i need to find out what capacitor value i need to provide momentary backup power to a 1Amp load operating at 6V for 1.5 minutes.

i am going to connect this capacitor in parallel with my 6V power supply. if for some reason, my power supply is interrupted, i'll have 1.5 minutes extra time to gracefully shutdown.

would you please explain and let me know formula?

thanks.

 

From Wikipedia:

A farad is the charge in coulombs a capacitor will accept for the potential across it to change 1 volt. A coulomb is 1 ampere second. Example: A 47 mA current causes the voltage across a capacitor to increase 1 volt per second. It therefore has a capacitance of 47 mF. It has the base SI representation of s4·A2·m−2·kg−1.

In simple terms, 1 A with a voltage change of, say 6.5 to 5.5 volts for 1.5 minutes (90 seconds) is a lot. 1st order approximation is 90 F.

John

 

Instead of a huge and expensive capacitor, maybe you should use a little inexpensive rechargeable battery.

 

Yes, the amount of capacitance required is completely impractical in terms of cost and capacitance required (note that a previous poster calculated it to 90 Farads). Even those big capacitors for automotive power amplifiers (the ones with the useless electronics and LEDs on them) are only 1 Farad, and they are big. You would require a large bank (90) of capacitors to achieve the capacitance required. Note that backup power supplies for computers are big, and all are based on batteries.

Capacitors are only used to get rid of AC ripple, or to allow for different DC voltage bias levels, and sometimes in timer circuits. In industry they are typically used for power factor correction to compensate for the inductive load of motors and flourescent lighting balasts.

 

So-called super- or ultra-capacitors are available with adequate capacity. Voltage ratings are 2.7 V per cell, so you would need need 3 in series. They are being sold for UPS applications.

See: http://www.tecategroup.com/store/index.php?main_page=product_info&cPath=18_20_67&products_id=1206

John