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Heltec (JK) 200A Smart BMS with 2A Active Balance

Hi, does anyone know if it's OK to parallel the Heltec/JK BMS? I want to build 2 16S packs, each w/ a BMS, and then parallel the packs. I read JBD's spec sheet, and it seems to specifically parallel BMS w/ this statement:

"Direct parallel connection of batteries is not supported (there is the problem of high current discharge from high voltage batteries to low voltage batteries due to direct parallel connection of batteries)"

I can't think of a case where hooking up battery banks in parallel would cause a high current discharge between them, unless 1) one of them shorts out or 2) you connect a batteries together that are in different states of charge. If the 2 packs are at the same SOC when you hook them up, this shouldn't be an issue, right?
Andy at the Off Grid Garage has recently done testing on different SOC cells placed in parallel. No sparks, but he saw up to 200 amps moving between the cells once connected.

That was with a direct parallel, and not what you are suggesting, which I believe is to connect two seperate batteries via a busbar. That is exactly what I am doing with Lishen 280ah 16s batteries using two Heltec/JK BMS's. No issues. I made sure both batteries were very close in SOC before connecting them up.
 
I agree, running two separate battery systems with separate BMS units should not be a problem. But you do need to be sure the two are at the same resting voltage (State of Charge) before the two systems are connected. Due to the very low internal resistance of good Li cells, even a small voltage difference could cause a very high current between the two battery banks when they are connected.

Here are my thoughts on a worst possible case.
If for some reason, one of the systems has the BMS go into a protection disconnect, there could be a problem when it reconnects. Here is an example that could be a problem. The system is charging up. One pack has a runner cell that goes over voltage early and disconnects the charge current. The rest of the cells in that pack are low and not being charged any more. The total pack voltage could be quite low. The other pack continues to charge and does reach a full charge. As the system begins to discharge, the runner cell has a chance to settle back down and clears the over voltage fault. The charge side mosfet switch turns back on and is basically shorting the nearly full charged pack to the partially charged pack. I see two possible things happening. If the current is high enough, the BMS will again go into a protect mode. Or the one runner cell will once again run as soon as the connection is made and it will turn off the charge mosfets again. The two battery banks should also have fuses that should also stop it from doing anything horribly bad. So there are things that could go wrong, but I don't see a case where it would destroy anything as long as the fuses, wiring, and BMS settings are good for the cells. Once the system is well balanced and reasonably matched, it should work just fine.

As I have said on other threads about parallel batteries though, you can't expect to be able to draw the full current of all of the cells. No mater how well you try to match everything, one parallel bank is likely to pull more current than another. If you have 2 banks that can each handle 100 amps, when you put them in parallel, only expect 150 amps. So even if they are not well balanced, you know you are safe. Parallel banks are great for more run time, not for a lot more peak current.
 
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I agree, running two separate battery systems with separate BMS units should not be a problem. But you do need to be sure the two are at the same resting voltage (State of Charge) before the two systems are connected. Due to the very low internal resistance of good Li cells, even a small voltage difference could cause a very high current between the two battery banks when they are connected.

Here are my thoughts on a worst possible case.
If for some reason, one of the systems has the BMS go into a protection disconnect, there could be a problem when it reconnects. Here is an example that could be a problem. The system is charging up. One pack has a runner cell that goes over voltage early and disconnects the charge current. The rest of the cells in that pack are low and not being charged any more. The total pack voltage could be quite low. The other pack continues to charge and does reach a full charge. As the system begins to discharge, the runner cell has a chance to settle back down and clears the over voltage fault. The charge side mosfet switch turns back on and is basically shorting the nearly full charged pack to the partially charged pack. I see two possible things happening. If the current is high enough, the BMS will again go into a protect mode. Or the one runner cell will once again run as soon as the connection is made and it will turn off the charge mosfets again. The two battery banks should also have fuses that should also stop it from doing anything horribly bad. So there are things that could go wrong, but I don't see a case where it would destroy anything as long as the fuses, wiring, and BMS settings are good for the cells. Once the system is well balanced and reasonably matched, it should work just fine.

As I have said on other threads about parallel batteries though, you can't expect to be able to draw the full current of all of the cells. No mater how well you try to match everything, one parallel bank is likely to pull more current than another. If you have 2 banks that can each handle 100 amps, when you put them in parallel, only expect 150 amps. So even if they are not well balanced, you know you are safe. Parallel banks are great for more run time, not for a lot more peak current.

