Dumb question about modern Lionel

[SCD]

Is it possible / advisible to operate modern Lionel locomotives and their sound features on tracks set up for post war trains and a ZW transformer? Specifically, a new Lionel #11119 steam switcher with TrainSounds, synchronized fan-driven smoke unit, etc. I ask because the smoke unit does not appear to work (yes, the smoke control is "on"), and the sound system seems to work only when the train is in neutral. At other times it emits a static sound.

[chuck]

It should work.  The issues may be noise from the track or power supply interfering with the on-board electronics.  You may also have a "polarity" issue with the DC spikes from the hot and neutral wires being reversed to the track/lockons.  Smoke unit may need to be looked at to  make sure the whicking is in good shape and where it actually belongs. 

You will probably need to add an external sound activation switch to get the "bell" controls.  It is possible that the rectifier discs in the ZW are shot and not producing appropriately sharp spikes or interfering with the booster windings that normally cut in when you hit the whistle button.  In this case, use a pair of sound activation buttons wired back to back to produce the appropriate spikes.

[eZAK]

SCD,

You should be fine with that set up.

If you put fluid in the smoke unit let it run for several minutes. You should start to see puffs of smoke.

If not we can help further on.

 

[SCD]

Thanks guys. I appreciate your response.

[lionelsoni]

I wouldn't call the superimposed DC for whistles a "spike", "appropriately sharp" or otherwise.  It's just a DC component that's added to the usual AC voltage.  All that really matters is its amplitude.

[LocoPops]

I wouldn't call the superimposed DC for whistles a "spike", "appropriately sharp" or otherwise.  It's just a DC component that's added to the usual AC voltage.  All that really matters is its amplitude.

Bob,

How does DC voltage give an AC engine a power boost when the whistle rectifier is shot?

Ed 

[johnandjulie13]

Hello SCD:

 

Regarding the electronics of the new engines, you may want to add some circuit protection (fuses, breakers, etc.) that will trip faster than the breakers inside the old ZW.  This will help protect the electronics inside today's modern engines.

Regarding the smoke unit, in addition to the smoke fluid, make sure that the voltage level is high enough.  There may not be enough power going through the smoke unit to generate the sufficient heat if you just have the engine moving puttering along the tracks.

You may also want to clean the track (and the rollers on the engine).  This may also help clear up some of the static.

Regards,

John

[chuck]

How does DC voltage give an AC engine a power boost when the whistle rectifier is shot?

It doesn't.  The old PW transformers used copper oxide disk rectifiers that were pretty inefficient.  To compensate for the voltage drop caused when these were cut in, Lionel wired in a secondary tap on the transformer to boost the power back up.

[LocoPops]

How does DC voltage give an AC engine a power boost when the whistle rectifier is shot?

It doesn't.  The old PW transformers used copper oxide disk rectifiers that were pretty inefficient.  To compensate for the voltage drop caused when these were cut in, Lionel wired in a secondary tap on the transformer to boost the power back up.

Thank you, Chuck. 

 

[lionelsoni]

Copper-oxide rectifiers are not particularly inefficient.  In fact, they have a lower forward drop than modern silicon rectifiers.  Their main weakness (apart from their much greater size) is that they can't stand much reverse voltage.  So, for many applications, a number of elements had to be connected in series, multiplying the forward drop and the losses, whereas a single silicon rectifier can be gotten that will withstand hundreds of volts.  In toy-train transformers, only a single element is needed; so in that case copper oxide compares favorably with silicon.

The whistle switch has three positions.  In its normal position, it simply passes the variable transformer voltage out to the track.  In its intermediate position, it connects the 5-volt winding and the rectifier in series between the variable voltage and the track.  The 5-volt winding tends to compensate for the voltage lost because of the rectifier.  But this voltage is not lost because the rectifier is inefficient.  Rather, it is lost because the rectifier blocks completely every half cycle of the AC voltage.  If it were not for the added 5-volt winding, the rectifier would drop the RMS voltage at the track by about 30 percent.  In the fully off-normal position, the switch shunts the rectifier with a resistor, which allows a significant portion of the previously blocked half cycles to get past the rectifier, reducing the DC component to a level that suffices to keep the already operated whistle relay from dropping, and further increasing the RMS voltage, to compensate for the extra current drawn by the whistle motor. 

[LocoPops]

Bob,

Thank you very much for the explanation.   Could you define a couple of terms for me?  What are "forward drop" and "reverse voltage"?

Thanks again.

 

[lionelsoni]

An ideal rectifier or diode conducts electricity perfectly in one direction and not at all in the other direction.  A real rectifier has a small voltage across it when it is conducting that a perfect rectifier would not have.  This is about 600 millivolts for a silicon rectifier and about 400 millivolts for a copper-oxide rectifier, although it varies somewhat with the amount of current that is flowing.  Since the current is flowing in what is considered the "forward" direction, this is the "forward voltage drop".  It wastes a little power, which becomes heat in the rectifier.  If you try to get current to flow in the reverse direction, it won't.  That is, it won't until you put more than the maximum "reverse voltage" across the rectifier.  At that point, a lot of current flows and the rectifier may be destroyed.  So, when using a rectifier, you have to get one that can stand whatever reverse voltage your circuit will throw at it.  In our case, that is at most a few tens of volts.  The cheapest silicon rectifiers, like the venerable 1N4001, can stand 50 volts; and many common types can stand hundreds of volts.  But copper-oxide rectifiers must be connected in series so as to divide the reverse voltage among several elements when high voltages are used.

