3-phase on-grid system, 28kWh battery

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Here’s my latest project:

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I have had my 10kWp east/west PV with a Huawei Sun2000 inverter for about a year now, and have now (nearly) completed it with an ESS that will have the whole house on the AC Out side, including the (cFos PowerBrain) EVSE. The transfer capacity of the MP-II 3000 fits nicely with the 32 Amps that are available.

3 MultiPlus-II 3000, 2 batteries with 16 EVE LF280K cells each, JK Inverter BMSes, and a modded Lynx Power In are the main components.

The positive side of each battery has a NH1 250A fuse, because that one actually is rated above the expected short circuit currents the LiFePOs can produce (there’s 125A Mega fuses on the Lynx for the MPs). The cells are compressed with springs, because then one can measure their compressed length and calculate the force; probably overkill, but springs are cheap and easy to integrate.

On the software side, my grid meter that is interfaced via AMS reader is integrated via MQTT (venus-os_dbus-mqtt-grid), as is the PV inverter (where I wrote a perl script to read the values via ModBus and export to MQTT and then read it with venus-os_dbus-mqtt-pv) and the EVCC service that manages my EVSE comes via dbus-evcc. The BMSes are interfaced via dbus-serialbattery and dbus-aggregate-batteries, VenusOS runs on a Pi 4 with a Waveshare isolated CAN/RS485 hat. A lot of data points are exported to graphite so I can monitor every detail in nice colorful grafana charts :slight_smile:

The fact that this all works not only makes me happy as an IT guy who attended an EE school decades ago, but is also a testament to the openness and flexibility of the Victron ecosystem.

All that needs to be done now is for the electrician to connect the AC side of things, and we’re done. (The system is currently experimentally connected to one MP on AC-In on a 10A circuit to allow me to configure and test things, and it’s already working pretty nicely).

PS: did you know you can cut your 70mm² cables easily and cleanly with a sharp axe and a big hammer, in case you forgot to order appropriate cable shears?

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:rofl:

Love it

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Nice. The NH1 fuse could potentially be smaller sized with the MultiPlus Ii 3000 Correct?

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My thinking was: I have 3x 3000VA, and at my cutoff voltage of 2.9V/cell that gives 194A; so I went one size up for peaks. Also, that calculation is based on a single battery bank, so I can run everything even if one is down for maintenance.

But others have shown systems with NH00 and 160A fuses, so that certainly is also OK.

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Have you ever measured the actual maximum current draw at your batteries?

Think about it this way; the sooner the fuse(s) burns up, instead of a cell, the safer your battery is. A little headroom is ok of course. The main problem is that people will find out that their fuse(s) was/were too big when it is too late already.

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Those fuses are primarily to protect from dead shorts, like dropping a wrench across the busbars. I hope any overload would be handled by the BMS. I hope I’ll never know whether I am correct with this…
(Also, there are 125A Mega fuses on the Lynx outputs to each Multi).

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the basic rule for fusing is: you can not make the fuse current rating bigger than the wire connected to the fuse can carry, otherwise your wire becomes the fuse :slight_smile:

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That is true, but I also keep an eye on the maximum C rating of the battery… For example. My battery wires can easily handle 200A, hardly even fit on a MultiPlus II, but the EVE prismatic cells that I have, do actually have a maximum C rating of 0.5 (EVE MB31) and that simply means that I need to rate the T class fuse to 150A. In short. It’s not just the wires that you may want to protect, but your battery as well.