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The Williams True Blast Plus sound system is great - except for the instant sound cut-off when switching directions. Does anyone know of a method of preventing complete sound shut-down every time the reversing unit is sequenced? What kind of system could be used? Battery backup? A trickle of current from a capacitor?

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Which version do you have?

00252

If something like the above, can you read the marking on the circled part?  Some other versions have a similar looking part (3-legged) but standing up.  This is likely the voltage regulator chip and its part number would be the first layer of peeling the onion.

You can ballpark capacitor sizing by computing the stored energy required.  For example, if the audio power is 2 Watts and you want to sustain this for, say, 1 second (when there's no track voltage), Energy (in Joules) = Power (in Watts) x Time (in sec), so you need 2 Joules of energy.

A capacitor's stored energy = 1/2 x Capacitance (in Farads) x Voltage x Voltage.  So, for example, it appears this board has two 1000uF capacitors.  Let's say they put them in parallel (2000uF or 0.002 Farads) and they get charged up to 15V which might be typical for running conventional control mode.  That's a stored energy of "only" about 1/4 Joules.

So it's no wonder there's not enough on-board energy to sustain a 1 second power loss.  And of course that energy must also supply the processor chip other electronics - and there are losses so you can never access all of the theoretical stored energy in the capacitors.

The suggested "super-cap" method is probably where to go because this technology has superior stored-energy density vs. the traditional electrolytic capacitor technology as used in the photo.  For about the same size as one of the 1000uF capacitors, you can get a 1 Farad, 5V super-cap for about $3.  If charged to 5V, that's a relatively whopping 12.5 Joules of energy which should be sufficient. 

There are i's to dot and t's to cross but I think it's do-able.

Ought of curiosity, if you are in neutral and crank up track voltage to, say, 18V when pressing direction, does the sound still cut-out as quickly as if you were at, say, 9V when pressing direction?  And/or if you lower the volume (if it's adjustable) can you alter the cut-out time - that is, does sound cut-out as quickly at low volume than full-volume?

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  • 00252

I think we need more info on exactly what he has.  A closeup photo of the board's components would be useful.  If these modules only use 150 mA with horn...I'd think it much less with just the prime mover sound which I'd think relaxes the stored energy requirement.  That is, is it required to maintain sounds while simultaneously pressing the Horn button and the Direction button?

Anyway, if the stored energy requirement goes down to a fraction of a Joule, it almost becomes practical to just crank up the electrolytic capacitor (a few more thousand uF) rather than messing with a super-cap.

Not trying to get too far ahead of myself, but we know the processor in this module must be measuring the track voltage since it has to detect DC offset voltages to trigger the Horn.  I can imagine a design where that same function simply turns off the audio when track voltage is lost for some period of time...rather than letting the drooping voltage cause funny audio thumps, clicks, or pops.  In other words, wouldn't it be annoying to add a super-cap to keep the circuitry running but the software on the board has already shut-off the audio output because it has detected a lack of track voltage!

Last edited by stan2004

A new ERR RS Commander was on the bench, convenient to test.  I connect my bench meter in AC current across a sine wave output Z-4000, connected a speaker, and turned it up to full volume.  The prime mover alone pulled around 80-110ma, it danced around a bit as the voltage (and pitch) changed.  When I blew the horn, I went around 230-240ma max for the current.  It's hard for me to believe the Williams board would draw more, I've seen this ERR board drive two 16 ohm FatBoy speakers to some great volume!

So was this at command voltage - 18V AC?  Then prime mover sound (full volume) is pulling almost 2 Watts and with Horn over 4 Watts.   Now that I think about it, I don't think it's possible to blast the Horn when pressing Direction.  Since Direction removes track voltage, how can there then be a DC offset on the track to activate the Horn?  Or maybe there are train transformers that do so?

So if 2 Watts of power is needed for just the prime mover it does sound like super-cap territory.  It's easy to say just put a low-voltage (5V or whatever) super-cap on the output of a low-voltage regulator but I think some homework is required before firing up the soldering iron.

 

I varied the voltage from around 9 VAC to 18 VAC, it did little to change the current. 

I tried an older RailSounds board on the old ERR RS Commander power base, it got basically identical results.  I did test some older conventional board with the ERR Sound Converter when I was doing the beta test several years ago, none of them draw more than a couple hundred MA in any operation.  I think most of the energy consumed is actually in the amplifier circuit for any of these boards, so I don't think older boards would necessarily draw lots more current.

Without an actual board to look at, it's pretty hard to suggest a specific cure, but I'm sure this should be pretty easy to do for most audio boards.  It would be interesting to see what the board does when the track voltage is removed but it still has internal DC power.

Depending on how long you need to hold up the power, a larger filter cap may be the path of least resistance.

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