G Scale Model Train Forum banner
1 - 20 of 27 Posts

·
Super Modulator
Joined
·
21,340 Posts
Discussion Starter · #1 ·
I'm starting a new topic to bring some information forward about the Aristo smoke units.

I am talking about the one referred to as the "prime mover" type, that is a rectangular box about 1 x 1 x 2 inches has a fan in the bottom. It's in all the newer locomotives, like the SD45, GP40, dash 9, etc.

The unit has 4 screws on the top, and removing the top cover reveals the back side of a circuit board. Pulling the board out reveals the housing has 2 chambers, one for smoke fluid and one that encloses the fan and electronics.

The smoke chamber has a capacity (advertised of 75 drops), and is dominated by a 5 ohm heating element, which has a thin wire spiral wound on it (probably nichrome), and a piece of fiberglas wicking that is clamped around the element and with the ends sitting down into the bottom of the fluid chamber.

There a a "Wall" that devides the 2 sections and there are 2 small notches in the top to admit pressurized air from the fan. The top of the circuit board over the element has a hole that the smoke is blown through. The full wave bridge rectifier is also on this "half" of the circuit board, 4 discrete diodes.

The circuit "half" of the board has the fan and motor and a number of components. There are no heat sinked devices, and the board obviously regulates the power to the heating element and the fan, though the fan runs at constant speed. It's a pretty good guess that the way it works is that the IC on the board is a small PIC processor functioning as a pulse width modulator to regulate voltage/current.

These units have various problems and many users are plagued with short run times, like 1-5 minutes.

This is the problem I'm investigating. There are also other problems, like the smoke fluid getting all over the circuit board and swelling the rubber plugs in the ends of the electrolytic caps and popping them off the board. Also, when the electronics fail, the unit often turns "turbo", the fan spins at a verh high speed, and it makes a lot of smoke for a very short time. Continued running usually kills the board.

A properly functioning Aristo unit (remember, only this model) will run in excess of 20 minutes on 75 drops. The ones I have that work run about 31 minutes before shutting off. There is still some fluid, and you can usually get 5-8 more minutes just cutting power and re-applying. (Thus the microprocessor guess)

Aristo's first response is "are you using our fluid?" The fluid makes no difference in failing or not, although continued use of some fluids tend to clog the wick.

One user has reported he put a 300 ohm 1/4 watt resistor in parallel with the 5 ohm element and that fixed it. This is highly unlikely, since 300 ohms in parallel with 5 ohms yields 4.92 ohms. Obviously that's very little difference in resistance, and the difference it would make in current drawn. It's also obvious that a 1/4 watt resistor could not be contributing to the heat output in a significant manner, since it would carry 60 times less current than the heating element, and 1/4 watt resistors aren't large enough to make any heat (for any length of time).

One interesting observation was my monitoring of the current of the unit while it was operating to see if I could determine what the system was doing to signal "time to shut down".

The current started (I tested at 14 volts dc) at .4 amps, and quickly settled down to .312 amps until the very end of the run, then it began to drop down to about .291 amps.

This all makes sense, the resistor would draw less current when not making smoke, i.e. running out of fluid. (The action of vaporizing the fluid MUST use more current than when the element is "dry").

What I will do next is try to closely monitor the voltage of the element, so as to calculate the current drawn, and see if I can deduce the "shutdown algorithm".

Possibly this may lead to an understanding of why some of these units never perform properly.

If anyone has the ability to measure the cold resistance of their element (a very good ohmmeter) that additional information would help.

I have a few friends sending me units that shut down prematurely to see if I can gain further understanding.

Why am I going to all of this effort? Because while the Aristo warranty is honored, most units back from repair have the same problem.

I'll try to post some pictures of the guts.

Please, I don't need comparisions of different smoke units, I'm trying to solve a problem, not hear "MTH is better" or "Mine is fine". I do want to hear from people who cannot get 20 minutes or more on their Aristo units.

Regards, Greg
 

·
Super Modulator
Joined
·
21,340 Posts
Discussion Starter · #3 ·
Not normal, or how it was designed. Since nothing else can be changed, I'm hoping that it's the variation in the heating elements.

The one from my mallet is the one that runs 31 minutes. Refilling it will give another 31 minutes. I'll bet yours will restart and run for another 5 right after interrupting power.

Regards, Greg
 

·
Premium Member
Joined
·
1,704 Posts
I've also had this issue - it worked for a short time then quit and the only way to get it to start up again was to recycle the power. What I noticed was that any glitch in the power pickup caused the unit to stop, but apparently the lost power glitch wasn't enough to recycle the power on the unit. So I expanded the power pickup for the smoke unit to my tender, not just the loco, and it got rid of the problem.
 

