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Supercaps in place of battery in Sierra


Screwy Nick
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On another forum someone posted a schematic using super capacitors (three 2.7v 6 - 10 Farad wired in series) in the older Sierra sound systems.  All of my batteries have gone below the ability to re-charge due to my lack of attention.  Here are my results:

Base Test: Sierra switch ON, no battery, no caps, system stuttered and came alive @ 12V.
First Test: Sierra switch ON, caps in place of battery, ran it for 45 sec, (I was slow to react on the video) removed track power and the sound continued for 60 sec before the caps were fully discharged just as I was about to add track power. 
Second Test: Switch ON, ran for 60 sec, removed track power. Sound system idled for 45 sec, restored track power and sound ramped up. 
Third Test: Ran for 30 sec and disconnected the caps. When the caps were reconnected the system started up with no stuttering. I published the First test, have the videos of the other two and if requested will upload them also. 

 

 

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No, pick up continuity is not the issue, the Sierra performs smoothly no matter what the track condition, even without track power, like if you stopped for water or to pic up passengers,  the sound system keeps producing for a period of time, then cycles down.  My problem is I can't properly maintain the batteries.  They are Gel Cell and if neglected for more than 3 or 4 months they discharge to the point they will no longer accept a charge.  Using the Supercaps just drop the loco on the track and away you go, no matter how long they have been sitting.     

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Now to assemble the components for the 'low voltage cut off' circuit.  Not really necessary, just keeps some charge in the caps so the next start up doesn't start with the stuttering, and for me, just because.  

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And it works.  I just need to find the 'sweet spot' on the potentiometer,  the Supercaps are storing the juice instead of a battery.   Also can switch the system OFF and the caps will still store, but this was more fun. 

image.thumb.png.0766f4ea8b43bfaffaf31813a0d51f5a.png

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Here's what I learned:  The person who designed the circuit runs his trains at 14volts or more.  He confirmed to me that anything below 10 and it reverts back to operating as though it has no battery, and the super caps discharge.  So in effect, not for me who operates on straight DC.  BUT, since I put all that into it, going to continue testing and messaging the circuit till I get the results I want, or close. 

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  • 4 weeks later...

A lot has happened since then:  An entirely new design, by someone much more qualified than I, still using Super Caps.  I did message the design a little and it works perfectly, almost.    

  I didn't use a combination Buck/Boost board, found more choice of boosters that started at a lower voltage and added a limiter to the output. Sounds contradictory, but not.  The booster can take 4V of track power and boost it up to 8, and it keeps climbing until it peaks at about 14 then levels out and stays at track power.  The limiter keeps the voltage at a constant 7.5 to charge the caps and run the board through out the entire range of track power.  Also the sound will continue to run for 75 seconds after track power is 0.  If the main switch to the Sierra board is turned off before that time, the caps still hold the remaining charge till turned back on at a later date.   I didn't use the C1, R1 or the D1 diode just after R1.  Also I didn't advance the circuit from the Super caps directly to the Sierra board.  I connected them to the Battery Input leads, so the On/Off switch is still in the circuit.  This allows the switch to go OFF and the caps will still hold the charge.  I am hoping, with the guidance of the engineer that designed the circuit, to use the contacts in the 6V relays from the previous print to replace the I/O switch. The charging jack is still in the circuit in case anyone is brave enough to attempt to charge the caps with the power supply Sierra supplied, I haven't tried that yet.  All suggestions are appreciated.     As an after thought:  I wonder just how many of us out there still have the older Sountraxx boards.  They haven't been supported by Sierra for about 14 years and the little batteries are no longer available.  Maybe I am just having fun all by myself!!!!   

EDIT:  recently received an explanation for the need of R1, easing the dead short upon start up of the cap charging which is causing B1 to heat. I will rectify both the print and board.  

 

   

Sierra Battery replacement print.jpg

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The auto off timing circuit is presently on paper, just waiting for components. For my first conversion I am using an Aristocraft FA locomotive set. The motors on these units start the wheels rolling at 4 volts at the track, same as the boost board coming into effect. To give myself a small window of operation I added diodes to drop the track voltage to the trucks. The wheels now start to move at 5.5V. I will have to change Set Up Step 1: Start Voltage setting on the Sierra board to correspond with the new movement.  

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  • 3 weeks later...

   I didn't abandon the project, it took a while to receive all the components for the time out circuit. I tested using power from a transformer and an ohm meter to watch the contacts. A BEAUTIFUL SIGHT. Variable resistor came from factory set in the center so 5K ohms. The input voltage also effects the relay hold time. Using 6V the hold time was 45 sec, 7V was 60 sec. So between the input voltage and the variable resistor there should be a very wide range of cut off timing. Interfacing the two boards is a simple matter of picking up power from the limiter output and using the NO contacts in place of the I/O switch, but before I do that I want to play some more. I'm sure this has helped many of us make use of existing if outdated sound systems. Toddalin, great engineering and design and once again THANK YOU VERY MUCH. 

Attached is the final schematic.  I had fun, and the result was very rewarding. 

EDIT: Top pic is just the cut off timing circuit, the bottom pic is the actual battery replacement circuit.

fullsizeoutput_555.jpeg

Sierra Battery replacement FINAL.jpg

fullsizeoutput_55c.jpeg

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Made another timing board this morning, with a wiring error, easy fix. There seem to be variations in this set of components, so adjusting the variable resistor for the time I want. It is critical that I measure the limiter output so I can adjust the timing properly when setting it up on the bench. 

    Cataract surgery '21 days and a wake up', can't come soon enough.

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Playing: using 7V input, after the initial charge takes minimum 60 sec to get a full charge, longer had no effect but shorter lessened the time out. Using the uxcel Variable Resistors 10K ohm 5W from Ebay. (ref the pic) from factory A-B is 55K, B-C50k, pretty close to the 60 sec I wanted. Found 2 revolution of the adjustment screw changed the release time by 4 seconds, up or down depending on which connections you used and what direction you turned the screw. 
B-C CCW raised, CW lowered resistance----- A-B CCW lowered, CW raised. Hope that makes it easier for those doing this. Also if the relay doesn't go off normal when applying power, the diode is in backwards----19 days and a wake up.

fullsizeoutput_55e.jpeg

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  • 2 months later...
 
 

My F units have a speaker in each.  Sound board is in the A unit and a connector brings the sound to the speaker in the B unit.  Can't tell it's the same source, different speaker and they are wired opposite polarity.  Too lazy to do this set. 

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Additional design: Geep has the optional Time out circuit. The board needs 5V on track ONLY ON INITIAL start, and there is no stuttering as the caps still have power from the last use. Second shows there's plenty of time for a slow freight manouver, I have this one timed for 45sec. Yup, still havin' fun. 

 

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