08-02-2017, 10:03 PM
Okay, progress today, EXCELLENT.
Today I reset the breakers on the autotransformer, and voila, everything powered back up!
After talking to Outback a little more, now I understand how the system is set up:
1. Both inverters are wired in series, so each one feeds one of the two 120V legs in the inverter subpanel.
2. In addition, the transformer is wired between the two legs of the subpanel.
3. The inverters are configured in "Outback stacking" mode, wherein one is the master and one becomes the "OB slave".
4. When the master inverter observes no incoming shore/gen voltage, it switches to invert mode and engages a relay in the transformer that puts the coils into the circuit.
4b. At this point, even though the master inverter is wired to L1, the transformer can shift up to 25A (3kW) onto L2 to supply any loads there. Basically, the first inverter in the stack is allowed to service all the loads on the entire subpanel.
5. "Outback stacking" really means "only power up the second inverter if the first inverter's load exceeds 1@A." So, if the total load on the subpanel gets above about 1.4kW, the second inverter will spin up and share the load. In this 2.8kW*2 config on my coach, that means 5.6kW can go to any single load or combination on L1+L2.
When the autotransformer tripped its coil breakers, there was no more balancing transformer between L1 and L2. The master inverter was powering up just fine, but it could only supply power to L1 loads. Moreover, because L1 on my coach is just the compressor and some TVs and a microwave, the load never got high enough to trigger L2 on. But my refrigerator and other critical loads are on L2!
If one doesn't care for the autotransformer, or it fails for some reason, one can just switch off the autotransformer and reconfigure the slave inverter as a "Classic slave" instead of "OB slave." Then, both inverters will power up all the time and supply L1 and L2 independently. This does mean, though, that it would be harder to drive one or more roof airs given the relative lack of headroom.
As to why the autotransformer tripped? Newell says "oh, we see that all the time." Outback says that there is probably a flaw in the way the neutral bonding happens when switching from shore to battery and that we might need to look at that.
As it happens, I'm planning to rip and replace the entire electrical system, so this is not something that will make my list of things to follow up on. But I did learn a little something today.
Whew!
Today I reset the breakers on the autotransformer, and voila, everything powered back up!
After talking to Outback a little more, now I understand how the system is set up:
1. Both inverters are wired in series, so each one feeds one of the two 120V legs in the inverter subpanel.
2. In addition, the transformer is wired between the two legs of the subpanel.
3. The inverters are configured in "Outback stacking" mode, wherein one is the master and one becomes the "OB slave".
4. When the master inverter observes no incoming shore/gen voltage, it switches to invert mode and engages a relay in the transformer that puts the coils into the circuit.
4b. At this point, even though the master inverter is wired to L1, the transformer can shift up to 25A (3kW) onto L2 to supply any loads there. Basically, the first inverter in the stack is allowed to service all the loads on the entire subpanel.
5. "Outback stacking" really means "only power up the second inverter if the first inverter's load exceeds 1@A." So, if the total load on the subpanel gets above about 1.4kW, the second inverter will spin up and share the load. In this 2.8kW*2 config on my coach, that means 5.6kW can go to any single load or combination on L1+L2.
When the autotransformer tripped its coil breakers, there was no more balancing transformer between L1 and L2. The master inverter was powering up just fine, but it could only supply power to L1 loads. Moreover, because L1 on my coach is just the compressor and some TVs and a microwave, the load never got high enough to trigger L2 on. But my refrigerator and other critical loads are on L2!
If one doesn't care for the autotransformer, or it fails for some reason, one can just switch off the autotransformer and reconfigure the slave inverter as a "Classic slave" instead of "OB slave." Then, both inverters will power up all the time and supply L1 and L2 independently. This does mean, though, that it would be harder to drive one or more roof airs given the relative lack of headroom.
As to why the autotransformer tripped? Newell says "oh, we see that all the time." Outback says that there is probably a flaw in the way the neutral bonding happens when switching from shore to battery and that we might need to look at that.
As it happens, I'm planning to rip and replace the entire electrical system, so this is not something that will make my list of things to follow up on. But I did learn a little something today.
Whew!
2008 Newell #1234
Boulder, CO