How Often dO YoU Top Balance YoUr LFP BaNk?

[MrM1]

I go to the dentist for a cleaning twice a year. I think I my teeth are clean, but apparently not.

I top balanced my EVE 230 x2 and Calb 280ah x 1, 24v LFP banks 18 months ago when new . They seemed to stay pretty tight, but recently have started to drift above 3.45v per cell.

How often do you "re" - top balance? Never? Once a year? More? Hey if it's good enough for you're teeth ... ?

Here's the worse one. The 200a 24v overkill built in balancer just can't seem to catch up and keep up with the difference.

 

[Any name you wish]

Both my batteries have the 5A balancers installed on them from Heltec.

Both are JBD BMS. One from Overkill and another from Sriko. Left is cylindrical LFP, right is Prismatic LFP Calb cells. The right is starting to get higher than I like but it is nearly full whereas the left is still bulk charging. Before when I only had the left one, I had it start going out pretty bad near the high and low voltages. I attributed that to being a cylindrical cell setup. I just leaving them balancing full time as I don't do full single day discharges and always have sun in AZ to keep them topped up. I also only allow for 3.45V/cell voltage so that I don't have one cell get crazy run away voltages or even close to 3.65V.

 

[Lt.Dan]

Only time I have top balanced is if I had to disassemble the pack and or increase the size of the pack.

If the balancer in the BMS cannot keep the cells in balance, you either need to charge slower in the upper knee and give it more time, or there is a problem with a cell that needs to be addressed.

 

[Ampster]

It has been a year since I parallel top balanced and assembled my pack. My Orion JR2 does not have enough balancing current to keep my 42 kWh pack balanced so I turn of the balancing and use a JK Amp active balancer to keep the pack balanced. I guess you could say I top balance every charge cycle which is typically every day.

 

[MrM1]

It has been a year since I parallel top balanced and assembled my pack. My Orion JR2 does not have enough balancing current to keep my 42 kWh pack balanced so I turn of the balancing and use a JK Amp active balancer to keep the pack balanced. I guess you could say I top balance every charge cycle which is typically every day.

That's a lot of trips to the hygienist ?

 

[scubadoo]

Top balancing?
Our 4 cell 300Ah Sinopoly battery has now survived 9 years of full-time travel without ever being top balanced since the original careful 3.65V top up. There is no cell balancing or usual BMS circuitry involved.
The battery both starts our 3.1l turbo engine and powers the motorhome. No charging source exceeds 14.1V at which point the battery is always at 100% SOC. It can still deliver c4000Wh.
HV and 12.1V LV Victron protection is installed. Never triggered.

A recent forced charge to 14.5V took about 20 seconds at 30A. It still required no balancing.

PS I am about to add an extra 4 cell 280Ah EVE battery without balancing or added BMS to the mix. It will be interesting to compare the differences.

 

[callmeburton]

My batrium BMS resets my 100% SoC daily right now ... it is hooked up as a battery backup right now but every day at least once a day the battery is topped off and all cells go into bypass mode and the SoC is set to 100% ... So in some ways they are constantly top ballanced with this system :D

 

[time2roll]

I have yet to "top balance". The Heltec active balancer does a fine job. Or maybe that would be considered continuous balancing.
One battery actually does better than the other but even the worse one is much better than the 154 mV your app is showing.

And the dentist cleans my teeth three times a year

 

[Darren67-72]

I'm in for, every 6 months. Unless I see something getting way out. Although, spring and fall I'm topped off most days.

 

[Dynoman]

I go to the dentist for a cleaning twice a year. I think I my teeth are clean, but apparently not.

I top balanced my EVE 230 x2 and Calb 280ah x 1, 24v LFP banks 18 months ago when new . They seemed to stay pretty tight, but recently have started to drift above 3.45v per cell.

How often do you "re" - top balance? Never? Once a year? More? Hey if it's good enough for you're teeth ... ?

Here's the worse one. The 200a 24v overkill built in balancer just can't seem to catch up and keep up with the difference.

View attachment 135523

The Overkill BMS is a very good BMS, but not very good at keeping my non grade A 271 ah Lifepo4 battery banks balanced at the upper knee of the voltage curve. I needed to go with the Heltec 5A active balancer to assist the Overkill BMS in keeping a good balance of all the cells. By using this approach the cells only needed the initial top balance.

