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Active balancer, make it smart!?

Visusolar said:
I don't know about the 16s ones (i don't understand why they would have to overlap two or more balancer boards across a central common cell), you might be right about that one. Maybe @BradCagle could chip in some thoughts about that.

I noticed one thing, cell 16 (B16) was the highest (minimum 20% more capacity than the lowest cell) after letting the active balancer stay connected 24/7 over a couple of months. In Andy's video it was the same, cell 16 was the runner cell. Not sure how that phenomenon is created.
Click to expand...

I haven't examined the 16s, only 8s, and 4s. But I couldn't image they would do something weird like overlapping. I mean all they have to do is share a common parallel buss, and the switching signal to be in sync across both sides. Looking at the pictures of the 16s the two halves are back to back right where the parallel bus is. Stands to reason they would be connected there. Of course take that with a grain of salt, just speculation.
 
Actually may be possible to link two 8s (or 4s) balancers together at the parallel buses. Now the switching will be out of sync, but might could add an extra (larger) cap to compensate.
 
That should certainly be possible, but the pictures I see of these balancers does not seem to offer that option.

One other issue of directly linking together (and synchronizing the switching) would be the voltage rating of the mosfets.
 
Visusolar said:
Updates on testing HANKZOR's customized active balancer:

The kind customer agent i was always referring to was actually the very well known Nami many know here already. She does really a great job, they must be proud to have her!

So this is the information Nami supplied me with so far (she said after the weekend she can reply more accurately):
Only the voltage of B1 (cell 1) is measured. These are the specs of the chip which is doing that.
View attachment 99038
She wrote:
"Sorry, the engineer checked the resistance of the sample and found that the resistance used by this sample is 3.3V. As long as B1 is lower than 3.3V, it will stop. The voltage detection chip only detects the voltage of B1. When B1 is lower than 3.3V, it will stop, and when B1 is higher than 3.465v, it will restart. 3.3*1.05=3.465 startup"

As well:
"It can be made more accurately and needs to increase the cost"

I checked and according to my new JBD BMS and pretty accurate RC3563 voltmeter which seconds the BMS measurement to the mV, my customized active balancer starts if B1 is at 3.456V and stops again if B1 reaches 3.323V.
Click to expand...
0.165 V is not bad......if you shooting for 3.4 V for cells max V that will bring you in worst case scenario up to 3.565 . Definitely interested in more details. More tight ( accurate) deltaV trigger will be better choice.
 
Warpspeed said:
That should certainly be possible, but the pictures I see of these balancers does not seem to offer that option.

One other issue of directly linking together (and synchronizing the switching) would be the voltage rating of the mosfets.
Click to expand...

The parallel buss on these things never see voltage higher than the average of all cells so max 3.65 (or 4.2 for li-ion) Therefore the mosfets never see a voltage higher than that, even if they were linked. The parallel bus is on at the rear of the balancer (or middle for the 16s). You can scratch the enamel down to the traces, and solder wires there.

Again just speculating about what can be done through modding. I have attached to the parallel bus on these and can read the average voltage there.
 
Warpspeed said:
Yes you are right.
But the problem with all those flying capacitor balancers is, they can only move charge and balance between two adjacent cells.

If for example there is a string of 16 cells, and cell 1 is low, cells 2 to 15 are perfect and cell 16 is very high.
Cell 16 cannot transfer charge into cell 1 directly.
Click to expand...
This is true for many "flying capacitors" Balancer, but does not apply to the concerned Hangzu / Heltec Balancer.
See the above video which explains how these Balancers work. I have tested in detail quite a number of these Balancers for 12 V and 24 Volts.
My conclusion: the best Balancer available for the price,.......but only, if you turn it off below some 3. 35 V, and turn it on above 3.37 V.
 
Visusolar said:
Updates on testing HANKZOR's customized active balancer:

The kind customer agent i was always referring to was actually the very well known Nami many know here already. She does really a great job, they must be proud to have her!

