I have a question for Gunrunnerjohn or others much smarter that me. I have gotten pretty deep into TMCC/Legacy but in S gauge and it looks as though S is being left behind here. I am looking for a way to convert the 19v AC power from my Powerhouses to smooth DC power 15v-20v that will fit inside an S gauge GP or similar engine and be used to power the Soundtraxx Blunami decoder. I am not sure of the components that I might need or if it's possible, so looking for some guidance.

Thanks

Ray

Original Post

@Rayin"S" posted:

I have a question for Gunrunnerjohn or others much smarter that me. I have gotten pretty deep into TMCC/Legacy but in S gauge and it looks as though S is being left behind here. I am looking for a way to convert the 19v AC power from my Powerhouses to smooth DC power 15v-20v that will fit inside an S gauge GP or similar engine and be used to power the Soundtraxx Blunami decoder. I am not sure of the components that I might need or if it's possible, so looking for some guidance.

Thanks

Ray

# Level DC (Smoothing Pulsating DC)

14 A basic power supply circuit can be divided into four sections, as shown in Figure 11.31.

Questions
A. If you use a center-tap transformer in a power supply, how many diodes would you need to produce a full-wave rectified output? _____
B. Will the power supply circuit shown in Figure 11.31 result in full- or half-wave rectification? _____
C. What type of output will the rectifier section of the power supply circuit shown in Figure 11.31 produce? _____
A. Two
B. Half-wave
C. Pulsating DC

15 The function of the smoothing section of a power supply circuit is to take the pulsating DC (PDC) and convert it to a “pure” DC with as little AC “ripple” as possible. The smoothed DC voltage, shown in the illustration on the right in Figure 11.32, is then applied to the load.

The load (which is “driven” by the power supply) can be a simple lamp or a complex electronic circuit. Whatever load you use, it requires a certain voltage across its terminals and draws a current. Therefore, the load has a resistance.

Usually, the voltage and current required by the load (and, hence, its resistance) are known, and you must design the power supply to provide that voltage and current.

To simplify the circuit diagrams, ...

Smoothing capacitors are used to suppress voltage ripples, usually on power supply lines. They do this by periodically storing and replenishing energy. The image below shows a very common use case of these capacitors in a full bridge rectifier.

As you can see, the smoothing capacitor discharges and replenishes energy when the output voltage drops. This "evens out" the output voltage, which is why this capacitor is called a "smoothing" capacitor.

Last edited by ThatGuy

I think what Ray is looking for is an off the shelf unit not more than 1/4”x3/4”x3/4”, rated 2A or greater. The empty space inside the S gauge American Models diesels is very limited due to the power train design.

Go here for a comprehensive guide:  https://ogrforum.ogaugerr.com/...c/177398551947214218

S gauge engines draw less current than O, so smaller FWB rectifiers and capacitors can be used.  A FWB rated at 3-5A should be sufficient.  The 2A Blunami cards are similar in size to the American Models reversing unit cards and should fit those engines.  The DC>DC converter/regulator isn't needed in S, as track voltage need not exceed 12-14 V.

Last edited by KarlDL

Karl, we are using AC track power since we are also running TMCC and Legacy engines on the layout. In S gauge, Older Legacy and most TMCC will not work on DC track power, hence the need for the in-engine rectifier for Blunami. 2A is generally adequate for the AM single motor diesels. My AM diesels draw a full 2A pulling a 15 car freight up a 2.2% grade.

S gauge Legacy engines will not work reliably at 12V to 14V. For full smoke volume and 100% reliable operation of the electrocouplers at least 15V at the engine pickup wheels is required.

Be careful rectifying 18VAC with a bridge and filter cap, the output voltage will be around 25-26 volts DC.  That exceeds the Blunami maximum voltage of 22 VDC.  You should add a regulator of some type instead of using raw DC.

Actually Tom if I can build this to fit inside the shell that would be fine, what l don't know is what the rectified voltage is, I would like it at 15-19 volts.

