question

timsmithlx avatar image
timsmithlx asked

Multiplus and 150/45 MPPT and VenusGx (Pi3) - do i need a smart shunt

I have an outbuilding at the end of my garden that has solar panels on the roof, and feeds power to a server and 3d printer. Im trying to run this as "off grid" as possible, but if there is not enough solar and batteries drop to empty, then the multiplus to charge them up and do the switch over so i never loose AC to the server / printer.


I currently have the multiplus, and an Epever MPPT Solar Charger


I will have:

1 x 150/45 MPPT Solar Charger

1 x MultiPlus 24/800/16-16 230V

1 x 484ah AGM Battery Array

1 x Pi running Venus OS

1 x SmartyShunt (if required)

2 x VE.Direct Cables (MPPT / shunt)

1 x VE.BUS cable - Multiplus


Question1:

Do i need a smartshunt to measure the Solar charge current even though i will have the MPPT linked to venus os with VE.Direct??

Can the VenusOS not use the data from the MPPT for this already and then have a summed SOC from both MPPT and MULTIPLUS??

I also have a small amount of DC usage from the batteries <10w @ 24v - can i use the same smart shunt for that as the charge side of MPPT, or do i need a 2nd smart shunt?

Question 2:


I want to prioritise the SOLAR to charge the battery array and use as much of that as possible with the MULTIPLUS inverter, only using the MULTIPLUS charger when absolutely necessary, and it sitting in inverter mode the rest of the time.

I do not want the MULTIPLUS to feed back to grid EVER


Whats the best way to do this... ESS? IgnoreAC?

Thanks All


tim :)



Multiplus-IIMPPT SmartSolarVenus OSSmartShunt
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1 Answer
JohnC avatar image
JohnC answered ·

Hi @timsmithlx

A reliable and well tuned SOC is a great asset. The Multi's SOC is adequate if solely using it for charging at a consistent rate, but doesn't cut it when you add in solar, which can vary a lot and upset the 'sync' point.

I grabbed a Smartshunt solely to use the battery charge Current to terminate the mppt's Absorb phase (mppt Tail function). This can be passed across to the mppt by VenusOS (DVCC), and ensures a reliable Abs time, and you can never overcharge your batts. Highly recommended for both reasons.

I wouldn't bother with another for a small DC load. With 'Has DC system' ticked an estimate is made by difference. I find that adequate.

ESS will just overcomplicate things, IgnoreAC will work fine.

Priority is given to solar if the Multi's charge setpoints are set lower than the mppt's. You could even set the Multi to charge at a flat Float V, so when AC isn't ignored it will serve loads and only charge lightly, leaving room in the batts for tomorrow's solar.

I'd probably go with Assistants in the Multi to set the logic, and all the DVCC functions ticked. Tinkerers might step up to NodeRed, just to tinker.

You could 'get by' without a shunt, but will find it brings your system together. If mine broke, I'd get another.

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