·
Super Modulator
Joined
·
21,340 Posts
Discussion Starter · #8 ·
Yes, there are a number of reports that glitches under power cause it to stop, and also it's not clear what the minimum voltage is.

When you consider that it is microprocessor-based, these symptoms all make sense.

Regards, Greg
 

·
Premium Member
Joined
·
2,910 Posts
I'm a complete ignorant novice with electricity, so please if this makes no sense just ignore it.

But I wonder if the issue with track power and smoke units could be solved with the right capacitor? Tube amps use electrolytic caps to smooth ripples in DC, and I'm using 1000 uf 35 volt caps, with a bridge rectifier, to eliminate flicker in LED coach light. It works pretty well--the lights don't flicker at all, they stay lit and gradually fade as power is removed. If the problem is "ripple' in the DC couldn't it be smoothed out with filter caps? Or maybe just a single cap placed in the circuit to minimize voltage drops?
 

·
Premium Member
Joined
·
2,910 Posts
Oops!!!

Also I should add that I've had the same issue with the loco on my test bench, sitting unmoving on a piece of track--the smoke generator cuts out and then starts again if power is restarted. Kind of works against the whole capacitor idea suggested above
 

·
Super Modulator
Joined
·
21,340 Posts
Discussion Starter · #11 ·
I'm still characterizing the failure modes, but it seems that long term low voltage will shut it off too, a big electrolytic will only help with short term "brown-outs".

I first want to solve why on perfectly constant DC voltage, with the unit out of the loco sitting on a bench, they still shut off prematurely.

Regards, Greg
 

·
Premium Member
Joined
·
254 Posts
As the fluid level gets lower, the resistor heats up causing it to draw less current. The drop in current triggers the pic processor to shut down.
So, there are two things I found that cause the drop in current.

(1) The resistor is a wire-wound. It uses a resistive wire wrapped around a fiber core. The core is much like a cigarette filter, sort of soft, but not as soft as a cigarette filter. The wire leads are spot welded to two metal disks. During manufacture, the Disks are crimped onto the ends of the resistor much like an old fashioned Coke bottle cap. This crimping, captures the resistive wire between the cap and the fiber core to make the electrical contact. The manufacturers of this type of wire wound resistor always warn the buyer with the following: "Do not use insertion equipment. Bend the leads by griping the lead firmly between the end cap and the bend. Do not apply force to the resistor body when bending the leads." (paraphrased.)

So, if you grip the resistor with one hand, and bend the lead with the other, the force on the cap will damage the fine wires wrapped around the soft core material. I ordered four replacements from Aristocraft and found that the resistor measured as "OPEN" with a meter on two of them, right out of the package. Even if the resistor is not open, the cap, if shifted, does not make good contact with the restive wire. When power is applied the wire will heat up right at the damaged spot on the end of the wire where the cap has "moved" and scraped the wire. It is very important that the resistor be supported by griping one lead ( needle nose pliers) between the cap and the end of the lead. Then, make the bend between the pliers and the end of the lead so that no force is applied to the cap/resistor crimp. The same thing MUST be done when installing the resistor leads into the smoke unit. Griping the two leads and applying any force in any direction may damage the resistor and greatly shorten it's life and change the resistance due to heating at the end cap instead of uniformly along the length of the resistive wire.

You can sometimes spot this condition by looking at the resistor in near total darkness. The resistor may appear to be glowing red at one end of the resistor.

SECOND PROBLEM
(2)This has to do with the smoke hole being plugged by oil. When the smoke starts to exit the smoke unit it meets cooler air and the cooler tube near the top of the smokestack. Some of the smoke condenses on the sides of the smoke stack. The condensed oil then runs down to the bottom of the tube and forms a drip due to surface tension. The drip is circular. It extends around the circumference of the tube. When the drip is big enough, it joins to form a bubble closing off the bottom end of the tube, stopping the air flow. This traps heat and trips the pic logic. On the older locos without the pic, IE the first run Pacific) one could simply blow a sharp puff of air down into the smokestack or tap a finger on the top of the smokestack to break the bubble and the loco would immediately begin smoking again. With the newer locos, (IE the RS3) this still works if you catch it right away and break the oil bubble before the pic shuts down the smoke unit, Otherwise, you need to remove power for at least two seconds to drain the 22,000 uf caps on the pic processor board and reset the pic logic.
The solution to this problem depends on the loco, For the old Pacific, replace the brass tube with a longer one and grind the bottom of the tube so it looks like an old fashioned fountain pen with the small tip extending down into the oil in the reservoir. For locos with the shorter, wider smokestacks and no brass tube, glue a string inside the plastic smokestack and let the string hang down into the bottom of the oil reservoir. This will provide a wick to pull the condensed smoke away from the bottom of the stack and drain it back into the reservoir. BTW, LGB oil seems to work better at solving this problem than Aristo Oil. Thinning the Aristo oil with mineral spirits also reduces the surface tension. NOT A RECOMMENDATION!!!



