How to go about adjusting different accessory voltages on a new spur serviced by a fixed voltage bus line?

For accessories that will run on DC voltage, I would look into adjustable AC to DC buck converters; like this one:

This listing from eBay includes free shipping. Cut and paste this number in the search box:

323405457109

A potentiometer alone will not do the job.

Trouble with potentiometers/rheostats is that as the load increased, the voltage drops.  What are the specified voltages for each of the items you list? 

Pots generate heat too. I am with rjr, find the voltages and use different color wire and transformer winding for each. I have some items at 10 volts on a 1033, a number at 14 on a zw, some at 16 on the other handle, and one at 18 (rocket launcher, the gantry is really slow at lower volts) using a 1034 if  i remember.

I have  the same 3 accessories (barrel loader, sawmill, and coal loader) on my layout. I run them from the same variable tap on a Type Z transformer. My solution is to just run one accessory at a time and adjust the voltage accordingly. 

Many accessories will operate well using DC rather than AC. When they say that they will operate using AC or DC power, the first thing you will find in the circuit is a bridge rectifier followed by a fairly large smoothing capacitor to clean up the pulsating DC voltage from the rectifier.

When DC is run through this initial stage of the accessory circuit, it remains DC with only a small drop in voltage across the diodes.

Buck converters use high frequency pulses through a switch mode component to achieve a drop in voltage that can be adjusted with a potentiometer.

Linear voltage regulators can also be used but will use up excess voltage in the form of heat. Buck converters generally do not generate a lot of heat.

   Even simpler; if your volt drop isn't radical, and if they will run on dc you may only need general purpose diodes rated for each acc. on each acc drop. (or to create a second or third, etc. bus if diode amp ratings a8re big enough to handle it.)

 Each diode will use about .7 v.  So two is -1.4v, three -2.1v, etc.  The result isnt pure, constant fed dc yet, but pulsed DC "Ac minus the negative wave"[or pos wave. if the diode is inverted]   So being pulsed, some ac vibration motors may even work.

  Chances are good anything modern may already have internal caps used for ac. (an acc. may want more capacitance though if it flickers or stutters..?)

  Regulators will all make heat, going overkill on amp ratings and shrink tube will help direct contact issues with the diodes. 

  Note except for certain transformers, the acc. and track draw is happening off of one transformer, so the operating of one takes from the stability of supply to the other and may show as flicker or stuttering when a draw gets heavy.   I.e., powering accessories from their own power source would give less perceptible flicker if any at the track while blowing a whistle or during a jackrabbit start on a heavy load, etc..

  You ought to start racing some trains just to watch "the big kids" at the club squim with bullet-proof-envy as pounds of trains crash hard into the stops but keep running again & again

Adriatic is right about dropping voltage with diodes. With alternating current, you have to wire them back to back with the anodes and cathodes in opposing directions.

An inexpensive way to achieve this is with the four diodes in a bridge rectifier wired with the plus and minus hooked together. Then you use one of the AC pins for input and the other AC pin for output. That gives you 2 diodes back to back for a voltage drop of about 1.4 vac.

These can be strung together one after the other to give a combined voltage drop of 2.8, 4.2, 5.6, etc. If you need to fine tune it, you can still use 2 diodes back to back to give the smaller .7 voltage drop.

You would still have AC going to the accessories with this method. As Adriatic points out, however, these will generate some heat. That's why these rectifiers have a hole in them. They can be screwed down to a heat sink if necessary.

Here's a beefed up schematic version of the bridge rectifier diode method for voltage reduction.

If you use individual diodes, wired back to back, the picture at the bottom would be cut in half vertically between the 2 groups of diodes. Each set of diodes produce an AC voltage drop of about 0.7 volts. With the rectifier, you get double that.

Two industry trends, IMO. Many accessories are supplied with their own power supply,  110 volt plug-in wall wart that power the accessory, Or Accessory voltages are listed as very wide   eg.  10 to 18 volts.  Check each accessory.  Again IMO.   Mike CT.  This animation module has several different wall warts.   (5) in this picture.    I recently added a 24 volt (Heating control) transformer to operated a 24 volt relay on this module. 

