New SOK Bluetooth BMS for DIY

[joshwalee]

Normally to have the discharge FET off with a voltage above LVCO would mean an overcurrent event. Usually this is because something with a large capacitance is connected like a large inverter causing a temporary high in rush current.

I can't think of a reason why the BMS would disconnect discharge FET simply due to no load, makes no sense. I do wish they would put a event log on these BMS's that told you reasons why the BMS did what it did. Even just recording last 10 events would be immensely valuable in troubleshooting.

Maybe HighTechLab from CurrentConnected will see this and have some more insight.

Thanks again for the response. I've actually already come to the same conclusion and isolated it down to the 1000W Renogy inverter. It has been confirmed as the trigger point for the discharge FET when it is switched on direct, remote, or connected directly with main cables. I have removed the inverter and will be replacing/testing with a 700W to see if my woes are gone.

 

[jharrell]

You can also do a pre-charge resistor setup with a switch to limit inrush, would be nice if the inverter had that built in or the BMS could temporarily limit current by PWM'ing the FET's, maybe we will see that in the future as this seems to be common issue with BMS's and large inverters.

Surprising the inverter does it with remote, my Magnum inverter has no relay switching on the DC side so turning off by remote does not disconnect input caps so no inrush when turned back on, only way I get inrush is if I use my manual disconnect switch between batteries and inverter.

 

[joshwalee]

You can also do a pre-charge resistor setup with a switch to limit inrush, would be nice if the inverter had that built in or the BMS could temporarily limit current by PWM'ing the FET's, maybe we will see that in the future as this seems to be common issue with BMS's and large inverters.

Surprising the inverter does it with remote, my Magnum inverter has no relay switching on the DC side so turning off by remote does not disconnect input caps so no inrush when turned back on, only way I get inrush is if I use my manual disconnect switch between batteries and inverter.

I agree that this seems to be an inverter and/or BMS design gap. The remote switch behavior is also surprising to me. I did not have a particular use case for the 1000W inverter and was simply trying to build the system to capacities. It appears I may have overreached unless I were to add a pre-charge resistor. A smaller inverter footprint is actually welcomed in my setup and will likely be my applied countermeasure. Guess I have a nice inverter up for grabs... ?

 

[corn18]

I agree that this seems to be an inverter and/or BMS design gap. The remote switch behavior is also surprising to me. I did not have a particular use case for the 1000W inverter and was simply trying to build the system to capacities. It appears I may have overreached unless I were to add a pre-charge resistor. A smaller inverter footprint is actually welcomed in my setup and will likely be my applied countermeasure. Guess I have a nice inverter up for grabs... ?

I would not count on a smaller inverter not causing an issue with over current protection with the BMS. It will probably fix the issue, but might not. Would be a lot easier to use a precharge of some sort which costs $12 vs. buying a new inverter that still trips the BMS.

 

[joshwalee]

I would not count on a smaller inverter not causing an issue with over current protection with the BMS. It will probably fix the issue, but might not. Would be a lot easier to use a precharge of some sort which costs $12 vs. buying a new inverter that still trips the BMS.

Thank you for the response. I understand it is not a guarantee. Following basic math for a safer unit peak I decided to try an inverter that (should) not exceed BMS current limits. Mark 2 includes a 600W inverter that fits better overall and has been confirmed not to trip the discharge FET upon connection or power on. Overall I am happier with the design and do not need the extra wiring involved for the pre-charge resistor.

 

[joshwalee]

Just a follow up... Since the inverter change the BMS is performing beautifully. Bench testing capacity and land at 112Ah while pushing a 90A discharge to low voltage cutoff. The only minor complaint I would have is the very limited range of the BMS BT. It's a small gripe since I really only use it for an occasional cell balance view. Now it's time to put it through the ringer in normal usage and monitor longevity. Looking forward to (sub)freezing testing next winter season! I have a cold room for vehicle testing at my workplace and am considering usage for enhanced testing.

 

[kinyoubi]

Looks like SOK finally has a Bluetooth version of their BMS and are selling separately as a DIY piece. Seems they have up its rating slightly to 70 amp charge / 120 amp discharge, but if its like their current BMS which looks identical its actually 150 / 150 continuous:

https://www.us.sokbattery.com/product-page/sok-bms-for-12vlifepo4-battery-diy

Might replace the BMS's in my 206ah SOK's if this one works well as having Bluetooth to keep an eye in the individual batteries would be nice, I would imagine their plug and play batteries will get these at some point.