As far as the algorithm is concerned, the electronic modules all seemed to perform exactly identical when combined with a particular resistor or loco smoke stack. IE changing the PIC board from a working RS3 to a non working RS3 does not fix the RS3. The problem was always associated with the resistor, or stack not the pic processor board.
There may be other problems, but these are the only two I found.
B0B
 

·
Super Modulator
Joined
·
21,340 Posts
Discussion Starter · #13 ·
I should have known to contact you Bob! Doh!.

Yep, I have been leaning towards differences in resistance in the element. I also remember (now) about breaking the contact between the caps and the wire.

I got 5.00 ohms cold on element on the unit I have that works well, have you measured any of yours?

I was not aware the RS3 unit had any intelligence, but I have not opened mine yet, focusing on the so-called "prime mover" SD45 type.

Regards, Greg
 

·
Premium Member
Joined
·
254 Posts
Yes, 5 ohm is the correct value. Even one with damaged wires under the cap will measure 5 ohms. It is only when they heat up and you calculate the resistance from the applied voltage and current that you will be able to measure the break under the end cap and determine that the resistor is damaged..

The RS3 has the same circuit, but the pic is not located on the smoke unit board, it is located on the switch board under the access hatch of the long hood.

I ordered replacement resistors from an electronics house and got ones that had a black coating over the wires. They work just a well, and a whole lot cheaper than buying the entire assembly from Aristo, especially when the Aristo units had a 50% DOA rate. Just be very gentle when installing the resistor. Bend it to fit the screws, and use longer screws with pairs of brass washers to prevent the wires from moving when you tighten the screws. Also, make sure the wick is TIGHT and spread out to cover the resistive element.

For those who run DCC, bypass or disable the smoke board. Calculate a new resistor value to produce 500 to 750 ma (depending on the amount of smoke you want), at your track voltage. The wattage of the resistor should be SMALLER or equal to the calculated wattage for your resistor/voltage combination.

The huge capacitors on the Aristo smoke regulator board can cause some weird ringing problems on DCC.

Typical symptoms caused by the Aristo smoke board are:
LGB sound cards that sometimes chuff even when the loco is not running.
Missing commands to Lenz decoders.
Transponding not working in any zone occupied by a smoke unit equipped Aristo loco.
Routes on turnouts not working properly.
Auto reverser "chattering".
Reading CV's in OPS mode reading wrong values or not reading at all.

I have removed all the Aristo regulator boards and replace them with wire wound resistors controlled by small relays and programed to shut down automatically when the loco is NOT moving.

I'd be remiss if I did not mention to analog DC users that the surging problem many experience with the RS3 at about 7 volts is also caused by the smoke regulator. Remove the regulator, or buy a really big DC power pack with a low impedance then change rail to all brass or NS rail and keep the feeders short and at least 12 ga.
 

·
Registered
Joined
·
5 Posts
Hello

I have 12 locomotives that use AC smoke units, mostly Bachmann 1:20.3 that I have converted. Last night I ran 2 Bachmann 2-6-0's, with the capacitors resoldered and the 1/4w 300 ohm resistor installed. I was getting 15 to 20 minute "smoke" times. The outside loop I ran at a constant voltage the inside I varied the voltage (speed), when the units shut down, they needed fluid. I know the resistor may not make sense but I took a unit into work and gave to the electronic engineers, they recomended the resistor, try it,/DesktopModules/NTForums/themes/mls/emoticons/doze.gif what do you have to loose.

Hope this information is helpful.

Russ

P.S. Ran 1 engine tonight, with the same results.
 

·
Premium Member
Joined
·
254 Posts
Question, when they shut down, does the fan stop or does it just stop smoking?

EDIT:
This question is directed to the smoke units with the 300 ohm resistor in parallel.
 

·
Registered
Joined
·
5 Posts
As far as I can tell they shut all the way down, no smoke or fan, I stop the engine and refill the unit and off we go.

Hope this helps

Russ
 

·
Super Modulator
Joined
·
21,340 Posts
Discussion Starter · #18 ·
OK, more info.

First, on the Aristo forum, there is a well intentioned gentleman trying to talk about the Aristo units. Unfortunately the ideas are completely off base. I don't post there, pe you read here.

1. He hypothesizes that turning power off for a bit allows the unit to cool off, thus enabling restarting. Nope. The unit has a small PIC processor, and when it's program says shut off, you can reset it immediately and it will start right up again, fluid or no fluid.

