Troubleshooting a ?Kitchen Timer? I made some 20 years ago, I found the culprit was the capacitor, nominally 1500uF but now lifeless. Its actual original value is unknown. There are 8 markings on the knob of t he timer?s linear pot (1 to 8 minutes) and 11 on the knob of a 1Px12W rotary switch (from 10 to 150 minutes) . As a first (arguably optimistic ) first step I want to calculate its value, for the replacement. It? ?s not practical to replacie the pot and all 11 resistances, some of them with more than one resistor and/or reposition all 19 markings individually . Nor does my temperament allow me to bin it.
The alarm is activated when C?s voltage from a 9.0V supply reaches1.45V. If I stop-watch the time (in seconds) taken to trigger the alarm wit h a known value of C (uF) and R (megohms), what formula will then give me the new value of C needed to change that time to its original value, as mar ked please?
I will then average such estimates from the 8 tests using the pot and as ma ny from the longer duration rotary switch values as patience allows.
BTW, I expect to have to parallel two electrolytics to get close to whateve r value is calculated. Will that have a detrimental effect on leakage?
Terry, East Grinstead, UK