I have a SANGEAN RCR-5 Alarm Clock Radio that I use to play its radio each morning at the set alarm time.
The RCR-5 radio has excellent audio quality for such a small unit – not tinny at all, with nice bass and treble. I really like this radio because (1) the radio receiver is sensitive and can easily pull in a distant station that I like; (2) when the radio turns on the volume gradually increases until it reaches the maximum that I set for that alarm – I don’t like to be shocked into wakefulness; (3) it has good audio for its size. This radio has many features but one that is important to me is for the time and settings to be preserved through minor power outages. The RCR-5 claims to preserve time and settings through a 10-minute power outage. This is quite inadequate but worked through 90% of the very brief outages common to where I live. Alas, I noticed in recent months that my RCR-5’s backup capability had shrunk to five seconds. Now that was truly worthless! The clock only cost around $30 so sending it back for repair didn’t make sense – I could buy a new one for what repair was likely to cost.
I purchased a replacement (not a RCR-5) and it will soon be returned. It has a sensitive receiver but the audio quality is terrible – quite tinny – like an old 1970s pocket radio. I decided that it was time to attempt a DIY repair on my RCR-5.
After removing four screws the RCR-5 interior was easily accessible. I quickly located the Super-CAP (See Image 1 & 2 below). What an anemic, puny little Super-CAP – why did they bother! It is unmarked and is about 5mm wide and 1.5mm thick. Also, the capacitor appeared to have leaked. Obviously it had failed, which is why the RCR-5’s advertised 10 minute settings/time backup didn’t work. The voltage across the capacitor in situ was zero. I removed the Super-CAP and measured its feed pins and it was 3.1VDC. Apparently, the capacitor was internally shorted.
I had three Super-CAPs left over from and old project and decided to install them into the RCR-5. These Super-CAPS are rated 10 Farads at 2.7V. While they “might” have survived the slightly higher charging voltage I decided to wire two of the 10F capacitors in series, yielding one 5.4V Super-CAP of 5F. I substituted this new SUPER-Super-CAP in place of the defective RCR-5 original. See Image 3, below.
I haven’t tested how long the new SUPER-Super-CAP will preserve time and settings in the RCR-5 but it kept its memory for the 20-to-30 minutes that it took for me to reassemble the RCR and move back to the bedroom. I don’t intend to test this – I’ll wait for the next prolonged power outage to find out.
UPDATE: We recently had a 2-1/2 hour power outage and the super caps kept the clock running – stations, settings and time preserved! Thankfully we haven;t had a longer outage.