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What battery voltage should I auto connect / disconnect my inverter load ?

I'm sure this has probably been discussed before but cannot find a definitive answer...

I have a 650W off grid solar PV system with a Victron MPPT 100/20 charger, four 95Ah Exide AGM batteries linked as 2 x 24v pairs and a Victron 800W 240v inverter. I'm powering my computer servers, as they run 24/7, via a UPS that allows me to manually transfer the power connection from grid mains to PV power and back manually without interrruption. The computers are drawing ~250-300 Watts at present.

I'm building an automatic switch to handle the switching between grid mains and PV power, PV power having priority when available, else grid mains being connected. This has to be self contained due to its physical location.

I have an Arduino SBC monitoring the PV and battery voltages and currents, the plan being to use the Arduino to control the inverter remote on-off with a relay, hence causing the (remote) automatic power switch to connect the PV power to my computers when it's on and grid mains when it's off. I also have a Raspberry Pi running the Victron Venus OS.

I've been running the system for a couple of months, manually switching the power between grid mains and PV power based on the weather and data from the Arduino monitor and Venus OS.

I've trawled through endless notes and discussions and come to the conclusion that I should disable the Victron inverter when the battery voltage drops to ~24v on load, which seems to indicate ~50% battery discharge. I should re-enable the inverter when the battery voltage reaches ~26.0v on charge but off load. This appears to give me a sensible cycle between grid and solar power whilst attempting to maximise the life of the AGM batteries.

I'd appreciate any comments on this scheme from those much more knowledgable than me on this. I'm aware I can probably achieve this set up using standard Victron equipment but there's no fun in 'leggo electronics' :-)



paulm asked
paulm commented ·

1 Answer

Inrush current Quattro 230V 48/10000VA for BMS dimensioning


I am currently looking to build or buy a battery pack for my old Quattro 230V 48/10000VA unit. Talking to some manufacturers they are a bit hesitant to recommend battery packs due to the fact that the Quattro apparently have a quite high inrush current due to the large inductor/capacitor inside the unit. They are a bit vague on it, but are recommending me mush larger battery packs than what i want at this point.

Are there any recommendations regarding what peak inrush currents I can expect with the Quattro 10000 VA unit ? I guess that I will need to find a BMS with sufficient inrush rating based on that.

Or is a precharge recommended/needed when using the Quattro 10000VA together with lithium packs with BMS ?

jontm asked
netzerodude commented ·

3 Answers

Odd behavior from alarm port on BP-100

Hello, I'm preparing to use a BP-100 in a 24V LiFePO4 system, to disconnect DC loads in an under-voltage event, and as a convenient cut-off switch for those same loads.

I did some testing with my bench supply, and it behaves as expected - it detected system voltage, and I was able to select a specific set of parameters.

My issue is with the alarm feature. I'd like to have it illuminate an LED-resistor pair on my main panel to indicate an imminent disconnect. This should happen 12 seconds after a low-voltage state is detected by the BP, with loads disconnecting at 90 seconds.

That all goes to schedule, except that when reading potential between the alarm port and ground with a multimeter, I get some strange readings. I get about 1.74V initially, and at the 12-second mark, this drops to 5-6 mV. Needless to say, an LED wired in here doesn't work.

My electrical experience is very limited, but I've confirmed multiple times that the BP is set to mode A7. Appreciate any insight from the folks here.

merlmabase asked

0 Answers

Full solar Setup Advice

Hi Everyone

We're going completely offgrid due to the distance we are from power lines. I'm needing some guidance on a good offgrid setup and how to go about building it and programming it. Here's what I'm planning on using:

- Victron 48/500/70

- Victron Colour control GX

- Victron 85 amp controller

- JA Modue Solar 390W panels

- BYD 4.0kwh x4 with BMU and unit OR 4x Pylontech 3.55kwh

- Timber ground mount with flush mount system

I'm having a couple of electrician buddies coming around to give me a hand installing it all but they haven't every installed offgrid solar before.

My questions are:

1. Is installation a fairly straightforward process for your average electrician or even home handy man?

2. Is there anything I need to be aware of before we get to work?

3. Is the programming fairly straight forward?

4. Is there any issues with either of these setups or recommendations on a better setup?

5. Good bang for buck?

Thanks in advance!

lcollis asked
kevgermany answered ·

3 Answers

Off grid system - need guidance

Hi there.

Trying to size my system correctly with Victron products.

I am going to setup a 3 phase system using 3x multiplus II/3000/48V + 2x Smart Solar MPPT RS

I have a DIY 20 KWH battery with batrium BMS.

I will feed grid into the inverters.

- How will the multiplus act, if i pull more than 3000 watt from one phase? I see peak is 6000 watt, but there must be a limit for how long time it can deliver 6000w peak?

- What will happen if i install the system without a battery, for starters?

- Is it nessecary for the Victron to talk to my Batrium BMS - the unit should be able to measure the battery voltage by itself?

- Can i prioritize the system to deliver power from panels, before delivering from battery?

m1kkel asked
Matthias Lange - DE answered ·

1 Answer

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