Hi Justin!

Dan from the Facebook SOK group.

Just FYI for anyone considering updating to the Bluetooth BMS..

Overcurrent Disconnect on this BMS occurs at around 120 amps. As was pointed out, the old BMS didn't cut off until around 200+ amps.

From my original Facebook post regarding this topic:

I did testing as well as a bit of reverse engineering the BMS. From my testing, it cut out at around 120-125 amps. To get this current I was running a microwave with a bench charger on to slowly ramp up the battery current.. however power requirements from the microwave aren't very stable so that's why I could only get an estimated range. The BT BMS uses a completely different battery management IC. Now it uses a BQ76920. The current sense resistor bank is ten 5mOhm in parallel, so .5mOhm total.. looking at the spec sheet for the BQ76920, there are discrete R sense voltage values that are set via the MCU. I'm guessing it's set to 61mV because that would be 122 ish amps.

 

[joshwalee]

Hi Justin!

Dan from the Facebook SOK group.

Just FYI for anyone considering updating to the Bluetooth BMS..

Overcurrent Disconnect on this BMS occurs at around 120 amps. As was pointed out, the old BMS didn't cut off until around 200+ amps.

From my original Facebook post regarding this topic:

I did testing as well as a bit of reverse engineering the BMS. From my testing, it cut out at around 120-125 amps. To get this current I was running a microwave with a bench charger on to slowly ramp up the battery current.. however power requirements from the microwave aren't very stable so that's why I could only get an estimated range. The BT BMS uses a completely different battery management IC. Now it uses a BQ76920. The current sense resistor bank is ten 5mOhm in parallel, so .5mOhm total.. looking at the spec sheet for the BQ76920, there are discrete R sense voltage values that are set via the MCU. I'm guessing it's set to 61mV because that would be 122 ish amps.

Odd since the spec sheet shows 330A BMS cutoff. I agree, it is actually quite lower since I could not run a 1000W inverter due to peak current on connect.

 

[jharrell]

Odd since the spec sheet shows 330A BMS cutoff. I agree, it is actually quite lower since I could not run a 1000W inverter due to peak current on connect.

Seems like more people are reporting issues with inverter cap charge and generator starting with the new Bluetooth BMS, so it seems like the surge ratings are lower. Was hoping the Bluetooth would be the other way around since the published continuous is higher.

Really need more definitive information on how SOK BMS handles over current since the documentation is all over the place. Maybe HighTechLab / CurrentConnected can do another awesome video on over current instead of over voltage and clarify .

If SOK could do one thing better is proof read and cleanup their website and documentation its inconsistent and vague on important specifications. Their new spec sheet list only 20 amps recommended charge rate for both the 100ah and 206ah while the website still says 40 amps for the 206 neither of which makes sense.

 

[kinyoubi]

Odd since the spec sheet shows 330A BMS cutoff. I agree, it is actually quite lower since I could not run a 1000W inverter due to peak current on connect.

Yeah, those specs look like they were carried over from the non Bluetooth BMS, so they should be updated.

You have access to a SOK battery with the Bluetooth BMS? Do you have a means of pulling and controlling a 120+ amp load? I would like for anyone who can to confirm for themselves and post their results here. I'm sure anyone who sees just my post will be skeptical of a new comer with just one (now two) posts on this forum.

 

[corn18]

Yeah, those specs look like they were carried over from the non Bluetooth BMS, so they should be updated.

You have access to a SOK battery with the Bluetooth BMS? Do you have a means of pulling and controlling a 120+ amp load? I would like for anyone who can to confirm for themselves and post their results here. I'm sure anyone who sees just my post will be skeptical of a new comer with just one (now two) posts on this forum.

I might give this a go tomorrow. I have 2x12V 206Ah SOK with bluetooth in my 5er. I can unhook one and do a load test.

 

[HighTechLab]

Alright, I've been after video ideas so I suppose I'll make a video on this. My electronic DC load can push 120a max in its current configuration, but it wouldn't take much to get it reconfigured for about 140a (1800w is my limit). Charging is so much easier than controlled loading.

