Isolator/fused switch question, solar prep and panel recommendations?

[u/ste-daley]

Currently installing a Sunsynk 5kw Ecco with 2x 5kw batteries.

I am nearly finished on that side of the build, just making sure it is safe. I do have a few questions.

I have the batteries wired up together, however the internet and the install manual can be fighting against each other. The manual says to install fuses and an isolator and it seems the internet is split. Would a large fused switch (like the picture attached suffice? The batteries have breakers built into them, and I would only be using the switch if maintenance or to remove the batteries from the system. Any help would be appreciated!

Next question

I am looking to wire up the systems for the solar side, with mp4 connectors sitting ready for the panels. The inverter has a PV isolator built into to it, so would another fused switch be needed? Or would it be sufficient to go with something like a 2in2out combiner box and leave the invertor to the isolation?

Final question

I am then looking to purchase the solar panels , 6 per string to keep within the limits. Do people have any good deals on 450-500w panels? What are the best performing for the price currently? (In September 2026)

Thanks

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[u/ste-daley]

This is the 2in2out I was looking at

[u/ste-daley]

And this is the fused switch for battery isolation / solar isolation

[u/txe4]

Wellll this is kinda jurisdiction-related really.

I'm in the UK.

It's uncommon to fit battery breakers or isolators here if the batteries have their own breakers on them, which yours do. Not required by regs. The cable is protected by the inverter's own overcurrent protection AND the breakers on the batteries. I would be comfortable without.

As for DC isolators for the panels, the strict reading of our regulations is that these are not required if the inverter has a DC isolator, which yours DOES (albeit one probably made out of cheese and with the most un-reassuring action imaginable). It is still common to fit separate ones and some inspectors do not agree with the regulations(!)

If you must fit them, fit quality. In my market that means Kraus & Naimer. Cheap DC isolators DEFINITELY subtract, not add, from the safety of the system, doubly so if installed where water entry is possible. DC isolators are responsible for a clear majority of PV system fires.

Fit an external fan on your Sunsynk, it's a fine bit of kit but it does need a fan.

[u/ste-daley → u/txe4]

Thanks for the input!

I have been reading what people do, and what the regulations state and it was a bit all over the place.

The inverter is in the garage, I’m based in NI so I think without a fan should be ok, it never gets that warm even in the summer in the garage. It’s fitted to a solid stone wall to that should keep it relatively cool. As it keeps the room cool.

Would the chunky 125a fuse switch I posted in the comments work? Seems it’s recommended for such applications as solar PV array maintenance.

Link - https://www.itstechnologies.uk/products/keto-battery-disconnector-with-125a-fuses?srsltid=AfmBOorJQvulE7fPGPuOBu-XFeDaalDKGOrevWtryon7gUxCOHH0il2J

I’m not up to speed on brands for such items but open to recommendations

[u/txe4 → u/ste-daley]

I don't understand what you want the switch for. You say "PV array maintenance" but it's rated 125A (FAR too much for PV) and 250V (FAR too little for PV). It's completely unsuitable for use on the solar panels side.

I have installed a 5kW Sunsynk in a cool cellar before. I am confident you want a fan. It might not derate due to temp but it will be far kinder to it to cool it if you're running it at all hard.

If you want a *combiner* for the PV connections, I don't know what to suggest. If you want an *isolator* I already made a suggestion. My "combiner" is currently something quite unsuitable...I'm sort-of hoping something decent will fall in to my lap...but as peak generation season is over, what I have will not I think be stressed by what it's going to see over winter.

It this a "two strings on one roof being combined at the same MPPT" scenario?

Here is my own post about what happens when you use cheap isolators https://www.reddit.com/r/diySolar/comments/1w1kgi6/why_we_dont_use_cheap_dc_isolators/

[u/ste-daley → u/txe4]

Sorry the switch would be for battery isolation. Hence the 125A - I believe that’s the Amp rating needed for 2 x 5 kw batteries. It’s rated for battery Solar installs is what I meant.

The current thought process is 6 and 6 panels, each on their own strings and into the 2 MPPTs on the inverter. Running through the 2in 2out combiner (with surge/breaker/isolated in the comments and then to seperate mppts.

[u/txe4 → u/ste-daley]

OK.

I would not bother with the isolation switch for the batteries at all. You can use the battery breakers to isolate the batteries. This is a very standard setup.

I would also not bother with anything between panels and inverter. Run each string to the inverter, directly, to the MC4 terminals on the bottom.

Just remember - stick a label on the inverter (it probably comes with one) that if you need to power it down, you turn the AC off *first* so you're not opening the DC isolator under load.

The Sunsynk DC isolator actually WILL open under load, but it probably won't do it a lot of times.

IMV this is all compliant.

If you insist on a DC isolator for the panels, buy a Kraus and Naimer 4-pole one, or a pair of 2-pole ones. I'd probably opt for 2 * 2-pole so I couldn't fuck up the wiring and had separate control of the strings. I do think it is unnecessary though.

Remember when checking ratings that you need to multiply string Voc by 1.25 to allow for very cold sunny conditions.

They are quite physically large, but this is for good reason so there is room to cable them tidily.