Found it best in my system to only enable the active balancer when the the cells are above 3.4 volts. This can be accomplished by simply plugging & unplugging the Heltec active balancer or solder a switch on the Run solder pad. Some automate the process by switching the Run solder pad by a remote device.

On my system I use the Victron BMV-712 Smart Shunt relay to switch On the the Run pad of Heltec 5A active balancer(s) at 27.4 volts and Off at 27.2 volts (24 volt system). There is a 0.2 volt dead band with a 5 minute delay by the BMV-712 so no switching on/off when sun goes behind clouds for a few minutes.

When there is enough sun the cells balance at 28.5 volts for 20 minutes in absorb with no problem (no high voltage disconnects with setting of 3.65 cell over voltage). This works even if it has been a couple of months since the batteries were in the upper knee while using a high charge current.

The MPPT SCC float voltage is also set slightly above 27.2 volts so the cells balance while in float also.

 

[MrM1]

The Overkill BMS is a very good BMS, but not very good at keeping my non grade A 271 ah Lifepo4 battery banks balanced at the upper knee of the voltage curve. I needed to go with the Heltec 5A active balancer to assist the Overkill BMS in keeping a good balance of all the cells. By using this approach the cells only needed the initial top balance.

Found it best in my system to only enable the active balancer when the the cells are above 3.4 volts. This can be accomplished by simply plugging & unplugging the Heltec active balancer or solder a switch on the Run solder pad. Some automate the process by switching the Run solder pad by a remote device.

On my system I use the Victron BMV-712 Smart Shunt relay to switch On the the Run pad of Heltec 5A active balancer(s) at 27.4 volts and Off at 27.2 volts (24 volt system). There is a 0.2 volt dead band with a 5 minute delay by the BMV-712 so no switching on/off when sun goes behind clouds for a few minutes.

When there is enough sun the cells balance at 28.5 volts for 20 minutes in absorb with no problem (no high voltage disconnects with setting of 3.65 cell over voltage). This works even if it has been a couple of months since the batteries were in the upper knee while using a high charge current.

The MPPT SCC float voltage is also set slightly above 27.2 volts so the cells balance while in float also.

Yeah agreed about the Overkill BMS. Where did you get the active balancer?

 

[RCinFLA]

I go to the dentist for a cleaning twice a year. I think I my teeth are clean, but apparently not.

I top balanced my EVE 230 x2 and Calb 280ah x 1, 24v LFP banks 18 months ago when new . They seemed to stay pretty tight, but recently have started to drift above 3.45v per cell.

How often do you "re" - top balance? Never? Once a year? More? Hey if it's good enough for you're teeth ... ?

Here's the worse one. The 200a 24v overkill built in balancer just can't seem to catch up and keep up with the difference.

View attachment 135523

The picture does not provide too much info as 2.3A charging current is pretty low. With 2.3A charging current cells 2 and 6 may not quite be fully charged, but close.

You are getting close to a BMS cell overvoltage shutdown due to cell 5. There should be balancing dump indication on cell 5 which does not appear to be happening.

Your BMS may require seeing charging current to enable balancing. I am not sure if 2.3A is charging or discharge current. If it is charging current, it may just be below the BMS trigger for minimum charging current to enable balancing.

There may be a setting to have balancing only during charging. Normally, always having balancing for charging or discharging above 3.45v is best, but some BMS only allow a setting of balancing during charging or, if you turn off 'charge balancing', it only does balancing when discharging, which is stupid BMS operation. Turning off 'charge balancing' should allow balancing during charging or discharging, not just during charging. A fully charged cell will have a rested, no load, open circuit voltage of close to 3.45v which is why balancing dump should stop at 3.45v if you allow balancing during discharge.

Other settings is cell voltage for start of balancing. Normally 3.40v but if you allow balancing during discharge set it to 3.45v, other is bracket voltage range on cells which must be exceeded for min to max cell voltage to enable balancing. 5 mV is okay for this bracket range which is about the resolution limit of BMS cell voltage reading accuracy.

Amount of required balancing depends on ambient temperature cells see (higher temps have greater cell self leakage), aging of cells, and use case of maximum load current seen during discharge. Also depends on BMS balancing current capability.

Looks like some balancing is needed but it is not too far off.

Need to keep up with balancing as it will get worse over time if ignored and become a lot of work and time to get a large variation back in balance especially if BMS has low balancing dump current rate.

