how do i find out what size capacitor to use?

Question

i have a hand held radio with memory and 2 batts.when 1st batt goes dead and i remove and install 2nd batt i lose memory. i want to install a capacitor to hold memory for a few seconds(20 or 30) while i change batts.i dont want someone to tell me what capacitor to use,i need to know the formula to find out because i want to use it for other projects. thanks....plz use laymens terms

Answer 1

If it's a decent radio, it already contains a small battery, probably lithium-ion, to maintain the memories while no battery is connected. If that's not keeping the memories, it probably needs to be replaced. Meanwhile, to improve your chances, be sure the power is turned off before changing batteries.

If the radio has an AC supply/charger that can be connected to the radio (rather than to the battery), you can probably use that while changing batteries. If it doesn't, then you wouldn't have a good place to connect a capacitor. There certainly wouldn't be room enough inside the radio to install a capacitor with enough capacity for the purpose.

Check the radio manual for standby current or power-off current. With that, use the reference to calculate the capacitance needed to maintain your current flow for the 20 seconds without dropping the voltage more than 15-20%.

Answer 2

Using the "Research your answer" bar, go to Wikipedia & type in "Formulas for capacitance", then left click the search button.Scroll down to "Capacitor", then left click. Then scroll down until you find the formula(s) you need. Good luck from a fellow technician.