2. He hypothesizes that increasing the size of the wick will help. Nope, completely off base again. Of all the units tested, the wicks varied, mostly from use. Several units with new wicks ran 20-30 minutes. The current record holder has LESS wick (part of it frayed off). It ran for over an hour.

The problems are associated with the "perceived" temperature of the heating element. I say perceived because the only method of measurement is voltage of the heating element.

From all the recent testing, there are similarities that reveal that it's all about when the unit decides to turn off, and if the wick is damaged.

If the wick is in good shape, and the element is about 5 ohms cold and not damagedl, you can get 1/2 hour to 45 minutes out of 75 drops.

If the wick is frayed a bit, it will smoke slightly less, and smoke longer, like our 1 hour champion.

If the unit is defective, like the element is damaged, or wrong resistance, or you get too little airflow, the unit will sense the decreased current (out of fluid or higher ambient = less current) then the unit will shut down.

Normally it takes about 10-14 milliamps of current decrease to trigger the processor to say stop.

If a unit shuts down prematurely, you can restart it immediately, since you are resetting the processor and the program.

Lately, the new Aristo Rogers and the brand new C16 are having units that shut off right away, they also have the most restrictive airflow into them.

We also found that there is a difference running the units out in free air, and in even a nice large loco shell like a SD45.

So, what can you do?

First of all, return the unit to Aristo to have it repaired if it will not run in free air for 30 minutes with 75 drops of smoke fluid.

Second, you can inspect the unit for damage from the smoke fluid. Yes, the fluid will damage it. It will swell up the electrolytic caps and tear them off the board. I had someone bring a defective one to me, that had been repaired by Aristo. The cap was resoldered, but 2 cold solder joints on it! It ran for 10 minutes when I got it. Removing the cap, cleaning the leads so solder would stick, and resoldering had it running for more than an hour (this is our leader so far)... the unit is old, but the element is in good shape.

If you are testing yours, you could use these numbers for reference: (I tested at 14v).... initial current draw about 430 milliamps... most units settle down to about 310-320 milliamps and stay there for most of the run time... then you will see the current drop by 1 milliamp bit by bit... when the unit "thinks" it's out of fluid, then you will see the current drop 10-15 milliamps and it will shut off right then.

If there still is a lot of fluid and the unit shut down prematurely, it might run for some time right after, about 50% of the initial run time.

Hope this helps... more later when I find a replacement source for the elements and wicks... the electronics seem ok except for the fluid condensing and slowly killing the caps on the board... and that is a design flaw that there is little hope for.

Regards, Greg
 

·
Premium Member
Joined
·
4,716 Posts
No doubt it's attempting to measure the temperature by the current the resistor draws to detect low fluid. Perhaps variations in values cause some to trip too early?

I rarely use mine. It goes 30 to 45 minutes per fill, for several hours, then I can't get it to go again, and fluid is dripping out the bottom of the loco. I've found the old syringe I used to measure fluid with. I measured the box and it looks like you want to put about 4.5 ml of fluid in. There's no way I could count 75 drops. I'm guessing it quits working when I put too much fluid in and immerse the resistor.

Good to know it draws about 1/2 amp. My 3.8 AH battery runs the loco continually about 3 hours without smoke, so it must be drawing a little more than an amp. With smoke, I'm guessing it would go about 2 hours. Maybe I'll use it more:D

They really used a PIC processor? Seems like overkill to me.

Not sure I understand Bob's problem number 2. The drop of condensate closes off the exit hole? I'd have thought the little fan would blow hard enough to clear that, but wicking the drop back down into the unit sounds like a reasonable, and simple, solution.
 

·
Super Modulator
Joined
·
21,340 Posts
Discussion Starter · #20 ·
Yes, it is sensing the voltage across the element. Thus it senses current.

Yes, variations in "hot" temperature will cause some variation in run time.

The real story is the fragility of the element. The element is nichrome wire wound on an insulating center. Then 2 caps are CRIMPED on each end. That is the sum of the electrical connection between the heating element and the leads of the device. Bending, tweaking, etc. can make this connection poor or erratic. The manufacturer states that to bend the leads, one must take great care to support the lead right next to the cap so no torque is transmitted to the cap, and thus the connection between the element wire and the cap.

I will get a syringe and determine the equivalent of 75 drops.

You cannot immerse the resistor, I believe, I will measure this to be sure.

The PIC processor is the same one used as the PWM regulator in the SD45, using it as a regulator is inexpensive. Since the smoke unit needs a regulator and an algorithm for shutting down, a processor is required for the last task, so the regulator being handled by the processor saves more cost. A clever design.

The fluid has a pretty high surface tension, and small holes can block the air flow. The little fan is got ok volume, but not a lot of pressure.

Regards, Greg
 
1 - 20 of 27 Posts
Top