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AC and DC changeover switch


RobN
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Dear forum,

I am new to the forum, but have been lurking for a while and have learnt a considerable amount.

So, I have installed a UPS with a hybrid inverter (OHM aka SunSynk 8 kW) that is fed from my main distribution board and feeds to a sub board to supply most of the household.
Currently only have a 3,5 kW/hr Pylontech Li-ion battery, but intend sourcing a second unit as soon as the current situation situation allows it.  System is working, but not tested under load-shedding yet (temporarily suspended), but cannot use high-draw appliances (kettle) with the current limited battery storage. There is a manual changeover switch on the sub board (1 - 0 - 2) to bypass the UPS/inverter supply.

The plan is to add PV panels soon and use those for charging the batteries instead of the grid as is the case now.  To meet the City of Cape Town's regulations, I suspect that I need to keep the setup as "off-grid".

My question:  Is there a changeover switch available that will allow switching between PV panels (400 V DC) and grid (230 V AC) supply to the inverter?
I foresee a situation in Winter, when there are a few cloudy/rainy days with no sunshine to recharge the batteries from solar, that I would need to use the grid to do so.  I expect Eskom will continue to have load-shedding once this Corona virus lockout is lifted and industry will be playing catch-up.

To be provocative, I have thought of a possible solution that may horrify the sparkies.
Mount an appropriate AC isolator and a similar appropriate DC isolator side-by-side, but upside-down, on the DIN rail and then connect the handles with a connecting bar, obviously suitably labelled with warnings etc.  Probably not a true "break before make" switch though.
I suspect this would be non-compliant, but am interested in hearing the comments/outrage at this suggestion

Thanks for a great forum,

Keep safe,

Rob N

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Hi Rob

Just a question.  Why would you want a change over switch from DC to AC?  The Sunsynk has 2 x MPPT ports for the DC feed from the Solar panels and an AC grid input feed.  The device can manage the charging of the batteries automatically using either Solar power or the Grid as available.

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Halcyon,

Thanks for the reply.

CoCT, in their wisdom and the way I understand it, won't allow the inverter AC grid feed to remain connected to the main supply, once the solar panels are installed.  If the system is to be classed as "off grid", it has to be completely isolated.  If there was a changeover switch, then the PV cells could be disconnected and the grid-feed reconnected on non-productive days and the system would revert back to being a UPS (it might require changing the inverter mode). 

I do not believe that my system will be permitted to operate in "Grid-tied with no feed-in" mode, as the inverter (on the CoCT approved list) exceeds their limitation (although neither the solar panels nor the batteries will initially be able to exceed 3,5 kW).  I have a 60 A main breaker on the DB, although it appears that the supply point breaker is 80 A single phase; which implies either a 3,5 or 4,5 limit.

I agree that "Grid-tied with no feed-in" would be first prize, and once operational I may well jump through the hoops to see if they will permit it; but in the meantime I am designing this as an "off grid" system.

If you see any other way round the regulations, I would be pleased to hear them.

Regards,

Rob

 

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Hi Rob, Ok understood. Sorry I do not have experience with regard to the COCT regulations and the limitations thereof for a Hybrid setup.  One would think CoCt should accept an inverter set to limit power supplied to HM (total home power) with zero export to grid as long as CT meter is set up correctly.  As far as I know the Sunsynk inverter is on the CoCt approved inverter list?  Hopefully someone with more experience on this subject will jump in on your question.

 

BTW I am having an issue with my Sunsynk where it is reporting an incorrect LD (UPS LD number) on the screen. You have not by any chance noticed something similar on your inverter?  I have actually submitted a detailed post to this forum on the matter. 

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Halcyon,

I read your other post in connection with your 5 kW Sunsynk inverter, but must admit that my setup has only just gone on-stream and I have not delved too deeply into the inverter settings yet.  At the moment it is purely in UPS mode and appears to be functioning as such.  The readings on the inverter appear to correspond to the usage meter I have connected (also an Effergy)

Also OHM, although the same as a Sunsynk inverter, has a slightly different user interface and will require some puzzling out as I cannot find an OHM manual, only the Sunsynk one.

Rob

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