Active balancer, make it smart!?

[RCinFLA]

Hi did anyone reverse engineer the schematic for these Chinese switched capacitor units like heltec etc

Video not precisely correct, there are two parallel banks of capacitors sequenced, but principle of operation is correct.
There are small series resistors to limit current, ('U') marked resistors connected to cells.

Net stack voltage on series capacitor stack will be slightly lower due to losses so there will be some small amount of net discharge to total battery stack.

All done in full parallel sequence.
1) collect each individual cell voltage on capacitors.
2) Pool the caps together to equalize their charge voltage.
3) Separate charge equalized caps and reapply to each cell

I would not permanently leave this balancer connected to battery pack all the time. If input capacitor shorts out or has significant leakage current you will put your battery pack at risk of damage, which your BMS has no control over preventing. There is a large ripple current stress on these capacitors for significant SOC difference between cells. Large ripple current with capacitor ESR results in capacitor internal heating.

Due to 5 to 10 mV of cell overpotential voltage for very small cell current, there is the same limitation on balancing cells that just passively paralleling cells have for balancing.

 

[Daddy Tanuki]

disclaimer; I am not an electronics specialist nor a geek.... I wonder what would happen if you were to de-solder the caps and throw some real capacitors on that board? makes me want to try something stupid.

 

[RCinFLA]

disclaimer; I am not an electronics specialist nor a geek.... I wonder what would happen if you were to de-solder the caps and throw some real capacitors on that board? makes me want to try something stupid.

Electrolytic capacitors are the least reliable component in just about any electronic device. Having higher voltage rating capacitors to their actual use case operating voltage improves their reliability but you pay the price in physical capacitor size.

LED light bulbs claim 50,000 hour+ lifetime but the electrolytic caps in their switching power converters usually die much sooner.

 

[Goboatingnow]

Video not precisely correct, there are two parallel banks of capacitors sequenced, but principle of operation is correct.
There are small series resistors to limit current, ('U') marked resistors connected to cells.

Net stack voltage on series capacitor stack will be slightly lower due to losses so there will be some small amount of net discharge to total battery stack.

All done in full parallel sequence.
1) collect each individual cell voltage on capacitors.
2) Pool the caps together to equalize their charge voltage.
3) Separate charge equalized caps and reapply to each cell

I would not permanently leave this balancer connected to battery pack all the time. If input capacitor shorts out or has significant leakage current you will put your battery pack at risk of damage, which your BMS has no control over preventing. There is a large ripple current stress on these capacitors for significant SOC difference between cells. Large ripple current with capacitor ESR results in capacitor internal heating.

Due to 5 to 10 mV of cell overpotential voltage for very small cell current, there is the same limitation on balancing cells that just passively paralleling cells have for balancing.

Where is the ripple current coming from ?

I’ve one of those boards in order so will look at tracing circuit

 

[Daddy Tanuki]

Electrolytic capacitors are the least reliable component in just about any electronic device. Having higher voltage rating capacitors to their actual use case operating voltage improves their reliability but you pay the price in physical capacitor size.

LED light bulbs claim 50,000 hour+ lifetime but the electrolytic caps in their switching power converters usually die much sooner.

definitely does not make me want to stop... keep whispering into my ear their Voldemort....

 

[Goboatingnow]

Looking at the pictures and bearing in mind thisI suspect the Chinese versions are this simple with 4 caps in parallel ( ie4x3) for 4S

Or the double tiered version

 

[RCinFLA]

Looking at the pictures and bearing in mind thisView attachment 114758I suspect the Chinese versions are this simple with 4 caps in parallel ( ie4x3) for 4S

Or the double tiered version

This is a 'leap frog or bucket brigade' balancer. It transfers charge up and down the series stack by neighbor to neighbor transfer. Totally different design from Heltec capacitor balancer.

There is also an inductor switcher version of this leap frog design using the ETA3000 chips but the chip has a major flaw in that its voltage comparison test is corrupted due to the neighbor overlapping chip operating asynchronously, pumping charge current while the neighbor is making cell voltage comparison. It would be a great design if they synchronized all the chips in the series overlapping stack so they don't interfere with each other's cell voltage comparison.

 

[Goboatingnow]

This is a 'leap frog or bucket brigade' balancer. It transfers charge up and down the series stack by neighbor to neighbor transfer. Totally different design from Heltec capacitor balancer.

There is also an inductor switcher version of this leap frog design using the ETA3000 chips but the chip has a major flaw in that its voltage comparison test is corrupted due to the neighbor overlapping chip operating asynchronously, pumping charge current while the neighbor is making cell voltage comparison. It would be a great design if they synchronized all the chips in the series overlapping stack so they don't interfere with each other's cell voltage comparison.

View attachment 114775
View attachment 114776

Not sure what you mean, how is the Heltec different , It’s a standard sequential sequential capacitor design from the face of it

All the Chinese switched capacitor are leap
Frog systems. Ie they sequentially transfer excess charge down the series string. This does mean it’s very inefficient where the imbalance is between non adjacent cells.

You can have switched capacitor versions ( ie the single large capacitor ) which can selective couple to the required cells but there’s a much bigger mosfet switching system required and hence iv not seen it in current active balancers.

 

[Hans Kroeger]

Not sure what you mean, how is the Heltec different , It’s a standard sequential sequential capacitor design from the face of it

All the Chinese switched capacitor are leap
Frog systems. Ie they sequentially transfer excess charge down the series string. This does mean it’s very inefficient where the imbalance is between non adjacent cells.

Not true for the Heltec balancers. See the video above. They are superior to the leap frogs......

 

[Goboatingnow]

Not true for the Heltec balancers. See the video above. They are superior to the leap frogs......