So this is the information Nami supplied me with so far (she said after the weekend she can reply more accurately):
Only the voltage of B1 (cell 1) is measured. These are the specs of the chip which is doing that.
View attachment 99038
She wrote:
"Sorry, the engineer checked the resistance of the sample and found that the resistance used by this sample is 3.3V. As long as B1 is lower than 3.3V, it will stop. The voltage detection chip only detects the voltage of B1. When B1 is lower than 3.3V, it will stop, and when B1 is higher than 3.465v, it will restart. 3.3*1.05=3.465 startup"

As well:
"It can be made more accurately and needs to increase the cost"

I checked and according to my new JBD BMS and pretty accurate RC3563 voltmeter which seconds the BMS measurement to the mV, my customized active balancer starts if B1 is at 3.456V and stops again if B1 reaches 3.323V.
Click to expand...
Good job! Thank you for sharing this information.
I will think about which voltage level would be the best compromise, taking into account the a.m. hysteresis.
Nevertheless one drawback is the fact that it is only cell 1 being monitored. This is no problem, once the cells are balanced. But one objective of a Balancer is to accept unmatched / unbalanced cells and bring them to a balanced status.
 
Hans Kroeger said:
Good job! Thank you for sharing this information.
I will think about which voltage level would be the best compromise, taking into account the a.m. hysteresis.
Nevertheless one drawback is the fact that it is only cell 1 being monitored. This is no problem, once the cells are balanced. But one objective of a Balancer is to accept unmatched / unbalanced cells and bring them to a balanced status.
Click to expand...
Welcome, my pleasure.

I also asked about why only B1 is measured and she answered:
"Measuring the voltage requires self consumption of power, which not only needs to consider the power consumption, but also the cost. The balancer is cheap, so no more changes will be made"

Yes for an unmatched pack one will have to take the Arduino road or buy more expensive equiqement. These relay boards with an integrated esp32 module cost just 4 usd. Hardware is cheap and no issue, there is just no code available for that yet. Should be rather easy to do for someone who can code.
 
BradCagle said:
The parallel buss on these things never see voltage higher than the average of all cells so max 3.65 (or 4.2 for li-ion) Therefore the mosfets never see a voltage higher than that,
Click to expand...
The parallel bus certainly never sees more than one cell voltage ACROSS THE BUS. And neither do the capacitors.

But what if you have a 100v battery string of thirty cells?
There will then be a 100v difference between the first lowest cell, and the thirtieth highest cell.
The mosfets that are off might then see up to 100v across them.

Its not a big deal for 12v to 48v batteries, but there will be a definite limit to how many of these you may be able to stack and link up together.
 
After some more testing i can say i am very pleased with it. It balances as good and fast as my stock one and on top of that it can't mess up my top balance anymore.
IMG_20220618_163001.jpg

It goes to ? latest at 3.311V (3.323V to 3.311V). There is only 4-5% of capacity at 0.26C charge and discharge between 3.456V and 3.311V (tested multiple cycles). So as soon as it starts balancing (3.345V to 3.346V) the balancer has a minimum of 4% of capacity to do its job before going into ?mode again.

In my case most of the time it will by in sleep mode (which i like) anyway since i don't go over 3.45V often. I will only charge higher if i see that my battery needs a new top balance. Then the balancer will be ready help with that in a convenient way. So that fits my battery usage very well.

If i forgot something you are interested in let me know.
 

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Visusolar said:
After some more testing i can say i am very pleased with it. It balances as good and fast as my stock one and on top of that it can't mess up my top balance anymore.
View attachment 99056

It goes to ? latest at 3.311V (3.323V to 3.311V). There is only 4-5% of capacity at 0.26C charge and discharge between 3.456V and 3.311V (tested multiple cycles). So as soon as it starts balancing (3.345V to 3.346V)the balancer has a minimum of 4% of capacity to do its job before going into ?mode again.

