Heltec BMS' (up to 350A) with Active Balancing & Independent Active Balancers

Stepandwolf

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Been debating a Heltec but ran into a snag. The Alibaba rep said they don't make an 8S Smart BMS, only dumb. I saw a YT video of a guy using a 12S for an 8S build. A diagram from that BMS company had him combine 5 leads for one cell. It wasn't a brand I had heard of, but could the 12s Heltec work the same way to make it 8s compatible?
 

ArthurEld

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GXMnow

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Been debating a Heltec but ran into a snag. The Alibaba rep said they don't make an 8S Smart BMS, only dumb. I saw a YT video of a guy using a 12S for an 8S build. A diagram from that BMS company had him combine 5 leads for one cell. It wasn't a brand I had heard of, but could the 12s Heltec work the same way to make it 8s compatible?
When I first got my JK BMS (Same as the Heltec smart BMS) with active balancing, I did a bit of testing with it. The documents say 14S to 24S but I tried it with as few as 4S and the setup app allowed the setting and it worked just fine. The only problem is that you do still need a 40 to 100 volt power source to run the BMS electronics. I do not know how much power it actually needs. I did not measure the current, but it does not seem like much. You can use a small boost regulator to produce 48 volts from your 12 volt battery bank and it should work just fine as long as it is common negative. Once you power it up, set it for just 4S and reboot it. And it all works correctly.
 

Sanwizard

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When I first got my JK BMS (Same as the Heltec smart BMS) with active balancing, I did a bit of testing with it. The documents say 14S to 24S but I tried it with as few as 4S and the setup app allowed the setting and it worked just fine. The only problem is that you do still need a 40 to 100 volt power source to run the BMS electronics. I do not know how much power it actually needs. I did not measure the current, but it does not seem like much. You can use a small boost regulator to produce 48 volts from your 12 volt battery bank and it should work just fine as long as it is common negative. Once you power it up, set it for just 4S and reboot it. And it all works correctly.
I just bought this one directly from Heltec:

14-24S 200A Smart BMS with 2A Active balance Li-ion Lipo Lifepo4 LTO via bluetooth GPS for shared car Support CAN / RS485​


Overview

Quick Details
Place of Origin: Sichuan, China
Brand Name: Heltec Model Number:???

String (Lifepo4): 16-24SString
(Li-ion): 14-24SOutlet method:
Same Port
Cell voltage: 1-5V
Voltage acquisition accuracy: ±5mV
Continuous discharge current: 200A
Discharge current(MAX): 350A
Equilibrium current: 2A
GPS remote: Optional (contact us)
Other interfaces( CAN, RS485,etc,.): Optional (contact us)


Is that similar to yours?
 

Sanwizard

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I will dig out my scope and take some measurements. I only used the Low ESR electrolytics so far. These are very high grade, they came out of a variable speed motor drive, so they were intended to filter high frequency switching DC loads. With only 3,600 uf total, I was not expecting much of a spark, but wow, 50 volts made a nice snap. I will use my pre charge resistor next time I connect them. Glad it didn't pop the 30 amp MRBF fuse feeding it.

I am certain there is nothing wrong with Cell 12. The XW inverter/charger runs up to 80 amps charging or discharging and no cell deviates more than 10 millivolts under those loads, and with the little buck converter off, Cell 12 is smack in the middle of the cell voltage range. And even when the 12 volt buck converter is running and the cell voltage readings are going stupid, my Fluke meter shows all of the cells stable as a rock and within 10 mv from highest to lowest. And the way the cells are in the Chevy Bolt bricks, I can't really swap around cells. Cell 12 is actually 6 cells, consisting of 2 groups of 3, in 2 different sections of the top brick. Cells 1 through 10 are each 3 cells in the bottom brick, paralleled with the matching 3 cells in the middle brick. The Cells 11 through 14 are the top brick. It was originally an 8S3P setup. I cut the middle buss bar, and paralleled the back 4 groups with the front 4 groups to make it 4S6P. The balance leads of the 2 separate 3P strings are all fused at 7 amps and tied between them with #16 wire to the BMS #20 balance leads. The small wire resistance between the strings parallel balances the 2 groups and reports the average between them to the BMS. I was very careful to keep all the resistances matched. When the balancer is moving 2 amps, I see 1 amp to each group on the balance leads. The two main current paths are the factory Chevy Bolt Buss bars, and #2 cables, fused at 125 amps to the main buss bar. So swapping cells around is not really an option.

