Sunsynk 8k + External Victron MPPT

Would it be possible to use an external MPPT like a Victron Smartsolar 250/100 in conjunction with my Sunsynk 8k charging the 24kwh Lifepo4 battery bank ?

Let’s say the Sunsynk is maxed out on connected PV and one adds extra panels and the Victron MPPT.

Technically, how would this work in terms of which component limits/controls the charging current ?

The Victron mppt works on volts, if the battery voltage is below setpoint the mppt will charge and when the battery reaches voltage it will stop… In this case you will not be able to controll the charge current.

I can think of a way to do it, but you would need some more blue toys to make it work. (assuming your battery can communicate with blue?)


Would you not be able to hookup a basic grid tied inverter to the aux input?

A grid tie can work but you need to ensure that the grid tie inverter output is lower than your loads if you do not feedback to the grid as the sunsynk will not be able to stop the excess generation.

I’ve used a hoymiles microinverter on my 5kw and it worked great until the battery was fully charged and the excess power had no where to go. I would then see a lot more power being fed back to grid.

I used the aux port but the sunsynk was not able to control the hoymiles. Eventually I created automation to enable and disable the zero export based on the battery soc.


If you are using CAN port for communication between battery and inverter

Yes it is possible. Like Jaco stated “need some more blue toys” You would need a GX device that would share the CAN communication
I have setup and have been using it for about a year now. Works perfectly !!!

Technically, how would this work in terms of which component limits/controls the charging current ?
Battery controls both inverter mppt and external mppt via CAN port (as Jaco stated assuming battery can communicate with blue) in my case I have pylontechs

The main problem with hooking up additional chargers to the battery, is that the main device (which thinks it is in sole control) cannot account for the extra current going into the battery, so its state of charge estimation will be wrong.

If the inverter gets its SOC reading from the battery anyway (via CAN-bus), then there should be no problem.

There is however no way the MPPT will know that it should current limit. You could add all the extra goodies to communicate the battery current limit to the MPPT(s), but it would not know how much of the “budget” was already filled by the Sunsynk that is already in the system. It’s going to be hacky no matter how you look at it.

However, this only matters if you have a battery that is extremely picky about current limits. In my experience, batteries will only squeeze down on the current control right at the top, and even then it is more of a suggestion than a rule (they generally don’t switch off if you exceed it, unless they get hot), so if you configure that extra MPPT to aim just a little lower than the peak voltage where the battery is full, it might work just fine.

I would not expect such a setup to make more power available for loads. It will only help to recharge the battery a bit faster. I agree with others that if you want more load-carrying capacity (while on grid), install a PV-inverter.

Does anyone know if the Sunsynk supports PV-inverters on its output?

If one has to buy a GX device and an MPPT and it’s still a hack at the end of all that, is it not easier to sell the SunSynk and then get a Victron inverter too? Then you can have any mix/match of MPPTs that works for you.


Haha! I was thinking the exact same thing. Which is why I went with Victron. The modularity that enables the system to expand with your needs.

It might be cheaper to buy another 8k Sunsynk…

I bought the Smartsolar 250/100 Tr when I started my solar journey two years ago… and then decided to go Sunsynk. Been sitting on the shelf, unused, ever since.

Just wondered if it could still easily be incorporated in the long term …seems not.

Before buying extra Blue toys I would much rather buy another Sunsynk.

Very happy with mine.

Thank you for all your responses.

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Yes it does

Correct it does not make more power available for the load but if battery voltage drops below certain voltage mppt starts up and feeds battery which intern feeds the load, might be wrong but that is indirectly feeding the load especially on bad weather days

Setup sunsynk to charge at 3/4 of total current battery allows and the external mppt to the balance

In my case Pylontech controls what happens to both Sunsynk and Venus GX charging wise that is

Thank you to @suly willing to give me some telephonic advice.

It seems splitting the CAN cable from battery into two - going to a) the Sunsynk and b) Venus GX controlling the Smartsolar , works.

Not sure if I am ever going to need the extra MPPT capacity.

Eventually I will have three 8k Sunsynks. One in each of three houses on our smallholding.

Each one capable of handling 10 to 12kw PV.

The aim is to get as close to Offgrid as possible thereby making it possible to downgrade to a smaller Eskom connection.

Current Eskom fixed line fees are around R4,000/month before the upcoming increase.

I incorporated my 150/35 into my system very easily and successfully.

I just set the charged voltage on the MPPT to 1 V below the Hybrid Inverter (at the time an Infinisolar).
The Victron string charges as soon as the voltage is below this level. Yes this is not ideal and the hybrid can’t incorporate the data but it works and allowed me to charge the batteries faster.

As I understand the Sunsynk is similar in topology to the Goodwe, and also the Victron Multi RS. It is essentially a PV-inverter that converts the PV directly to high voltage DC from where it is switched onto the grid. It then has a buck/boost stage going to the battery. It is designed so that the PV can be converted into AC for the loads very efficiently, that is to say the AC capability is very close to the PV-input capacity.

If you add extra PV to the low-voltage DC side, it does not increase the max AC power the device can generate, so you end up with an oversized situation: You have more PV than you can directly feed to the loads.

That is what I meant by it allows recharging the battery faster, but doesn’t really increase the amount of (peak) loads you can carry from PV only.

@leonvrhyn Why not get all the PV Gen and Batteries as close to the Eskom source as possible. Then run all 3 houses off the AC output of your own “Power Plant”.

You could put panels and Grid Tied inverters on the houses as well.
I think consolidating the power storage and generation will make things alot more efficient.

@plonkster if I understood the explanation by Keith of Sunsynk correctly, it is a Bi- directional inverter which, with grid present, can either charge or discharge batteries - not simultaneously.

Mppt charging of batteries seems to be a separate circuit.

If that is true, and the setup was at a “tipping point” meaning not enough PV and batteries run down to a minimum.

Then, instead of switching over to charging mode, and running the load from grid, the external MPPT might have kept the batteries topped up enough to avoid this.

That is if my technical comprehension is not letting me down.

I know that on the Goodwe the bidirectional inverter is between the battery and the HV DC bus. I don’t expect the Sunsynk to diverge from this topology, as doing so would mean duplicating a lot of electronics…