# Anti-Sputter & Instant Recovery When Using SuperCaps with the Sierra Soundtraxx



## toddalin (Jan 4, 2008)

I devised a circuit that will shut down the Sierra Sound Board powered by supercaps just before the caps run out of juice (~4.6 volts) and start motorboating.

Additionally, when the system is re-powered, it starts from 4.6 volts, rather than 0 volts, so recovery is instant.

After the first use, it also takes a big amperage surge off the board (1.3-1.4 amps) that occurs when starting from a discharged cap.

Put a voltmeter on the cap and adjust the pot so that the relay opens at ~4.6 Volts. If the pot is adjusted incorrectly either the system will motorboat because you're letting too much voltage to the relay holding it open so the voltage to the board gets too low and motorboats, or the sound cuts off earlier than it could because you are opening the relay before you needed to to avoid motorboating. The actual value of the pot is ~1K, but this is very sensitive.

If you find the relay "chatters" (mine didn't), put a capacitor across its coil. Use a 16 volt capacitor and start with a small value (e.g., 16 mfd) increasing until the relay latches and the chatter goes away. Watch the polarity on the cap and the relay is polarity sensitive.


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## toddalin (Jan 4, 2008)

I made a change to the schematic. In the prior version, when the supercap was disconnected, it would still slowly discharge through the pot and relay coil (~1,450 ohms) or about 3 milliamps.

This was necessary to let the big cap charge in either the off state (though ~1,000 ohms) or on state (directly) of the relay. If the cap could not charge in the off state, it would draw too much current when switched on pulling it from the relay coil and this would unlatch the relay causing it to chattter.

I revised the schematic to totally isolate the cap and it now holds its charge indefinitely when the relay disconnects. A small 10 mfd cap across the relay charges instantly and holds the relay on avoiding the chatter.


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## toddalin (Jan 4, 2008)

I found that the value of the pot is fairly critical and my pots weren't giving good consistency. Also, some of the relays show better consistency in their drop-out than others.

We want the relay to consistently drop out when the cap is between 4.45 and 4.6 volts, with lower being better in that it lets the sound run longer before disconnecting. Below 4.40-4.45 volts, the Sierra SoundTraxx units will sputter.

Most of the referenced Aromat relays (I checked eight of them a dozen times each after breaking them in >100 times each) dropout fairly consistently within 0.1-0.2 volt, but some will sometimes spuriously go lower on occasion. If that happens, there would be a bit of sputter from the sound unit, but it still disconnects and never drains down and starts right up as compared to when relay isn't in there. Buy a couple and check them for the most consistent. The others are still fine and well within spec and you will eventually find use for them.

The pots I have didn't work well in that they were inconsistent in that they could also result in sputtering or not connecting the relay on occasion, especially when/after handling. So I figured out the value of the pot and replaced it with fixed value resistors. Now it consistently breaks at 4.47 volts, just before the sputter. You need to figure this resistance out for each relay as even a few ohms can make a difference.

Finally, I changed the value of C2 to 30 mfd. It works fine, maybe better than the 10 mfd, and I had it.

If it's of interest to some, maybe I could make a video showing an engine equipped with supercaps and no relay, and the engine with the relay.


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