Once a month for a couple hour soak at 3.55v per cell x number of cells in series stack charge absorb voltage should be enough but it depends on BMS balancing current capability, aging of cells, matching of cells, and if they are subjected to moderate to high discharge rate which accelerates their state of charge divergence.

To put time in perspective. A bit less then 1% divergence in cell state of charge can cause a cell to trip BMS charge shutdown for cell overvoltage when attempting a full absorb level charging. For 230 AH cells, 1% is 2.3 AH state of charge delta. A BMS with only 100 mA balancing dump current will take 2.3 AH / 0.1A balancing dump current = 23 hours held at absorb stage charging to rebalance cells.

This is why you do not want to ignore keeping cells in balance. If you begin to notice less capacity from battery array you are likely 4-6% off in state of charge balance. That will take about a week to get rebalanced and have a lot of BMS overvoltage charging shutdowns along the way.

A BMS overvoltage cell charging shutdown can make the charger think battery is fully charged due to current drop off so it drops to float voltage so even when BMS bleeds out the overvoltage cell and resets charging the charger will stay in float mode until battery is discharged enough to start a new recharge cycle. This endless cycle of overvoltage shut down of charging by BMS, and charger dropping to float mode can result in never getting any absorb time to balance cells.

For a timed charger absorb cycle, a BMS shutdown, bleed overvoltage cell, and reset BMS charging, eats up allocated absorb timer so again insufficient balance time can result.

 

[Browneye]

I would put my lightbulb bleeder on the high one(s) to bring them back to even. I've done this a couple of times early on, but don't charge past 3.55Vpc and they stay balanced up to there.

Remember, 3.45Vpc is 100% state of charge. Looks like you have a couple of sleepers there. By bleeding off the high one it lets the low ones catch up. I have managed to get mine all within a few millivolts at 3.45 - and still charging. Overkill calls that full. My charger terminates at 14.0 with 5% tailcurrent, so within minutes here it shut down charging - I didn't catch the end.

 

[Dynoman]

Yeah agreed about the Overkill BMS. Where did you get the active balancer?

I picked mine up a couple of years ago on Ebay from this seller.

US Stock 6~8S Battery Balancer 5A Active Equalizer Universal For LTO LFP LI-ion | eBay

Find many great new & used options and get the best deals for US Stock 6~8S Battery Balancer 5A Active Equalizer Universal For LTO LFP LI-ion at the best online prices at eBay! Free shipping for many products!

www.ebay.com

Here is a link for Amazon.

https://www.amazon.com/Heltec-Capacitor-Equalizer-Balancer-Titanate/dp/B08D9D4NGW

@MrM1
If I did not already have the 5A active balancers I would also look at the Neey 4th generation smart active balancers for my two 8s 24 volt banks. Only down side is it needs 30 to 100 volts to power it (and cost more), but could just run a couple of wires to the 2 8s 24 volt banks in series for 48 volt to power the Neey or use a little solid state 48 VDC power supply.

Also reviews of the iOS app say it works, but not as good as the Android app that Andy uses in his video.

Here is Andys video on the 4th generation Neey smart active balancer. Nice job Andy!

 

[ocular]

JK active balancer gets switched on manually when 16s pack gets to 56V and delta V is > 30mV -50mV maybe X2 /yr aiming for <10mV

 

[JJJJ]

I have a third pack that is less “behaved” than the others. I currently have it off line and am using a bench tester and using a charge and settle approach in an effort to coax some cooperation between cells. Time will tell…

 

[Dynoman]

I have a third pack that is less “behaved” than the others. I currently have it off line and am using a bench tester and using a charge and settle approach in an effort to coax some cooperation between cells. Time will tell…

Before installing Heltec 5A active balancers to keep my two 8s 24 volt Lifepo4 battery banks balanced I used both an old 6 volt car head light (as previously mentioned) or a 2 ohm 100 watt resister to top balance cells.

I found the Heltec 5A active balancer works better on my battery banks IMO.

Top Balance Runner LIFEPO4 Cells With BMS Connected (preferred by some since BMS protecting cells)
First ensure all connections are good on each cell of the battery and the BMS is correctly wired to the Lifepo4 cells that are wired in series.
Set BMS for a 3.65 volt cell high voltage disconnect (Cell Over Voltage).

