Hi

Recently after having a power failure with being rainy and overcast the previous day, I woke up to find my house without power despite having an 8Kw Sunsynk inverter with 500ah batteries.  It was 5:30 am so I took my torch and investigated only to find I had completely depleted my batteries.

I had recently coupled my geyser to the grid from gas as I had added more PV panels and had ample power (9000w) to use. I also have to power a borehole pump and aux pump from the JoJo tank.

I have a 6Kw petrol generator coupled to the inverter which can be switched to the grid or aux (gen) input without an auto-start. I proceeded to start the generator and switched the generator to the grid input, only to find that this did not work. I was very annoyed and then switched over to the aux (gen) input to find that this also did not work.

I thought I had it all sorted when I installed my system and bragged about my installation, however to my regret, I got a wake-up call.

After checking the generator voltage indicator, I saw it did not show any voltage. I was convinced that this was a generator fault and did not try to put the generator in the bypass mode. I proceeded to switch all the large loads off (borehole pump, switch the geyser to gas, and only use the gas hob). After taking my grandchildren to school the sun was up and my PV panels did power the house to my relief and not to get an earful from my wife.

After getting help (4 guys) to remove the generator (100kg) from its bricked housing I started my fault-finding. To my surprise, only the mechanical voltmeter was broken.

 What now as it was not the generator?

I took the time to clean the generator and put it back in place with help. I did all the switchovers again only to find it still did not work.

Just to mention that I have spent more than 40 years working with electronics and instrumentation.

One of the most important things I have learned over the years is to go back to read and follow the instructions. 

This is what I did. I also followed up with videos from Sunsynk and this was the result.

1.       The biggest problem was the frequency which was 54.6 hz.  I had to adjust the frequency on the generator under load as close to 50hz as possible. This can be done by adjusting the screw on the linkage arm of the carburetor which will correct the speed and frequency.

2.       The frequency band on the inverter also needed to be adjusted for a larger band to accommodate the frequent load changes of the generator.

3.       There are other settings as well that affect the inverter if the generator is grid-coupled or aux-coupled. It also matters if you use timed settings as this will override the start and stop charging settings of the battery. The grid-tied generator to the inverter is much less forgiving to frequency change.

4.       The charging of the batteries from the generator needs to be set lower on a grid-tied generator.  if you set it too high there will be no power for the household load. The best Installation is to have a generator twice the power of the inverter so that it can charge the batteries without affecting the load. This is always not possible so be sure you have adjusted the settings for the size of the generator.

5.       If you have an electrician do the installation, make sure that he has done all the checks and has tested it before it is signed off. It will always be up to the owner to read the instructions so you can be sure the electrician has done all the tests and correct settings or else when the generator is needed it might fail and you might need to pay again to have it set correctly.

6.       Finally, the earthing of the generator.

A.      If it is coupled in the grid mode, the neutral has to be coupled to the earth as there is no link to neutral for a series earth leakage (RCD) to work if the mains neutral is decoupled.

B.      When the generator is coupled to the aux (gen) input the inverter should already have an earth bond relay installed to protect the system with the earth leakage (RCD) in series when the neutral is decoupled from the mains in the inverter during a power failure. I use an automotive 12vdc relay which can handle 30a.

In a complete circuit, there must only be one earth-neutral bond.

I see many installers fitting a permanent bond between earth and neutral on the inverter. This is illegal as now there are two earth-neural bonds when the mains power is present. (one in the inverter and one in the DB. Box).

I find it pure laziness that an electrician cannot use a relay to couple the neutral to earth even if the inverter does not provide a signal or voltage output as he can use the 220vac mains power input to the inverter as the signal to connect the bond.

NB: THE earth-neural bond must be the bond of the neutral on the output of the inverter to earth and not the neutral input from the Mains Power input.

 

The earth-neutral bond done on the Mains input is only done when the Mains Power is disconnected (live and neutral) and a Generator is used as the Mains Power input.

All is now good and working as it should.

I hope this will help someone who wants to couple a generator to an inverter and avoid the same problems and frustrations I have gone through.

Edited April 13, 20251 yr by Peter Topp

16 minutes ago, Peter Topp said:

The best Installation is to have a generator twice the power of the inverter so that it can charge the batteries without affecting the load.

That seems excessive (and VERY expensive). I have a 5kW generator supplying a 16kW Deye (set to draw a maximum of 3kW) and it all works perfectly, obviously as long as your average loads do not exceed the 3kW.

2 hours ago, Calvin said:

That seems excessive (and VERY expensive). I have a 5kW generator supplying a 16kW Deye (set to draw a maximum of 3kW) and it all works perfectly, obviously as long as your average loads do not exceed the 3kW.

I think the reasoning is so that you dont have to worry about overloading the generator.

Many times, people overload their inverters. A family member overloaded their 2 x 5kw inverters when his daughters decided to turn everything on, AC, kettle, microwave, hair dryer, etc.
Now image the same but the power is coming from a generator half the size.

17 hours ago, Bl4d3 said:

I think the reasoning is so that you dont have to worry about overloading the generator.

The OP has a Sunsynk and batteries. That allows him to limit the power drawn from the generator. Not all inverters have that ability.

Hi I want add some more input to this topic.

I recently found a question in my mailbox from a member with the same problem, and would like to sort it out. The generator link does not work when it is tied to the inverter.

This was my reply.

Hi xxxxxxx

I see your problem.

The biggest problem with a small generator is this.

Firstly, the generator needs to be adjusted to just under 50Hz under load. The biggest problem is that when the load changes, the frequency also changes. This effect stops the generator connection and is not ideal. The problem is also that you will charge the batteries and run the house.

My best suggestion is that you have a changeover switch that runs the house only from the generator and allows the batteries to charge for the PV panels at the same time. The way to stop the problem is to put the changeover switch in series with the output of inverter. Now you can switch the changeover to either run the house from the generator or inverter while still charging the batteries from the PV panels. This configuration does not have a frequency issue with the inverter.

It is difficult if not impossible to set a small generator to have the correct frequency under different loads.

I have both generator connections and only use the changeover that directly powers the house, as I suggested.

I am most sure most installers do not understand this problem, or they would have tested the configuration or warned you.

Lastly, any installer or electrician can do my suggested installation of the changeover switch.

Just make sure the earth is connected correctly for the suggested configuration so that your earth leakage works.

I hope this will help you overcome the problem.

I did this modification for a family member with a small coffee shop with the same problem, and now they are happy.

I am not an electrician or installer, just retired with 45 years of electronics, instrumentation experience.