New Fogstar 15.5kWh upright solution

vaugi · 2023-11-19T11:17:06Z

Just noticed Fogstar have a new upright solution (coming soon). Given that it's Grade A cells, battery heater, cell balancer and 8yr warranty at £2500 incl VAT, is there much point DIYing with a Seplos anymore (at least for single bank solutions)?

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Batpred

(@batpred)

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Joined: 10 months ago

Posts: 76

16/10/2025 12:21 pm

These techno geezers seem to have some learnings related to the Seplos firmware.

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Transparent

(@transparent)

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Joined: 4 years ago

Posts: 2590

16/10/2025 12:37 pm

Yes, there's a mass of technical assistance available from contributors to the DIY Solar Power Forum.

They tend to be more technically knowledgeable than us here on the RHH Forum, but they may not appreciate how their projects affect the grid.
The majority of them are based in the USA, and a sizeable proportion use solar-power and batteries in RVs (vehicles).
Bear those points in mind when reading what they post.

Save energy... recycle electrons!

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Batpred

(@batpred)

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16/10/2025 3:14 pm

So an update on the Solis inverter settings and rcbo circuit protection.

Have to say that the Solis European wide support has been solid.

So to recap, we had two concerns:

- the grid rcd/rcbo needing to be one specifically spec'ed for bi-directional use (mcbs are bi-directional). For background, see "isolating the system for a planned power cut"

- the recommendation from solis to use 100ma sensitivity RCD/RCBO, instead of 30ma ones.

This system is expected to provide continuous power to some critical loads, for which could be using any of the available sources (PV, battery, AC, generator), depending on configuration. Right now we are considering it will power those loads from grid power and if the grid fails, it will convert and supply battery dc into ac.

The rcbo is bidirectional.

Several inverter startup scenarios needed to be considered (and there is no PV at the moment):

1- boot from DC port and then connect to the grid. The inverter will form the wave for the AC signal. When the grid circuit is closed/connected it should switch to take the frequency signal. This will be a noticeable blip on your domestic appliances, depending on how many ms it takes.

2- the inverter is initially powered by the grid and then starts. In this case, the inverter will form its wave from the grid and just keep it.

3- there are other scenarios, given that this inverter will work as a UPS when connected to the battery but for simplicity we will not get into it

What I am experiencing is that in scenario 1, a minute or so after the grid connection is closed, the bi-directional 30ma rcbo trips. This has been raised with Solis and it may be that they will just insist that the circuit is 100ma, in which case this will have to be swapped.

I believe the Solis grid team will now be lopped in to provide further advice.

So it is still not possible to try the charge and discharge cycles to get the battery cells balanced. Hopefully the battery charge will outlast these tests...

And before anyone asks, given that Solis was at some point considering whether an external ATS could help or not, it is not the time to share diagrams. More concerned whether there'll be space in the Solis for the extra ATS.. I thought the 18 way+SPD recent consumer unit would outlast this project!

I'd like readers here to employ a properly certified electrician.
This is not a DIY matter!

This post was modified 40 minutes ago by Batpred

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