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Calculating Time

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E2K

New Member
Hi guys
How do i calculate time for a circuit or device from its Current?
Example:
If a 10mA LED connect to a 6V 4.5Ah battery with a 1K series resistor what is the maximam time of glowing LED ?
 
E2K said:
Hi guys
How do i calculate time for a circuit or device from its Current?
Example:
If a 10mA LED connect to a 6V 4.5Ah battery with a 1K series resistor what is the maximam time of glowing LED ?

hi,
If you connect a standard LED, which has a forward voltage drop of 1.5V, then you will have 6-1.5= 4.5v across the 1K0.

So the current thru the 1K0 and LED will be 4.5/1000= 4.5mA..

To calculate the endurance of a fully charged 4.5Ah battery, in good condition, you divide the 4.5/.0045 =1000 hours.

This is an approximate calcultation as the current is so low, also the LED will continue to glow when the battery reaches it recommended discharged voltage of about 5.4V. The LED should be disconnected when the battery voltage fall to 5.4V for a lead acid battery.

EDITED:
 
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E2K said:
same formula can use for other circuits like a timer,flasher or others?

Thats correct.
Its important to know the voltage drop across the LED, look at the LED specsheet, then subtract the LED voltage from the battery voltage.
Some of the higher powered LED have voltage drops in the order of 2 to 3Volts or more.

Does that help?
 
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