Simple circuit to test batery from solar panel

[MrMelin]

Hi guys,

I have a PLC with solar panel powered, and I want to know the charge of battery (12VDC), and input the signal to PLC (0-5VDC or 4-20mA)

Any suggestion will be wellcome.

Thanks
Melin

 

[m3]

Hi,

To get a voltage from battery, you nedd a voltage divider in 0-5V input. For calculate a divider, you nedd know a input impedance from PLC. See in PLC manual.

For top charged battery, voltage is 14V, for mesure this put a resistor between positive battery terminal and PLC input, this resistor have 2x input impedance for 0-15V range.

Regards,

M3

 

[dlandry]

Generally, analogue inputs have high impedance and can generally be neglected (if it is not the case, the voltage reading will be inexact). With the high price of the solar energy, you don't want to use too low impedance. If you use too high value resistors, the system will be too sensible to noise. As precision of your analogue input is generally very much that you need, try to protect the input considering the maximum voltage to be 20 V. Your system will be more reliable like this. To evaluate the resistors divider, you can use:

R2 = R1 / (Vmax/5V - 1)

To be relatively immune to noise and with low power use, I propose to use:
R1 = 100K, 1/4 Watt
Vmax = 20 V

Computation give R2 = 33K, 1/4 Watt

Note that the Wattage must be evaluated if you lower the value of the resistors, else the resistors can become too hot (and can become a fire hazard). On your PLC program, you can scale the input to convert the result in the right voltage scale.

 

[hacksaw]

you might consider tracking monitoring the AH delivered by the solar panel as a means to get an early waning to insufficient charging (poor batt. performance,inadequate sun, etc.). the voltage monitoring works but is more or less after the fact