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AC connection to Multiplus 2 10kw

Hi, I am pulling what hair I have left out over this problem. My system is all up and running as an off grid system with Life04 Batteries. I also have several deep discharge leisure batteries and a 24 volt 15KW chinese inverter which is brand new and I had the idea that on a sunny day my solar power can charge up my Lead acids with my Victron 24 volt blue charger and then on poor solar days I could put some extra charge into the lipo's by connecting the 220 volt output of the Chinese inverter to the A/C input of the Victron Multi. and selecting charge only. Seems simple enough!
When I test it, I put the Multi into Charge only mode then switch on the inverter, the Multi flashes a green led in the A/C input display, then there is a clunk of a relay and it goes into an OVERLOAD fault condition, the Cerbo reports
"Warning Inverter overload" There is no way it's overloaded, first of all it's in charge only mode, the charge current was reduced to 20 amp for testing. I set "Shore power on the A/C input, tried Generator still the same, set the shore power current to 30 Amps set the system to accept a wide range of input frequency and a low of 180 to a high of 270 but always the same Overload, Have I a faulty Multi 2 or am I doing something wrong?

Multiplus-II
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Alistair Warburton avatar image Alistair Warburton commented ·
That setup should work, at least it should work if all you setting choices are correct...

I have two multi's as 24/5000 and a 48/5000 connect in seriese, 24 feeding 48. Iam also off grid and this is how I know it should work.

Importent points...
Current limits are neither hard or instant so it is possible to get an overcurrent before the dynamic limit get hold of the situation. I have seen this a few time when trying to connect AC in, for charging, when the battery is very low.
It isnt something I do oftern as I dont generally fully discharge th packs. Mistakes have been made on a couple o occasions though.

In charge only bypass is still possible, as far as I know, so your system could be attempting to power loads, dipping the AC voltage as a result and causing an inverter overload due to high current when charging.
There is only one bridge which is either charging ,idle or inverting,

Have you checked the setting of th ground relay? I had so odd trip issues when I neglected to disable the ground relay switching on the 24.

Have you looked at UPS and Assist settings? I dont think either would be active in charge only mode but you shoud know what is set and what effect that will have in all modes.

Happy to share config files if that helps at all.

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wedgehog avatar image wedgehog Alistair Warburton commented ·
Hi Alistair, thank you for your help and reply, I note everything you say, I wondered if maybe the charge current was too high and it was pulling it down into the fault, so I set the charge current in the Multi to just 20 amps to eliminate it. Made no difference. I have no assistants at all and with the Multi in charge only mode there is no A/C load at all as I only use one A/C output because being off grid the Lifep04's are constantly powering my house, when I select charge mode only, the house A/C is shut down.

Interesting one about the ground relay, The electrical system in my house in th UK does have the Neutral shorted to ground so under normal conditions I do have the ground relay on, I will try it in the off position in charge only mode and see what happens when I select the exteral A/C
UPS? well that's supposed to kick in the batteries if the A/C goes off so I don't really see how that would help.
The assist is supposed to bring in the batteries if the shore power, or mains supply cannot deliver enough, wouldn't make sense because then the multi would be charging itself if you see what I mean. I will try the ground relay tomorrow and let you know, it could be the chinese invertor doesn't like having the N shoreted to ground?


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wedgehog avatar image wedgehog Alistair Warburton commented ·
Hi Alistair, well I just about tried everything today. I started by dissabling the earth relay, made no difference. While we are talking about that, I don't really understand the thing because my house has the neutral and the ground already shorted together so what difference does it make to have the relay on or off in the inverter? it will always effectively be on whether the relay is on or not?

So then I tried UPS, assist, I dropped the output of the inverter to 220 which is what the Chinese inverter gves out. I don't know where you live but if not in the UK, the UK mains is 240v. none of it made any difference, I checked the chinese inverter hadn't got the live and neutrals mixed up, nope. I did notice that when the relay clunks on in the Victron the 220 on the Chinese inverter takes a dive and that may be why it drops out. The Chinese inverter claims to be 15KW. I have tried just about every possible combo of settings even reducing the Victrons charge current to 10 amps so as not to load the other one, even set ud DVC and told it to limit the current to 10 amps, no change. I can only assume that no matter what I set, because the Victron is a 10KW with a peak of 18 it has massive caps which are going to charge no matter what and it's all too much for the Chinese inverter. I was starting to think the Victron charge circuit was U/S but it occured to me that with the Victron in charge only I could switch the house back to mains and feed the grid into the charger. Worked perfectly and instantly, no fancy settings, ups off power assist off weak a/c off I re set the current to 30 amps, no problem, so I guess I will just have to accept it is not going to work with this Chinese crap, I will order a 30 amp 48v charger and see if the Chinese crap can power that.



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