Adri76

I've checked and the pv voltage and output voltages are 100% correct, so it's only the batt voltage that is a problem. If I can replace 1 or all the resistors on each of the rails with a single pot, I should be able to adjust the voltage to match the actual voltage, or will it create another error when the voltage changes? It's been a while since I've used voltage dividers.

There's a pic on the 1st page of this post showing the firmware versions. Let me know if you need more info.

I just got an idea, maybe I should replace the resitors with variable resistors so i can adjust the voltage

I'm going to try that. At this point I'm a bit fed up with the inverter as it seems to be impossible to track the problem. As soon as I've had it open and disassembled it starts working fine for a few hours and then the voltage starts moving up or down, and it is random, so there's almost no way to find the problem and without some kind of circuit diagram and my limited knowledge of these inverters it seems like a battle I cannot win.

Is it possible to use the inverter without the controller or control it manually?

The only problem would be if the inverter thinks that the battery is low it will cut out. I'm not sure how to bypass the low voltage disconnect.

I think maybe I should just get a stand-alone mppt charge controller and pure sinewave inverter and just use an arduino with solid-state relays to do the grid-solar switching and call it a day. So I can tell it to use solar as much as possible and just switch to grid when the batteries reaches a low cutoff voltage.

It does look like the resistors are connected to the battery terminals if you look at the tracks on the pcb.

The Axpert type 3kva units were selling for about R4500 a while ago, now it's R7k plus. 2kva Units are sold out everywhere.

The problem is that I'm not at home during the day and a while ago it took the batteries to 29v on solar and was displaying 26v so it was trying to charge the batteries although it was already above the safe cutoff voltage. I do not want to risk damaging the batteries, I would rather get a new inverter. I've been looking for a inverter for almost a month now, but nobody has stock and the people who have want to charge almost double the normal price as there is a stock shortage at the moment. Catch 22

Last night the inverter was at 24.9v and the real voltage was 24.6v. Then after I connected the power at 27v it was 100% This morning the inverter was at 27v and the batteries at 26v

This morning the inverter is off by 1v again, I think I will just scrap it and get a new one.

I've now connected power from the grid to the inverter to boost the battery voltage a bit and after about 3 min the voltage on the external voltmeter matched the inverter voltage.

Ok, so I've removed the "suspect" resistor and replaced it with a non-smd one. Now my external voltmeter and multimeter shows 24.6v and the inverter shows 24.9v, so only 0.3v difference. If it stays like that I can live with it and will just change the settings to accommodate the 0.3v difference. I will check tomorrow to see if it changes again. Thanks for everyone's input.

All the resistor marked 1004 on my board measures about 0.8mohm, but the 1st one fluctuates a lot it starts at about 0.47m and then slowly goes up to about 0.7m, the other stays constant. Is that even possible or might it be my multimeter.

I think it's exactly the same hardware. Are the voltage dividers (resistors) on the back at the bottom? I am going to try and resolder the resistors to see if that might solve my problem with the incorrect voltage readings. I wonder if the individual resistors can be replaced with single non-surface mount ones. (replace the whole bank of resistors with a single one of the same value as the combined value)

Strange that inside, your inverter looks like mine, but the screen differs.

It seems like mine has newer firmware, and I don't have problems with the charge voltages when it is read correctly. It charges as expected from solar and grid, but after a while my voltage readings vary and it under and over reads the battery voltage. If there is a way for me to download the firmware from my unit I could mail it to you, but I don't really know if it is possible.

Hi Thanks for the info, I have not yet found the problem with mine reading the wrong voltages and this will help as I can now have a look at the voltage sensor.

Here's a pic of the control board.

I checked this morning and it was reading 2v too high, this afternoon it is reading 2v too low. The control board has 2 connectors, where would I find pin 5 and 6?

Ok, so I've cleaned everything again and sprayed the pcb's front and back with q30. I let everything dry, and connected it to the battery and now it's showing 1v too high. (Actual voltage 25.4v and inverter is showing 26.8v) I'm out of ideas. I suppose it would be impossible to get a circuit diagram for the motherboard.

It looks like this should work, one of my suppliers stock this. http://www.q20.com.my/products/q30/

Ok, thanks, I will have a look.

I was thinking of using some kind of corrosion protection spray, but most of them are oily and would attract dust and probably make things worse.