SOK 206AH battery installation

[booster]

Originally Posted by hbn7hj

No.

I thought BMS’s keyed off voltages but the 200AH bank stopped charging at 13.8 volts. I left the two banks combined and let the 400AH bank continue to 98%. Never did reach 14.3 volts. Next charge I’ll take it to 14.3 volts and set both banks to 100%

After you charge it, take a look at the voltage at the SOK battery to see how much it sags. It is highly likely that one cell got to voltage it would see as overcharged as that can happen really quickly if you are charging at relatively high amperages. One of mine did that also and when I looked at the cell voltages one was high. The SOK only shuts off the charging and if you let it sit with the full charge voltage on it I would bet the charge would have come back on. When it hit high voltage cutoff, it should also have started the balancing so that would take power out of the high cell and put it to the lower voltage cells as soon as the highest one got low enough the charge would come back one. I have been messing with it for about a week now and they two of my three are pretty well balanced now, but one is still lagging.


I ordered a cheap power supply from Amazon to put on it for balancing as needed, if needed, in case I can't get the Magnum to stay on well enough to do it. You only need a couple of amps of regulated output to do it.

[hbn7hj]

Your scenario could explain what is wrong with my two defective Battleborns. The SOK’s never quit charging. At 86% and 13.8 volts they were charging at 70 amps. The good Battle borns had quit at 100% at 13.8 volts.

I’ll keep them together while discharging and work with the charging issues. It does appear I have 600AH to work with if I need it, The Battleborns charge better than the SOK. I assume it means they have less internal resistance. They certainly track with each other on discharge.

[booster]

You may have already seen this video, but the guy describes what you are seeing indicating the need to balance the batteries.

https://www.youtube.com/watch?v=BIYRlnikWY8

[hbn7hj]

Thank you. News to me. Will upgrade my charging voltage from 14.3 to 14.4.

Need to float my removed from service batteries at 14.4 volts for a day or two. I think my Iota 100 amp charger I have not installed yet can do that.

[Winston]

Originally Posted by booster

. . . Many of the brands seem to be going to automatic top balancing, some like SOK want it on every recharge cycle if possible. The auto balancing is not initiated until the charged voltage hits 14.4v in many cases like SOK and maybe Battleborn also.

I have not been able to get much of an answer on just how far off the voltages of the individual cells can be before it is an issue as it would make sense to stop the charging at the lower voltages than 14.4-14.6v that the balancing takes.

Nearly 7 years have passed since we installed our lithium 500ah pack as part of our DIY Promaster conversion. "Drop-in" lithium replacement batteries were gaining popularity at that time, but we elected to go with the "assemble our own" arrangement using 20 x 100ah prismatic cells with an external BMS. Actually this was quite simple as the cells, BMS and virtually everything one needed was supplied by one vendor, Elite Power Systems. You don't have to be an electrical engineer to go this route.

We bring this up 7 years later because it appears that the DIY community has all but forgotten this alternative. And, after reading this thread and others, it appears that the approach we adopted has significant advantages.

First, the BMS does not in any way limit the charge or discharge rate. Charge and discharge rates are solely set by the battery/battery manufacturer. Prismatic battery banks have comparatively large (and importantly fewer) cells which result in there being essentially no jumpers or internal buss connections internal to each cell. We surmise that the need to interconnect literally dozens of smaller cells in many of the 'drop-in' alternatives may be responsible for some of their low charge/discharge specifications. In theory, our prismatic cell/pack can be charged or discharged at 3C or 1,500 amperes - - an insanely high number well beyond that which any user could ever reach.

Second, while we understand the most 'drop-in' battery BMS's monitor all the cells - - this granular detail is generally not available to the user. With just 20 cells total, our prismatic pack BMS displays these 20 cell voltages making the monitoring of battery/pack health and details relating to cell balancing possible.

Booster, we didn't understand your discussion of SOK balancing. But our BMS simply monitors each cell and when any cell hits/exceeds 3.55 volts, it throws a "1/2 amp resistor" across the cell which serves to minimize the continued charging of that already fully-charged cell until the other three cells (4 series cells per 13 volt string) catch up. This is equivalent to a total pack voltage (if fully equalized) of 14.2 volts.

So, as you suggested, balancing is automatic and, if you don't want to balance, operate at a lower charging voltage.

[@Michael]

We surmise that the need to interconnect literally dozens of smaller cells in many of the 'drop-in' alternatives may be responsible for some of their low charge/discharge specifications.

AFAIK the 100Ah Battleborn's are made up of small cylindrical cells, but most other drop-ins are using prismatic cells. Will Prose has disassembled dozens of them, and every one that I've seen him tear apart has used prismatic cells.