[ben10ben]

Bob,

On other forums, the suggestion gets tossed around a lot to replace the old Cu2O rectifiers with modern silicone diodes.

I have always taken the alternate path and replaced the original Cu2O rectifiers, when bad, with modern reproductions of the same part.

I've replaced several of these, and the replacements in all instances perform exceptionally well.

I'm curious to hear your take on it, however, as I presume you know much more than the adminstrator on another forum who locked a thread where I inquired about obtaining replacement rectifiers. In fact, I was told that "there is absolutely no reason to use anything other than a silicone diode-end of story". 

 

Thanks,
Ben

[lionelsoni]

Of course the 200 millivolt difference is no big deal; but copper-oxide rectifiers are in fact a little better than silicon as far as forward voltage drop is concerned.  "Absolutely no reason"--I think not!

Interestingly, there is a special type of silicon diode, called a Schottky diode, that has a forward drop comparable to copper oxide, about 400 millivolts.  Coincidentally, Schottky diodes also have trouble with high reverse voltage, much like copper oxide.

[ben10ben]

Thanks, Bob.

Incidentally, my main reason for continuing to use the cuprous oxide rectifiers is because they mount in place in the way they were designed from the factory, and don't require jerry-rigging as does the installation of a silicon diode. Jerry-rigging on the inside of a transformer case makes me uneasy, so with that in mind, I've never seen the need to bother with anything other than a modern replacement rectifier. 

Thanks for confirming that I'm not completely crazy

By the way, Schottky diodes get mentioned a lot in the classic camera repair world. The idea behind them is that they can be used to convert the stable 1.55 volt output of a silver oxide cell into the stable 1.35 volt output of a mercury oxide cell. This is important, as many older cameras had built-in meters that relied on the stable 1.35 volt output, and higher voltage throw off the meter reading. Silver oxide cells are readily available, while mercury cells are not, so the desire is to be able to use this proper meter reading. From what you're saying, though, it sounds as though the Schottky diode produces twice the desired voltage drop. 

My solution is just to use a zinc-air cell, which has a stable output at the desired voltage, but has a relatively short life. Most other folks claim it's too inconvenient to change the battery every month.

 

[lionelsoni]

Well, as I said, the drop does depend (weakly) on the current; so, if the current draw is very light, Schottky might work.  Germanium diodes do have about a 200-millivolt drop and might work better, although they are considered obsolete and are a little hard to find.  (I have a stash!)

[LocoPops]

  If you try to get current to flow in the reverse direction, it won't.  That is, it won't until you put more than the maximum "reverse voltage" across the rectifier.  At that point, a lot of current flows and the rectifier may be destroyed. 

Bob,

I actually understood most of your explanation!   Except...  What is the reason for the existence of reverse voltage.  That is, how/why does reverse voltage happen in our transformers?

Thanks.

 

[lionelsoni]

The reverse voltage is just whatever voltage you put across the diode in the direction in which it doesn't conduct.  Every diode is rated according to the greatest reverse voltage that it can stand without being damaged.  Suppose you have a transformer that puts out 21 volts (like a ZW).  When you operate the whistle control, that voltage goes up to 26 volts; but the rectifier is supposed to block every other half cycle.  The peak voltage of those half cycles that are supposed to be blocked is about 38 volts.  So the rectifier in the whistle circuit needs to be rated for 38 volts reverse voltage.  That is, we have to be sure it won't be damaged by that much voltage if we try to blow the whistle with the speed control all the way up.

[LocoPops]

Bob,

OK.  I know this will sound dumb as heck to you.  But I thought conduction means in a specific direction.  That is, I didn't think voltage went in a direction that was not intended.  So what makes voltage go in a reverse direction?  

 

[lionelsoni]

A diode has two terminals, called the cathode and the anode.  When the anode is more positive than the cathode, that anode to cathode voltage is called "forward" by convention.  The forward voltage is never very much, because the diode conducts in that direction and the forward current can become very large.  Diodes are rated for the forward current that they can carry without burning up.

When the cathode is more positive than the anode, that cathode to anode voltage is called "reverse" by convention.  The reverse voltage can be large, because the diode does not conduct in that direction.  Diodes are also rated for the reverse voltage they can stand without breaking down.

A diode is a lot like a check valve in plumbing.  You can't put much pressure (voltage) across a check valve in one direction (which we might call the "forward" direction), because the water (current) flows easily in that direction.  You can't get any water to flow in the "reverse" direction, even with a lot of pressure.  But, if the reverse pressure is too great, you destroy the check valve.

If you hook two wires to a battery, one of them is positive compared to the other, the other is negative compared to the first.  If you swap the wires at the battery, you have reversed the polarity of the voltage.  In that case, it is you that makes the voltage go in a reverse direction.

If you are dealing with alternating voltage, perhaps out of a train transformer, the generator at the power plant makes it go in a reverse direction 60 times a second.

[LocoPops]

Bob,

You're the man.  Thanks for the explanation.  Great stuff.