Two industry trends, IMO. Many accessories are supplied with their own power supply,  110 volt plug-in wall wart that power the accessory, Or Accessory voltages are listed as very wide   eg.  10 to 18 volts.  Check each accessory.  Again IMO.   Mike CT.  This animation module has several different wall warts.   (5) in this picture, (One 3 ft X 6 ft display module).    I recently added a 24 volt (Heating control) transformer to operated a 24 volt relay on this module. 

Consolidated Leo posted:

For accessories that will run on DC voltage, I would look into adjustable AC to DC buck converters; like this one:

This listing from eBay includes free shipping. Cut and paste this number in the search box:

323405457109

A potentiometer alone will not do the job.

What he said!  The only thing is- by "a new spur" and listing the accessories, I assume that you are running ONLY those accessories, not trains.  And if that's true- then at a 2.5 amp limit, the buck converters are the answer. 

Another point- each will output based on available voltage- so- the more of these running off the same input bus, you might not be able to set their outputs at high enough levels.  So, you'll want the bus running at near full available voltage.  When the highest output one won;t get where you need it- jack up the transformer (the stepdown bucks will still limit output at their set levels).  

Buy 4 or 5 (spend less than $15 and wait 3-4 weeks) and set one each up to:

1. output DC 1.5 v (for, say incandescent streetlights)

2. one at 3v (for say a Menards building that is supposed to have 4.5 v- but is too bright)

3. one at 8v for some other LED lighting, and

4.  one at full-tilt boogie 12+ volts DC (or run the higher-voltage accessories using AC off your bus).

This what I have done- I use 7 Buck Converters mounted under the layout to boards, and that allows me to use:

-cheap (Menards- $ 4.99/ pair Sku # 2897620- 3v running at 1.5 DC for longevity) streetlights

- Menard's York Hotel- (it has its own buck converter since it draws about 2.5 amps), running at about 3v

- running Todd Architectural Stauffer's building (at 8.5 v.) 

- Several Menard's buildings at 3 of the recommended 4.5 v. so they are more realistic.

The converters allow you to set each accessory based on it's needed voltage and current requirements.  I have bought 8, and one shorted out (now in the landfill).  At $ 2.70 who cares?

There are also converters that have digital voltage readouts w/ knob adjustment:

e-Bay No. 173806650164

This one is the least expensive one I could find (that has DC output as low as 1.25 v., and has a heat sink).  IMO these are features I would recommend.  BUT- in my experience, once you set them they stay at the set output.

As BMORAN noted (below, next post) the advice he gives is correct- the converters will only be used on accessories that can use DC- and you see that all of mine are related to lighting. 

 I don't want to mislead.

It should be noted that not ALL accessories are DC compatible, including the barrel loader and saw mill OP mentioned. They use vibration motors which rely on the AC 60Hz cycle to generate rapid oscillations (vibrations) to create movement. On DC, there would be no cyclical oscillations and no movement along with the bonus potential to overheat/damage the components of the vibrator motor.

 

P.S. - I'm not saying DC is good or bad or better/worse than AC. I'm simply stating the fact that not all accessories are DC compatible. Bottom line, it would really suck for someone to attempt to follow the advice above on using DC when it isn't applicable and potentially damaging to their accessories.

 

P.S.S. - Multiple variable taps from a transformer(s) is what is needed. This can be done with something like a Z transformer that has 4 variable voltage taps, or by phasing together smaller single variable voltage transformers.

If you are considering the diode-drop method, take a look at this recent thread aptly titled:

what-to-do-when-accessories-like-different-voltage?

I copied a photo from that thread below showing what appears to be the exact situation you're asking about.  This voltage dropping method does not convert the "starting" AC voltage to DC...and hence is compatible with those accessories that require AC.

There's assembly and wiring involved so it's not plug-and-play, but out-of-pocket cost is well less than $5.

Stan has a good answer for Bob C's question: We just set up a new spur with a 16v ac  bus line from a variable transformer. We would like to operate the following equipment off this spur and add more at a later date. Our problem is supplying a different voltage to each accessory while trying to use just one transformer. 

No dc, and no additional transformers.

I missed the previous thread Stan mentions, excellent idea.  Curious for a recommendation of how this would be fused / protected and how we might estimate the total connected wattage limit.  I guess the simple idea might be to fuse the incoming line for 7A  (or less? -rating on rectifiers is 10A) and based on that, target a total conservative connected load at less than 100 watts?   Thoughts?