Wire alligator clips to each end of a 2 ohm 100 watt resistor. Ensure resistor and wire is approximately 2 ohms by clipping the alligator clips to accurate ohm meter. Don't want a direct short.

Charge entire battery bank (through BMS) at a high enough current to get cell running toward BMS overvoltage cutoff. Carefully clip the alligator clips on the 2 studs of the runner cell observed on the BMS app. Watch the runner cell bleed down on the BMS. Repeat as necessary on each runner cell while slowly increasing voltage up to around to 3.60 or so volts for each cell as read on the BMS until all cells are balanced at a vey low current.

As long as the BMS is connected and set for 3.65 volt per cell high voltage disconnect this method should safely top balance a battery with the cells wired in series.

With a cell at 3.60 volts the 2 ohm the resister will bleed the cell at a rate of 1.8 amps. I = E/R 3.6Volts/2ohms = 1.8 amps. This is usually sufficient to bleed down a runner cell when charging the battery at a low current. If runner cell still going into over voltage lower battery charging current.

2 ohm 100 watt resister link.

https://www.amazon.com/dp/B07CVRH6DF

 

[MrM1]

Carefully clip the alligator clips on the 2 studs of the runner cell observed on the BMS app.

The positive and negative of the same cell? And while the wholly bank is in series? Can this be done to more than 1 cell with more than than 1 resistor at the same time? How long does it take to bleed down say a 0.120v difference?

 

[MrM1]

Dynoman said:

Carefully clip the alligator clips on the 2 studs of the runner cell observed on the BMS app.

And why 2 Ohm? What would 4 or 10 Ohms do?

 

[Dynoman]

The positive and negative of the same cell? And while the wholly bank is in series? Can this be done to more than 1 cell with more than than 1 resistor at the same time? How long does it take to bleed down say a 0.120v difference?

Yes, clipping the alligator clips wired to the resistor on the positive and negative of the same cell, with the entire bank wired in series, will bleed off the cell at a rate of about 1.8 amps. The current is dissipated as heat from the resistor. It has been a while, but if I remember correctly 0.120v could bleed off in a few minutes once in the upper knee of the voltage curve. This can be done on multiple cells at the same time with multiple resistors, but gets tricky with more than 2. The Overkill BMS does the same, but with a larger value of ohms resistor to bleed off cells at a much smaller current.

Have to watch the BMS app and adjust the power supply accordingly to bleed the cells. Takes a little while to get the hang of it and it worked well for one of my battery banks. The other battery bank charged into the knee would often need to bleed again to prevent BMS overvoltage which is why Heltec 5A active balancers were installed and on both banks to be consistent.

So it seems it depends on how good the cells are matched in the bank for how well the resistor bleed will work.

The Heltec 5A transfers current from multiple cells at the same time automatically and does not blead, which is why it is significantly better in IMO.

 

[Dynoman]

And why 2 Ohm? What would 4 or 10 Ohms do?

2 ohm resistor works well at 1.8 amps. A 4 ohm might work, but at only 0.9 amps bleed. A 10 ohm I = E/R 3.6Volts/10ohms = 0.36 amps and not much better than the Overkill BMS bleed.

 

[JJJJ]

I noted they are now providing the 6s. Any experience with this?

On the other hand, the Neey 4th generation has received positive feedback as well. I like the ability to provide voltage settings where it turns itself on and off.

 

[Browneye]

If my battery cells were constantly getting out of balance I would be installing an active balancer as well. Easy-peasy.

 

[Dynoman]

I noted they are now providing the 6s. Any experience with this?

On the other hand, the Neey 4th generation has received positive feedback as well. I like the ability to provide voltage settings where it turns itself on and off.

My 8s 24 volt Lifepo4 battery banks use the 6 - 8s 5A flying capacitor active balancer (Heltec) and works well. I purchased them a while ago and at the time the 4th generation Neey was not available.

Today the Neey 4th generation smart active balancer would probably be at the top of the list. The ability to observe and adjust the Neey 4th gen with the app is a great feature although it does cost more than the Heltec 5A.

With the Heltec 5A there is just an LED that indicates when it is enabled and it is on the back side of the board so had to mount the board upside down so the LED could be seen.

The Heltec 5A works good for my application, but the Neey 4th generation smart active balancer looks better IMO.

 

[Lt.Dan]

If mine were constantly out of balance, I would attempt to solve the problem rather than attempt to band-aid it with a balancer.

Just my $0.02.