Perfidus

Problem solved as expected, with new OpAmp with compensation terminals, and adjusting offset on the current transducer on board with the coulombmeter. I'm dissapointed by technical support of the Sorotec and Easun, nobody answer to my emails. Anyway, going to the forums was a big idea as I learnt a lot about this type of solar chargers/inverters. Cheers!

Update: Output offset is the result of bad choice for opamp, with large figures for input offset voltage. Because of the gain setting in the OA, 10kohm/100ohm =100x, 10mV of input offset = 1 V output shift. Tested with some improvised compensation circuit, and managed to pull the output of U7 to zero voltage, for the DSP to think that it has zero PV current. The fans stopped, and after 15 minutes the PWM circuit deactivated (no more back feed of battery voltage into solar panels) and "PV charging" with current drain for battery clearly stopped, putting the inverter to OFF, so the firmware does its job properly. Now I order a new op-amp, I selected OPA228 from TI, with 10uV input offset voltage and optional external offset adjust inputs.

It just appear to me: what if the op amp has his output drifted with exactly 1 Volt? It should be easy to check replacing it with another one. Normally if the inputs are tied to the shunt ends, which are at (PV-) 0V, with 100ohm series resistors, the output should be also around 0V with zero PV current... I will go back and trace schematic around this LM308. Edit: actually the output could be offset with a reference voltage in the feedback network so until I trace the schematic I don't know.

A few moments later😀: I found that for PV current there is a shunt after all in this machine. It has 4 resistors marked 2m0 and it's measurements goes to PWM board via opamp code U7. I'm almost sure now that those measurements are further calibrated in software, because on the OA output (pin 6) i found pretty consistent values in respect to real PV current ( measured by my lab power supply that simulates a solar panel. Now i have to guess the calibration procedure.

Ahem. Of course, the discharge battery current is also showing wrong. May I take this as a coincidence or is something wrong with a common piece of hardware? In the photo attached i hooked a 40w load and the battery meter shows almost exactly 43W (3,66 A ) and inverter reads the load as only 1 Amp. The power scale indicates 0W / 0%. Where do i find those traced schematics from Axpert devices? Thanks for help Edit: with a larger load it shows the right current and wattage (10 amps approx and 120W power from battery with 100W load ) so only in the lower range indication is non linear. Good to know!!

I have the same problem with an iSolar SPR 1000 a clone similar with Sorotec Revo VP 12V 1k ( i mean wrong calibration). If you have more info about the subiect it could help me to find the guilty piece. First trouble is the PV current which is registered with about 19 A offset, so the inverter shows about 260W of solar charging even after the panels are disconected. This is the reason why the inverter never stops if it is offgrid and in absence of solar, and so it depletes the battery overnight. The fans also run at full speed. I don't see a shunt in the PWM charging circuit so it might be a hall device that is way offset. Thanks in advance for any help. perfidus