I guess I could add 14 capacitors across each cell at the balancer end of the leads, but that will be a bit of a pain. About the only way I could see doing it wuld be to cut all the balance wires and splice in th caps about an inch from the connector. The balance wires are about 0.13 ohms from each cell, so even a 1 uf cap should filter a fair bit of RFI. Probable use a good film or ceramic type, but with 14 of them in a row, it will be an interesting experiment. Maybe I can slip a ferrite bead on each lead as well. 15 of those. Since it is measuring the voltage of each cell, I would just use low voltage caps wired the same as each cell at the balance connector.

First I tried an audio range digital scope and it was basically useless. So I pulled out my old BK Precision crt scope. The caps on the input side are certainly doing their job. I can't lock any voltage waveform on the input side of the buck converter, or on the lead to the batteries. I expected to see some 120 HZ as the XW inverter is pumping out 1,600 watts into my house right now. On the output side of the buck converter, WOW, it has all kinds of hash. I could see the 12 volt DC but the screen had a glow above and below it. I put it in AC coupled so I could center the trace without the 12 volt offset. Turned the gain up just a little and it was able to sync a waveform. To see the wave, I had to dial up my sweep rate to the highest setting, on a 15 Mhz scope. 1 us / div. The repetition rate of the main pulse is about 154,000 hz (6.5 us period). Then it has a ringing well over 2 Mhz after each pulse. The peak to peak voltage at the main switching pulse is OVER 12 volts. In DC mod, it went from below 6 volts to over 18 volts. The ring after the pulse quickly drops to about 1 volts, then tapers to just about nothing right as it hits the next switch pulse. Here is the best pic I could get on my phone.

View attachment 25217

The phone image does not really do it justice.
Here are pics of the toroid and the filter installed.

View attachment 25218 View attachment 25219

I am hoping some caps on the output of the buck converter might be enough to stop the balancer from going goofy.
Do you guys use shielded panels or plastic sheets between your cells when putting a string together, or just butt them up against each other?
 

GXMnow

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My cells were already in a pack that came out of a Chevy Bolt EV. They are pouch cells. There is an aluminum plate between each pair of cells, even though they are wired in parallel groups of 3 cells. The pouches are completely insulating plastic on the outside, so not issue there.

Many of the aluminum cased LFP cells do show some charge potential on the case, but I have not built a pack from those yet. They are typically shrink wrapped, but some do not trust that and do add a little more insulating material between the cells, though some say it is not needed as the slight current to the case is minimal leakage. I honestly don't know if it would cause a measurable drain on the cells or not.
 

Sanwizard

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My Heltec (JK) did work on just 4S so 8S won't be a problem, but there is one issue. You do need a 40 volt power supply to run the electronics. This can be a separate supply, or a DC-DC boost converter off of your 8S pack. It does not need much current at all. I have not measured it, but it is on a #22 awg wire. And when my pack sits at rest, I do not see any drop in pack voltage for days.

The current numbers are a bit more of a concern. Mine is rated at 200 amps. I am fairly confident it will take that as it barely got warm at 80 amps. I have not pushed it further, but the voltage drop and temp looks good. The newer rating I have seen for 300 amp appears to be a surge rating, and not continuous. It seems to have the same FET's as my 200 amp rated unit that does say 300 surge in the instructions.

On the full JK/Heltec BMS, you certainly can set a minimum voltage where it will shut off balancing. So if the pack is low, it won't waste energy trying to move charge around until you charge up again. All of the parameters are fully adjustable. If it comes with a password, try "123456" to get into the advanced settings menu.

