# 480 VDC Series Battery Bank - Solar PV Charging Current Feedback Control Circuit

I have a 480VDC Lead Acid Battery Bank (40 x 12VDC 50Ahr Batteries in Series) directly coupled to a 5.0 Kilowatt Solar PV Array [with an output range of 560-580 VDC and maximum output of 8.9 Amps). This simple coupled circuit works well but I want to add a feedback activated control device that limits the Battery Bank Charging Current to precisely 3.0 Amps maximum as the Solar Irradiation and PV Array Output Current varies. I am not concerned with the minimum Charging Current just the 3.0 Amp maximum. Any circuit suggestions would be appreciated.

• If the charge current is limited like you say which is a good idea what do you intend to do with the excess electricity? Commented Nov 18, 2015 at 11:42
• In principle all you need is a constant current regulator. These can be constructed from a floating voltage regulator and a feedback resistor - see diy-audio-guide.com/constant-current-source.html - but you need careful design and specialist components at those voltages and powers
– Icy
Commented Nov 18, 2015 at 12:04
• What output voltage will the solar bank rise to in full sunlight when supplying only 3 amps? Commented Nov 18, 2015 at 12:59
• Autistic the solar array services a varying load. Commented Nov 18, 2015 at 20:40
• Andy aka it will never exceed 600 volts Commented Nov 18, 2015 at 20:42

The schematic shows two simple linear floating current regulators connected in parallel.

With guesses of what the voltage ranges that the circuit has to operate, the voltage differential can be 150V. So the power such a linear regulator has to dissipate would be up to 150V x 3A = 450W.

450W seem like a lot to waste, but the sun energy would have converted to heat outside if it were not collected anyway.

So now, how to have such a floating current regulator dissipates 450W. I think one way is to duplicate it as many times as necessary and connect them in parallel. For example, with 10 of them, each one is set up to pass 0.3A and may dissipate up to 45W.

On one of the regulator, there is a suggestion of how to connect a DC fan.

simulate this circuit – Schematic created using CircuitLab

• Thanks @rioaxe here is an alt design logically similar to yours for your comment please. Sensing Cct - I visualize a precision [known] low value R in series with the batt bank [low batt side] such as a current shunt. From the known R [shunt R] and known I [3.0 A] - V Out [in millivolts] is calculated and used as a “trigger” that invokes a Control Cct attenuating the batt charging current by providing an alternative parallel current path. The 2 paths share the amps capability only when 3 A is resolved by the Sense Cct. At other current values [< 3 A] the control Cct remains off & draws no A. Commented Nov 19, 2015 at 20:27
• The alternative parallel path would be around 480V, so potentially even more power dissipation is involved. Take what have been given at face values, the solar panel supplies up to 5000W. You want to limit the battery charging to around 1500W (3A x 500V) by shunting the extra power. When there is no other load, then the shunt has to consume up to 5000W - 1500W = 3500W. Commented Nov 20, 2015 at 3:02