[SOLVED] regarding calculation of Resistor Voltage and Power rating

[yviswanathbe]

Hi,

Can some body help on the following.

I have a battery with 12 cells(each 1.8V) connected in series. I am designing Battery Monitoring System with LTC6802-1, Battery Stack Monitor(linear Technologies). as per the recommendation from linear tech i have connected all the cells with a Low pass Filter to the LTC chip (R=100ohm and C=100n).

Now i want to calculate power rating of the resistor and the maximum voltage.

if i have chosen 0.25W as power rating, the maximum Voltage to be applied to the resistor is
square root(P*R). Therefore max Voltage = 5V. But at the 12th cell the voltage will be 18V.

is this right? if i am wrong some body please correct and tell me how can i choose the resistor (both power rating and Voltage).

Thanks and Regards,
Viswanath

 

[alexan_e]

P=V*I and I=V/R
so P = V²/R so V= √(P*R)
but this voltage refers to the voltage across the resistor not the voltage of the batteries.

The resistor is just there to limit the current when the mosfet turns on to discharge a single battery (the 100 ohm is connected across a single cell) in which case you will have a voltage of about 1.8v so 1.8²/100=0.0324W

Alex