Thanks, interesting scenario that I hadn't thought of. But since you say proper BMS settings/fuses can protect from damage in this scenario, it's not problem, because this sort of situation is precisely why I want to use 2 parallel packs instead of one big pack. When a pack has an issue, I want to be able to take it offline to fix it without taking the system completely offline.
 
Hi, does anyone know if it's OK to parallel the Heltec/JK BMS? I want to build 2 16S packs, each w/ a BMS, and then parallel the packs. I read JBD's spec sheet, and it seems to specifically parallel BMS w/ this statement:

"Direct parallel connection of batteries is not supported (there is the problem of high current discharge from high voltage batteries to low voltage batteries due to direct parallel connection of batteries)"

I can't think of a case where hooking up battery banks in parallel would cause a high current discharge between them, unless 1) one of them shorts out or 2) you connect a batteries together that are in different states of charge. If the 2 packs are at the same SOC when you hook them up, this shouldn't be an issue, right?
I ran two batteries parallel with Heltec active balance BMSs and it worked fine.
The voltages were very close to even when I connected them together
My charge/discharge limits were under 100A.

Eventually I plan to connect four 48V batteries parallel. Each battery will have a 125A fuse.
 
I ran two batteries parallel with Heltec active balance BMSs and it worked fine.
The voltages were very close to even when I connected them together
My charge/discharge limits were under 100A.

Eventually I plan to connect four 48V batteries parallel. Each battery will have a 125A fuse.
Its like an addiction or potato chips. Once you build one, you need to do more.
 
I am in the process of doubling my battery bank as well. I have not decided if I will go with another JK / Heltec BMS or just go with a DALY for the second pack. The cells I am using are proving to be so well matched and balanced that I am seeing no drift and no balancer activity with the delta voltage set at just 0.006 volts. I do like my JK and since I fixed the balance lead harness, it has been flawless. But the 30 milliamp balance current on the DALY will be just fine on these cells. And at the lower cost, and with semi local availability, I will actually use 2 of them instead of tying the two strings together like I did with my first set.
 
I am in the process of doubling my battery bank as well. I have not decided if I will go with another JK / Heltec BMS or just go with a DALY for the second pack. The cells I am using are proving to be so well matched and balanced that I am seeing no drift and no balancer activity with the delta voltage set at just 0.006 volts. I do like my JK and since I fixed the balance lead harness, it has been flawless. But the 30 milliamp balance current on the DALY will be just fine on these cells. And at the lower cost, and with semi local availability, I will actually use 2 of them instead of tying the two strings together like I did with my first set

I am in the process of doubling my battery bank as well. I have not decided if I will go with another JK / Heltec BMS or just go with a DALY for the second pack. The cells I am using are proving to be so well matched and balanced that I am seeing no drift and no balancer activity with the delta voltage set at just 0.006 volts. I do like my JK and since I fixed the balance lead harness, it has been flawless. But the 30 milliamp balance current on the DALY will be just fine on these cells. And at the lower cost, and with semi local availability, I will actually use 2 of them instead of tying the two strings together like I did with my first set.
As an FYI, I am not sure if the Heltec suffera from the same issue, but this guy shared some useful info on real life cell protection with Daly.
 
Hi, does anyone know if it's OK to parallel the Heltec/JK BMS? I want to build 2 16S packs, each w/ a BMS, and then parallel the packs. I read JBD's spec sheet, and it seems to specifically parallel BMS w/ this statement:

"Direct parallel connection of batteries is not supported (there is the problem of high current discharge from high voltage batteries to low voltage batteries due to direct parallel connection of batteries)"

I can't think of a case where hooking up battery banks in parallel would cause a high current discharge between them, unless 1) one of them shorts out or 2) you connect a batteries together that are in different states of charge. If the 2 packs are at the same SOC when you hook them up, this shouldn't be an issue, right?
I'm already doing this.. i have 3x 16S packs, each with their own JKBMS, all connected together in parallel. In fact the parallel connection is then also connected to two inverters in parallel.. the higher voltage pack does end up slightly charging the lower voltage pack and you'll see this on the app when there's no external load, the -'ve A coming out of 1 pack is the +'ve A's going into another
 
I'm already doing this.. i have 3x 16S packs, each with their own JKBMS, all connected together in parallel. In fact the parallel connection is then also connected to two inverters in parallel.. the higher voltage pack does end up slightly charging the lower voltage pack and you'll see this on the app when there's no external load, the -'ve A coming out of 1 pack is the +'ve A's going into another
If my cells from rhe group buy ever get here, that will be my exact setup also.
 