Duh, I was half asleep when I posted. I didn't even think of opposing them to retain ac. You just fuse things normally; under the wire's max is the "must" while barely above normal usage expected is the "ideal" fuse rating to protect an item. Using fast or slow fusing can help "fine tune" circuits that have occasional peak draws very close to max or even above a fuses rating, but only for a split second...it all comes down to the thermal build rate. Diodes don't really degrade amps that pass by it. They just block power like a one way plumbing check valve and eat a voltage snack while doing it. Ideally, you fuse the lines at transformer for the max. expected to be used on that wire. A new acc. drop off the bus means another fuse for that drop alone or lessening the first fuse to match the lighter wire's max. Omiting this second fuse would likely leave you overfused for the accessory and underfused for the track. (track drops differ for fusing as there is an accumulation factor among the multiple small drops that allow power to flow across all of them at once, effectively increasing the gauge... bringing us back to the #1 transformer fuse used to protect that track wire circuit)

To more directly address Hokie (I think) yes you add up the amps being used and choose components 20-30% over that min., fusing it all as close as possible without them tripping.   One lone fuse is simply not always enough for a schematic design that shares power among items thru various gauges.

bmoran4 posted:

It should be noted that not ALL accessories are DC compatible, including the barrel loader and saw mill OP mentioned. They use vibration motors which rely on the AC 60Hz cycle to generate rapid oscillations (vibrations) to create movement. On DC, there would be no cyclical oscillations and no movement along with the bonus potential to overheat/damage the components of the vibrator motor.

 

P.S. - I'm not saying DC is good or bad or better/worse than AC. I'm simply stating the fact that not all accessories are DC compatible. Bottom line, it would really suck for someone to attempt to follow the advice above on using DC when it isn't applicable and potentially damaging to their accessories.

 

P.S.S. - Multiple variable taps from a transformer(s) is what is needed. This can be done with something like a Z transformer that has 4 variable voltage taps, or by phasing together smaller single variable voltage transformers.

Thank you bmoran4. You have saved me a lot of grief and time.

I think if you read the first sentence of my first post, you will see that recommending DC for accessories was duly qualified.

We don't expect to have folks just do what we say without doing their own research first. Our recommendations should simply be a starting point for gathering additional information.

I could not tell you which accessories will require AC voltage. But I immediately thought of the vibration motors that bmoran4 mentioned. These do require AC to operate.

But since Bob C did say that they would be using a bus of 16 vac to power the whole area, these things can be dealt with on an individual basis. You could use a buck converter with the lighting applications, use the diode method to drop voltage for other accessories; either AC or DC, and in a pinch, another transformer could also be in the mix.

Are we having fun yet?

  -- Leo

"We don't expect to have folks just do what we say without doing their own research first."

Leo, You have got to be kidding.  Many forumites look here for answers precisely because they recognize they their talents are in other areas than train electronics, so they'll check with the experts.

 

I guess I need to sign a waiver or something before I make any more suggestions. I expect people who ask for help  to understand that this is an open forum that gives advise in many forms; not just absolute answers.

As in this topic there are a number of ways to approach the problem. Some ways are more expensive than others. Some are mere suggestions or thoughts. We can not be aware of the entire situation and so some of it is guesswork. Sometimes it involves tinkering that evolves into a kind of coaching situation.

But I expect everyone here to take serious precautions in dealing with these issues and to take responsibility for their own actions.

Perhaps we should all adopt and paste the following to our posts:

DISCLAIMER: The author of the above post does not hold him/herself out to be an expert in the field of model trains and/or model railroading and any and all advice set forth herein is not intended to be, nor should it be construed as expert technical advice, but rather as a simple suggestion and potential solution to the Original Poster's question, and to be undertaken only in conjunction with and after consultation with an acknowledged model train expert, which the author is not.  Further, the author hereby disclaims all liability and responsibility for any damages - actual, consequential or incidental, incurred as a result of following the non-expert advice set forth herein.  

