diodes to slow down hill speed

Wherever you read about how/why of the paired-diode drop method presumably also explained you can use a bridge-rectifier which has 4 diodes.  A bridge can simplify inter-connections and can make for neater assembly/mounting as some packages have mounting holes vs. loose individual diodes.  This photo recycled from another thread about diode dropping.

4 diodes vs bridge 

10 Amp bridge rectifiers are about 30 cents on eBay free-shipping from Asia.  For example, KBU1010 is a widely available part number that you can also find on Amazon or other US sources.

kbu1010 10 amp bridge rectifiers

For hill speed control you probably don't need many pairs, but for mounting and assembly, terminal blocks/strips can come in handy to make a neat ladder of voltages.

diode ac drop using bridge rectifiers

 

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Unfortunately there is some tedious do-the-math on the need for heat-sinks, how big they need to be, etc..  I figure you'll probably need more than 1 bridge rectifier anyway, so why not use some scrap metal to double-duty as a mechanical mounting platform and a electrical heatsink.  As shown in the photo, I use "scrap" 1/8" aluminum sheet and mount the bridge rectifiers with #4 machine-screws into threaded holes.  But whatever you have lying around will work.  The purists will say to use heat-sink paste/compound (the outrageously priced white-stuff between the bridge and the heat-sink plate).  I can't argue with that but you'll get plenty of benefit by just firmly attaching the component to any metal surface!

Note that unless you have some funky operation, the voltage dropping diodes/bridges will never operate anywhere near their limits.  That is, this is dropping voltage (burning power) when the engine is going DOWN hill meaning power demand is by definition lower.  Stated differently, if you're burning anywhere close to 10 Amps going DOWN hill, then you'll have to trust me that you've got bigger fish to fry!  

My $.02 here... why wouldn't the original poster use something like a No. 95 rheostat, or other adjustable resistor, instead of rectifiers / diodes?  This would allow him to adjust the resistance for varying train lengths and locomotive types.  Note I haven't actually done this, but I'm pretty sure I read some old reference books that suggested this is how it was done "back in the day."

What are the pros and cons?  Are the rectifiers simply newer technology that wasn't available in the '50s?  Is there any provision for changing the number of diodes, and consequently the amount of voltage drop for varying train loads?  Good thread!

Creep, coast, and pull.  We're not talking about cold fusion here.

Make use of the four channels on a ZW or Z4000 transformer. A for level or main(variable), B for UP and C for down, with B & C being fixed, which leaves the D handle free.

A lot easier to tickle the UP & DOWN voltage for a different set of cars or engine change.

Carl

Arctic Railroad

Here's my caveman conventional approach. Going up full 12V from the transformer.   Going down a 48" insulated section supplied by track voltage with an inline 5W 1 ohm power resistor going to the center rail. Works fine.

Builder of the Hill Lines ( New Delta Lines). Recreating history for the model RR community.

What happens if the train is going in the other direction? Then this uphill / downhill terminology is bogus with respect to the track. You need to be able to turn it around. Switches would work if you don't mind the responsibility of manual operation. But some track sensors and relays could change the orientation of the diodes based on the trains direction.

I would think that a top-of-the-hill / bottom-of-the-hill sensor and a cheap asian relay board to steer the diodes would be all that is needed. Nothing fancy. This should be standard apparel for any conventional layout that has grades to manuever.

Consolidated Leo posted:

What happens if the train is going in the other direction? Then this uphill / downhill terminology is bogus with respect to the track. You need to be able to turn it around. Switches would work if you don't mind the responsibility of manual operation. But some track sensors and relays could change the orientation of the diodes based on the trains direction.

I would think that a top-of-the-hill / bottom-of-the-hill sensor and a cheap asian relay board to steer the diodes would be all that is needed. Nothing fancy. This should be standard apparel for any conventional layout that has grades to manuever.

Reverse voltage for B & C handles. A is still variable and level.

Hills are not a problem with command controlled engines with cruise control. But, many insist on playing these games and running conventional engines in ways they weren't designed to be operated.

So be it, become a good engineer and work the throttle(s).

Carl

Arctic Railroad

Ted Sowirka posted:

My $.02 here... why wouldn't the original poster use something like a No. 95 rheostat, or other adjustable resistor, instead of rectifiers / diodes? 

