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Venture into the PV/Inverter Rabbit hole


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Hi All.. Been doing quite a bit of reading on this forum and I must say that it's definitely a load of information so though I may as well just ask...

Like most, I want to be able to have a backup during load shedding and possibly add on PV panels at a later stage. My normal load for lights, TV, 5G Routers, laptop etc are around the 600W mark but decided to just work on 800W for 3 Hours (2.5 hours load shedding and a buffer to ensure batteries are not completely batteries completely). Have already decided on Lithium Ion batteries so did not even care to look at LA/AGM.

Ideally, I would love to get myself the Sunsynk 5kW + Hubble AM2 but my budget (40k incl. installation) will not allow. 

That being said, looking at the Kodak VMIII 3kw 24V + Hubble AM4. My only concern is that, according to the description of the Hubble AM battery spec, they speak of "compatibility and integration". Am I asking for trouble by going the VMIII route? I wouldn't mind a Growatt but have read that there are people who have had issues and I cannot keep an extra 10k for replacing an inverter. 

Looking forward to this journey and assistance from all the experts out here :) 

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Currently Kodaks (Voltronic inverters in general really) are only compatible with Pylontech as far as I've seen... But Hubble should be able to confirm that for you. There may have been a firmware update allowing more though. 

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2 hours ago, JaseZA said:

Currently Kodaks (Voltronic inverters in general really) are only compatible with Pylontech as far as I've seen... But Hubble should be able to confirm that for you. There may have been a firmware update allowing more though. 

Thank you for the response. 

According to the Hubble website, the AM4 is compatible with Voltronic Axpert via serial interface. Does this solve the compatibility question? 

Something else that i cam across now is the discharge cut-off voltage which is 22V. How long or at what percentage of battery drain would it actually cutoff at? Is there a way to calculate this?

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Great if the Kodak supports them! You may need to get a specific cable to go between them though.

For LiFePO4 type batteries (which almost all off-the-shelf solar lithiums are) you have a cell voltage range between 2.5V and 3.65V. 2.5V is completely dead and you shouldn't go there regularly. 3.65V is almost completely full and again, you don't want to be there regularly either to prolong cell life.

24V battery packs tend to be 8s - meaning 8 cells in series.
48V tend to be either 15s or 16s.

8 x 2.5V = 20V
8 x 3.65V = 29.2V

To complicate matters, LiFePO4 doesn't have a very uniform curve and is instead quite flat through most of the range with a rapid increase in voltage near full and a rapid decrease in voltage near empty. That's why they tend to have BMSes that monitor current to keep track of energy in and out of the battery. I personally run my bank between 3.0V and 3.45V per cell to increase longevity of the pack.

Ultimately this probably isn't a big concern as you can control a lot of these parameters on the inverter - charge voltage, cut-off voltage, back to grid voltage etc.

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I just had a look on the hubble compatibility list - unfortunately it's not great...

Voltronic Axpert - Serial - Requires ICC Raspberry PI

Basically it's not compatible in a true sense and requires a third party to interface between the inverter and battery.

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