For the current you are looking at, I would suggest doing it as 2 packs in parallel with 2 BMS units so the constant current is always under 200 amps per BMS. My maximum steady current should never exceed 150 amps, 6,800 watts on a 48 volt system, so the 200 amp rating is fine for me. For 300+ amps continuous in a single BMS, I would probably go with something like the Chargery with the external DCC contactor. Then you can add a Heltec balancer if you wanted the active balance feature. The JK works great and seems well built, but the current path is only a pair of #7 awg wires which seems suspect for anything over 100 amps for long term. I shortened them a bit. On the input they go to a buss bar withthe cables from the pack. And spliced them to a 2/0 cable on the output side to the output buss bar. The wires did not get warm on my 80 amp test, I have not pushed to 140 yet as I don't have a large enough load to use all that power. My current setup is limited to a 20 amp breaker feeding into my main panel. Pushing just over 16 amps back was how I hit 80 amps at the BMS.
I am building my solution based on some of your work I have been reading about here. I am starting off with the same Heltec 200A BMS you bought, and am waiting for my 16 x 280Ah Lishen cells. They will be connected to an MPP 6548 Inverter/charger. Would you be able to share your BMS parameter settings? Perhaps a schematic of your setup? That will help me get the BMS setup much faster. Any help greatly appreciated!
 

GXMnow

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My cells are NMC based, not LFP so my voltages are different. I only run 14S to get my 48 volt system. Actually 42 volts at minimum 3.0 volts x 14 and 58.8 volts maximum at 58.8 volts per cell x 14.

Most LFP cells have a minimum voltage of about 2.5 volts per cell, and 3.65 volts maximum at full charge. Those are the levels you should never exceed. I would set the BMS disconnect levels just inside of that range, something like 2.75 minimum and 3.6 maximum. And then set the Charger to do Absorption charge at about 56.8 volts for 16S. That is 3.55 volts per cell and should give you enough margin for balance drift so no cell should hit the 3.65 level. Your loads (inverter etc.) should shut down when the battery bank voltage falls below 46.5 volts or so. That works out to 2.9 volts per cell and gives you some room for them to go out of balance on the low end. The JK BMS app allows you to set a threshold voltage where balancing will only occur above that voltage. Most agree that large LFP banks should only be top balanced, so set this up around 3.4 volts or so and then as the batteries charge up, they will only balance near the top. LFP cells have a very flat charge/discharge curve, so over most of the area, the cell voltages should all stay close enough to not need balancing. Near the top, there is a voltage knee. The most charged cell will start to increase voltage faster. The active balancing in the JK (Heltec) will pull power from the cell that is going too high and then push that power to the cell that is the lowest. Once they get into close balance, it will basically just sit there and monitor 99% of the time. Mine hardly ever has to kick in any balance current.

Most LFP cells should not be charged when the cell temperature is below freezing 0C of 32F or above 50C or about 122F. Under discharge, they can handle a little wider range of -10C (14F) to 65C (150F) so that is usually less of a problem. The app on mine allows for low and high temp cut off levels.

Hope that helps. The BMS should never need to cut off charge or discharge current. If it does, it means something is wrong. It is a protection device, not a charge controller.
 

Stepandwolf

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Thanks, but I don't want to add yet another piece of electronics to make a higher S count work with my 8S.

I did hear back from Annie from Heltec and mentioned the person who added wired together to use all 12 and if that worked with the Heltec, she said: "Sorry, our products do not support this.".

This was after telling me they had no Smart 8s compatible product. I know you guys have had success, but I would feel more comfortable with a smart BMS made for 8S and it seems the Daly is all I have found that can handle 250A.
 
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Sanwizard

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My cells are NMC based, not LFP so my voltages are different. I only run 14S to get my 48 volt system. Actually 42 volts at minimum 3.0 volts x 14 and 58.8 volts maximum at 58.8 volts per cell x 14.

Most LFP cells have a minimum voltage of about 2.5 volts per cell, and 3.65 volts maximum at full charge. Those are the levels you should never exceed. I would set the BMS disconnect levels just inside of that range, something like 2.75 minimum and 3.6 maximum. And then set the Charger to do Absorption charge at about 56.8 volts for 16S. That is 3.55 volts per cell and should give you enough margin for balance drift so no cell should hit the 3.65 level. Your loads (inverter etc.) should shut down when the battery bank voltage falls below 46.5 volts or so. That works out to 2.9 volts per cell and gives you some room for them to go out of balance on the low end. The JK BMS app allows you to set a threshold voltage where balancing will only occur above that voltage. Most agree that large LFP banks should only be top balanced, so set this up around 3.4 volts or so and then as the batteries charge up, they will only balance near the top. LFP cells have a very flat charge/discharge curve, so over most of the area, the cell voltages should all stay close enough to not need balancing. Near the top, there is a voltage knee. The most charged cell will start to increase voltage faster. The active balancing in the JK (Heltec) will pull power from the cell that is going too high and then push that power to the cell that is the lowest. Once they get into close balance, it will basically just sit there and monitor 99% of the time. Mine hardly ever has to kick in any balance current.