Rheostats are the way to go. Quickly adjustable on the fly and when changing out your consist/motive power, and avoids the issue of fault currents across the secondary windings.

Rob

Moonman posted:
But, many insist on playing these games and running conventional engines in ways they weren't designed to be operated.

That's an unusual way to look at it. And just how are conventional engines designed to be operated? The last time I checked, they use a variation in voltage to run at different levels of power and speed.

I believe the OP asked about using diodes to vary the track voltage on a downhill grade. I would guess that he wants to avoid having to work three different throttles at the same time. Automation on the layout is not breaking any rules that I'm aware of. C'mon man!

Since going uphill will use full power, downhill is the only direction that would require the voltage reduction diodes. But you still need 2 sensors. One at the top of the hill and one at the bottom. These could be anything that delivers a positive DC voltage to a 5 or 12 volt relay module. Noise should not make any difference because the relays are setup to hold their position from one sensor to the other.

When the train reaches the top of hill sensor, the first relay kicks in. That sends power from the NO output to the NC input of the second relay. Since the second relay will be off, the NC and COM points will be connected. The COM connection runs to the COIL of the first relay so as to maintain power after the train gets past the top of hill sensor.

The "downhill" signal controls the third relay to route either full strength transformer power or diode reduced voltage to the center rail of the downhill track section.

When the train reaches the bottom of hill sensor, the connection between NC and COM on relay 2 will be broken and the COIL on relay 1 will disengage. This will restore full track power to the downhill section of track. If the train turns around or even backs up, it can engage the hill with full power.

Please examine this to see if I missed anything. If I did, please let me know. I'm sorry that I'm not in a position to demonstrate or test this out but in theory it should do the job.

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Consolidated Leo posted:
Moonman posted:
But, many insist on playing these games and running conventional engines in ways they weren't designed to be operated.

That's an unusual way to look at it. And just how are conventional engines designed to be operated? With less than a 4.7% slope that the trestles create. 

The last time I checked, they use a variation in voltage to run at different levels of power and speed. Correct.

I believe the OP asked about using diodes to vary the track voltage on a downhill grade. I would guess that he wants to avoid having to work three different throttles at the same

Only 1 -A - up and down voltage can be fixed time.

Automation on the layout is not breaking any rules that I'm aware of. C'mon man! yeah I get it. When it's a 4' high spiral for a Christmas train , something like Matthew B's. layout.

Sorry, it was little out of line. Playing with antiques and vintage items just isn't my thing.

 

Carl

Arctic Railroad

Unless I missed it the OP didn't say anything about multiple engines.

But when I first read his post my initial response was "Just back off the throttle when going downhill".

The problem with installing diodes is they also affect the speed going uphill or on a flat track.

MODELING SOUTHEAST VIRGINIA

Having A Blast Running BPRC

Ted Sowirka posted:

My $.02 here... why wouldn't the original poster use something like a No. 95 rheostat, or other adjustable resistor, instead of rectifiers / diodes?  This would allow him to adjust the resistance for varying train lengths and locomotive types.  Note I haven't actually done this, but I'm pretty sure I read some old reference books that suggested this is how it was done "back in the day."

What are the pros and cons?  Are the rectifiers simply newer technology that wasn't available in the '50s?  Is there any provision for changing the number of diodes, and consequently the amount of voltage drop for varying train loads?  Good thread!

In all likelihood, the OP could use some kind of resistor or variable-resistor/rheostat.  But that was not Tom's question. 

To answer your question, the diode method provides more stable voltage drops under varying loads.  By loads, I mean current required by the engine to pull itself and whatever loads.  So here's where the eyes glaze over.  

kbu1010 Vf characteristics

Let's say a train requires between 1-3 Amps of current.  A diode will drop 0.8-0.9V as shown in the datasheet.  A resistor that drops 0.8V at 1 Amp (i.e., a 0.8 Ohm resistor) will drop 2.4V at 3 Amps applying Ohms Law (Voltage = Current x Resistance).  So the voltage drop is much more stable/consistent for diode (0.1V) vs. resistor (1.6V).  The math gets more interesting and tedious as you delve into issues of whether your voltage is DC vs. pure-sine AC vs. chopped-sine AC but that's another discussion.

