Re: Big capacitors

In article <43e8dfd3$0$64357$892e7fe2@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Nick <me@xxxxxxxxxxx> wrote:

I need them to keep an ADSL modem alive during mains brownout
conditions. Tried a cheap UPS but it didn't stop the brownouts reaching
the modem and latching the firmware/hardware.

So rather than spend £400 on a true UPS, I thought I'd try a big
capacitor and a relay (to stop the capacitor shorting the supply) on the
low voltage side of the wall wart.

Depending on the modem's voltage and current requirements, you might
find it easier and cheaper to use a lead-acid "gel cell" battery. Use
a wall wart which can be adjusted to "float" the battery at its
preferred long-term standby voltage, while providing adequate power
to the modem.

A lot of consumer-electronics devices of that sort will take DC
voltages over a fairly wide range, and regulate down to 5 volts
internally. A "12-volt" 2 amp-hour gel cell floating at 13.5 volts,
running an ADSL modem drawing less than an ampere, would provide lots
of ride-through time.

--
Dave Platt <dplatt@xxxxxxxxxxxx> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
.

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