Expanding Battery Storage in a Rental — What's the Best Approach?

Inverters
42

At this point I am biased towards learning curve. Longer term goal is that I can take apart the system and repurpose differently. Maybe batteries get better and chemistries change. Point is I am thinking that what I will learn now will pay off later.

And spot on for ROI, I can ask someone to do it and it takes longer. But I don’t learn in that process. Not a hard no, just the thinking.

In this case I thought, can I invest today to save over the next 5-10 years over Eskom (I am assuming both the inverter and battery will only last that long, any longer is bonus. And if I move, this moves with me. Whether it is cities or countries.

It’s sad seeing that I return about 80 kWh a month to grid and also consume as much. And that’s now. I’ll be putting up a server and that’s going to add another 90 kWh to monthly use when it is up. The ideal is 0 sale, not so much 0 grid use.

43

Wish I knew what Midstream was going to do IF Eskom does win with its high fixed charge nonsense. That would help short term viability of this plan.

That said, on a different note. I’ve been reading a little about LMFP batteries. Key difference being higher cell voltage vs LFP. How do Victron and other inverters deal with newer chemistries? Do they need big design changes or firmware updates to deal with it?

44

Today, stick with Lifepo4. It is the safest out there.

Warning: RTFM, the specs.

Victron inverters, the 5kva MPII specifically, can go to 66v. As can my MPPT’s (66v) and BMS (72v) and the BMV I use.

Newer Victron ranges, I vaguely recall, lower than 66v, hence the warning.
Fuses used must also be rated higher than standard 58v we always get everywhere.

My point - Flexibility:
Have a 18 cell 280ah Lifepo4 DIY bank.
Charged to max at 3.45v per cell, so about 62.1v with some spare for balancing to take place at the top, if cells go over 3.45v.

Why 18 you may ask?
Phil here on this forum, he “made me do it”. It is his “fault”. :slight_smile:
See, I bought spare cells, my warranty cells.
Saw the 66v max … and promptly did it.

So now if a cells becomes faulty, I can:
Remove 1 cell, 17 cell bank.
… have a spare cell I recharge once a year, so I put that one in after top balancing the bank.
So 18 - 1 + 1 = still 18 cells.

Another fails, so 18-1 = 17 cell bank then.
Another fails, 16 cell bank, the default “out there”.
Another one fails, 15 cell bank, also some manufacturers default.

Plan a, b, c see.

Victron, each time a cell is removed I just adjust the system settings, MPPT settings, lower.

Outside the Box Flexibility.

But it is not for everyone.

45

To me, this answer is still better than having to give in all 16 cells to the supplier when something goes wrong (and has gone wrong twice for me) and not have any storage left when all that was wrong was 1 cell.

But yes you’ve put in the effort! So if I understood you’re running a 57.6V system that can climb down to 48V if you have faulty cells. Very clever :rofl:

46

62.1v (3.45v x 18) that can go down to 51.75v (15 cells).

Cause yes, bank to be sent in for one cell … not my cup of tea.

47

Do we have on the forum here, average life expectancies or failure rates of cells, for where people have gone the DIY route? Of course it is quality and setup dependent.

48

Ito DIY:
Bunch of us, few years back, did 'n group buy direct from Amy in China. Grade A Batch matched 280ah EVE cells.

I think out of the 2 orders of a few hundred cells total, there was, if memory serves, 2 cells in total that had issues. We all bought “backups”.

Lifepo4 in general use is fairly new. Couple of years in now.
Ask again in about 8 years (then it would be 10 years) or after the claimed 6000 cycles.

Brand names:
There are tests running. Stats are somewhere on the web.

49

Amazing. Sad I missed the boat.

Something a bit different I was wondering, a Victron with some whatever battery, in parallel with the existing Deye inverter. Is that a possibility/allowed, etc.?

50

Don’t have to. Get them here now:

Like both feeding the main DB of the house?

Let more clever people answer that … @plonkster , your opinion?

51

Yes like both feeding the main DB. Though I’m not sure how the Victron would charge the battery apart from being instructed to do so by Home Assistant when the Hubble is full.

Anybody here to vouch for Apexium?

52

Victron charges automatically or as per schedule set or manually on demand, you choose.
Once you get there, we can share ideas.

Apexium has been here for a while, no complaints that I heard.

53

Isn’t this basically what is being attempted?

What is the key difference between this MultiPlus and the MultiPlus II, etc. being recommended?

54

Multiplus II is NRS certified to connect to a SA DB legally.

Multiplus, the 500va one, more for like camping or home TV, some lights, alarm system system that. It has a AC charger built in, same as the MPII, bit no NRS certification.

Phoenix range comes out with no AC charger.

55

There’s roughly three ranges involved. There is the older aluminium Multis, which are not NRS097-2-1 certified and never will be. The transfer switch doesn’t have the proper double-redundancy setup that is required.

Then there is the newer Multiplus-II, which is in a steel case, same design, but has the transfer switch with the redundant setup.

And then there are the older “Multiplus compact” models that has more in common with the first gen Multiplus, with a couple of hardware differences that usually doesn’t matter too much. That’s the 500VA to 2000VA units. They can do ESS just fine, you can set them up as three phase, or in parallel. You can even wire them into your DB (as a UPS) as long as no solar power is involved, ie as long as it is not used as an embedded generator.

My father in law has a 1600VA unit installed in his house, into the DB. It works just fine, although it is of course limited in power. The transfer switch is rated for just 16A, so you would only run a few backup circuits through this, not the entire house or even most of the house.

56

Any idea on the noise levels of these compact models? Suitable as a UPS next to the device they’re powering e.g. in my case, next to a TV? Let’s assume 400W load on a 1kVA model

Also, in line with what I asked earlier (having a MultiPlus in parallel with Deye) - I see the Deye has a generator input option (I think shared with microinverter or something like that). Can one of these MultiPlus compact models not be connected to that port as a “generator”?

57

Here is a comparative test I did some years ago, to get an idea of noise levels. Apologies for the terrible accent and sniffing a few times.

1 Like
58

This is awesome. What I wanted and expected to see! I assume that’s a 12V Multiplus compact?

59

@TheTerribleTriplet Taking apart the 2x 24V battery to create a 48V array, any pointers? Maybe the case can be reused (since I can’t find 50Ah enclosures, unless I make one which I will suck at) with just wiring distributed across?

My thinking is to then add a BMS of choice and then we can link up with any of the 48V models we’re discussing.

60

I have the crazy ideas which I then promptly act on.

The bottom line:

  1. Connect all the cells outside the cases, in one parallel string. Top balance them.
  2. Once top balanced, connect them in 48v configuration (16 cells?).
  3. Same time, fit the BMS balancing wires.
    … and you have a 48v bank … then to make it look cool.

But I don’t have the touch to make it look cool.

@Gman and @Paul are people that comes to mind first, that make stuff look cool.

Maybe they can post pictures of what they did.

61

Right! So if I understand

  1. First is parallel to get all to 1 voltage (I.e top balance)
  2. Then all in series - in this instance 16 get you to 51.2V nominal.
  3. Add BMS

Happy!

Maybe a stupid question, please tell me there is no soldering involved. Nuts and bolts and crimping is all good. Solder is something I do not know how to do :grinning: