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

Maast

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Anybody know if this active balancer can be enabled/disabled via a switch?
I want to leave it connected along with my bms and only turn it for scheduled maintenance as required.
UPDATE: provide link for clarity
Nope, once it gets above its threshold differential limit it starts balancing - proportional to how big the cell differentials are.

You might be able to experiment by switching off the main negative but I have my doubts that'd work and might damage the balancer. On the other hand they're so cheap it might be worth ordering an extra and futzing around with it.
 

ArthurEld

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Hi,

I was able to extract 254Ah on my test before #1 cell triggered the 2.6V Low BMS trip. It had dropped rapidly once it approached 3V, took about 35mins, so looks like it's faulty. It was 531mV lower than the highest. 3 other cells also ended up lower than the others, but nowhere like #1. I'll have to contact Mr. Basen. Hopefully I can get a replacement for at least #1.

Drawing about 10A over most of the test. Ran the oven & evap. coolers for a time late afternoon. Started at noon, finished 10:40 next morning.

Took about 5 hours to re-charge to 260Ah.

I now have a red band across the top of the app, also the capacity set itself to 252Ah, from my 260Ah setting, which prevented the reading going higher. I had to change it back to 260, then cause the BMS to above the high trip and set the remaining Ah to 260.

dRdoS7

UPDATE: The red Band disappeared once I closed the app, and restarted it. Must be a warning that a fault condition has occured, and to check to log. Don't recall seeing that before. Maybe only for major trips?
There are a lot of possibilities as to why you are getting lower capacity than expected.
I assume your cells are 280Ah.
Also, I think the coulomb counters won't go above the capacity you set in the parameters.
They recalibrate when you charge above the setting.

The red band shows that you hit a limit. Each limit has a recovery timer setting. If you want the BMS to turn itself back on after a certain amount of time, you can adjust that. You need to think about how you set those because you can cause it to reset over and over.
 

dRdoS7

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Hi,

There are a lot of possibilities as to why you are getting lower capacity than expected.
I assume your cells are 280Ah.
I have set it at 260Ah because I am not going too high when charging, nor too low when discharging (except for this test). I got 254Ah out of the 260Ah, so not too bad. If the #1 cell hadn't tripped the BMS, I would have got a bit more.

Yes, as I posted, I have 18 x 280Ah. By doing this, I figured I have about the same Wh as I would have by using the full 280Ah of 16 cells.

Also, I think the coulomb counters won't go above the capacity you set in the parameters.
Correct. My Midnite Classic is the same, although there is also a Net Ah reading on that which give me an idea of how much it does go over. Usually only 1 or 2 Ah.

They recalibrate when you charge above the setting.
Yes, that's what I have been seeing.

The red band shows that you hit a limit. Each limit has a recovery timer setting. If you want the BMS to turn itself back on after a certain amount of time, you can adjust that. You need to think about how you set those because you can cause it to reset over and over.
Even after the low limit was reached, and it had risen above the reset point, the red band stayed. I have a reasonable differential between the 2 ponits so it's unlikely to cycle. Red band only disappeared when the app was restarted.

I'm going to do the same test again in a few days to see if having the balancing on full time instead of only above 3.4V, as I had previously, helps. I did change the balance start voltage to 2.6V when I saw the cell dropping, but may have been too late. Or, it would have made no difference.

dRdoS7
 

ArthurEld

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Hi,


I have set it at 260Ah because I am not going too high when charging, nor too low when discharging (except for this test). I got 254Ah out of the 260Ah, so not too bad. If the #1 cell hadn't tripped the BMS, I would have got a bit more.

Yes, as I posted, I have 18 x 280Ah. By doing this, I figured I have about the same Wh as I would have by using the full 280Ah of 16 cells.
That is interesting and I have heard of other people using more cells. I plan to research that possibility in the future.
Even after the low limit was reached, and it had risen above the reset point, the red band stayed. I have a reasonable differential between the 2 ponits so it's unlikely to cycle. Red band only disappeared when the app was restarted.
The recovery setting works as expected for me. For and over voltage alarm the cell need to settle to the over voltage recovery value then the alarm is cleared.