In my case most of the time it will by in sleep mode (which i like) anyway since i don't go over 3.45V often. I will only charge higher if i see that my battery needs a new top balance. Then the balancer will be ready help with that in a convenient way. So that fits my battery usage very well.

If i forgot something you are interested in let me know.
Click to expand...
It fits your needs, that is good news.
For my usage the switch on voltage level is a bit too high. The switch off voltage would be OK.
Just a note concerning your statement:
"the balancer has a minimum of 4% of capacity to do its job before going into ?mode again."
The "job of the Balancer" has nothing to do with the 4% of capacity. The Balancer just moves charge between cells until cell voltages are equal. The current which moves charge is proportional to the difference between the individual cell voltage and the average value of all cells. The higher the capacity of the cell is, the more time the Balancer will need to do its job. But this is all independent of the amount of charge (4%) to be moved between the switching points of the Balancer. The Balancer doesn't know anything about the charging or discharging process. It simply reads voltages.....
 
Warpspeed said:
The parallel bus certainly never sees more than one cell voltage ACROSS THE BUS. And neither do the capacitors.

But what if you have a 100v battery string of thirty cells?
There will then be a 100v difference between the first lowest cell, and the thirtieth highest cell.\
Click to expand...

None of the mosfets see more than a single cell voltage no matter how many cells are strung up.

Warpspeed said:
The mosfets that are off might then see up to 100v across them.
Click to expand...

I assume you're talking about the series mosfets. Mosfets in series the voltage rating is additive as long as they are all switched at the same time.
If you have 30 10v mosfets in series, and they are switch the same time you have 300v of maximum drain-source blocking capability.
 
Warpspeed said:
The parallel bus certainly never sees more than one cell voltage ACROSS THE BUS. And neither do the capacitors.

But what if you have a 100v battery string of thirty cells?
There will then be a 100v difference between the first lowest cell, and the thirtieth highest cell.
The mosfets that are off might then see up to 100v across them.

Its not a big deal for 12v to 48v batteries, but there will be a definite limit to how many of these you may be able to stack and link up together.
Click to expand...
Mosfets can easily handle drain to source voltages of 100 Volts and more.....
 
Hans Kroeger said:
It fits your needs, that is good news.
For my usage the switch on voltage level is a bit too high. The switch off voltage would be OK.
Just a note concerning your statement:
"the balancer has a minimum of 4% of capacity to do its job before going into ?mode again."
The "job of the Balancer" has nothing to do with the 4% of capacity. The Balancer just moves charge between cells until cell voltages are equal. The current which moves charge is proportional to the difference between the individual cell voltage and the average value of all cells. The higher the capacity of the cell is, the more time the Balancer will need to do its job. But this is all independent of the amount of charge (4%) to be moved between the switching points of the Balancer. The Balancer doesn't know anything about the charging or discharging process. It simply reads voltages.....
Click to expand...
Thanks, yes i know the job of a balancer has nothing to do with capacity but concerns only voltage.

Why i measured and mentioned it has following reason.
As you know already for especially lifepo4s voltage and capacity doesn't behave linear. A difference of 56mV (3.4V to 3.456V = 56mV) has a different significance depending where you are on the charging curve (it is 50%capacity in the flat curve area according to my testing). So i wanted to put the deviated (from what i ordered and was confirmed before ordering) switch ON and OFF voltage points in perspective. Is the difference from 3.4V (or 3.43V since that is the number they tested in their lab and shared with me before ordering) to 3.456V significant or not was my question. Will it be an issue since the deviation is higher than the 50mV they promised before? 3.43V (what they said they tested in the lab) would have been within the promised 50mV tolerance. 3.456V (56mV) was already outside but let's say that is still fine because my voltmeter has an 0.5% error at a scale of 0.001V. 3.311V (89mV = 78% higher than 50mV) was way out of tolerance. So after testing of how much difference it makes in relation to capacity i thought, well never mind, i can live with a +-2%capacity (-89mV 3.4V +56mV) tolerance (it will be of course more or less if i would reduce or increase the charge or discharge rating), not worth the trouble of complaining. Overall, although not perfect, this customized balancer is already way better, more convenient for me than the stock version. Of course i would also have preferred if it would have switched on at 3.4v. 3.456V is indeed borderlining but still usable since i know it and can adapt to it.
So I just shared the numbers of whatever i tested, the 4-5%capacity (in between 3.311V and 3.456V) was just an information for those who also have questions like me above.

