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Author Topic: A fun way to void your warranty! (playing out in the woods)  (Read 1094 times)


  • Apprentice
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A fun way to void your warranty! (playing out in the woods)
« on: September 28, 2013, 05:49:07 pm »
Problem:  Wanting to play my MiniBrute "out" - as in the backyard, in the garage, at a party, etc.... but
without being tethered to the AC line.

Additional data: I wanted to use my Crate portable battery-powered amp - the Crate uses a 12 volt
lead-acid battery- about 8 amp-hours worth of it.

The Crate even has a matching 12 volt power 5.5mm x 2.8mm power plug/socket.   BUT - the socket
on the Crate is "strictly input" - there's a diode in there so you can't pull power OUT of the plug.   I *could*
short the diode, but then there'd be no protection for the Crate against a reverse-biased supply.  And,
if my cord shorted, there'd be a direct short against the battery and quite the fire!

The fix: grab a "polyfuse" - a little thing that looks like a ceramic capacitor, but it's really a self-resetting
fuse- a chunk of polysilicon that conducts electricity with only a little resistance- but a BIG sensitivity to
temperature.  If there's a short, the polyfuse gets hot.  As it gets hot, the resistance goes WAY up,
WAY fast, limiting the current to a few mA.  Remove the short, and the polyfuse cools off, and resets

So, I soldered the polyfuse across the diode, and ... WHEEE !   IT WORKS!!!  The MiniBrute gets
clean 12.2 volts of power from the battery in the amplifier, and the amplifier isn't compromised in terms
of safety and short-circuit protection.  The polyfuse I used is a Bourns 1.1 amp polyfuse, available for
maybe fifty cents with your next order to DigiKey.

Of course, this isn't the "standard" power supply, so it may void the MiniBrute's warranty but hey, you
can't have everything.

    - Bill


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