So does it really matter if the voltage drop is stable under varying operating conditions?  That's a your-mileage-may-vary.  If you have some low-value resistors, say, 1 Ohm (vs. tens or hundreds of Ohms) lying around with suitable power-handling capability, say, 5 Watts or more (vs. 1/4W or 1/2W) it's worth trying.  And no doubt a variable-resistor like the Lionel 95 would make it easy to experiment.

ebay parts diode resistors rheostats

If starting from scratch and experimenting with the resistor or variable-resistor approach, cascading or combining multiple individual resistors might be less expensive albeit less convenient than a variable resistor.  I believe the Lionel 95 is adjustable 0-5 Ohms.

Using a string of individual resistors would allow tapping into the string to choose different voltage drops based on the situation.  So you could use an inexpensive rotary switch (e.g., salvaged from a multi-speed house fan) to select one of 3 resistor values.  Note that, to answer your question about adjusting the voltage drop, a rotary switch would also apply to select from one of multiple voltage drops in a string of diodes.

It's serendipitous that the diode method even applies to our trains.  In reality, an ideal diode has 0 voltage drop.  There are other diode technologies that are approaching the holy grail of 0 voltage drop but would be of no value for the matter at hand!  Google "synchronous rectification" or "synchronous bridge rectifier" if you want to be put to sleep.

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Consolidated Leo posted:

...

When the train reaches the bottom of hill sensor, the connection between NC and COM on relay 2 will be broken and the COIL on relay 1 will disengage. This will restore full track power to the downhill section of track. If the train turns around or even backs up, it can engage the hill with full power.

Please examine this to see if I missed anything. If I did, please let me know. 

Agreed going the other direction up hill would apply full track power, but wouldn't the train eventually trip the top-of-hill sensor and lock in the track lower voltage until the train makes a complete loop and trips the bottom-of-hill sensor?

stan2004 posted:

Agreed going the other direction up hill would apply full track power, but wouldn't the train eventually trip the top-of-hill sensor and lock in the track lower voltage until the train makes a complete loop and trips the bottom-of-hill sensor?

You are correct. This condition, although unplanned and annoying, does not matter. Since there will be no train on the grade when this occurs. When the same train or even another train trips the bottom-of-hill sensor, full power would be restored. And if a train should be going in the other direction (downhill), tripping the top-of-hill sensor again will still apply the reduced voltage.

Since the diode/rectifier circuit would be activated by that annoying condition, I thought that maybe prolonged periods in that state might result in some extra heat being generated by the diodes. However, with no train on that track section, the current draw would be minimal and I think that makes it tolerable.

Thanks for the feedback!

Moonman posted:
Sorry, it was little out of line. Playing with antiques and vintage items just isn't my thing.

Carl: Not a problem. I appreciate that there are many ways to approach a situation like this. I prefer to  operate trains with the controls in front of me. I'm not sure that I want to get into remote controllers or tethers or wifi on a smart phone. That just doesn't appeal to me.

I've seen that you contribute a great deal to the forums and that's excellent. I think ideas from experienced individuals is what makes all this reading and typing worthwhile. We have to let what advice we give speak for itself. We can't know the circumstances that others are in and what they will take from all the jibber-jabber. The give and take is rarely ever rewarded directly. But there may be some long term effects that seep in slowly over time.

So, keep it up my friend. You're doing great!

I use bridge rectifiers on a dial that I can add a rectifier at increments based on the size/speed of the train.  The switch is connected to 2 sections of track. Guy by the name of Dearborn Dave explained it well on another forum.  Being able to adjust the values is great so you can set it and forget it and train requires full power on an up hill and power reduction on a downhill   

Using handles of a zw is a bad idea and many have spoken of it numerous times on what types of bad things happen when you do this.  

bdobson posted:

Using handles of a zw is a bad idea and many have spoken of it numerous times on what types of bad things happen when you do this.  

Not necessarily a bad idea, nor particular to the ZW - one just needs to account for the crossing of power districts. In fact, many of Lionel's own layout designs used multiple power districts.

Image result for postwar lionel layout schematic

This one also uses a resistor on the downgrade.

Consolidated Leo posted:
stan2004 posted:

Agreed going the other direction up hill would apply full track power, but wouldn't the train eventually trip the top-of-hill sensor and lock in the track lower voltage until the train makes a complete loop and trips the bottom-of-hill sensor?

