Reading 60v DC via Arduino

Hello,

I have 12v dc batteries connected in series making a total of 60v. Each Battery is 12v 200amp. Now I want to monitor the voltages of the batteries combined . So for That I have used a voltage divider where.

Vin = 60v
R1 = 220k
R2 = 18k

Vout = 4.5v

Now I have used 4 watts resistors for this purpose, I want to know how can i calculate a safe wattage resistor for this purpose. Or if there is any other safer alternative, as I am not feeling very safe with this voltage divider.

Will it get too hot or burn or something. Please help me out with this i have googled a lot but you guys are great and always help me out .

Regards

P = U * U / R

Railroader:
P = U * U / R

U = ?

Umair78:
U = ?

Basics.

P=IV
V=IR

Thus P= V*V/R

There is always Ohm's law to help you with that.

220K + 18K = 238K Total resistance
60V / 238K = 0.00025 A Current through voltage divider and hence each resistor. (I = E/R)
0.00025 * 0.00025 * 18K = 0.00114W Power dissipated by 18K resistor (II * R)
0.00025 * 0.00025 * 220K = 0.01398W Power dissipated by 220K resistor (I
I * R)

groundFungus:
There is always Ohm's law to help you with that.

220K + 18K = 238K Total resistance
60V / 238K = 0.00025 A Current through voltage divider and hence each resistor. (I = E/R)
0.00025 * 0.00025 * 18K = 0.00114W Power dissipated by 18K resistor (II * R)
0.00025 * 0.00025 * 220K = 0.01398W Power dissipated by 220K resistor (I
I * R)

Dear,
Thank you for the reply. But my question is will my 18k 4 watt and 220k 4 watt resistors hold up to these batteries ?

Umair78:
Dear,
Thank you for the reply. But my question is will my 18k 4 watt and 220k 4 watt resistors hold up to these batteries ?

Is 4 watts greater than the wattage you calculate per resistor times 2?

adwsystems:
Is 4 watts greater than the wattage you calculate per resistor times 2?

No, It is not .

Umair78:
No, It is not .

Interesting. Did you come up with the same numbers as Groundfungus? What power dissipation did you come up with for each resistor (ie., what wattages did you calculate each resistor would dissipate)?

Perhaps a quick study of basic DC circuit theory would help you understand the relationship between current, voltage, resistance and power.

@adwsystems

V ?

Railroader:
@adwsystems

V ?

@Railroader

formulas.gif

U ?

formulas.gif

You also need to figure some input protection to cover the case if a wire falling off and putting 60v on an input .

How are you powering the (unspecified) Arduino.
Using default Aref might result in an unstable battery voltage readout.
Because any change in the Arduino supply will change battery voltage readout with the same percentage.
Could be better to use a ~1:60 voltage divider, and the more stable 1.1volt internal reference in code.
Leo..

@adwsystems
During my education to a Master of Science in Electronical Engineering the letter "U" was used for voltage even in international litterature.