I know this is a crazy question but do you happen to have a link or maybe specs to the transformers within that inverter or those inverters?
I don't. But I know there's three big transformers in there. I seen 'em when we had the covers off installing our inverters.
That 50 amps on the inverter output could very well be 250 amps at 48vdc on the input
It's more than that. I had 63 amps on the Fluke (with the house loads on). So it's more like 700+ amps with dual inverters (on 24 volt), 350+ amps on 48V. You get a voltage dip at the bus when they do that. So even if the bank is at 25 volts, the voltage dip will probably pull the bus down to 23.5 (24 volt system) when that 700 amp surge hits.
This is what I've been saying - if your bank can't maintain the voltage above 22 input to the inverter (with these particular inverters) they go into a cascade and kick out because they "see" overload. Already BTDT before I replaced my battery bank last April. When we first put these inverters in on April 4 last year the dealer told me my battery bank wasn't going to cut it. I thought, like DanB, that I had enough battery. But the dealer was right. $10,000 worth of batteries later I can run 'em at Full Dawg.
And I got a huge four bar DC power bus designed for 2,000 amps. If your power bus is just a couple bolts screwed into a piece of plywood I have my doubts you got enough parallel feeds to it to run two of these inverters at Max Dawg.
After we got our new battery bank even a dead short between the "hots" in the main panel won't shut them down - it just trips the mains in the inverters.
What I gathered is that DanB has an old forklift battery that he plays musical cells in when ever a cell goes tits up. And he's feeding two inverters with one series string of those cells. I got six series/parallel strings @ 1,310 amps EACH feeding mine. And the voltage of the system don't make any difference because for a given battery bank every cell in the bank has to deliver the same amps for the same watts, regardless of operating system voltage. The only difference is the cables from the bus to the inverters, which have to be bigger on 24 volt. Otherwise my sW Plus 4024's got the same surge capacity as his SW5548's.
If his new cord "fixed it", then it's all fine and will probably fill his needs. But I got an education on the fact that it takes power to make power if you want to be able to use big inverters to their full capacity. For us, where we got 240 volt water heating, electric range, electric clothes dryer, and everything my wife wanted, we use them at full capacity on a regular basis. When I picked 'em out the RE dealer where I got them told me that if we want to do all that there's only one inverter you can buy that's going to do it and stand up to the task day in and day out. But you can't run 'em on 1,200 amp-hours worth of batteries.
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Chris
Edit: I would bet you a shiny new nickel that if DanB would take the slave inverter out of the system and just run his welder with one inverter with a step-up transformer, that his problem would go away and one inverter would start the welder just fine. It really sounds to me like he got these inverters, bolted them to the wall, and forgot to install the rest of the system it takes to run dual inverters on split phase power (batteries, leg balancing transformer, and a four bar bus that splits the output of the bank for each inverter).