One day Keysight/Agilent will get some of my hard earned pennies for one of their bidirectional regenerative electronic loads I suppose, starting at $21,028. https://www.keysight.com/us/en/prod...ive-programmable-power-supplies-5kw-10kw.html
Should be perfect for battery testing. Just wish they made a 60v/300a model.

 

[jharrell]

Alright, I've been after video ideas so I suppose I'll make a video on this. My electronic DC load can push 120a max in its current configuration, but it wouldn't take much to get it reconfigured for about 140a (1800w is my limit). Charging is so much easier than controlled loading.

Just use some electric heaters on an inverter , can switch the heaters high and low to give some control. I did close to 300 amps using my Coleman AC and microwave at the same time. With a large inverter large loads are easy to come by, could also do hybrid load sharing to adjust current draw specifically.

I also did an inrush test using my Onan 4000 generator starter and clamp meter and got 280 amps which my two non BT 206's in parallel handle just fine. I should try and do that with my inverter caps too not sure if my clamp meter is fast enough even in rush mode though, need scope with amp probe.

Also saw your FB post noting the new bluetooth BMS has a 10mA draw at idle which I guess is higher than the old non BT one so it is not recommended to store at lower SOC for long periods of time (6 months) on the 100ah due to 1% drain every 5 days.

 

[kinyoubi]

Just use some electric heaters on an inverter , can switch the heaters high and low to give some control. I did close to 300 amps using my Coleman AC and microwave at the same time. With a large inverter large loads are easy to come by, could also do hybrid load sharing to adjust current draw specifically.

I also did an inrush test using my Onan 4000 generator starter and clamp meter and got 280 amps which my two non BT 206's in parallel handle just fine. I should try and do that with my inverter caps too not sure if my clamp meter is fast enough even in rush mode though, need scope with amp probe.

Also saw your FB post noting the new bluetooth BMS has a 10mA draw at idle which I guess is higher than the old non BT one so it is not recommended to store at lower SOC for long periods of time (6 months) on the 100ah due to 1% drain every 5 days.

SOK says that they will work on a software update to go into a low power state when not used for long periods. I'm not sure the details of how they plan to implement this.


Another thing that's different from the non Bluetooth BMS is the voltage required to recover from a SCD or OCD. On the old BMS, all you needed was about 9V at the terminals to "wake up" the BMS. With the new BMS, it takes about a diode drop MORE than the internal cell voltage. This isn't really an issue with one battery, but if you have 2+ in parallel and they all go into SCD or OCD, one battery may recover before the others and pull down the voltage to its own voltage, preventing the others from recovering and them remaining in discharge cutoff state.

 

[Koert]

Hi, I'm new to electronics and only know what I've learned while working on our RV. So, thanks in advance for bearing with me.

Yesterday, we received four SOK 206Ah batteries with Bluetooth and heating. The plan is to connect them in parallel and use them for day-to-day camping (usually using about 150Ah) and solar charging (840W with a typical sunny day gives us about 250-300Ah).

The extra battery capacity is to have plenty of overhead to get us through consecutive dark days and to be able to occasionally run the air conditioner when it's unbearably hot. In these situations we will be relying on our backup charging sources (generator/shore-power and alternator charging) which I had hoped to expand to optimize charging times for these "emergency" situations. (Two hours of running the engine and alternator together is very do-able. Six or more hours of running the generator alone is not practical.)

When I received the batteries I noted that one was about 30% charged and the others were close to zero. So, I figured that before connecting them in parallel, I should bring them all up to a similar charge. And, I decided the easiest way to do that would be to disconnect our old battery and connect the SOK batteries, one at a time, to the same RV charging sources.

I used solar alone at first, charging at about 38-45 amps. As the sun dropped, I switched to shore power through a Xantrex 2000W inverter/charger that is capable of producing about 80 amps. I was aware that there was a charging limitation so it wasn't unexpected when the SOK battery immediately went into protection mode (excuse me if I'm using the wrong terminology - it essentially "turned off" and quit charging).

Then I tried lowering the output current from the inverter/charger and found that I could get away with it set at about 65 amps. But then I went to sleep and, this morning, found that the charging had once again turned off after bringing the battery up to about 25% SOC.