Most LFP cells should not be charged when the cell temperature is below freezing 0C of 32F or above 50C or about 122F. Under discharge, they can handle a little wider range of -10C (14F) to 65C (150F) so that is usually less of a problem. The app on mine allows for low and high temp cut off levels.

Hope that helps. The BMS should never need to cut off charge or discharge current. If it does, it means something is wrong. It is a protection device, not a charge controller.
Thank you very much. That helps immensely. I think my BMS is exactly the same as yours, so I can leverage those guidelines. I think the sensors come with it too. Now I just need to find an old phone, as my company android will not let me install the app. Security.
 

Haugen

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Do you guys use shielded panels or plastic sheets between your cells when putting a string together, or just butt them up against each other?
I bought some thin foam sheets that im going to cut to size before I clamp the cells together I may leave a small gap in the middle for airflow. I have to refresh my memory on where the cells swell first.
 

Stepandwolf

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I bought some thin foam sheets that im going to cut to size before I clamp the cells together I may leave a small gap in the middle for airflow. I have to refresh my memory on where the cells swell first.
One buyer used slender adhesive foam sheets, 2mm..similar to what he used

My current plan is to frame my cells in with 3/4" plywood in my TT. I am creating a new board to reinforce and thicken the existing wall in the storage area and it will be what the components and battery bank will be on. I have been concerned about having the cells directly touching the wood wall so something like these foam panels might be the trick...between cells and around the outside.
 

Haugen

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One buyer used slender adhesive foam sheets, 2mm..similar to what he used

My current plan is to frame my cells in with 3/4" plywood in my TT. I am creating a new board to reinforce and thicken the existing wall in the storage area and it will be what the components and battery bank will be on. I have been concerned about having the cells directly touching the wood wall so something like these foam panels might be the trick...between cells and around the outside.
I bought very similar foam at JoAnn Fabric in the craft section. Not self adhesive, but only like $1 for a letter size sheet.
 

ArthurEld

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Guys, I'm having difficulties and there's no help from China this week.
Does anyone know if there is a way to a hard reset on these smart BMSs?
I am getting a CPU warning on one of my units and I can't clear it.

Also, for some reason, the JK app isn't on the app store any more. I downloaded the APK and I can't get it to work on an old phone that is at android 4. I am hoping to connect a separate phone to each BMS.
Does anyone know of an app that works from the play store?
Or, does anyone know of an app that works on an old android?
 

mmdb

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I have armor 6 and I downloaded it from link you gave me ..I installed it on my phone ...jk bms will arrive in few days and I will let you know .....
 

ArthurEld

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I have armor 6 and I downloaded it from link you gave me ..I installed it on my phone ...jk bms will arrive in few days and I will let you know .....
Thanks mmdb.
I am not sure what armor 6 is. Is that for Apple? I saw the Apple store link still works but the link for Play Store just starts a download.
The APK I downloaded from JK is called - enjpower-3
I think the phone I am trying to use is too old for the APK. I tried the APK from Heltec and got the same error. Something to do with unable to parse file.
I have a few other androids laying around I'll keep trying to hack my way in.
Eventually I'd like to leave an unused phone or two near the batteries. I have an android tablet too that I never use.

My regular phone is working fine so I can still see everything..
 

GXMnow

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Well, got some bad news. Today, shortly after my XW-Pro inverter started outputting power, I got a battery low voltage error. I checked it with a meter, and sure enough, the input of the XW was only showing about 35 volts. I went to the BMS app on my phone, and it shows Charge Off and Discharge Off. So it went into a protect mode. It was showing a battery voltage of 48 volts, but it is near full charged, so it should be over 56 volts. It is showing down 2 cells. And when I look down the BMS screen, Cells 3 and 4 are blank. No voltage. I measure the cells, and they are all just over 4 volts as expected. I even checked at the connector into the JK BMS and they all measure just fine. So it seems to be an internal failure in the JK BMS not seeing the lead between cells 3 and 4. I have the board out of the case, and I do not see any bad connection or burnt components. I am going to contact the seller and see what they say. I will probably get a DALY or a Chargery if they won't stand behind this. I will see if I can also make it still balance on the good leads since it has 10 more I was not using.
 
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