Decided to try something different, replaced my generator and solar with 2-EG4 Lifepower4 batteries.

[Zapper77]

Setup -
2 Lifepower4 Batteries
Victron 150/35 MPPT
2 BattleBorn
3000 watt inverter.

I didn't bother to bring any solar panels this time.

12 kWh of Lithium Batteries lasted 5 nights and 5 days with enough reserve for 24 hours. I ran the water heater on electric two nights (consumed around 3 kWh). Refrigerator was on propane the entire time. Batteries were used to Charge devices, two personal fans, microwave, led lights and 16 hours of TV.

I didn't run the generator or hookup solar.
Outside temperature 60-65 low and 75-80 high.

 

[sunshine_eggo]

Okay... to confirm:

48V EG4 batteries connected to PV input of 150/35 outputting to 12V battleborns/inverter.

Where is the fuse on the inlet of the MPPT to keep from exceeding the PV input current significantly? From community, Victron denounces use of the MPPT this way; however, when it's clear the user has their mind made up, they insist on using a fuse on the inlet, which should be done between any source and the load anyway.

Otherwise, cool experiment.

 

[justinm001]

Okay... to confirm:

48V EG4 batteries connected to PV input of 150/35 outputting to 12V battleborns/inverter.

Where is the fuse on the inlet of the MPPT to keep from exceeding the PV input current significantly? From community, Victron denounces use of the MPPT this way; however, when it's clear the user has their mind made up, they insist on using a fuse on the inlet, which should be done between any source and the load anyway.

Otherwise, cool experiment.

The batteries have fuses themselves so shouldn't that be enough? I didn't think the MPPT can draw more amperage than its rated for regardless of how much power is available its just the voltage to be concerned with. I thought you could overload your MPPT with solar without any risk.

 

[Samsonite801]

Okay... to confirm:

48V EG4 batteries connected to PV input of 150/35 outputting to 12V battleborns/inverter.

Where is the fuse on the inlet of the MPPT to keep from exceeding the PV input current significantly? From community, Victron denounces use of the MPPT this way; however, when it's clear the user has their mind made up, they insist on using a fuse on the inlet, which should be done between any source and the load anyway.

Otherwise, cool experiment.

Yeah, according to the pics (and what he is saying), it looks like he is feeding the batteries to the PV input on the CC hehe, theoretically it should work fine (depending on the brand of CC). I saw someone do that on a Prius but at 220vdc and works... And the others with the Chevy Bolts and such. I've never tried it myself, but have contemplated experimenting around with the idea...

BTW, I've seen in the Victron Specs sheets as they do current-limit themselves on the PV inputs, but they also specify a hard maximum to avoid on the solar panel wiring (for amps, based on the panel specs), so I suppose it could be possible to overcurrent under certain circumstances? You would think it wouldn't draw more than the 12v battery's max CC output current. Perhaps on an MPPT sweep or something it could also draw it up to limits for a second. I might put an amp-clamp on and do some testing and monitoring... Draw the 12v battery down to low limits and see what is max PV circuit current possible draw.

 

[Zapper77]

Okay... to confirm:

48V EG4 batteries connected to PV input of 150/35 outputting to 12V battleborns/inverter.

Where is the fuse on the inlet of the MPPT to keep from exceeding the PV input current significantly? From community, Victron denounces use of the MPPT this way; however, when it's clear the user has their mind made up, they insist on using a fuse on the inlet, which should be done between any source and the load anyway.

Otherwise, cool experiment.

I set the current limit in the MPPT
Fuse is in-line on both ends

 

[sunshine_eggo]

I set the current limit in the MPPT
Fuse is in-line on both ends

I'm pretty familiar with Victron stuff. You set the OUTPUT current, not the input.

Your unit has a PV input current limit of 40A. Your battery can exceed that greatly.

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-150-35-&-150-45-EN.pdf

Is the fuse on the PV side?

 

[sunshine_eggo]

BTW, I've seen in the Victron Specs sheets as they do current-limit themselves on the PV inputs, but they also specify a hard maximum to avoid on the solar panel wiring (for amps, based on the panel specs), so I suppose it could be possible to overcurrent under certain circumstances

No they do not. They current limit their output

 

[Samsonite801]

No they do not. They current limit their output

I had been referring to the footnote (1a) on the Specs sheets, my Victron 250|100 has a similar footnote, saying it will limit the input if the PV watts number exceeds what is on the nominal PV power...




The part where I wasn't 100% sure is what the Max PV short circuit current number they list. Perhaps it is limited to that number being the maximum it can pull from PV. But looking at the footnote 2) then adds confusion to the other footnote 1a)...

 

[sunshine_eggo]

I had been referring to the footnote (1a) on the Specs sheets, my Victron 250|100 has a similar footnote, saying it will limit the input if the PV watts number exceeds what is on the nominal PV power...

The part where I wasn't 100% sure is what the Max PV short circuit current number they list. Perhaps it is limited to that number being the maximum it can pull from PV. But looking at the footnote 2) then adds confusion to the other footnote 1a)...

1a) is clear because it indicates power, not current.
2) address current, not power.

While fuses/breakers are typically installed to protect wires, this is a use case for protecting the equipment. That battery could deliver 10kW and be within its ratings. That's 200A. Since the PV input current limit is 40A, and the output is 35A, there's literally no way it can pull more current from 48V than it can deliver to 12V. 35A * 12V / 48V = 8.75A. Thus, a 10-15A fuse on the PV input should be sufficient.

 

[Samsonite801]

1a) is clear because it indicates power, not current.
2) address current, not power.

While fuses/breakers are typically installed to protect wires, this is a use case for protecting the equipment. That battery could deliver 10kW and be within its ratings. That's 200A. Since the PV input current limit is 40A, and the output is 35A, there's literally no way it can pull more current from 48V than it can deliver to 12V. 35A * 12V / 48V = 6.25A. Thus, a 10-15A fuse on the PV input should be sufficient.

Good point of distinction (thanks for providing that), I was overlooking that detail in the difference, power vs amps. I've seen that in the Victron specs for years and overlooked that silly detail, but makes sense, obvious as it seems, like duh to me now hehe. So of course, one would be at more risk of going over on amps at lower voltages, rather than running closer to PV peak voltage, you'd be at less risk when reaching max watts, where input amps would still be well under limit.

 

[Zapper77]

You can double check my math. I'm using a 12 amp ADH FUSE on the PV side that is listed as fast acting. (Example below)

Example of Fuse and Holder


My math

 

[sunshine_eggo]

You can double check my math. I'm using a 12 amp ADH FUSE on the PV side that is listed as fast acting. (Example below)

It wasn't obvious to me in the OP, but I can see it now.

My math

Good math, and it's conservative.