Question about RCA RP3721 Clock Radio
What does this alarm clock use to keep time? Is it primarily a waveshaping circuit off of the 60hz AC that clocks digital circuit - or - does it run always off of a crystal time keeping circuit? I assume for battery backup, it has a crystal time keeping circuit. If it does use 60hz AC, how does it switch when power may be detected as low? The problem is that every once and a while the clock gains time, but no AC has been lost (as far as observed). Thanks. Larry Park
They used to use crystals to help the timer ics to keep time but since the development of Micropros. all this is built in to one chip. Now they will use a resonator or a small crystal for the timing clock of the micro but nowdays the manufacture uses that clock to keep all in check. If your gaining time you probably are having problems with your ac duty cycle as this also keeps clocks in check.. This would not affect most devices but could be a problem. But of course a defective Micro could also cause this gain in time And probably is?? Now a battery backup is nothing more then a battery in line with the Microproccesors B+ terminal through of course a diode as well as a voltage limiter resistor to take over the B+ when the units ac supply is absent..
Posted on Mar 24, 2006
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Battery back-up operation
* This clock radio is equipped with
a memory holding system that can
be powered with 2 "AA" batteries
(included). The power failure
protection circuit will not operate
unless battery is installed.
* When normal household power
is interrupted, or AC line cord
is unplugged, the batteries will
power the clock radio to keep
track of time and alarm settings
programmed into memory.
* When the battery backup functions,
the digital display will not light,
however, the function of alarm
still occurs during the power
interruption if remaining battery
power is adequate.
* Normal operation will resume after
AC power is restored so you will not
have to reset the time or the alarm
To install batteries:
1* Remove battery compartment door
(located at the bottom of the radio)
by applying thumb pressure to the
tab on battery door and then lift
the door out and off the cabinet
2* Insert 2 AA batteries (included).
3* Replace the compartment door
Replace batteries every year.
Power is fed to the unit even
when it is not functioning. To
cut the power supply off, the
power cable must be unplugged
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This will cause big problems. It will not work and will
likely cause both inverters to fail. Power
inverters must create the 60Hz sign wave from a crystal controlled internal
frequency driver. It's like a clock that
keeps the timing at 60Hz. 2 independent units will have slightly different
clocks both in time and frequency. This
would cause the output waveform of one unit to be out of phase with the
second. If they are out of phase, they
will look like loads to each other and likely fail. It would be possible if the inverters had a
way to link their clocks or use only one clock. This could be designed in
however I have never seen this feature. You
can hook up multiple inverters to the low voltage side (12VDC), just don't hookup
their 120VAC output side. Hope this
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