The ability to monitor individual cells via Bluetooth, serial and/or RS485 is also a common feature of modern drop-ins. On mine, I can adjust more than a dozen charge/discharge parameters and monitor dozens more using either the vendor-provided Android/iPhone apps or a direct serial/RS485 connection. In some cases (LLT/JBD based BMS's) the protocol used to communicate with the BMS is published and open-sourced, so there are a variety of apps available via GitHub or other open-source repositories.

Charge/discharge rates are somewhat limited on modern drop-ins though. A recommendation of .5C seems to be typical, even if the cell mfg. allows for higher rates. I suspect that might be related to thermal management and/or the capacity of the BMS electronics & internal wiring.

[booster]

Thanks, Winston, I thought you might chime in to this.


Do you have any information available how well your cells were balanced originally or what they now after a bunch of use?

[Winston]

Originally Posted by booster

Do you have any information available how well your cells were balanced originally or what they now after a bunch of use?

As a starting point, after 6 years of nearly continuous use with practically no regard to 'guildlines' that SoC's should not be continuously held at 100% (in practical RV use, we tend toward maintaining as high SoC's as possible - - even at the sacrifice of battery longevity) - - our battery capacity has dropped to 85% of 'new'.

On the issue of balancing, one of the earliest and most knowledgeable marine users of lithium commented that he's run hundreds, maybe more than a thousand, full discharge cycles (after his initial top-end balancing) and has never found need to rebalance his pack. We're not so sanguine and get nervous when we see 'apparent' mismatches/imbalances and frequently crank our charger(s) up to the 'balance' voltage of 14.2 volts. But it may be that we're all obsessing over 'balance' when it really isn't necessary.

We don't remember the precise starting SoC, but believe it was around 50%.

In the early years, our cells maintained very close voltage tracking, +/- 0.02 volts (our BMS does not resolve beyond 0.01 volt). Now we see variations of 0.1 volt and higher. We initially thought that this marked the impending death of the 'low voltage' cell - - but subsequently have seen that, over time, the low voltage cell can recover (balancing?) and often, another cell will assume the 'duties' of becoming the lowest voltage cell. Very mysterious. We continue to collect data and maybe this will all become clear.

For the present, we expect our total pack capacity to reach 80% by end of the 7th year. We can live with 80% but have heard that once lithium has reached its 'life', the decline is rapid. We had expected a 10 year life, but might have to settle for 7.

[Winston]

Originally Posted by @Michael

Charge/discharge rates are somewhat limited on modern drop-ins though. A recommendation of .5C seems to be typical . . .

Michael, you clearly have a more 'contemporary' knowledge of the marketplace than our dated research of 7 years ago. We did some additional research a couple of years ago in the anticipation that we might build our own system by matching cells from one source to a BMS from another. We were astounded by some of the clumsy BMS's we saw - - most notably one that passed all of the load and charging current through a large, odd-shaped 'dongle' with a pair good-sized wires protruding therefrom. It's no wonder that this arrangement had current limitations. We want nothing more in our battery lines than one of those brick-like 500 amp/50mV shunts with its two huge studs for wire connection. The attached BMS 'sees' no more than 50 millivolts - - and then, only when a near melt-down charge/discharge of 500 amperes is present. Michael, are you aware of any good stand-alone, shunt-based BMS systems?

[booster]

Originally Posted by Winston

As a starting point, after 6 years of nearly continuous use with practically no regard to 'guildlines' that SoC's should not be continuously held at 100% (in practical RV use, we tend toward maintaining as high SoC's as possible - - even at the sacrifice of battery longevity) - - our battery capacity has dropped to 85% of 'new'.

On the issue of balancing, one of the earliest and most knowledgeable marine users of lithium commented that he's run hundreds, maybe more than a thousand, full discharge cycles (after his initial top-end balancing) and has never found need to rebalance his pack. We're not so sanguine and get nervous when we see 'apparent' mismatches/imbalances and frequently crank our charger(s) up to the 'balance' voltage of 14.2 volts. But it may be that we're all obsessing over 'balance' when it really isn't necessary.

We don't remember the precise starting SoC, but believe it was around 50%.

In the early years, our cells maintained very close voltage tracking, +/- 0.02 volts (our BMS does not resolve beyond 0.01 volt). Now we see variations of 0.1 volt and higher. We initially thought that this marked the impending death of the 'low voltage' cell - - but subsequently have seen that, over time, the low voltage cell can recover (balancing?) and often, another cell will assume the 'duties' of becoming the lowest voltage cell. Very mysterious. We continue to collect data and maybe this will all become clear.