The amperage limits have a time recovery. That is the one I had resetting over and over. I was charging over the limit.
The alarm would occur then after one minute it would reset. Then my charger would hit the limit and cause the error.
It could have keep doing that for days if I didn't notice my living room lights flickering.
 

MisterSandals

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Yes, as I posted, I have 18 x 280Ah. By doing this, I figured I have about the same Wh as I would have by using the full 280Ah of 16 cells.
Things like this keep me awake when i should be sleeping...
How does one configure a battery with 18 cells? Do you have an 18S BMS?

Mind thrashing:
48v: 18S
24v: 2P9S or 9S2P
12v: <headache>
 

mmdb

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Can anyone recommend AliExpress shop to order heltec bms 16s with active balancer
 

fafrd

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I just fried my brand-new Heltec 300A min-smart BMS and am interested to understand whether anyone has successfully tested this 350A smart Heltec BMS beyond the limits of my test:

80A discharge for 3-1/2 hour continuous (full discharge of my 8S LiFePO4 battery).

My new BMS performed beautifully for the first hour of the test then started smoking (and is probably now fried).

I’m in dialog with Heltec now to understand whether my unit was defective, because I would expect a BMS rated for 300A ‘Max Working Current’ and 100A Max Charge Current to have no difficulty to manage an 80A discharge for 4 hours (or even longer).

So has anyone successfully tested this BMS for continuous discharge of 3.5 hours or longer at discharge current of 80A or more?

My BMS was passively cooled in a room that was at 25C (77F) so I’m also interested in whether anyone running their BMSes at 80+A for 3.5+ hours is relying on passive cooling or they are actively cooling with a fan?
 

ArthurEld

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Sad news and the 300A version.
I haven't discharged at 80A for that long.
Mine is the 200A version but it says right on it 350A discharge current limit.

I hope they stand by their product.
 

fafrd

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Sad news and the 300A version.
I haven't discharged at 80A for that long.
Mine is the 200A version but it says right on it 350A discharge current limit.

I hope they stand by their product.
Well on the one hand, it’s a bummer the BMS couldn’t handle 80A for 3.5 hours and likely got fried.

On the other hand, I’m exceedingly happy I discovered this issue now and before my entire build was completed.

If I received a defective unit, hopefully the replacement passes with flying colors.

And if these Heltec ‘dumb’ BMSes are overrated and either can’t handle 80A for 3.5 hours continuous or need additional care and feeding such as active cooling (fan), at least I know I need to either find a better BMS or rig up an active cooling solution...

I measured voltage drop between B- and P- @ 80A and it was 0.45V.

Others are telling me that is a very high voltage drop and probably indication of a defect.

Anyone else who has a Heltec BMS which they have tested at 80A or more, I’d be interested to know what voltage drop you are getting between B- and P-...
 

dRdoS7

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Hi,

Things like this keep me awake when i should be sleeping...
How does one configure a battery with 18 cells? Do you have an 18S BMS?

Mind thrashing:
48v: 18S
24v: 2P9S or 9S2P
12v: <headache>

I am using one of these:


It can handle 14-24S LFP, I run a 48V system.

It appears to be able to run less than 14S cells if a DC-DC boost converter is used to supply the B+ to the BMS. I have a 2nd of these, so may try it out one day. Need to buy 4 more cells for that. Might be handy for when the current caravan batteries fail. Hopefully a long time in the future.