You are correct. This condition, although unplanned and annoying, does not matter. Since there will be no train on the grade when this occurs...

Not sure we're talking apples-apples.  If the train is backing up the hill, say the caboose trips the top-of-hill sensor.  The way your relays are configured, the top-of-hill sensor always takes precedence (if both sensors are tripped simultaneously).  So the voltage would drop on the grade and the engine might get starved of voltage and perhaps even stall!  Likewise, you might have a MU consist or even a pusher engine configuration.  In such cases, as soon as the lead engine reaches the top-of-hill, any helper engines that are still on the up-hill (or that have not even started their ascent, might be starved of voltage.

I realize this is all just yakkity-yak...

Many schemes to slow engines on the down slope are presented here but I'll still stay with my 1 ohm 5 w resistor to the center rail on the insulated 48" section of the down slope. This basic technique only works on the down direction but that's the way I keep that loop running. If I want to reverse direction I can also make the up side an insulated block and interchange the series resistance and track voltages to each block with a DPDT switch. Simple and cheap.

Builder of the Hill Lines ( New Delta Lines). Recreating history for the model RR community.

stan2004 posted:

Not sure we're talking apples-apples.  If the train is backing up the hill, say the caboose trips the top-of-hill sensor.  The way your relays are configured, the top-of-hill sensor always takes precedence (if both sensors are tripped simultaneously).  So the voltage would drop on the grade and the engine might get starved of voltage and perhaps even stall!  Likewise, you might have a MU consist or even a pusher engine configuration.  In such cases, as soon as the lead engine reaches the top-of-hill, any helper engines that are still on the up-hill (or that have not even started their ascent, might be starved of voltage.

Guilty as charged. It's not a perfect solution for all possible scenarios. I was just thinking of running in conventional mode with a lead engine up front and moving forward. Even then, any lighted caboose or passenger cars could suffer from changing voltages as they move on the grade. But that might be okay. It just seemed to me rather awkward not to be able to adjust for uphill / downhill movements. I can't think of how you would cover any other situations and still keep it simple and cheap.

No charges were filed.  But you did ask for feedback on your idea.  I think the take-away is that diodes and/or bridge-rectifiers suitable for train usage have become remarkably inexpensive and readily available.  Likewise, relays have become remarkably inexpensive hence practical to incorporate into layouts for whatever reasons.  When I saw your 3-relay diagram I immediately thought of the 4-channel relay modules that end up less than a buck per relay (free shipping from Asia), and even has screw-terminal connectors so no soldering required!

ebay 4 relay module less than one buck per relay

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stan2004 posted:

ebay 4 relay module less than one buck per relay

Wow! $2.89 !!! That's a great price! But my preference is for the 5v versions. Those I have run directly off the I/O pins of the Arduino. I've also noticed a newer design floating around on eBay. I can't be sure but just from the pictures and the look of the silkscreen I think they're different. Just the idea of being able to carry 10 amps at 30 volts makes these a great choice for the trains.

stan2004 posted:

Did I hear you say 5V?

ebay 4 relay module 5v

 

Thanks! You've got the magic touch when it comes to eBay searches. I looked earlier and couldn't find the ones with the "hi-low" trigger option. I've just placed an order for 4. With a discount and free shipping it comes to $10.20 total. Wow!

My order of relay boards from Asia arrived today (about 4 weeks). I hooked one up to my latest Arduino signaling experiment on a breadboard. I added some code to make them turn on and off with various changes in signal aspect. They worked perfectly.

Next step is to get some RS485 chips included in the circuit (SN75176BP) so that I can send serial messages between multiple processors.

If command-control is not an option, you could install engine electronics that has built-in speed control.  Not plug-and-play and not low-cost but a MTH PS2/PS3 upgrade kit could be installed.  I'd expect the conventional speed control in PS2/PS3 going downhill (and/or uphill) would be as good as the 95 rheostat or the diode method.

I can't imagine anyone doing this since the rheostat or diode methods are just a few bucks.

There was a short window of time when command control was just taking hold where it might have made sense for an electronic reversing-unit manufacturer to offer speed control similar to PS2/3 conventional speed control.  But that window is closed.

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