Ray

Ray, that is what GRJ posted above. 18VAC RMS into a full wave bridge outputs about 17VDC. There is about a 1V drop across the diodes. If we add capacitors to smooth the waveform it basically makes the output DC voltage equal to the peak voltage input rather than the RMS voltage. For a sine wave, peak is 1.414 times the RMS voltage, hence GRJ's 25 to 26 VDC.

There are two choices, add an adjustable voltage regulator or set the input  (track) voltage to 13VAC. The problem I have found with 13VAC on the track is the electrcouplers on the Legacy engines do not reliably fire.

@AmFlyer posted:

My AM diesels draw a full 2A pulling a 15 car freight up a 2.2% grade.

S gauge Legacy engines will not work reliably at 12V to 14V.

I measured a stall current of 2A on an AM GP35, so I'm surprised at your number unless it's for more than one powered diesel.

NMRRC's S gauge inventory doesn't include any Legacy S gauge.  It does not surprise me that such engines have voltage requirements similar to their O gauge counterparts.  For us, not having any Legacy engines nor intending to buy any, we can keep the voltage lower and avoid the regulator issue.

As much as i don't like linear regulators ahead of Blunami cards, that may be the easiest and most compact approach for S engines, if compatibility of track voltage with Legacy is required, given the likely current drawn.

@AmFlyer posted:

Ray, that is what GRJ posted above. 18VAC RMS into a full wave bridge outputs about 17VDC. There is about a 1V drop across the diodes. If we add capacitors to smooth the waveform it basically makes the output DC voltage equal to the peak voltage input rather than the RMS voltage. For a sine wave, peak is 1.414 times the RMS voltage, hence GRJ's 25 to 26 VDC.

There are two choices, add an adjustable voltage regulator or set the input  (track) voltage to 13VAC. The problem I have found with 13VAC on the track is the electrcouplers on the Legacy engines do not reliably fire.

We’re talking Blunami, no? 13v RMS on the track will fire a coupler if you apply it directly to the coupler via a relay. Legacy boards don’t use track power directly to the coupler.

Pete

Norton, the problem is not the Blunami engine, it is the Legacy engines on the layout that will also see the 13VAC.

Karl, I find some variation among my AM diesels. The GP9 and the RS11 are right at stall on the grade. Two more freight cars will stall those engines. The FA draws less current. All these are single motor. The E8's and TrainMasters draw the least current with a similar load. No idea why there is such a variation. The AF Legacy engines have the same voltage requirements as the O gauge Legacy engines, the S gauge Legacy engines will run without issue at 15V, but not less.

Ray, will this fit in your GP? Its a tad over 3”x1.5”. It will accept up to 38v DC. I use these with 4 amp Blunamis. Rated for 5 amps.

Pete

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@AmFlyer posted:

Ray, that is what GRJ posted above. 18VAC RMS into a full wave bridge outputs about 17VDC. There is about a 1V drop across the diodes. If we add capacitors to smooth the waveform it basically makes the output DC voltage equal to the peak voltage input rather than the RMS voltage. For a sine wave, peak is 1.414 times the RMS voltage, hence GRJ's 25 to 26 VDC.

There are two choices, add an adjustable voltage regulator or set the input  (track) voltage to 13VAC. The problem I have found with 13VAC on the track is the electrcouplers on the Legacy engines do not reliably fire.

Being in and out all day I  missed John's post, I will look into a linear regulator, don't want to cook my Blunami

Be careful rectifying 18VAC with a bridge and filter cap, the output voltage will be around 25-26 volts DC.  That exceeds the Blunami maximum voltage of 22 VDC.  You should add a regulator of some type instead of using raw DC.

Ray

Here is the track AC to regulated 15V DC converter I have used for years. The total parts cost is \$1.25 and it works well.

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Hard to imagine that will put out 3-4 amps without a problem, the filter capacitor has to be way to small for that amount of current.  That looks to be a 1.5A regulator.  The cap would have to be at least 2,000uf or more.