dRdoS7
 

GXMnow

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Sorry to hear it sounds like one of these has failed at just 80 amps. I never expected them to truly do 200 amps for long term, but 80 should not be a problem. My 200 amp rated JK (Heltec) BMS has only been used up to 80 amps so far. It ran that current for about 1 hour and was a little warm. I have it bolted to a 5.25 inch x 19 inch rack panel, so that does help pull some heat out. I then added a heat sink on the outside of the panel to help pull out heat, and I had a heat pipe CPU cooler on the face of the BMS for a while, but the thermal adhesive gave up and it pulled away. I will need to add a clamp of some sort to hold up the weight. I have not added a fan yet. Now that my system is up and running, I only run about 30 amps while the grid is up. Right now the sun is shining, and the battery bank is charging at just 28 amps. The rest of my solar power is running my house. In the evening, I discharge the battery bank at just 29 amps to zero out my grid use during the peak rate time for 5 hours. In this usage, the BMS only reaches about 3-5 degrees C above the ambient temp in my garage. Measuring the voltage drop from the ends of the cables, the total resistance through the BMS with the 6 inches of wire on both end works out to just under 1 milliohm. At 80 amps, that is generating 6.4 watts of wasted heat out of the BMS and the wiring. That is not a lot, but it is enough to need some air flow to keep it cool. I just grabbed a snap shot right now. This is cold weather for us at just 8C (46F) right now, and it was colder overnight. My garage has 2 common walls with the house so it does not get quite as cold as outside. The battery temp is reporting at 13 C, the Schneider battery temp sensor, which is current just hanging next to the battery cables also shows 13C. So that is probably the air temp in the garage right now. The BMS FET temp is showing 16C at my 28 amp charge current.

As for the number of cells....
Officially, they say it supports 14S to 24S, but I did a few tests on the unit, and found it worked perfectly even at just 4S as long as you provide it with 40 to 100 volts to power the BMS electronics. The setup app even let me enter 4S and it functioned properly and reported no errors. The only "issue" is the need for a separate power supply which is going to be less efficient. The board itself does appear to run at lower voltage, but the DC to DC converter they built on the board needs 40 volts. It may be possible to supply it after that converter, but it would require a bit of experimenting to see what it would take. It does not seem to measure the full pack voltage. It looks like it just adds up all of the cell voltages. I had it powered at 42 volts, but it only reported the 4S pack at the correct 15.6 volts.
 

fafrd

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Sorry to hear it sounds like one of these has failed at just 80 amps. I never expected them to truly do 200 amps for long term, but 80 should not be a problem.

Yeah, I figured sizing at 150% of sustained capacity would be OK. I’m suspecting the unit was defective and in contact with Heltec to get it sorted out. I have a second unused unit but want guidance from them about what sustained current I should be able to pass for 4 hours with passive cooling only before testing it.

My 200 amp rated JK (Heltec) BMS has only been used up to 80 amps so far. It ran that current for about 1 hour and was a little warm. I have it bolted to a 5.25 inch x 19 inch rack panel, so that does help pull some heat out. I then added a heat sink on the outside of the panel to help pull out heat, and I had a heat pipe CPU cooler on the face of the BMS for a while, but the thermal adhesive gave up and it pulled away. I will need to add a clamp of some sort to hold up the weight. I have not added a fan yet.
Adding a better heat sink would obviously be a way to improve the capability of an all-in-one BMS like this - I just had mine passively cooled by ambient air.

I need an 8S BMS that can charge at 80A for 3-4 hours a day and can discharge at 80A for 3-4 hours a day and if that kind of use requires careful attention to heatsink design and possibly active cooling, I’m thinking the Chargery architecture may be a better way to go. They move the best-generating ‘switch’ into it’s own box with active cooling such as what you find on an inverter or a charge controller. Leaving the sensing and ‘smarts’ it it’s own relatively cool unit.

For sustained use at 80A of higher, that architecture is starting to appeal yo

Now that my system is up and running, I only run about 30 amps while the grid is up. Right now the sun is shining, and the battery bank is charging at just 28 amps. The rest of my solar power is running my house. In the evening, I discharge the battery bank at just 29 amps to zero out my grid use during the peak rate time for 5 hours. In this usage, the BMS only reaches about 3-5 degrees C above the ambient temp in my garage. Measuring the voltage drop from the ends of the cables, the total resistance through the BMS with the 6 inches of wire on both end works out to just under 1 milliohm. At 80 amps, that is generating 6.4 watts of wasted heat out of the BMS and the wiring.

So you measured 1 mOhm @ 29A meaning a voltage drop of 29mV @ 29A and you are projecting that you’d measure an 80mV voltage drop at 80A (but have not confirmed that with measurement), right?