As an FYI, I am not sure if the Heltec suffera from the same issue, but this guy shared some useful info on real life cell protection with Daly.
His does seem to be a pretty extreme case. It was only a 24 volt system, and his failed charge controller pumped out 96 volts. The mosfets had to withstand 96 - 24 = 72 volts. That does seem a bit low, but not really when it is a BMS for a 24 volt system. Most people would be using 32 volt rated fuses. Many common low RDS mosfets are rated for 50 or 60 volts. I would hope the 24S rated JK BMS is using some higher voltage mosfets. 24S of fully charged LFP cells would be 87.6 volts. So I would hope they used at least 100 volt rated devices. In most cases, when the battery bank shuts down, the voltage would fall and you would have up to battery voltage across the mosfets. But in his case, when the mosfets opened, the rail voltage was pulled up to 96 volts. What did that do to his inverter? He does not even mention that side in the video.

I am sure my Schneider XW-Pro would not be very happy if the battery input voltage jumped to 96 volts. That is a very bad failure. Maybe we need to install DC surge protection clamps. Something like an MOV at just 10 volts over the maximum battery voltage, and then fast acting fuses on the charge controller.

I may get a few of these
Parallel about 5 across my DC buss. They clamp at 80 volts. Each one can withstand a 250 amp peak. So 5 in parallel should have no problem popping a 100 amp fuse from the charge controller.
 
Has anyone tried these '16s' model in 12v 4s config?
I'm also building a 12v pack and wondering if it will work? I don't want to dismantle my 48v setup to test it out :(
I vaguely remember someone saying it does work, but cant be sure?
 
Depends on the model. The 200amp 2amp active is a 13-24s BMS, so 13 minimum, 24 maximum.
 
Here is what I found when testing mine a long time ago.

The BMS requires at least 40 volts to turn on. It does not need much current, so a small boost converter will run it. This can be a pain for anything less than a 48 volt system, but it is not impossible.

In the settings, at the time, with the firmware and app version I had, I was able to tell it just 4S and it all appeared to work just fine, as long as I had the power to run the BMS.

So what is the problem?
Well... If you use a small boost converter, it should all work just fine, but you will need to be sure your boost converter is powered from the BMS output. It will have a fair bit more standby current to keep it awake. At 40 volts, it only needs a few milliamps, but now you need 4 times the current from a 12 volt system. That is still small, but it can be a drain over time. So if it does drag down the batteries, let the BMS do it's job and shut it down. But this will also shut down the BMS, so it will not self recover.
 
Sounds a bit risky and reliant on the boost converter, which I wouldn't trust entirely.
May have to get an Overkill on this one.
 
wow.. this is a really detailed long thread.. I probably could have asked many of my questions here , rather than making new post.
But i didn't know Heltec was the same as JKBMS.
So I have a question to ask here about changing the name of a BMS, Since i will have 6 of these units soon... right now i have 3.
I can change all settings on mine, and password, But i cannot change the name of the BMS. It gives you the option , but nothing i do is accepted.
I wish to change them to BMS1, BMS2.......BMS6
Is there anything special to do to get the name to change ?

And I'd like to save settings so that i can just post them into the other BMS's since, they will all be set the same..

Thanks
 
wow.. this is a really detailed long thread.. I probably could have asked many of my questions here , rather than making new post.
But i didn't know Heltec was the same as JKBMS.
So I have a question to ask here about changing the name of a BMS, Since i will have 6 of these units soon... right now i have 3.
I can change all settings on mine, and password, But i cannot change the name of the BMS. It gives you the option , but nothing i do is accepted.
I wish to change them to BMS1, BMS2.......BMS6
Is there anything special to do to get the name to change ?

And I'd like to save settings so that i can just post them into the other BMS's since, they will all be set the same..

Thanks
What program are you using? I use the ENjpower app. You can change the BMS name under devices, where you scan for bluetooth access. There is a pen icon there to edit the name to whatever you like. I have not used the xioxang app, as enjpower works better for me.
 
What program are you using? I use the ENjpower app. You can change the BMS name under devices, where you scan for bluetooth access. There is a pen icon there to edit the name to whatever you like. I have not used the xioxang app, as enjpower works better for me.
the app I'm using is the JKBMS app, mine also has the pen.. i enter what i want, but the OK doesn't function..
 
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