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Sunsynk Whole House Backup Issue

 
Energy Storage
Last Post by Transparent 47 minutes ago
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 LostandConfused
(@lostandconfused)
New Member Member
Joined: 3 days ago
Posts: 1
Topic starter 12/01/2026 9:40 am  

Hi, looking for help and advice as my installer is useless and Sunsynk have washed their hands of this.

I wanted a battery backup system, non solar, that we can run the house off during the day and then charge overnight on cheap rate. We have regular power cuts here and so I also wanted it to be a whole of house UPS so we dont notice the power cuts, whenever they happen.

The company I used installed the following system last month - Sunsynk 5kw hybrid inverter, 3 x 5kw batteries and Fox EPS. However, whenever the power cuts out, we’re noticing it as the FOX eps switches between grid and back up. The strange thing is that not everything cuts out when the grid goes - the clock on the oven, for example, never resets (where as previously with power cuts it would, it doesn’t have it’s own a battery back up in it either.)

The system isn’t making use of the Sunsynks UPS as I wanted whole of house backup and was told it wouldnt be possible without an EPS.

I’ve spoken to Fox about this and they say the cuts outs when switching are because their equipment isn’t compatible with Sunsynk. I’ve tried getting help from Sunsynk, but they’ve been useless, saying talk to the installer who planned the system and the installer…well, they’ve admitted there is a problem and want me to spend about £1000 to put it right.

Before I spend more money, I wanted to do my own research and find out the best option.

Does anyone have experience in this or how to put it right? If I got another Sunysnk inverter and put them in parallel, creating 10kw, would we then be better off using the UPS output for whole of house back up? Would getting an ATS switch just be the answer for the current setup? Should I just admit defeat and not have whole of house backup, splitting the consumer board and making use of the Sunsynk UPS?

Since the system was installed, peak is about 7KW at any one time.

I’m lost and would appreciate advice.

Thanks in advance.



   
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Transparent
 Transparent
(@transparent)
Illustrious Member Moderator
Joined: 4 years ago
Posts: 2885
12/01/2026 12:04 pm  

Hi @lostandconfused - you're in luck.
And you're quite right to do some research here for yourself.

This issue is currently being discussed in the more general sense on the topic Recommended Home Battery Inverters.

Have a read through that Topic first because it introduces the overall concepts rather than diving straight into a technical problem.

 

The answer to one of your questions above is addressed in my response here in that topic

Posted by: @transparent
↑

The basic concept for deciding the number and size of of inverters and batteries is this:

If you need more power to run the home, then add inverters - that increases the kilowatts

If you need your stored energy to last longer, then add battery capacity - that increases the kilowatt-hours

 

I've got hands-on experience of installing hybrid off-grid battery storage, and I'm currently part-way through switching from three Growatt inverters
to three Sunsynk 5kW units.

Based on what you've just written above I don't think you should've needed a Fox EPS,
but I'd like the option to change my mind as you tell us more of what you want to achieve! 😀 

PlantRoomPMd

 

It would help if you (re-)posted your questions to the end of that other topic.
That will enable others to read the solutions in future.

Once I see you do that, I can close down this separate Topic.


Save energy... recycle electrons!


   
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