I find the description of the circuit operation. Strange

If you connect each cell to the cell , each cap with charge to the cell voltage. That’s fine.

If you then parallel all caps as he claims the voltage on the caps will the sum of all cell voltages / number of cells. Assuming all caps are the same.

Now you reconnect the caps. Only the higher voltages on the caps discharge into the corresponding cell. The caps with lower voltage will charge up to the cell voltage. ( fine such charging current will in theory lower the cell voltage

But given the only voltage transferred is the average value which is always lower then the higher voltages . this means only the cells

But this means

Not true for the Heltec balancers. See the video above. They are superior to the leap frogs......

Thanks indeed if the heltek is as described the series parallel versions is interesting

A research paper presented here usually looks at the process

https://www.researchgate.net/profile/Yuanmao-Ye/publication/274738118_Modeling_and_Analysis_of_Series-Parallel_Switched-Capacitor_Voltage_Equalizer_for_BatterySupercapacitor_Strings/links/565148f008ae4988a7abe111/Modeling-and-Analysis-of-Series-Parallel-Switched-Capacitor-Voltage-Equalizer-for-Battery-Supercapacitor-Strings.pdf?origin=publication_detail

 

[Hans Kroeger]

Important is what you get out fron this flying capacitor circuit.

 

[Warpspeed]

According to that curve, at 100mV difference, maybe 600mA
At a more realistic 10mV only 60mA.

If you have 280 amp hour cells, 60mA is going to take a very long time to do anything at all.

Not only that, if you need to transfer energy from cell number one, to cell number sixteen, it has to shuffle through every other cell to get there.
All very underwhelming I am afraid.

 

[Hans Kroeger]

According to that curve, at 100mV difference, maybe 600mA
At a more realistic 10mV only 60mA.

If you have 280 amp hour cells, 60mA is going to take a very long time to do anything at all.

Not only that, if you need to transfer energy from cell number one, to cell number sixteen, it has to shuffle through every other cell to get there.
All very underwhelming I am afraid.

A balancing current of 0.6 Amps at 0.1 V difference tapering off to 60 mA at 0.01 V difference is a good compromise compared with a constant balancer current of 50 mA.... 150 MA of many well known products on the market.
...... and it is not true, that the energy has to be transfered from cell 1 to cell 16. See the detailed explanation in the paper from research gate!

 

[Goboatingnow]

According to that curve, at 100mV difference, maybe 600mA
At a more realistic 10mV only 60mA.

If you have 280 amp hour cells, 60mA is going to take a very long time to do anything at all.

Not only that, if you need to transfer energy from cell number one, to cell number sixteen, it has to shuffle through every other cell to get there.
All very underwhelming I am afraid.

Two stage series parallel active balancers don’t sequence through each stage

 

[ocular]

Ok, back to the real world, which balances faster a JK 2A Active balancer, A 4A Neey Active Balancer, or Heltec Capacitor Balancer?

 

[Goboatingnow]

Heltec is a two stage series parallel architecture. To my mind this is the best of the current switched capacitor active balancers

 

[ocular]

@MullerEnergy-Australia
feel that Heltec is the way to go

 

[Horsefly]

Ok, back to the real world, which balances faster a JK 2A Active balancer, A 4A Neey Active Balancer, or Heltec Capacitor Balancer?

You asked which one balances faster, and I'm not sure that question really addresses the value of the balancing.

I've posted here elsewhere that the Heltec capacitor balancer does balance quickly, but it balances all the time. That means it will balance at the bottom of the charge / discharge curve as well as the top. This actually undoes any top balancing you may have done earlier, which is bad. You really want something that only balances at around 3.35V-3.4V per cell and above, to keep your pack top balanced.

I've also posted a bigger problem with the Heltec capacitive balancer. At one point I was all in on them, but used a switch to control when to balance. One time I left the switch on for several days, and something failed on the balancer board. No parts burned out or capacitors popped, but for some reason the thing started discharging one cell and the board got very hot. By the time I found it one of the cells was down below 3.0V and the rest were all about 3.35V. The board it self was too hot to touch.

These things are pretty cheaply made. I don't trust them much any more, and only use them (again, enabled with a switch) if I am there to check on it every few minutes.

If your cells were top balanced, the need for balancing is very infrequent.

 

[Skypower]

Ok, back to the real world, which balances faster a JK 2A Active balancer, A 4A Neey Active Balancer, or Heltec Capacitor Balancer?

I’ve used all three balancer types and speed of balance is valid is question. The best time to balance is typically above 3.4 VPC which is also above the “knee”. When above the knee there’s little capacity and once the cells enter this range the charge can finish quite quickly, and settle below 3.4 volts rapidly, hence little balance time. Some systems may go through may cycles before it reaches the balance threshold so balance time/power becomes more desirable. On the same group of batteries the 4th generation 4A Neey is hands down is the quickest, then comes the JK 2A bms and lastly the Heltec. The Neey, when active is always using 4 amps of balancing power and the JK 2 amps. Once those two balancers become active, they immediately work to bring down the highest cells first. The Heltec can develop 5 amps at higher imbalance (delta) but I’ve never had that level of issue. The closer to balance (small delta) the less voltage indifference the Heltec has to work with and less balancing power, and I’ve never seen anything over an amp. Even though the Heltec had less power, it never failed to keep the 2P/16S (300ah cells) in very good balance (.003 /.010 delta). The only reason it was replaced was for simplicity(start balance circuit eliminated), lack of Bluetooth and curiosity.

 

[Ellcon123]

The ONLY time to balance is in the knees. You need the voltage delta for balancing which you will not see in the flat part of the curve.