Sure everyone has a different system, different charging end points, different demands etc so i understand judging from your final charge voltage of 13.9V, 3.45V is too high since there could be instances where the balancer wouldn't even turn on which would render it a useless accessory.

After all one has to keep in mind, this customized version is their first try, a prototype, maybe they will improve it and then bring it eventually on the market. If they want to commercialize it, switch ON should be at 3.4V (or little bit lower), switch off at 3.3V (or little bit higher). that would cater most demands and charging profiles. I already gave them a feedback and recommended those numbers for a commercial special version for Lifepo4 batteries in solar systems.
 
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Visusolar said:
So a difference of (3.4V to 3.456V = 56mV) of 56mV has a different significance depending where you are on the charging curve.
Click to expand...
My experience is that the difference between 3.45 and 3.56 is less than 10 percent SOC because that is at the knee of the charge curve. The difference between 3.2 and 3.4 could be 80 percent SOC because it is away from the knee on the flat part of the curve.
 
Visusolar said:
Thanks, yes i know the job of a balancer has nothing to do with capacity but concerns only voltage.

Why i measured and mentioned it has following reason.
As you know for especially lifepo4s voltage and capacity doesn't behave linear. For example a difference of 56mV (3.4V to 3.456V = 56mV) has a different significance depending where you are on the charging curve (at 0.07C discharge current, it is 50%capacity in some curve areas according to my testing). So i wanted to put my deviated (from what i ordered and was confirmed before ordering) switch ON and OFF voltage points in perspective. Is the difference from 3.4V (or 3.43V since that is the number they tested in their lab and shared with me before ordering) to 3.456V significant or not was my question. Should i be concerned or not since the deviation is higher than the 50mV they stated before? 3.43V (what they said they tested in the lab) would have been within the promised 50mV tolerance. 3.456V (56mV) was already outside but let's say that is still fine because my voltmeter has an 0.5% error at a scale of 0.001V. 3.311V (89mV) was way out of tolerance. So after testing of how much difference it makes in relation to capacity i thought, well never mind, i can live with a +-2%capacity tolerance (it will be of course more or less if i would reduce or increase the charge or discharge rating), not worth the trouble of complaining. Overall although not perfect this customized balancer is already way better, more suitable for me than the stock version. Of course i would also have preferred if it would have switched on at 3.4v or even 3.43v. 3.456V is indeed borderlining but still usable since i know it and can adapt to it.
So I just shared the numbers of whatever i tested, the 4% was just an information for those who also have questions like me above.

Sure everyone has a different system, different charging end points, different demands etc so i understand judging from your final charge voltage of 13.9V, 3.45V is too high since there could be instances where the balancer wouldn't even turn on which would render it a useless accessory.

After all this customized version is their first try, a prototype, maybe they will improve it and then bring it eventually on the market. If they want to commercialize it, switch ON should be at 3.4V (or little bit less), switch off at 3.3V (or little bit more). that would cater most demands and charging profiles. I already gave them a feedback and a recommendation for a commercial special version for Lifepo4 batteries in solar systems. Switch on at 3.4V (or little bit lower), switch off at 3.3V (or little bit higher).
Click to expand...
Hi Max, I am 100% with you!
Taking into account that a high charging current has a strong impact on the SOC over Voltage curve, makes it even more difficult to select a fixed voltage level for turning on or off a smart active balancer.......but as always, we must live with compromises. I believe your proposed voltage level for the On/Off control is a good compromise.
Would be great if Hankzor modifies the balancer following your proposal. Would be a big improvement compared to the actual design.