So, I'm bummed. Not only can't the batteries be quick-charged, but they also "turn off" whenever the charging current exceeds 50 amps. I'd like to return the batteries to SOK and start over, but it looks like it will cost close to $900 to return $4,800 worth of brand new batteries.

Not knowing whether SOK will cut me some slack or not, I began weighing my options. If they are going to be sticklers on the return policy, I could simply install the batteries and not be able to use them as I intended. Or, I could salvage the cells and install BMS's that meet my needs.

Or, even better, if I could change the BMS's parameters so they could (very rarely) handle 100-200 amps of charging per battery, (and handle occasional start-up surges) without going into protective mode, then I would be a happy camper.

The first step, I'd imagine, is to figure out if the charging current limit is an adjustable parameter. The only setting I could find that's related to current is the "Taper Current" but that doesn't sound right. I'm hoping that you guys can provide some insight - and I'm happy to test anything else you are interested in.

Thanks for this thread. I don't know if it will take care of my issues, but at least now I have hope!

 

[jharrell]

I used solar alone at first, charging at about 38-45 amps. As the sun dropped, I switched to shore power through a Xantrex 2000W inverter/charger that is capable of producing about 80 amps. I was aware that there was a charging limitation so it wasn't unexpected when the SOK battery immediately went into protection mode (excuse me if I'm using the wrong terminology - it essentially "turned off" and quit charging).

Then I tried lowering the output current from the inverter/charger and found that I could get away with it set at about 65 amps. But then I went to sleep and, this morning, found that the charging had once again turned off after bringing the battery up to about 25% SOC.

I am very surprised they shutdown above 50 amps charging, being a single port BMS it should have no issue handling same charge as discharge which should be 120 amps. 50 amps is only 0.25C and would be a pretty ridiculous cutoff for the 206ah, for sure my non blue tooth 206 can handle 110amps continuous charging each and probably wouldn't shutdown until 150+ amps.

Did you verify the "C MOS" was shutdown in the app when this occurred? Also verifying charge voltages should 14.4-14.6v absorb and very important if coming from a old lead acid charger to disable temperature compensation.

 

[corn18]

I have 2 x 12V 206Ah SOK batteries that originally came with the non-bluetooth BMS. I ran a load test on them and could discharge @ 286 amps with the batteries in parrallel. I could charge @ 142A.

I bought the bluetooth BMSs for them without the heat function enabled. I just did a load test today and they shut down consistently @ 210A. I couldn't test the charge function, though. I would imagine the previous reports of 50A limit are accurate.

I don't like these new limits, so I am going to put the original BMSs back in. The bluetooth is nice, but I could push the batteries to the limits of my inverter (2400W) for load and use all of my solar and inverter/charger (120+ amps) for charging.

For those buying the new SOKs with BMS, you will just have to make sure that the printed specs of 100A discharge and 50A charge are good enough for your needs. No more margin.

 

[kinyoubi]

I have 2 x 12V 206Ah SOK batteries that originally came with the non-bluetooth BMS. I ran a load test on them and could discharge @ 286 amps with the batteries in parrallel. I could charge @ 142A.

I bought the bluetooth BMSs for them without the heat function enabled. I just did a load test today and they shut down consistently @ 210A. I couldn't test the charge function, though. I would imagine the previous reports of 50A limit are accurate.

I don't like these new limits, so I am going to put the original BMSs back in. The bluetooth is nice, but I could push the batteries to the limits of my inverter (2400W) for load and use all of my solar and inverter/charger (120+ amps) for charging.

For those buying the new SOKs with BMS, you will just have to make sure that the printed specs of 100A discharge and 50A charge are good enough for your needs. No more margin.

If the Bluetooth BMS's are still in your batteries, can you verify in the app at what current do they cut off for each battery? If they are sharing the load exactly then that's 105 amps which is about 15% different than what I measured at about 120-125ish amps.

 

[kinyoubi]

Hi, I'm new to electronics and only know what I've learned while working on our RV. So, thanks in advance for bearing with me.

Yesterday, we received four SOK 206Ah batteries with Bluetooth and heating. The plan is to connect them in parallel and use them for day-to-day camping (usually using about 150Ah) and solar charging (840W with a typical sunny day gives us about 250-300Ah).