 

Richie C. posted:

Perhaps we should all adopt and paste the following to our posts:

DISCLAIMER: The author of the above post does not hold him/herself out to be an expert in the field of model trains and/or model railroading and any and all advice set forth herein is not intended to be, nor should it be construed as expert technical advice, but rather as a simple suggestion and potential solution to the Original Poster's question, and to be undertaken only in conjunction with and after consultation with an acknowledged model train expert, which the author is not.  Further, the author hereby disclaims all liability and responsibility for any damages - actual, consequential or incidental, incurred as a result of following the non-expert advice set forth herein.  

 

I think we are getting carried away, but I agree that we don't need to pollute the form with silly, not quite applicable answers. For instance, if someone was asking where to get parts for a Lionel Legacy locomotive, we shouldn't simply post "Call Midge at MTH - she got me parts" and then to back up that answer when called out with "I use MTH traction tires on my Lionel locomotives for [insert reason(s) here]".

Where do I sign?

That is entirely the situation we have here. I think we have a lawyer in our forum. Good work!

  -- Leo

Back to the topic at hand. As I said before, since this application will use a 16 VAC bus to power the region, the appropriate voltage can be achieved with a mixture of solutions. They don't require a single method as shown here:

Just a suggestion. Bob C and his group can decide for themselves which avenue they wish to pursue. But I'm not an expert.

What Leo said.

As I interpreted the OP, the key requirement is in the thread's title: "fixed voltage bus line."   OTOH, if a multi-tap / multi-output transformer is allowed then the fat lady has sung and the thread is over.

Since the eBay modules are only a couple bucks each, I think mix-match of methods (AC-to-DC and AC-to-AC) makes lots of sense.  When dropping the voltage a lot like from 16V down to 4.5V (e.g., for Menards, Lemax, Miller building lighting), the AC-to-DC "buck" converters can save a lot of wasted power vs. the diode or rheostat methods.  In other words you can power more accessories.

As an aside, I don't know if it's been discussed much on OGR, but if all you have is DC you can always use an eBay audio amplifier module to convert from DC back to AC.  So if you have a vibrator-motor or other traditional O-gauge accessory that needs the 60 Hz to work use a low-cost audio amp module.  We all know audio amps are spec'd 20 Hz to 20,000 kHz and come in all power ratings from a few Watts to hundreds of Watts.  Why not "amplify" a 60 Hz signal with an audio amp to then drive a vibrator motor or whatever.  On eBay you can get a 50 Watt audio amp (which I'd think would be good enough for most O-gauge accessories) for just a few bucks.  The audio amps use DC power.

In fact, with DC-powered Lionchief engines and DC-powered PS2/3 engines, I can imagine layouts that only use DC power!  In that case, if you wanted to install a traditional accessory that requires 60 Hz AC, you'd use an audio amplifier module to generate the 60 Hz power! 

Consolidated Leo posted:

Where do I sign?

That is entirely the situation we have here. I think we have a lawyer in our forum. Good work!

  -- Leo

Nice call !!

Get yourself an old Lionel “Z” Transformer which will give you 4 Variable outputs of AC Voltage!  These can be picked up at Train Shows very reasonable!  Pretest each Accessory before you install it on your Layout to determine which it operates best!  Put a small piece of tape on it and mark down that Volage !  Now you can group those and set the output voltage of one of the Oitputs on the “Z” to Mach each Group!! 

Simple and workable!!

Fredstrains

Fredstrains posted:

Get yourself an old Lionel “Z” Transformer which will give you 4 Variable outputs of AC Voltage!  These can be picked up at Train Shows very reasonable!  Pretest each Accessory before you install it on your Layout to determine which it operates best!  Put a small piece of tape on it and mark down that Volage !  Now you can group those and set the output voltage of one of the Oitputs on the “Z” to Mach each Group!! 

Simple and workable!!

Fredstrains

Thank you for your reply. I have gotten a lot of advice and it all has helped me get a much clearer understanding about my options. Right now I am leaning to toward your suggestion with other members having suggested a very similar type of fix. It looks to be the most practical and least involved solution. I will now present the choices to my group and we will pick the way to go. 

Hi Bob,  I'm in and around MB a couple times a month.  If you could share your Mall location and times, I would like to visit with your group.  Close to Murrells Inlet, I hope??  My contact is in my profile.

Thanks

Tommy