For the present, we expect our total pack capacity to reach 80% by end of the 7th year. We can live with 80% but have heard that once lithium has reached its 'life', the decline is rapid. We had expected a 10 year life, but might have to settle for 7.

Thanks Winston, great to see more real world experience and particularly life data on a well designed, but used in the real world, lithium system.


Many of us have been very skeptical of the crazy high claims of the early lithium sellers in regards to cycle life and other specs like charge/discharge rates and such. I think we are starting to see that lithium is not going to last nearly as long as claimed, but with prices coming down very quickly still can look like a good alternative to lead acid for larger systems.



I have been trying to figure out what the deal is with the wholesale reduction in charging/discharging recommendations, even by those suppliers that have BMS systems that are capable of the higher amperages. I really don't have a great idea yet, but am suspicious that the combination of going totally full and high charge rates may be part of it, along with the transition away from high current relays to BMS solid state switching of the power lines.



We are testing now on 3 SOK 206ah lithium batteries that state that the charge rate is 50 amps per battery and 100 discharge, but more recent SOK literature is listing 70 amps charging for the 206ah batteries, with the 100ah version still at 50. I have seen a pic of the new Bluetooth BMS and it says it is rated at 70 amps though on it's case so if the wiring is big enough I would expect the 70 amps to be correct.


We actually were going to order only two of the 206ah batteries as it would be similar to our 440ah of AGM in all practical things, but decided to go to 3 to get the higher charge rates. We currently have two stages of charge rates via the remote alternator regulator set at 120 and 180 amps for the AGM and that has proved more than adequate for how we use and charge them. We use the 120 amp setting 98% of the time I would guess.


We have no complaints on the AGMs as they are approaching year 8 and still test at spec capacity, but we have noticed a bit of decline in voltage holding on 100 amp discharges to run the microwave or other high drain items, so we know their time is running out in the next few years and that makes it a good time to test and learn if lithium is really for us or not, as long as the price penalty for lithium is quite small compared to new Lifelines.

[@Michael]

Originally Posted by Winston

Michael, are you aware of any good stand-alone, shunt-based BMS systems?

The only one that I know of offhand is Electrodacus (https://electrodacus.com/).

Instead of current flowing through the BMS like the ubiquitous Chinese BMS's, it sits on the side and uses external signaling to enable/disable your charge sources and loads using either the existing remote on/off capabilities of your equipment or solid-state relays.

I have no experience with that product, but would not hesitate to use it.

[hbn7hj]

The SOK’s are working very well. I’m charging to 14.5 volts.

[booster]

Originally Posted by hbn7hj

The SOK’s are working very well. I’m charging to 14.5 volts.

Did the cells finally appear to get balanced out after a bunch of charges to that voltage?

[hbn7hj]

I can’t tell since I didn’t get the bluetooth.

[booster]

Originally Posted by hbn7hj

I can’t tell since I didn’t get the bluetooth.

Does it still shut the charging on and off like it did at the lower voltage? I think was because of misbalanced cells so if that went away they probably got better over time.

[hbn7hj]

The only batteries that do that were the Battleborns I took out of service. SOK’s are connected all the way through 14.5 as are the still functioning Battleborns.

[booster]

Originally Posted by hbn7hj

The only batteries that do that were the Battleborns I took out of service. SOK’s are connected all the way through 14.5 as are the still functioning Battleborns.

Yep, I remember about the Battleborn balance issue. I took (take) the comment you made about SOK staying at 13.7v until nearly end of the charge cycle to indicate that they were out of balance and tripping out at 13.7 on the high voltage disconnect when one cell got that high before the rest. All three of my test ones did the same, but at various voltages around that amount. Once they were balanced well, they went all the way to 14.5 readily and didn't hover lower.

[hbn7hj]

No change. Still hover at 13.7 then climbing to 14.5 volts. Everything seems to work well.

[booster]

You may want to get one of these cell monitors, which are really pretty low priced. I think they are just 4 wires to connect after you remove the cover and you can monitor the cell voltages without Bluetooth. You could leave it on if you cut a small slit for the wires between the cover and base.


https://www.amazon.com/ISDT-Battery-...07797N9BG?th=1


You could easily tell balance and if the battery was balancing.

[hbn7hj]

Originally Posted by booster

You may want to get one of these cell monitors, which are really pretty low priced. I think they are just 4 wires to connect after you remove the cover and you can monitor the cell voltages without Bluetooth. You could leave it on if you cut a small slit for the wires between the cover and base.


https://www.amazon.com/ISDT-Battery-...07797N9BG?th=1


You could easily tell balance and if the battery was balancing.

I will do that this fall when I get home. Thank you.