Cherry67
Member
- Joined
- May 13, 2018
- Messages
- 518
Hello to all,
My diy powerwall description is located here.
https://secondlifestorage.com/t-Grid-Tie-modular-and-flexible
Defined as something modular and flexible I chose a different approach in organizing the cells.
The usual Pattern I see here is putting a load of cells together to an 1sxp block together, say a 1s80p. Then a couple, say 7, of these 1s80p blocks are connected in serial to a 7s80p. (Shown are 4 Blocks)
My approach described in above link is to block a number of cells, say 48, together as a 6s8p block.
(The Picture shows 3s2p Blocks).
This block has to be assumed for the moment ats being properly protected and balanced.
Building several of these I can put them in parallel, on the level of the positive and negative connector.
(Thats the status of the picture)
Having a modular system now. I can pull out any of the blocks at (nearly) any time, even under load, and the others will take up the load and continue to supply. By this I have easy manageable block sizes (in weight and in size), which can be pulled out and serviced quite easily, while the bulk of them are still in operation. I can start with a smaller block count and add more of them later, giving the chance going on-grid quite early and upgrading it step by step.
So far, so good. Now, how to solve the above mentioned protection and balancing of each single block? If I try to supply any sort of state-of-the-art balancing I have to provide that for each block, which is surely neither a simple nor a cheap solution.
Leaving all considerations aside which i have done to come ti this, pls think about the following.
What do I get now ?
So far, so good.
Question now from me, what do you specialist think of this approach?
Any comments on safety, on efficiency, advantages and disadvantages ?
All comments welcome.
My diy powerwall description is located here.
https://secondlifestorage.com/t-Grid-Tie-modular-and-flexible
Defined as something modular and flexible I chose a different approach in organizing the cells.
The usual Pattern I see here is putting a load of cells together to an 1sxp block together, say a 1s80p. Then a couple, say 7, of these 1s80p blocks are connected in serial to a 7s80p. (Shown are 4 Blocks)
My approach described in above link is to block a number of cells, say 48, together as a 6s8p block.
(The Picture shows 3s2p Blocks).
This block has to be assumed for the moment ats being properly protected and balanced.
Building several of these I can put them in parallel, on the level of the positive and negative connector.
(Thats the status of the picture)
Having a modular system now. I can pull out any of the blocks at (nearly) any time, even under load, and the others will take up the load and continue to supply. By this I have easy manageable block sizes (in weight and in size), which can be pulled out and serviced quite easily, while the bulk of them are still in operation. I can start with a smaller block count and add more of them later, giving the chance going on-grid quite early and upgrading it step by step.
So far, so good. Now, how to solve the above mentioned protection and balancing of each single block? If I try to supply any sort of state-of-the-art balancing I have to provide that for each block, which is surely neither a simple nor a cheap solution.
Leaving all considerations aside which i have done to come ti this, pls think about the following.
- I put a cheapo BMS without balancing to eack 6s8p Block. This BMS will check cell-exact the voltages and cut the supply out (for this block) on cell under- or overvoltage.
- I connect all cell connection of same xs Level to a Central point, attaching a resistor of (say) 2 Ohms. This central point is in the main surveillance station of the whole pack, it is not near the cells.
- From this CP i cant connect to any cell level of all packs simultaneously, but only over the 2 Ohms resistors.
- This CP provides a different type of balancing. Instead of surging an Pack in the usual style, or a cell level in my modular struckture, i provied to supply that level with loading current.
What do I get now ?
- All cells of same level are connected via the resistors. So they level out their voltages to the same level, assumed to the same SOC. (like all cell in an xp array)
- All Modules (my structure) have a cheapo BMS to safety protect their cells.
- All levels are connected to the Main control to being balanced from there, over the resistors. There is no surging BMS near the batteries, there is no heat near the batteries, there is no surging at all, no additional losses.
- Balancing is done by charging a cell level, instad of discharging. That means it can and will be done any time i like, not (only) at top voltage level to prevent overcharging.
- The connections between the modules run over resistors, which limit the currents, so i can use cheapo JST XH connectors, qualified for 3 Amps. Means I can (theoretically) charge quite more, because the current is distributed (supported by the resistors) over the blocks.
- There are 2 possible reasons why I have to balance: The blocks are out of same SOC by history, or they contain bad cells surging power for their losses. The latter would cause the first as well. So, when I charge a Level/Block I target the possible reason for that directly. Otherwise I had to surge all other blocks for the same amount of energy . and dissipate that.
- When loading targets the questionable blocks/levels directly, a logfile about the balanced levels give significant info about seviceable levels.
- when cells in one of my module heavily go out oft sync, the Module will be cut-off by the BMS. Surveillling the current of each block will show cuts-offs and point to Errors immediately. Pulling the block out gives an 6s8p array to be investigated (where only one p-row ist in question, regarding Balance protocols), which would give little problems.
So far, so good.
Question now from me, what do you specialist think of this approach?
Any comments on safety, on efficiency, advantages and disadvantages ?
All comments welcome.