ElectricLove
New Member
- Joined
- Jan 2, 2020
- Messages
- 7
I built my own Power Wall in my system using Group 31 batteries from a local company (local for me but they ship all over from their website, www.ohmmu.com/group31). My photo is ugly but the system is just plain simple! 2x10 to build the battery rack and 4AWG welding cable to connect all the batteries, not much else to it!
We plan to upgrade it further in time (add more batteries) but here is what we got so far:
1st phase: we bought 12 of the "Generation 1" Group 31 batteries (www.ohmmu.com/product-page/group31), 3 banks of 4 batteries. We wired them in separate groups so we could "build" the pack with multiple channels and keep similar cells/batteries with one another in series.
12 x Ohmmu 1.28kWh; ~15kWh total storage
2nd phase; we bought another 8 units from Ohmmu of their "Generation 2" Group 31 (weren't available when we did our first order, https://www.ohmmu.com/product-page/gen2group31), 2 more banks of 4 batteries. we added these in parallel with the existing 3 banks
8 x Ohmmu 2kWh; ~16kWh storage added
So our system is now sitting at 31kWh in total capacity which is awesome for a few reasons:
1. We drive Electric Vehicles, so if we drive and are out for the day while the sun is shining and come home to plug in it could take 10-20kWh of energy just to charge the cars up!
2. I want to have large top-end buffer zone to ensure longevity of our battery bank. In our current set up we have the SCC set to charge up to 57.2V which comes to 14.3V per battery. The 100% charged voltage on these units is about 14.7V so we have a nice buffer, we are only charging them up to around 85-90% of total capacity, which is "ideal" and will ensure long-life.
3. I want to have large bottom-end buffer zone to ensure longevity of our battery bank. In our current set up the XW inverters are set to only draw our battery bank down to 49.2V which comes to 12.3V per battery (likely "under load" so the unloaded Voltage would float up a bit); this should be about 10-15% capacity remaining in the batteries, which is again "ideal" and will ensure long-life.
I know some folks buy LFP batteries under the stipulation that they will use 100% of the capacity and still get 4000 cycles out of them, but that is unrealistic, your best bet is to do a battery bank bigger than you "need" (our need is about 20-25kWh) and leave 10% on the top and 10% on the bottom as buffer zones you never touch (unless you have to). For our system we use a max of 21-24kWh from "full" to "empty"; this is a lot of energy and we feel good about that.
The other things we consider important; leaving a bigger buffer on top and bottom also ensures that adding more banks in parallel has less of a detrimental effect on the system (eventually we will add separate "channels" and test each battery on its own (each bank on its own and then each battery on its own) to ensure good balance and health. If you don't do that then you shouldn't add batteries at all, its in the top and bottom of the cell curve that the "differences" will show up and thermal runaway or other "bad stuff" will happen, stay out of those zones and you will be better off, you will get maximum performance for as many cycles as possible.
Would love to hear what others think of my system and discuss further on LFP batteries in general!
Future plan: add another 16 of the Gen. 2 Group 31 batteries from Ohmmu as well as an additional 4kW of solar panels! Then we can go 100% off-grid...
We plan to upgrade it further in time (add more batteries) but here is what we got so far:
1st phase: we bought 12 of the "Generation 1" Group 31 batteries (www.ohmmu.com/product-page/group31), 3 banks of 4 batteries. We wired them in separate groups so we could "build" the pack with multiple channels and keep similar cells/batteries with one another in series.
12 x Ohmmu 1.28kWh; ~15kWh total storage
2nd phase; we bought another 8 units from Ohmmu of their "Generation 2" Group 31 (weren't available when we did our first order, https://www.ohmmu.com/product-page/gen2group31), 2 more banks of 4 batteries. we added these in parallel with the existing 3 banks
8 x Ohmmu 2kWh; ~16kWh storage added
So our system is now sitting at 31kWh in total capacity which is awesome for a few reasons:
1. We drive Electric Vehicles, so if we drive and are out for the day while the sun is shining and come home to plug in it could take 10-20kWh of energy just to charge the cars up!
2. I want to have large top-end buffer zone to ensure longevity of our battery bank. In our current set up we have the SCC set to charge up to 57.2V which comes to 14.3V per battery. The 100% charged voltage on these units is about 14.7V so we have a nice buffer, we are only charging them up to around 85-90% of total capacity, which is "ideal" and will ensure long-life.
3. I want to have large bottom-end buffer zone to ensure longevity of our battery bank. In our current set up the XW inverters are set to only draw our battery bank down to 49.2V which comes to 12.3V per battery (likely "under load" so the unloaded Voltage would float up a bit); this should be about 10-15% capacity remaining in the batteries, which is again "ideal" and will ensure long-life.
I know some folks buy LFP batteries under the stipulation that they will use 100% of the capacity and still get 4000 cycles out of them, but that is unrealistic, your best bet is to do a battery bank bigger than you "need" (our need is about 20-25kWh) and leave 10% on the top and 10% on the bottom as buffer zones you never touch (unless you have to). For our system we use a max of 21-24kWh from "full" to "empty"; this is a lot of energy and we feel good about that.
The other things we consider important; leaving a bigger buffer on top and bottom also ensures that adding more banks in parallel has less of a detrimental effect on the system (eventually we will add separate "channels" and test each battery on its own (each bank on its own and then each battery on its own) to ensure good balance and health. If you don't do that then you shouldn't add batteries at all, its in the top and bottom of the cell curve that the "differences" will show up and thermal runaway or other "bad stuff" will happen, stay out of those zones and you will be better off, you will get maximum performance for as many cycles as possible.
Would love to hear what others think of my system and discuss further on LFP batteries in general!
Future plan: add another 16 of the Gen. 2 Group 31 batteries from Ohmmu as well as an additional 4kW of solar panels! Then we can go 100% off-grid...
