Hello My first post here, I am in the process of assembling my first 16s lifepo4 battery bought on Alibaba, my system consists of Easun 5kw inverter, 16pcs 280Ah lifepo4, 10pcs 320w solar panels, 16S daly bms 100A, 16S Neey active balancer, so is it possible to do a top balance and what is the correct procedure with only inverter, bms and Neey balancer? Thank you
Top balance
- Thread starter TR52
- Start date
This is a good resource..
diysolarforum.com
Top Balancing LiFePo4 Cells using a low cost benchtop power supply.
To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...
diysolarforum.com
DIYrich
Solar Wizard
If you don't have a power supply to charge each cell to at least 3.40 volts, then your only option is to build the battery, and let the BMS balance the cells. It could take MONTHS under a worst case scenario.
Not based upon any experience, but this might work:
See how unbalanced the cells are.
Set the BMS to start balancing at something close to the lowest cell voltage (start it balancing right away).
If the cells are close, then charge to 54.0v, and slowly increase in 0.25v increments until you reach the desired pack voltage.
If the cells are not close, then charge at pack voltage + 0.25v, and slowly increase in 0.25v increments.
You can increase the charge voltage when the pack is near the charge voltage, and the cells are not too far apart (hi-low no worse than when you started). You want to avoid the highest voltage cell getting anywhere close to 3.60v until the pack voltage gets to 56.0v.
With each increase in voltage, the cells will charge a little more, and let the BMS balance the cells. If a few cells are running away (charging faster), you may need to wait a while for the BMS to bring them down. Rinse and repeat.
With a 280ah pack, you are shooting for the cells to be within 0.005v when fully charged. I'm guessing a 0.1v differential when under 53.0v would be fine.
A more bolder approach would be to:
Charge at pack voltage + 0.25v.
When near charge voltage, check voltage of highest cell. If 3.5v or less, then you can increase by another 0.25v.
If a cell ever gets to near 3.5v, then I would switch to the more conservative approach.
The idea is never to get close to the 3.65v max on one cell until all cells are at least 3.50v.
The other option, which I and others have done is to fully charge the pack with BMS protection in place. Then manually discharge any runners with a 12V car bulb. Bench PSU is still useful to charge up and laggers - this can be done with BMS in place and inverter disconnected.
See my postings here:-
One EVE 280Ah cell tripping BMS high voltage at top end
I have a self-built 280Ah 48v battery pack, that was working great. I initially did a top balance, parallel to 3.65v For a couple weeks now I've been having issues with one cell, #16 which happens to be my main positive for the entire battery. At the top end when the inverter is pushing the...
diysolarforum.com
One EVE 280Ah cell tripping BMS high voltage at top end
I have a self-built 280Ah 48v battery pack, that was working great. I initially did a top balance, parallel to 3.65v For a couple weeks now I've been having issues with one cell, #16 which happens to be my main positive for the entire battery. At the top end when the inverter is pushing the...
diysolarforum.com
Sure - but technically that is not doing a top balance, which your question was about. A bench PSU is a useful tool to have though and entry level ones can be purchased for under €100.
hwy17
Anti-Solar Enthusiast
I just did a 304Ah top balance with 200mA passive balancing current.
It took me maybe 8ish hours of actual balancing, 18ish hours total for charge and balance.
I would say as a general strategy, using an adjustable voltage charger charge to 53v, see if any cells are in balancing, try 53.5, see if it pushes them into balancing, etc, .5v or .2v bumps as you get closer and ending up at 55v or 55.2v.
It took me maybe 8ish hours of actual balancing, 18ish hours total for charge and balance.
I would say as a general strategy, using an adjustable voltage charger charge to 53v, see if any cells are in balancing, try 53.5, see if it pushes them into balancing, etc, .5v or .2v bumps as you get closer and ending up at 55v or 55.2v.
hwy17
Anti-Solar Enthusiast
I take issue with the term top balance being interpreted as only parallel balancing if that's what you're saying. Top balancing is also an ongoing strategy and measurable achievement in a series string with any balancer.
OTRwSolar
Solar Enthusiast
- Joined
- Apr 5, 2021
- Messages
- 208
We quit formally top-balancing cell packs in a parallel configuration using a power supply a few years ago. We started installing active balancers with an on and off switch. We turn-on the active balancer to perform the initial top-balance, then leave it off until such time as another top-balance is needed. It's just matter of when, not if---especially if you do high c charges/discharges on a regular basis.
We've found a 5a active balancer can resolve significant deltas (100-200mv) down to 1-3mv in an hour or so (smaller deltas only take a few min.). Lot easier to flip a switch for the occasional top-balance vs. disconnecting a slew of sensor wires, reconfiguring the cells in parallel, and connecting a power supply (then doing all this again in reverse to configure back to normal series operation). For us, it's just not worth it to achieve the same 1-3mv delta.
We've found a 5a active balancer can resolve significant deltas (100-200mv) down to 1-3mv in an hour or so (smaller deltas only take a few min.). Lot easier to flip a switch for the occasional top-balance vs. disconnecting a slew of sensor wires, reconfiguring the cells in parallel, and connecting a power supply (then doing all this again in reverse to configure back to normal series operation). For us, it's just not worth it to achieve the same 1-3mv delta.
Last edited:
I was saying that... but I see your point... the words "top balance" obviously just means getting cells at same voltage at top range of permissible voltage and doesn't specify means of achieving that.
hwy17
Anti-Solar Enthusiast
Sort of a bit like how we say Lithium Ion for NMC but Lithium Ion is also the whole category I guess.I was saying that... but I see your point... the words "top balance" obviously just means getting cells at same voltage at top range of permissible voltage and doesn't specify means of achieving that.
for sure
OTRwSolar
Solar Enthusiast
- Joined
- Apr 5, 2021
- Messages
- 208
With the BMS and active balancer both installed, we start charging the battery pack with the active balancer off. Once "most" of the cells have risen above 3.450 - 3.500v, we turn-on the balancer. We let the active balancer resolve the delta to as near 0mv as possible using our normal bulk charge voltage. Some folks prefer to push for a final top-balance with the cells between 3.600 - 3.650v (57.6 - 58.4v for 16s). Do what's comfortable for you. In either case, once the delta has dropped to near 0mv, we turn-off the active balancer. Top balance is complete.
One note, if your cells are significantly unbalanced (large deltas) the BMS's high voltage disconnect (HVD) may activate while attempting to charge the cells above 3.450 - 3.500v. This shuts-off charge current, but the active balancer continues to operate. The HVD will eventually release and charge current will start to flow again. This HVD and release will continue to occur until the active balancer resolves the delta (imbalance) to a low enough level to allow the cells to charge normally (and top-balance) without any further HVD's.
Last edited:
Ok, thank you very much, I assume the HDV is set to 3.65, how much A is the inverter set to, and do I have to reduce the current on the inverter when the active balancer turns on?
OTRwSolar
Solar Enthusiast
- Joined
- Apr 5, 2021
- Messages
- 208
Lifepo4 cell level high voltage disconnect (HVD) is typically set to 3.650v. It's not necessary to reduce charge current with the active balancer active.
However, if you have significantly unbalanced cells (high deltas), you may find the balancing process goes a bit smoother if you use a lower charge voltage initially. It'll cut down on the number of HVD's.
Last edited:
