# Photovoltaic Charge Controller

#### CoderJohn

Joined May 22, 2014
16

I was messing around with the idea of a circuit that could be used as a basic charge controller and came up with the circuit above. The voltage source and resistor are meant to represent how a potential battery might affect the system depending on the charge on the battery.

I am using a 5 volt source to bias the opamp such that it outputs 13.6 volts constantly. In practice the upper rail voltage of the opamp might be tied to the output of the photovoltaic panel. I am making the assumption that the solar panel will always be outputting atleast 14-18 volts.

On a physical circuit I would probably implement some kind of circuitry to detect if the voltage is less than 14 volts to enable/disable charging. The npn transistor at the negative side of the battery is biased such that it will only allow 40mA to pass through.

I am wondering would this be a viable circuit to charge a battery from a panel assuming the solar panel has high enough voltage to supply the op amps upper rail and if not what recommendations would you make and could you explain why. Additionally on a physical implementation I would probably use either the battery or the panel and a 5 volt regulator to get the 5 volt source.

Note: I am aware this is probably far from efficient I am just curious as to if it would work and whether or not it would destroy a battery or even charge it at all.

Edit: The potentiometer is for adjusting the constant voltage.

Below is the code that can be used with the falstad website's circuit applet to examine the circuit there.

Code:
\$ 1 0.000005 2.9224283781234943 52 5 50
w 112 128 256 128 0
v 32 272 32 192 0 0 40 5 0 0 0.5
w 128 208 128 272 0
w 128 272 32 272 0
w 256 192 352 192 0
r 352 192 352 256 0 10000
r 352 192 352 144 0 40000
w 352 144 432 144 3
w 352 256 352 272 0
w 256 160 256 192 0
174 32 192 112 208 1 10000 0.46040000000000003 Resistance
w 80 208 80 240 0
w 80 240 112 240 0
w 128 192 128 208 0
w 112 240 112 128 0
w 352 272 496 272 0
w 32 192 32 96 0
w 32 96 448 96 0
t 464 192 496 192 0 1 0.5730767538654631 0.49160986557326697 100
r 496 96 496 48 0 30
w 464 192 448 192 0
r 448 192 448 160 0 10750
w 448 160 448 96 0
w 432 144 464 144 0
w 464 144 464 48 0
w 464 48 496 48 1
w 496 208 496 272 0
w 496 176 496 160 0
v 496 160 496 128 0 0 40 13.6 0 0 0.5
w 496 128 496 96 0
p 528 96 528 160 1 0
w 496 160 528 160 0
w 528 96 496 96 0
409 256 144 352 144 3 0.6 -12.753501166068662 1 0
172 304 64 304 16 0 7 15.04 18 10 0 0.5 Voltage
w 304 224 304 176 0
w 128 272 304 272 0
w 352 272 304 272 0
g 304 272 304 304 0
w 304 224 304 272 0
w 304 112 304 64 0

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