Addendum on the charger / welder

The new welder arrives!

I ordered one of the cheapest inverter welders I could find on Amazon that had a decent power output and duty cycle.

"Arc Welder Dual Voltage 110V-220V IGBT Inverter DC Welding Machine 200A High Frequency Household Smart Welder for Novice Welders fits below 3.2mm weling rods"

Cost was $119.00 not including tax. For comparison, the battery charger I previously had (which I went through two of them!) was $179.00. It also had no monitoring or charging customization (which I have via the MPPT). It also was not nearly as efficient in converting grid power to charge power. It was also limited to 40 amps.

While the previous charger was using around 15 amps, this was drawing a little over 9 amps for the same output to the MPPT. This makes it safe to use with a "smart plug" which is rated for 15 amps.

Results

The graph above is what I would call a "mixed day". I had solar input, but it was spotty and because of this and my old batteries, I had to top them off with the welder. What you see in the graph is input from the panels from 9:00am until dark at 6:00pm and then the welder coming online at around 6:30pm until around 9:00pm.

Note that I am still running parallel MPPT's. Because of this the welder began the full 4 stage cycle all over again because it was a different MPPT. Another thing I will bring to your attention is the voltage drop at about 5:30pm. This is very indicative of a bad cell or battery in the chain.

Summary

As long as things keep up like this, and there are no surprises, I doubt I will ever go back to a separate grid charger. Not only was my experience with that horrible, but the experience with this is so far wildly better than expected.

Addendum 1-11-2020

Yesterday I had windows installed on my house. Because of this I had to disconnect and move the panels. This gives me a "trace" on the system with only the welder as a charger (without suppliment from the panels) for a 24 hour period.

There are a couple "telling things" from this trace. The biggest thing is the overall condition of the batteries.

What this has been telling me about the batteries is I somewhere have a weak or dead cell. This can be seen by how the quickly voltage pulls down but then stabilizes. The other telling thing is the intervals of voltage drop. I still dont know for sure what these are but my speculation is that is the defrost cycle on the fridge (the only load on the system).

As for the charge cycle, this tells me that this setup will be very good for litium batteries. What you are seeing is what the batteries can readily absorb. This is shown by the low voltage and high wattage (blue being volts, green being watts). As the voltage reaches its peak you can see the wattage dropping off rapidly. This is followed by welder shutoff and then the fall off of the "skin charge" on the batteries (most likely by another defrost cycle).

Since its a crappy day weather wise, I think I will leave the panels disconnected. Tonight I will run a charge cycle but will keep an eye on the voltage level. After the "peak" I will then shut down the welder and see how the batteries hold up without a long "equalize" cycle. If my hunch is right, then I may be able to reach a "full days charge" with 1 1/2 hours of charging. That would actually be closer to what I saw with charge versus discharge wattage.

Addendum 1-16-2020

Below is the 12 hour trace of todays power. The first item of note is the PV panels and the welder/charger running at the same time. with a low light day the second is the evening top off with only the welder/charger providing power.

This is what the readout looks like when running the two MPPT's in parallel