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kaid asked

MPPT 75/15 load output to charge solar generator

So as to not bury the lead, I have a solar panel with 46.6 Voc and a SmartSolar MPPT 75/15. I'd like to use them to charge a Bluetti EB70S from the Load output of the MPPT without anything connected to the Battery output.

The Bluetti has a single input for solar, DC, & AC charging so I can't bypass its MPPT. There is another thread on this site that indicates the SmartSolar MPPT Load output follows voltage profile of the charge profile. If there isn't a battery connected to Battery output, will this work at all? I could also connect the Bluetti from the Battery output of the SmartSolar MPPT, but two MPPT controllers seems like a bad idea.

If you think this whole setup is a square peg in a round hole, you would be right. I was planning on finalizing & installing a 24v system *after* a long summer trip to pick up our new camper and then use it for a month. But then yesterday StarLink announced a service for RV's that would let me do some work from the campground rather than seeking out cell service/wifi/shared workspaces. It requires 120v AC and we leave to pick up our camper in 3 weeks, then straight into our trip. There's no reasonable option for installing a whole new system on the road, let alone sourcing it all.

I have slowly been acquiring components for the permanent install, which currently consist of only a couple of panels (VoC 46.6v) I would be wiring in either series or parallel depending on the MPPT input specs. The panels came with a SmartSolar MPPT 75/15, so I have two of those but hadn't decided yet whether to use them or not in the permanent install.

So, for the immediate need I'm pivoting to purchasing a Bluetti EB70S and keeping it charged with one of my existing panels & the MPPT 75/15 if that will work.

MPPT Controllerssmart solar set-up help
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1 Answer
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kaid answered ·

For other's future reference, I am charging a Bluetti EB70S from the Load output of the MPPT controller without a battery connected. The Bluetti has a single charging port that auto-switches between MPPT solar and a constant voltage DC charger.

In the Victron MPPT, I set the charge profile to 27v for both absorption and float. Then I set the load output to always on. Bluetti is connected to Load, nothing is connected to Battery.

From additional reading about the Victron, the voltage of the load output is set by the voltage of the battery output.

The Victron app reports the battery voltage between 26-27v before slowly dropping to 12.5 - 14v from a steady 80-84 watts from my single 120 watt panel on a partly cloudy day. I'm guessing the Bluetti MPPT is causing the voltage drop. The Bluetti has a max input of 8 amps so at 14v or so I won't be able to parallel a second panel for faster charging.

Given that the Bluetti input is settling into 12v charging range regardless of the 27v setting in the Victron, I'm probably going to just go ahead and connect it to a 12v lead acid battery as well and use the Victron as intended. I was hoping to charge the Bluetti at higher voltage in order to use a second panel.

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