Can you ask Hankzor to think about a "next generation" smart active balancer which is monitoring the total voltage of the 4 cells in order to switch on at 13.5 V, and switch off at 13.3 V, with an accuracy of 0.1 V or better.

Regards Hans
 
Ampster said:
My experience is that the difference between 3.45 and 3.56 is less than 10 percent SOC because that is at the knee of the charge curve.
Click to expand...
Very true, unfortunately...... At 3.45 V an LifePO4 cell may be slightly overcharged with a very low current. The same cell may be well below 80% SOC at a high charging current.

In case the charger goes to a floating mode the voltage must be at or below 4 x 3.4 V = 13.6 V. Otherwise the cells are continuously overcharged which reduces their lifetime.
 
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Hans Kroeger said:
Very true, unfortunately...... At 3.45 V an LifePO4 cell may be slightly overcharged with a very low current. The same cell may be well below 80% SOC at a high charging current.

In case the charger goes to a floating mode the voltage must be at or below 4 x 3.4 V = 13.6 V. Otherwise the cells are continuously overcharged which reduces their lifetime.
Click to expand...
Hi Hans,
According to your testing and experience, if you never charge above 0.16C (peak, maybe 1h long) but most of the time around 0.04C, what voltage would you recommend as a charge stop voltage (no Absorption, no floating, just a charge resume voltage at 13.3V) in order to not reduce the lifespan?
 
Hans Kroeger said:
Hi Max, I am 100% with you!
Taking into account that a high charging current has a strong impact on the SOC over Voltage curve, makes it even more difficult to select a fixed voltage level for turning on or off a smart active balancer.......but as always, we must live with compromises. I believe your proposed voltage level for the On/Off control is a good compromise.
Would be great if Hankzor modifies the balancer following your proposal. Would be a big improvement compared to the actual design.

Can you ask Hankzor to think about a "next generation" smart active balancer which is monitoring the total voltage of the 4 cells in order to switch on at 13.5 V, and switch off at 13.3 V, with an accuracy of 0.1 V or better.

Regards Hans
Click to expand...
Hi Hans

Sure i can. Could you explain to me why you think monitoring total voltage would be significantly more advantageous or better than just the B1 voltage? I mean i should also give them a good reason why they should go through the trouble to change the design.
 
Hi Hans
Wouldn't 13.6V and 13.3V be better?
13.6V would be, with a accuracy of 0.1V, 3.375-3.425.
13.5V would be 3.35-3.4V.
 
Visusolar said:
Hi Hans,
According to your testing and experience, if you never charge above 0.16C (peak, maybe 1h long) but most of the time around 0.04C, what voltage would you recommend as a charge stop voltage (no Absorption, no floating, just a charge resume voltage at 13.3V) in order to not reduce the lifespan?
Click to expand...
Max,
From my experience an end of charge voltage of 13.9... 14.0 V is a good compromise. 3.5 V max cell voltage keeps the stress low, gives you 100% SOC after the current has tapered off, guarantees ample margin to the 3.65 V max cell voltage and a 3.7 V overvoltage disconnect.
13.9 V to 14.0 V is too low for the normal passive balancer. But this drawback is compensated by the usage of "our smart active balancer" .
I am glad you brought up and continue to pursue this important issue.
Cheers Hans
 
Visusolar said:
Hi Hans

Sure i can. Could you explain to me why you think monitoring total voltage would be significantly more advantageous or better than just the B1 voltage? I mean i should also give them a good reason why they should go through the trouble to change the design.
Click to expand...
I must run, will get back to you later
 
Hans Kroeger said:
You may be Wright, I will think about it.
Click to expand...
I mean you want the balancer active when the cells start to drift apart (knee). Before that it wouldn't be necessary. Of course since we talk about total voltage at 13.7V the chances are higher than at 13.6V that you already have one cell way ahead. To also think about people with unmatched cells, to be safe, i also think 13.5V is better.
 
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