Last edited by gunrunnerjohn
@KarlDL posted:

I measured a stall current of 2A on an AM GP35, so I'm surprised at your number unless it's for more than one powered diesel.

NMRRC's S gauge inventory doesn't include any Legacy S gauge.  It does not surprise me that such engines have voltage requirements similar to their O gauge counterparts.  For us, not having any Legacy engines nor intending to buy any, we can keep the voltage lower and avoid the regulator issue.

As much as i don't like linear regulators ahead of Blunami cards, that may be the easiest and most compact approach for S engines, if compatibility of track voltage with Legacy is required, given the likely current drawn.

Karl I'm curious, why don't you like to use the linear regulators?  Are they somehow detrimental to the Blunami card, or to signal reception?  If not, why would the card care whether straight-line DC comes from a battery, or rectified and smoothed track voltage?

Also- if you don't need to pull stumps with a single unit, replacing a rubber-tired wheelset with a metal wheelset might allow the loco to spin its wheels when heavily loaded, instead of stalling the motor.  This may reduce the peak current draw in actual service, and allow you to get away with a lower amp rating.

Last edited by Ted S

Main problem with linear regulators is heat especially when current draw is near max or the voltage delta (V in vs V out) is greater. Switching regulators are far more efficient. Thanks to all the production coming out of Asia prices on switching regulators are barely more than linear regulators.

Pete

@Ted S posted:

Karl I'm curious, why don't you like to use the linear regulators?

Same response as Pete.  The switchmode DC>DC converter/regulators dissipate much less power and therefore are much better suited to O gauge locomotives, if sufficient space is available inside the carbody/hood.  Assuming 18V input to the Blunami card and 18 VAC track voltage, a switchmode regulator in a dual can motor engine will dissipate around 2W, half of what a linear regulator would burn up in heat.  At lower regulator output voltages, (such as 13-14V for a single-motor locomotive) the efficiency advantage is even greater.  Not to mention avoiding dissipated heat melting nearby plastic surfaces!  But at the lower current levels and available space of S gauge, they may be a good means of protecting the Blunami card from overvoltage, as long as the Blunami input voltage is only a few volts less than the rectifier DC (or RMS) output voltage.

Last edited by KarlDL

Thanks to all who replied to this, in the immediate future I may do similar to smaller gauges and put  the switching converter into another car with a tether.

The way electronics are evolving there may soon be a switching converter developed in a much smaller package.

Ray

@Norton posted:

Ray, will this fit in your GP? Its a tad over 3”x1.5”. It will accept up to 38v DC. I use these with 4 amp Blunamis. Rated for 5 amps.

Pete

Norton,

I found something very similar but a little over 2 inches long and 1 inch wide, tight but it fits, rated a 5 amps also, I did unfasten the coil and lay it on its side for height clearance. You can see that I had to put the cap below the drive shaft on the other side of the motor. I have run the engine with a heavy pull of freight cars for a good amount of time, the warmest thing was the motor. I can now run this Blunami diesel on 18.5 volts ac. Continuing to try more Blunami's but in smaller AM diesels, am waiting now for another buck converter rated at four amps but a much smaller package, stay tuned for more.

Ray

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I have an update, this is something that will apply especially to American Flyer/ S gauge folks. On another thread there was a recommendation for the voltage regulator from Pololu, these are approximately 3/4" square and rated at 2.8 amps. I ordered one to check out the possibility of using these in American Models diesels supplying DC power to the 2200 Blunami decoder. I tested it wired to a full wave rectifier and a 1000mfd cap and and than wired it to the track, I then powered the track and ran the AM GP 9 with a string of cars for about 30 minutes. The temp of the regulator only got to 105 degrees F, looks like an answer to S gauge conversions.

Another source for voltage regulators is pololu.com. Click on their regulator link.

One that might work in a Plymouth is rated for 50VDC in max, 12v DC out, 2-3 amps and about 3/4” square. Of course you would have to add a rectifier bridge to the input.

More expensive than what is found on ebay and Amazon but its the first I have come across that might fit.

Pete

Thank you Norton

Ray

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