# For Noelw - Sierra Sound and SuperCaps



## toddalin (Jan 4, 2008)

Noel, you have your messages blocked. In response to your question about using supercaps in the Sierra system:

Yes, many have used the 10F, 2.7 V (2.85 V peak) with sucess (or at least no reported failures).

You can leave the charger plug/switch in place, or not. Even if you "pre-charge" the cap it will still bleed down in ~2.5 minutes and have to recharge from the rails.

Also, the voltage that comes out of the Sierra-supplied charger may be higher than the Sierra sound board charges the caps at (mine is). Be sure that the charger voltage is less than that for the 3 caps before you try to charge them that way.

Take care,

Todd


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## noelw (Jan 2, 2008)

Tk's Todd for the comeback. I was getting confused on if have dead caps on start up... so guess I will install a 1 ohm @ 1 watt Resis. in series with the three caps for small voltage safety hit and on the charging jack, rewire it to be in parallel with the caps so I can plug in a 6 volt batt. to keep the sound card on for set up program if needed on the Sierra card. When using the 14 toots or more, and other setting on the card may die before it get set. What you think? Noel


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## toddalin (Jan 4, 2008)

Haven't needed the resistor (I tried it), and it is just that much longer before the caps come to charge, and they die a more painful death (i.e., more "sputtering" before they loose their charge).

While my charger does put out more voltage than the Sierra board, it was still within the working range of the caps and does no harm.

When I programmed my board, I also ran across the "timing" issue, so I put a 6 volt battery pack across the cap (parallel) so I had plenty of time to set the parameters. I don't leave it on there afterwards. The jack would be nice and makes use of it, but once I set the board, it pretty much stays set and is not reprogrammed often.


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## noelw (Jan 2, 2008)

TK's Todd..


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## Dan Pierce (Jan 2, 2008)

For fast discharge and protection I use a diode and resistor in parallel on supercaps.
Resistor for slow charge, and diode for fast discharge when needed. 10 ohm resistor to limit current to .6 amps but full current via the diode for discharge.


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## toddalin (Jan 4, 2008)

Dan Pierce said:


> For fast discharge and protection I use a diode and resistor in parallel on supercaps.
> Resistor for slow charge, and diode for fast discharge when needed. 10 ohm resistor to limit current to .6 amps but full current via the diode for discharge.


Except that through the diode you drop the voltage of the cap so that the system dies faster with more sputter. Been there done that..., just wasn't necessary.


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## Dan Pierce (Jan 2, 2008)

I believe in limiting current draw for charging on super caps and even leds.
I would rather be safe than sorry in protecting my equipment.
Others can do what they want/get away with and a diode only drops .3 volts which in large scale is a very small amount.
Also, I add supercaps on DCC decoders and limiting current is a requirement as the system will shut down for a current surge/trip and all engines will abruptly stop.

So, the resistor limits the charging current, but the diode allows for full current flow to the discharge path as the resistor and diode are in parallel. to the power source.


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