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mildred avatar image
mildred asked

second battery bank on the MultiPlus grid ?

HI,


I have a working system with PV panels charging 220Ah/48V victron batteries connected to a MultiPlus providing AC, and optionally recharged by grid or (soon) a fuel generator. It is monitored by a VenusOS device.


I have the opportunity to have a second different battery bank (I already got them) and I would like to use it to extend the capacity of the system. The batteries are very differebt and I'd not want to connect them in DC with the first bank.


I wanted to know if it was possible to connect them on the AC local grid, possibly giving more power (sometimes the loads exceeds the first multiplus capacity). I'd imagine connecting them to a Quattro or Multiplus. Is it possible ? How can the second battery bank be instructed to recharge when the generator is up or on excess solar energy, and discharge when load is needed ? Is it automatic somehow ?


Additional question. When I have excess solar energy available, I'd like to power up some devices (heat up the water tank). Is there some way to do that ? At a distance (much like how the electrical grid sends signals over the wire to trigger the day/night mode)


Thank you

MultiPlus Quattro Inverter ChargerCCGX Color Controlgrid
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alan avatar image
alan answered ·

It’s definitely possible to add them to another multi and have that unit connected in series with the other unit. Ac out to ac in.

it’s also possible to connect the second multi to the same venus device with a mk3 adapter

However monitoring is limited to the device menus data.


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alan avatar image
alan answered ·

You can't run 2 multi's in parallel off two different banks.


The pwm pulse length (which determines the ac voltage of the sine wave, 400 different pulses per 1/50th of a second) is dictated by the master unit.

If the DC supply voltage of the two units is different, then so will the AC voltage between the units. Resulting in current flow between the units/banks and uneven AC output between them.

Even off the same bank, hence same voltage, if the DC wiring is not symmetrical then the two unit will supply uneven current flow


Parallel units require to be hooked up to the same battery bank, with as even resistance and rating as possible DC wiring.


https://www.victronenergy.com/live/ve.bus:manual_parallel_and_three_phase_systems


Even though the above link states the same thing for 3/split phase, it may be possible to use 2 different banks this way, as long as those phases are separate but in that case I just simply wouldn’t and have them running completely separate, or just series them.


as for controlling depth of discharge, if you run the second unit in ESS, this will help control. And would need a separate venus device, the raspberry pi or venus gx are the cheapest options.

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Jmarc avatar image
Jmarc answered ·

I would recommend to have two identical Multi in parallel each fed from the separate battery banks. Thus the venus can monitor the system as one unit. charging profile For each battery will have to be set-up. you should not use dvcc.

Monitoring of the battery will be limited. You could have a separate battery monitor for the second battery bank. Data still can be viewed on the individual pages.

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Jmarc avatar image
Jmarc answered ·

I was incorrect. Please disregard my answer...

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mildred avatar image
mildred answered ·

I didn't think of putting them in series, that's a good idea. It limits the max power to the second multi power though.


I was originally thinking of a grid tie inverter hooked up to a battery bank. Perhaps like this : https://www.powerconceptsnz.com/technology/5kw-grid-tied-battery-inverter/ (but I don't know how it works and it requires the multi to accept an energy source, not load, on AC out)

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alan avatar image alan commented ·

What you have linked is essentially exactly the same as a multiplus

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