# Simulating Battery Charge using Fixed Load Voltage Readings of PV Panel

Discussion in 'The Projects Forum' started by pochd, Mar 26, 2011.

1. ### pochd Thread Starter New Member

May 6, 2010
13
0
Is it possible to simulate battery charging (battery is never full/continuous discharge) of a 20W PV(Photon PM 0020) system equipped with a charge controller(Conergy SCC 5 eco) and 12 V lead acid battery given just voltage readings across a 12 ohm resistor taken at 1 minute intervals? I thought of just rejecting power outputs below battery voltage. Would this be correct?

2. ### Bernard AAC Fanatic!

Aug 7, 2008
4,175
397
Should give a reasonable approximation of charging capability, Cut off will be about 12.7 V, float charge,just a few 10s of mAs; most charging above 13V

3. ### russpatterson Member

Feb 1, 2010
351
16
I simulate panels with a bench power supply all the time. Just get the open circuit current and voltage of your panel (let me know if you don't know how). Then set your supply to not deliver more than the amps your panel puts out at full sun. I usually set the bench supply at around 16V and it gets pulled down to the battery voltage when the current is limited (either by your charge controller or the supply itself).

Don't let your battery over charge or it'll seriously turn it into a big capacitor that won't hold a charge more than a few minutes.

4. ### pochd Thread Starter New Member

May 6, 2010
13
0
I interpret this as having to disregard any panel(kWh) of integration(trapezoidal) wherein any of the voltage readings defining such would fall under 12.7 volts(as caused by low irradiance/cloudy conditions). I assume this is so since batteries would not charge if the source's voltage is lower than the batt. Is this correct? What would be your suggested equation to simulate battery power accumulation?

5. ### pochd Thread Starter New Member

May 6, 2010
13
0
I interpret this as having to disregard any panel(kWh) of integration(trapezoidal) wherein any of the voltage readings defining such would fall under 12.7 volts(as caused by low irradiance/cloudy conditions). I assume this is so since batteries would not charge if the source's voltage is lower than the batt. Is this correct? What would be your suggested equation to simulate battery power accumulation?

6. ### Bernard AAC Fanatic!

Aug 7, 2008
4,175
397
I did not find the SCC 5 controller; but a smart controller can convert almost any combination V & I from panel to most efficient charging current. I have found that over a usefull range that if a load resistor which lowers panel V out to about 75% of open circuit V will track peak power point over a fairly wide range of solar conditions. The 12 Ω might be fairly close. I would use cut-off V at 13V if neglecting charge controller capabilities. V X V / R = P, as R is fixed ,time spaced V measurements should give a reasonable measure of panel capacity.

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