question

Hi.

I Would start to look at the AC cable lenghts. Are the input cables the same lenght and the output cables the same length.

also make sure the inverter is running the latest firmware, as it has a parallel issue with 433.

let me know

Hi @oliver.claude

It could be that one of the units is defective, try running them as stand-alone to see if one of them is causing this.

PS. with issues like this: when you are sure the wiring is ok, the fastest way to get things resolved is to contact your dealer / distributor.

Edit - please also do the parallel online training in Victron Professional.

And post a system wiring diagram, and some photos of the installation. It may help to see.

Ok. So this morning I replaced all the wiring on the AC side. I ran overly long cables from my distribution board to my inverters. They are less than 1 meter apart, but my cables are all 3 meters in length. They are all exactly the same type and thickness and all circuit breakers are identical.

I cant believe it is a cable problem. As I have now done this on both AC and DC side.

Will see if I have time to swap the inverters around on the wall again tomorrow. This way I can check if the problem moves with the inverter or stays with the cabling/installation.

OK, I have made some progress.

I was busy testing all the inverters to see if they function as standalone units. (I expected one to be faulty.) And low and behold they both work 100% in standalone mode.

Afterwards, I was busy putting all the old configs back.

I put them in parallel and sent the config. Then I configured the master inverter and sent all the changes to all the inverters. (Without any assistants setup). I was shocked to see that the inverters were producing the same voltages, normally the slave inverter was always a good 20V below the master inverter. I then set up an ESS assistant on only the master, sent the config and they are still producing the same Voltage on AC1 out.

This is the first time I have got the two voltages on the outputs to be the same before bridging the outputs.

Question: Do I have to put another ESS assistant on the slave? At the moment I'm running without and seem to be doing fine!

Lastly, I then connected all the outputs to the house and started testing with large loads, and for the first time, the slave is actually sending some power. They are not close the balanced, but at least it is sending something. Will push the output higher tonight and see how close to balanced they are.

I have noticed that the current through the inverters, when in passthrough mode, are not perfectly balanced, so I will focus on getting them perfect first, then focus more on the DC side.

The system has now had a few days to stabilize and I found that the AC cables running through my inverters are carrying the same current during passthrough. Or withing my 95% tolerance criteria anyway. So happy with the AC cables.

The low inverter is still only carrying 25% of the total load, so next, I will redo/reconnect all the DC cables. Starting with the DC bolts and I will make sure to tighten them all to the same torque. Each inverter has 6 bolts/lug connections across the positive and negative cables.

If that doesn't balance the inverters better. I will consider adding lugs to my cables running into my fuse boxes to make the connections more uniform.

Will keep everyone updated.

PS. Thanks a million for everyone that has posted/messaged me ideas to hunt down.

Claude

@oliver.claude have you managed to solve the problem? I am experiencing the same problem and have not been able to resolve it yet.

Experiencing a similar problem. 2 x MP II in parallel which overloads on grid failure and switches off. Load is usually between 3 and 4 kw when this happens. Have checked all wiring and connections...