In any case, it’s pretty clear that by the time I used my DMM to measure the BMS voltage drop, something was wrong.

The primary purpose of my test was to check for cell voltage droop under 0.3C discharge and to measure battery capacity under sustained 0.3C discharge. I was checking cell voltages and temperatures constantly but not really focused at all on the BMS. Since I had it and had never tested it, I thought I might as well connect it and figured I test LVD at the end of the discharge and HVD after charging back to 100%. But it never occurred to me that a 300A BMS would struggle with only 80A of current, so I didn’t really focus on the BMS until an hour into the t
That is not a lot, but it is enough to need some air flow to keep it cool. I just grabbed a snap shot right now. This is cold weather for us at just 8C (46F) right now, and it was colder overnight. My garage has 2 common walls with the house so it does not get quite as cold as outside. The battery temp is reporting at 13 C, the Schneider battery temp sensor, which is current just hanging next to the battery cables also shows 13C. So that is probably the air temp in the garage right now. The BMS FET temp is showing 16C at my 28 amp charge current.

Smart BMSs with reporting definitely have an advantage over dumb BMSes like the one I have when it comes to detecting a problem before it’s become a failure.

I was running my test using space heaters which warmed the room to 24C (75F) which didn’t help with cooling, but it gets that hot in the summer so if a BMS like this needs enhanced cooling to manage 80A for 4+ hours continuous, better to understand that earlier than later.
As for the number of cells....
Officially, they say it supports 14S to 24S, but I did a few tests on the unit, and found it worked perfectly even at just 4S as long as you provide it with 40 to 100 volts to power the BMS electronics. The setup app even let me enter 4S and it functioned properly and reported no errors. The only "issue" is the need for a separate power supply which is going to be less efficient. The board itself does appear to run at lower voltage, but the DC to DC converter they built on the board needs 40 volts. It may be possible to supply it after that converter, but it would require a bit of experimenting to see what it would take. It does not seem to measure the full pack voltage. It looks like it just adds up all of the cell voltages. I had it powered at 42 volts, but it only reported the 4S pack at the correct 15.6 volts.
Inspecting my failed BMS, it looks like an entire P- copper busbar was poorly-soldered - I can slip a piece of paper under it most of the length. So whether that could have led to the high resistance and heat buildup I experienced or not, I can’t say, but it certainly didn’t help.

After this experience, I will either move to a Heltec Smart BMS like yours or switch to Chargery...

The need for a seperate power supply to operate at 8S is a PITA but not a showstopper - how much power does it consume?
 

ArthurEld

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After this experience, I will either move to a Heltec Smart BMS like yours or switch to Chargery...
I personally like the Heltec BMS with active balance.
Overkill is probably the most highly recommended 8s BMS on this forum.
So, if you want a sure thing, I'd check into that.
 

fafrd

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You don't mean the smart BMS with active balance do you?
No, it was a typo (that I can no longer fix). My BMS was non-smart. I’m thinking about moving to a smart BMS like yours (but still concerned about charging current limit).
 

fafrd

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I personally like the Heltec BMS with active balance.
Overkill is probably the most highly recommended 8s BMS on this forum.
So, if you want a sure thing, I'd check into that.
Overkill is also all-in-one, correct?

Seeing how much heat can be generated moving 2kW let alone 3kW, I’m starting to think about the Chargery architecture where the cut-off switch is external and has active cooling...
 

ArthurEld

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No, it was a typo (that I can no longer fix). My BMS was non-smart. I’m thinking about moving to a smart BMS like yours (but still concerned about charging current limit).
I would be very disappointed if these Heltic BMSs with active balance couldn't handle 80A discharge.
I know Heltec had a bunch of really cheap non smart BMSs on their website. I don't know which one you have.
Chargery seems to be good for high amps but I hear plenty of complaining about them too.
 

ArthurEld

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Overkill is also all-in-one, correct?
It doesn't have active balance if that is what you mean. Active balance has it's uses but I don't at all think it is a must have.
I think people assume it will work faster than it does. I doubt even 10A active balance is fast enough to give a lot of extra Ah
 
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