The extra battery capacity is to have plenty of overhead to get us through consecutive dark days and to be able to occasionally run the air conditioner when it's unbearably hot. In these situations we will be relying on our backup charging sources (generator/shore-power and alternator charging) which I had hoped to expand to optimize charging times for these "emergency" situations. (Two hours of running the engine and alternator together is very do-able. Six or more hours of running the generator alone is not practical.)

When I received the batteries I noted that one was about 30% charged and the others were close to zero. So, I figured that before connecting them in parallel, I should bring them all up to a similar charge. And, I decided the easiest way to do that would be to disconnect our old battery and connect the SOK batteries, one at a time, to the same RV charging sources.

I used solar alone at first, charging at about 38-45 amps. As the sun dropped, I switched to shore power through a Xantrex 2000W inverter/charger that is capable of producing about 80 amps. I was aware that there was a charging limitation so it wasn't unexpected when the SOK battery immediately went into protection mode (excuse me if I'm using the wrong terminology - it essentially "turned off" and quit charging).

Then I tried lowering the output current from the inverter/charger and found that I could get away with it set at about 65 amps. But then I went to sleep and, this morning, found that the charging had once again turned off after bringing the battery up to about 25% SOC.

So, I'm bummed. Not only can't the batteries be quick-charged, but they also "turn off" whenever the charging current exceeds 50 amps. I'd like to return the batteries to SOK and start over, but it looks like it will cost close to $900 to return $4,800 worth of brand new batteries.

Not knowing whether SOK will cut me some slack or not, I began weighing my options. If they are going to be sticklers on the return policy, I could simply install the batteries and not be able to use them as I intended. Or, I could salvage the cells and install BMS's that meet my needs.

Or, even better, if I could change the BMS's parameters so they could (very rarely) handle 100-200 amps of charging per battery, (and handle occasional start-up surges) without going into protective mode, then I would be a happy camper.

The first step, I'd imagine, is to figure out if the charging current limit is an adjustable parameter. The only setting I could find that's related to current is the "Taper Current" but that doesn't sound right. I'm hoping that you guys can provide some insight - and I'm happy to test anything else you are interested in.

Thanks for this thread. I don't know if it will take care of my issues, but at least now I have hope!

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Are you saying you want to be able to charge all 4 batteries at 100-200 amps each or charge them individually at 100-200 amps? If the former, how are you going to get 5,000-10,000 watts of charging power on your RV? Would be interesting to see such a system!

Unfortunately, the over current in discharge and charge protection is not an adjustable parameter as far as I'm aware (I asked Min from SOK directly about this and he said it cannot be adjusted in the app).

 

[Koert]

I am very surprised they shutdown above 50 amps charging, being a single port BMS it should have no issue handling same charge as discharge which should be 120 amps. 50 amps is only 0.25C and would be a pretty ridiculous cutoff for the 206ah, for sure my non blue tooth 206 can handle 110amps continuous charging each and probably wouldn't shutdown until 150+ amps.

Thanks for giving me hope!

Yes, the problem is not just the unusually low charge rate but the fact that the battery shuts down when it is just momentarily exceeded. If I could get 110A continuous charging (per battery) then I wouldn't worry about a slight surge bringing down one battery, which would have a domino effect and bring down the others.

Did you verify the "C MOS" was shutdown in the app when this occurred? Also verifying charge voltages should 14.4-14.6v absorb and very important if coming from a old lead acid charger to disable temperature compensation.

I think I remember that the C MOS was shut down but I'm new to this and wasn't paying close attention. (My inverter/charger is set to 14.6V absorption, no equalization, and no temperature compensation.)

Are you saying you want to be able to charge all 4 batteries at 100-200 amps each or charge them individually at 100-200 amps? If the former, how are you going to get 5,000-10,000 watts of charging power on your RV?

My current charging setup is about 50A from solar (840W, an additional 750W of panels planned), 80A from the generator (potential to expand to 300A), and 90A from the alternator (option to add an auxiliary alternator for 200-300? more amps).

If the Bluetooth BMS's are still in your batteries, can you verify in the app at what current do they cut off for each battery? If they are sharing the load exactly then that's 105 amps which is about 15% different than what I measured at about 120-125ish amps.

I just got the batteries two days ago and have only charged them individually. I would like to discharge one of them and do the test you suggest, but I'm concerned that at some point SOK will decide that these are no longer "new" and refuse a refund (which is the route I would prefer to go).