Why? Start at zero man… 
You’re going to run into issues where the auto-selection is going to choose a BMV over your BMS, in systems that have both. Unless you want it that way… and in that case, I’d start even higher to make absolutely sure it’s higher than anything connected via VE.Direct. At 256, there’s going to be some undefined behaviour.
The CAN-BMS driver, btw, uses 512.
Yea, also wondered about that cause there is also the matter of data stored on Device ID 1 on VRM … 
I didn’t even think of that. Yes, the effect would be that if people upgrade, then they will have two batteries on the VRM device list. The one will eventually go stale (last seen 2 weeks ago, etc), and there will be a new battery that has all the latest data.
For backwards compatibility, start your DeviceInstances at 1. That way, people who upgrade should see no change.
Yes, my batteries’ BMS has 51Ohm resistors that it uses for balancing. These will draw maybe 68mA at a cell voltage of 3.5V (probably less because there are transistors in the circuit as well which will have a bit of a voltage drop). Unfortunately it stops doing balancing if there is less than 2A charging current since it can’t measure less than 2A. The problem that I see is that the cells that are going to get a bit high tend to do that right at the end of charge when the current has already tapered to around 2A or less, so it really doesn’t do much balancing at all.
I used the Ve.Direct 256+ as a base, but can start at zero/one
This is not an issue. If the ID was 1 before, it will keep that ID unless you rebuild the GX/Pi without the /Data/ store. VenusOS keeps a list of the IDs that is already in use for each device. I know, cause when I tested the new IDs it took quite some debugging to figure out why my instance kept the 1 instead of the new start instance I supplied.
So, I once took 8 x 100ah 3.2v cells drained them to where the inverter cuts out due to low voltage. Then I manually drained them down to 2.9v. Why, they where vastly out of whack.
Then I connected the cells in parallel and left them as such for about 48h. Bottom balancing.
After that I disconnected them all and left them for 24h, all their volts where still near identical.
Then I connected them for up and recharged them, slowly, using a car brake light bulb to further “help” the BMS balance. Top balancing.
On the part of connecting them in parallel, no power source, I was told that it makes no difference cause cells cannot balance themselves. There must be a current flowing in … fact that one cell has more charge than the rest, does not count for a “current flowing”.
Seems that is not 100% correct: Li-Ion BMS - White Paper - Balancing cells by parallelling
I think doing both is kinda pointless. If you use my water tank analogy, where you have multiple almost-identical tanks. That’s like draining them evenly until one is too low to extract any more (aka empty), and then individually draining those that aren’t empty yet to the same level, and then connecting them all in parallel until they are all equally empty…
and then after all that, you fill them up evenly. And of course the smallest tank is full first. And if you just stop right there, then the bank remains bottom-balanced (but not top-balanced). But you don’t. You know go to additional effort to make sure that every tank is full to the brim (top balancing). But doing that means they are no longer bottom-balanced. If you now drain them to empty again, the smallest tank runs dry first, and the other larger tanks have water left… just like before you started.
So do one or the other, but other than doing a capacity test, I see no reason to discharge to empty, and I certainly see no reason to spend time on a bottom-balance if you’re going to top-balance immediately afterwards.
Did it to learn more. The end result was positive though as the severely imbalanced batch of cells ended up in a very VERY small difference between the cells after that exercise.
O, less I forget, what was supposed to take weeks, took <4 days to balance that bank.
But the core point was, which I was told does not “work”, was:
Not sure why anyone would think that does not work. If you connect them in parallel, then those with a higher voltage will dump current into those that have a lower voltage, until they have the same voltage.
But that does not mean they have the same amount “charge” (aka coulombs). Perhaps that is why some say it does not work. Perhaps they mean it is somewhat meaningless
As a thought experiment, consider what happens if you connect a 7Ah SLA battery to a 80Ah car battery. Well, they are probably going to settle somewhere around 12.5V, and until that happens some current will flow from the one to the other.
