Will smoke up a storm but might burn out faster.  These units might be designed to take 18V.  If running in conventional, the variable voltage should be OK.  Just weak smoke at lower voltages.   

[laz 57]

I put in a new turbo smoke unit in my Lionel Mohawk last nite that I purchased from TAS.  It wasn't to bad to put in hooked up all  the wires and tested it, wouldn't work in forward, so changed wire leads around and now it won't work in reverse.  Got to call the TAS GIZ today and ask why it will only work in one direction?   There really isn't that much to hooking the smoke unit up, 3 wires, one hot one ground and one that goes to the cherry switch.  Maybe those GIZ will tell me whats going on?

Otherwise the most difficult thing was making a harness to hold the smoke unit in place.  Not a big deal with ZAP a Pak instant glue it was a breeze that stuff works great.  Its super glue with an excellerator that you spray on the glue and hardens instantly.

I'll let you know what the TAS GIZ say?

laz57

[laz 57]

I'll let you know when I start OLE1.  I'm getting the unit hopfully on friday at YORK.

laz57

[ole1]

Hi Laz 57

I've been looking into doing a similar project with a Lionel Hudson.  Hope you can give us and update and maybe some pictures when you complete the job.  In my case I know just from looking at the dimensions of the unit that it would be a tight fit and would probably mean coming up with a new way to get the headlight mounted.  Good luck

Ole

[laz 57]

Took apart the Lionel Mohawk that TAS worked on , last nite.  Interesting how they had epoxied the unit into the top of the shell.  They kinda made a harness out of plastic the epoxied it to the shell to hold it in place. 

   While at YORK on friday I will pick up another unit and do the same.  They really put out the smoke.  Chuga chuga woo woo!

laz57

[laz 57]

Thanks LUTHER,  I am going to take the one apart and check it out.  The GIZ at train America Studios are at YORK and I will also ask them about it.  I don't think it will be that hard to do being it is going into another Lionel Mohawk.  I just don't want to send it out and have about a 8 week wait til it returns.  They did a great job on my other engine with the smoke unit and EOB unit. 

THANKS again.

laz57

[luther_stanton]

Laz,

I installed one in a Williams Berkshire.  I had to get a length of brass pipe to run up to the stack on the loco smokebox and fabricated a small bracket out of sheet metal.  I basically made a compressed U shape.  You need to be careful to make sure everything lines up OK - the pipe and the stack, etc. That was the trickest part - I took off the smoke box door and worked with needle nose pliers.

If I recall correctly, electrically it was pretty simple - they provided instruction for mechanical driven off the wheels and electronic driven by TMCC, etc.

I estimate 3 - 4 hours from start to fininsh?

Take a look at the one you had installed to make sure it will fit in your new application.

- Luther

[laz 57]

CHIEF, is that just regular pink insulation?

laz57

[ChiefEagles]

Wouldn't think so.  Especially with your knowledge.  Took one apart and it had what looked like a blonde wig for a wick.   Added some pink and it smoked better. 

[laz 57]

Did any of YUZ GIZ ever put the Turbo Smoke units in that TAS has.  I sent them my LIONEL MOHAWK and they installed one for me works great.  But I don't want to send another one cause of the turn around time.  Is this a tough thing to install?

Thanks,

laz57