Understanding Sunsynk inverters

[Isetech]

Time to discuss a few of the topics which might be a little confusing for some.

Lets start with pass through current:

Lets use an 8 kw inverter as an example.

The max. "continuous" pass through current on an 8 kw inverter is 50 amps, what does this mean.

You first have to understand how an inverter works, it has a built in change switch inside the inverter.

When there is grid power the changeover switch is closed which allows the power to flow from the utility through the changeover switch and out the other side to the essential side of the inverter. If you measure the power input and output to the essential/output side of the inverter, it is exactly the same.

This is why it is so dangerous to do a permanent bond, its like connecting any part of your electrical installation neutral to earth ( not going to go into details about the regs, you should be familiar with the regs by now)

When the grid power is lost, then the changeover switch in the inverter switches over, which means that the power from the grid is isolated (islanding mode) at which point you need to do a neutral earth bond. Now you have lost the star point of your transformer, which is why in some cases you need an earth rod (not if you are connected to a TN-S earth system)

What I am going to start doing with our TN-S earthing systems, is to install an earth rod at the meter box, which will be connected to everything, including the 6 mm earth wire bonding my panels.

If lightning protection is required then lightning specialist will be required and they will need to do what they need to do with the earthing and spikes.

[Isetech]

For those who feel the need to push this permanent bond crap, creating a dangerous environment, especially on sites which use a TN-S earthing arrangement, best you read the Susnynk installer manual

Page 27 it clearly states that the bond must only be done when in islanding mode.

"Since the inverter is a true hybrid, then the bond must only be made when the inverter is operating in Islanding Mode."

[Andrew_van_Zyl]

Correct. Also see NRS 097-2-1:2024

[Isetech]

Page 11

5.4 Neutral to earth bonding when forming an intentional island

5.4.1 To prevent a SSEG neutral connection to the the utility neutral through an earth conductor whenthe SDU opens, the SSEG shall not have a permanent neutral bonding to earth.

Who is going to pay to make all those permanent bonds compliant, the same people threatening legal action against people who have been doing it right from day one?

Correct. Also see NRS 097-2-1:2024

[Isetech]

5.4 Neutral to earth bonding when forming an intentional island

5.4.1 To prevent a SSEG neutral connection to the the utility neutral through an earth conductor when the SDU opens, the SSEG shall not have a permanent neutral bonding to earth.

5.4.2 A hybrid system intended to form an intentional island on the load side during utility supply interruption shall open the SDU to prevent unintentional island on the utility side.

5.4.3 Since the SDU opens the neutral on the utility side, the intentional island neutral shall be bonded to earth within 200 ms after the SDU operation using a neutral to earth bonding unit (NEB).

5.4.4 The NEB shall open within a time period of 200 ms before the SDU reconnects the inverter to the utility supply.

5.4.5 The NEB shall consist of an electromechanical switching device rated at the nominal current rating of the inverter. NRS 097-2-1:2024 125.4.6
The total clearance between the inverter neutral and earth conductors when the NEB is switched off, shall be equal the clearance of the SDU in its open state or more.

5.4.7 The NEB shall be an internal inverter component or an external device that is activated by a dedicated control port of the inverter.

5.4.8 The inverter data sheets shall indicate that it contains an internal NEB or a dedicated NEB control port for external devices.

5.4.9 Installation requirement: Inverters equipped with the NEB control port only, shall have external electromechanical NEBs installed that are SANS/IEC 60947-1 and SANS/IEC 60947-4-1 certified.


To add, I believe the inverter should have a means of detecting the bond is made and a warning signal if not. The control port should have a fail safe N/C contact , if the contact doesn't switch there should also be a warning.

[Isetech]

Back to pass through current, a few google results..

An inverter's AC passthrough current is the maximum current that can pass through the inverter to connected loads without the inverter needing to do anything to the power. It's used to cover loads on the output of the inverter when solar and battery cannot supply the load. It can also be used to charge the battery.

It can "pass through" AC current, meaning that the inverter is not converting the DC power in the batteries to AC, but just passing through the AC current from the grid. Conversely, AC output power would be when it is not connected to the grid, the amount that it is able to convert from DC batteries to AC power.


I do believe this is false information or should I say incorrect information, which has since been corrected, the 8 kw can only pass thru 50 amps not 90 amps, it could explain why Sunsynk had to make a video about burnt relays.

Pass through current is the maximum current that can pass through an inverter to connected loads without the inverter needing to do anything to the power. This current is used to cover loads on the output of the inverter when solar and battery cannot supply the load. For example, a 5 kW Sunsynk hybrid inverter can push through a maximum of 4998 watts, while an 8 kW Sunsynk can go to 20,700 watts. (this should be 11,500 watts)

I see we have discussed this in the past.

https://www.theforumsa.co.za/forums/showthread.php/28674-Pass-through-current

[Isetech]

Why would you need 50 amps pass through current, none of my installations would allow for 50 amps to pass through the inverter and out to the essential/load side of the inverter. I have 32 amp circuit breakers protecting the output.

The only reason I would need 50 amp pass through current to power the 25 amp output and the balance (25 amps) to charge the battery or maybe 50 amp pass through if used as a grid tied inverter.

I think this pass through current has created a lot of headaches for Sunsynk service centers. There are social media posts with pic of people with over 9000 watts on the output of an 8 kw inverter.

[Isetech]

If you understand how a true bi directional hybrid works you will know that you dont need to feed all the power through the output/ essential, the solar will back feed into the non essential load, or back to the grid, then you can push 10 400 watts back to the input/ non essential while the grid is switched on.

Maybe that is what the pass through means, back to the input/non essential, not like some think through the output/ essential.

Maybe if this was cleared up it would save the service center a lot wasted time.