Schneider SW4024 Mystery

Desert Rat

This is regarding a system I installed many years ago at a neighbor's house. The house is unoccupied at present, and I check on things there every couple of weeks. 3096 watt solar array, Schneider 4024 inverter, SCP control panel, 2 Outback charge controllers, 2 24V 200AH EG4-LL LiFePO batteries (installed August 2022), 9KW Generac generator (not installed by me), and Magnum Energy auto start controller. The generator has not been used for several years. Last month the battery voltage went very low (don't ask), and the inverter shut down. I charged the batteries back to 100%, but the inverter would not come back on. No AC output, and the SCP display was blank. I contacted Schneider, and after several back and forth emails, the tech asked me to disconnect the AC input wires from the generator and try again. I couldn't imagine how this could help, but I went ahead and did so. I disconnected the AC input from the generator, and still nothing. I reconnected the AC input, and turned on the inverter breaker once again. Lo and behold the inverter and SCP came on, and are now working normally. I asked the tech to explain, and he only said that this often helps. The system could have just as easily had no AC input connected, so I don't get it. Can anyone explain?

BB.

I am guessing the genset was not running at the time (no AC output from generator to inverter)?

Is the genset connected to AC1 (utility) input or AC2 (genset) input of the Schneider inverter?

-Bill

Desert Rat

No, the generator was not running. There is only one set of AC input terminals on this inverter.

BB.

That is wild...

In very olden times, some automatic gensets transfer/control boxes would feed a little bit of DC power on the AC (or 120 VDC) lines... This was so that the "genset controller" could detect if a load was turned on (i.e., genset was off, then some lights/heater/motor was cycled on, the controller would see the small current flow and start the genset... The last system I saw this on was probably close to 100 years old now...

But something like this (feeding any sort of voltage out the AC lines to detect loads) would be one way of "confusing" the inverter.

Another possibility would be if the inverter was setup in Hybrid mode (i.e., feed energy back to the "utility" in "GT" mode...

During the low battery adventure, the inverter tried to feed energy back to the genset and did some sort of fault shutdown (generator/transfer switch shutdown, did not qualify for GT Mode?)....

Many generators use a simple 120 VAC charger for the genset starting battery... No AC power to genset (off grid), the genset battery would go dead (one solution was a smallish solar panel+charge controller connected directly to genset starting battery). Again, a "weird load" on the genset AC connection to inverter?

-Bill

Desert Rat

BB. said:

During the low battery adventure, the inverter tried to feed energy back to the genset and did some sort of fault shutdown (generator/transfer switch shutdown, did not qualify for GT Mode?)....

Thanks, Bill. I'm thinking that you're on the right track here.  Even though the auto start controller was turned off, there must have been some sort of communication between the inverter and generator/AGS that triggered a fault.