Custom made UPS/ Energy Storage

[nkef]

Hi all,

this is my first post in the forum, I would like to thank you beforehand for your great contributions.

I looking to build a "custom" made ups/energy storage to replace all my PB UPS units when the power is cut and also to use it as power source when I have no PV production for my electronic equipment only (computers, cameras e.t.c).

I am living in a remote area in Attica Greece, with a real terrible power line, where we may have multiple voltage sags in a week for no apparent reason, the situation is worse with bad weather and It gets terrible in hot summer days. I had the unfortunate luck to buy multiple from the same APC UPS , which have two PB batteries in series without balancing , where always one them dies in a very short period. After multiple PB batteries failures I have decided that I had enough.

I have already a PV system based on Fronius Symo Gen24+ with 22kWp installed with a net metering contract, I bought the hybrid inverters with the intention to add batteries later but they are only compatible with the Fronius inveters are the unobtainium BYD HVS batteries 1000€ per Kwh (or something near that) , so I never got to install the batteries and I am using a diesel Generator which I already had as a backup power source.

I made small research and Ι found that the Victron Energy MultiPlus-II 48/3000/35-32 supports switching to battery in less than 20ms in case of power loss so it should probable be suitable to act as UPS.

For charging the battery from excess solar, by looking in the Victron ESS, I understand it can be programmed to use excess solar via a power meter, programmed in the appropriate modbus registers, enable / disable battery charging e.tc. I still have not exactly figured out how to automate the grid A/C enable/disable from inverter to force it to battery when on demand but I think it should be possible.

For battery I was looking a 5kWh 48v battery, initialy I was looking for the Polytech U5000 but I read about the 15cell setup and some negative comments about the reliability so therefore I would not go for it. Another battery is the Deye SE-G5.1 Pro-B, 5.12kWh.

I am trying to keep the total system cost about 1500€ + VAT for (Victron Energy MultiPlus-II, Deye SE-G5.1 Pro-B , Cerbo GX MK2 ) for the main system components.

I am asking for your advice, if I can accomplish my intentions with the above setup.

Thanks,
nkef

 

[wpns]

Briefly:

UPS batteries are not made for deep or frequent cycling, so not surprised you are having issues.

Go with 16-cell LFP batteries, that's the industry standard now.

Many (most?) inverters can switch to off-grid mode when the grid gets unstable, either voltage or frequency getting out of range. You may not be able to set these parameters independently, as regulatory agencies are very concerned about their grid stability.

@sunshine_eggo is one of the many Victron experts here, maybe he can shed some light.

 

[ricardocello]

I still have not exactly figured out how to automate the grid A/C enable/disable from inverter to force it to battery when on demand but I think it should be possible.

There is a modbus register to “Ignore AC Input”.
When set to 1, the AC grid power will not be used (inverter mode).
When set to 0, the AC will be used to power the loads and charge the battery if the voltage/frequency specs are met.

For a pure UPS application, ESS is probably more than you need.
ESS is grid-interactive, meaning it runs in parallel to the grid power and can feed back, which is probably not what you want.
ESS can also cause the UPS function to be less reliable during grid brownouts, and you don’t want that either.

 

[nkef]

@wpns and @ricardocello thank you for the advice, any suggestions for the 48V LFP battery to get ?

 

[caki]

I have been building something similar to your plan so I have one circuit in my house on UPS. I'm in the US so equipment is different, but I have:
- Cerbo GX
- Multiplus 48 3000
- Lifepower 4 V2 5.2Kwh Lifepo4 battery.
I'm planning to add solar charging soon, but right now I just keep the battery charged using AC power.
I'm using Node Red, a feature of the Venus OS Large image that lets you automate the operation of the inverter and do anything you want to do. It is impressively flexible. Right now the flow I'm using is illustrate by the picture, but I keep the battery between 45% and 80%. It slowly charges at 0.2 amps until it hits 80%, then discharges to 45%.
So to your question, you can do all that you mentioned above specially if you use Node Red. I'm going to soon add improvements to the flow where if it detect the cell voltage difference, it will charge to 100% so it does cell balancing.

 

[nkef]

I have been building something similar to your plan so I have one circuit in my house on UPS. I'm in the US so equipment is different, but I have:
- Cerbo GX
- Multiplus 48 3000
- Lifepower 4 V2 5.2Kwh Lifepo4 battery.
I'm planning to add solar charging soon, but right now I just keep the battery charged using AC power.
I'm using Node Red, a feature of the Venus OS Large image that lets you automate the operation of the inverter and do anything you want to do. It is impressively flexible. Right now the flow I'm using is illustrate by the picture, but I keep the battery between 45% and 80%. It slowly charges at 0.2 amps until it hits 80%, then discharges to 45%.
So to your question, you can do all that you mentioned above specially if you use Node Red. I'm going to soon add improvements to the flow where if it detect the cell voltage difference, it will charge to 100% so it does cell balancing.

View attachment 289684

Very Impressive work, I will keep a note !