Schneider XW+ 6848 AC2 breaker setting

Riley

Does anybody have thoughts on how “fussy” the setting is for the generator AC2 breaker size on the XW+ 6848? I see from older threads that other manufacturers settings aren’t all that accurate and some tweaking might be required.  

Secondly, if the inverter detects the AC2 current is exceeding 80% of the breaker setting, does it disqualify the AC2 source OR back-off the charging of batteries? OR maybe either depending on the scenerio.

Note: it seems very conservative that we derate a 40A wired circuit to 30A for the breaker and then derate the load another 20% within the generator SW. I know that’s the normal derating for breakers and appliance loads but in this case, it might be excessive when dealing with in rush currents and fast detection monitoring software in the inverter. 

The XW manual states that the invertor backs off the battery charging as the AC2 current approaches 80% of AC2. While I can see sometimes it reduces the charging current if the load is fairly steady/constant but I think if a pump (or dishwasher heater element) switches on, the inrush current might quickly exceed the AC2 setting and cause the AC2 to be disqualified and it drops out (relay click and stops charging until requalified).

I am aware that the disqualification of AC2 and “unplanned” relay drop out is hard on the inverter components (relay contacts I assume) so I really try to avoid this (hence my post).

Note that I am running a small AC2 breaker (30A and 8 AWG wiring) to a 12KW 240V generator. I can see that the currents between L1/L2 are balanced (except maybe with the dishwasher element on).

The generator cable needs to be upgraded after installing my new 12KW (larger) generator, but I won’t be able to get to that until summertime (buried cable). The new 12KW is steady as a rock under this light load so I don’t think the frequency is dropping. Perhaps the voltage has a quick drop with the inrush current (due to cable loss) but that’s hard to see without a storage scope.

I am thinking of pushing up the AC2 setting slightly above the 30A breaker to see if that improves things OR reducing AC2 voltage lower limit as an experiment until I can get the cable/breaker replaced/upgraded.

Thoughts?

RCinFLA

I dislike they changed the name of what should be called AC input current limit to 'AC breaker amperage'.

The limit tries to avoid having AC input current exceed the user set limit.  This is great when using a generator AC input to avoid overloading the generator.   There are several limiting factors to keeping the AC input current below the set value.  Most common is surge AC loads like a motor start up surge current.  The inverter has to detect and response to the sudden current increase which takes some time.  A few milliseconds of excessive leak through will make it to AC input above the set current limit before inverter can react and supplement the load current.

Second is current sensor accuracy.  CT transformers have poor accuracy outside of 10-90% of their rated current.  To be conservative they may cutback some percentage lower than actual user setting.

AC input current limiting uses inverter/battery power to supplement AC output load in excess of AC input current limit setting.  AC output has priority on available AC input power, so charging from AC input source is backed down first.  It does not shut down inverter, at least directly.  If inverter supplementing requires more power from inverter then its surge limit it may shut down inverter due to an overload situation.  The momentary current leak through to AC input loading may cause a generator to bog down causing inverter to release from generator due to a sudden frequency shift by a bogged down rpm of generator.

Victron inverters have an advertised feature that dynamically activates AC input current limiting at a lower level of current based rate of rise of load current.  It will start supplementing by inverter/battery power early if it detects a rapid rate of load increase.  Not sure how effective this is as there is not a lot of time to get visibility to increasing loads and react to it early.  If might be a little better than waiting for the actual AC input current to approach limit before engaging supplementing by inverter.

Riley

Thanks, that aligns with my understanding.

What I am wondering is if it's possible that the inverter would disqualify AC2 because of the AC2 current exceeding 80% of the breaker setting? I would expect it to reduce the charging rate but maybe in my case, it can't do that fast enough so it just drops AC2 and goes back to invertor mode. 

I am going to try some experiments with raising AC2 setting.