But that does not mean they are now equal. The same applies, although on a much smaller scale, between almost-identical LFP cells
Edit: But, because the cells are ALMOST identical, putting them at the same voltage does help in the sense that they will then be ALMOST charged the same. It eliminates some of your problems. You probably don’t need more than a few hours for this to work.
If the 7ah was fully charged, the 80ah not, then in the end the 7ah will have a lot fewer coulombs whereas the 80ah a teeny weeny bit more, correct?
Flip side, 80ah is fully charge, 7ah is weaker, the 7ah will have more coulombs at the end, the 80ah a teeny weeny bit less, no?
I’m using your water tank analogy, the water will flow till the water level it is “level” ito bottom balancing.
Ps. I agree with top and bottom balancing, which is heavily dependent on age of cells and manufacturing quality. Did it to see if it would speed up vastly unbalanced cells, and it did. BMS takes too long.
From what I’ve read up on this is fine and works, but as the voltage line is relatively flat on lithium batteries it may take a long time for them to balance themselves out when connected in parallel without a power source.
The way I understand it is that a quick way to get an initial balance on a new 16s DIY bank which should then already have cells at a high SOC (or you just charge them normally for a used bank) is to put them in parallel with a power source. You connect all the cells up in parallel, connect a power source up at 3.6V and push current into the pack. This will do a quick top balance of the batteries and you can then connect them up in series and hook up the BMS and there should be no need to wait for a BMS balancer to do its thing. As long as you don’t have a faulty cell you shouldn’t have issues that needs manual intervention and the BMS balancer will kick in every now and then to keep them in shape.
Exactly this. Hooking them up in parallel and pushing current will do a faster top balance than what a BMS will do when they’re connected in series.
I guess the only thing is to just keep an eye on those cells. You may have a faulty cell in which case you’ll keep running into issues like this at which point it may be better to just replace the faulty cell if it keeps going out of whack.
Edit:
Ah, I found the video that I was thinking of. I guess the only thing is that you’ll need such a charger / power supply to get it done quickly.
(197) How to Top Balance LiFePO4 Battery Cells Quickly (and when you need to do it) - YouTube
So all this talk about the maximum voltage and what constitutes 100%… made me think of this. This is how a Trombonist would explain their instrument to a piano player (such as myself):
I think the SOC scale vs voltage has the same quality, an additional 0.1V becomes a really small increment in SOC as you go higher up.
I have now set everything in all the systems to 3.45v and max SOC of 90%.
Lowest draw of 30%
Charging:
48v system charges at 60amps
12v system charges at 20amps
No chance on this earth that I’m gonna split them 16 cells into a parallel bank … I touch it something BLOWS!
My Masters Doctatorial Degree in “WTF NOT TO DO”, says so.
Ps. The BMS says 100% SOC at 3.5v, so now I’m seeing that jump to 100% SOC IF a cell gets there. So far it is not happening.
Now THIS makes a LOT of sense - and he talks about Victron …
All because of one cell, not the bulging one … I ran the system down low, to recharge back up.
The BMS SOC is seriously affected by the cell voltages.
But, I also heard the point about the BMV not being connected to each cell individually. For months they where in sync. Till that fateful week. 
Looks like you need to keep an eye on your cell voltages so you can see which cells need balancing. I’m doing that using graphana. Here is an example from when the cells were badly balanced.
Yup. It is an estimate, and your BMS likely takes the approach that if one cell is full… then all of them are
I assume you wanted to say the BMV is not connected to each cell. The BMS is linked to each cell (those thin balancing wires) while the BMV is not (just the big battery pole connections).
Cell no 4 … can see it on the Venus or via Bluetooth, and the BMS stores the cell data per cell.
Jissie, this is a mission to get cells in balance fast on a working system …
Fixed. Thanks.
The first time the BMS and BMV are in “agreement” again after that week of the drama.
Dropped the charge volts and amps even lower, 3.42v and like 10 amps, slowly bringing them back from this morning’s low low discharge … will do the same again tonight, and slowly again tomorrow recharge them UNTIL cell 4 “behaves” again.
Thinking is that if BMS and BMV mostly agree on the SOC again, cells are again like 0.011v difference when charged, it should be fine again.
