Active Equalizer

E-HP

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This might be a better question for the battery forum, but I thought, possibly, the answer could be dependent on the application, so since we're generally pretty demanding on batteries, I'm asking here.

I've been reading more about battery building, and also getting more experience using lipos, so while poking around, came across these "active equalizers" that look like are used in addition to a BMS. They start balancing whenever there is a 0.1 V difference between the highest and lowest cell/cell group. The inter-cell current transfer in the examples is 1.5A, and finishes balancing when the highest and lowest are 0.03 V apart. Supposedly the losses are really low.

Thinking out loud, I'm not sure what the maximum difference the unit could handle. If a pack has a weak cell, but is initially balanced, how much greater is the voltage sag contribution of the group that cell is in, relative to the healthy ones, when we're pulling high currents?

I was looking at the connectors on the board, and it looks like my lipo balance leads would plug right in. I also see they go up to 16S but I saw in the Q&A that they can be daisy chained, too. Plus, 16S means it can be used with anything up to 16S. If they work, then adding it to my pack would allow charging up to any level without ever having to worry about balancing. Any thoughts?

https://www.amazon.com/Li-ion-Lifepo4-Battery-Equalizer-Balancer/dp/B07XD824JS/ref=cm_cr_arp_d_product_top?ie=UTF8&th=1

https://es.aliexpress.com/item/4000812177140.html?src=google&albch=shopping&acnt=494-037-6276&isdl=y&slnk=&plac=&mtctp=&albbt=Google_7_shopping&aff_platform=google&aff_short_key=UneMJZVf&albagn=888888&albcp=9765122064&albag=101238896618&trgt=892975210062&crea=en4000812177140&netw=u&device=c&albpg=892975210062&albpd=en4000812177140&gclid=EAIaIQobChMIo6rwxLnd6wIVJQnnCh1jBQ56EAQYCCABEgK-AfD_BwE&gclsrc=aw.ds
 
I just (couple weeks ago) built my first pack using an active balance board, no BMS. It's 12S, used on a bike with 40V LVC, so the cells are safe on the low end at roughly 3.3V. On the high end, I have set up a Meanwell power supply to deliver 48.6V. And I have a luminous voltmeter that turns on when the power leads are live, so I can keep track. The bike's controller uses at most about 22% of the cell pack's maximum current, so I reckon the bases are all covered.

It seems to work just about like any other battery that's working.
 
AKA "non-protective BMS"

I would not leave a balancer hooked up

just use when balancing is needed, with a good healthy pack might be only one cycle out of 50 or even less frequently

Key specs

what is the actual balancing current? does that vary depending on the delta?

can choose any SoC / voltage to start balancing at? (pick one point and use that consistently, do not balance at say 3.5V and then also do so at Full SoC after charging)

Make sure if your protective BMS also has a balance function, that that is disabled.
 
john61ct said:
AKA "non-protective BMS"

I would not leave a balancer hooked up

just use when balancing is needed, with a good healthy pack might be only one cycle out of 50 or even less frequently

Key specs

what is the actual balancing current? does that vary depending on the delta?

can choose any SoC / voltage to start balancing at? (pick one point and use that consistently, do not balance at say 3.5V and then also do so at Full SoC after charging)

Make sure if your protective BMS also has a balance function, that that is disabled.
I'm thinking ordering a few and using them for my lipos, so no BMS. My charger has a very low balancing current, so it takes forever to balance even if cells are just a tiny bit out of balance. So, I was going to try keeping the equalizers in place all the time and just bulk charge the lipos, and let the equalizers take care of balancing.
The effect on balancing current varying due to the delta is really my main question, since I could see frying the equalizer, if the delta grows when cells sag under load. Thoughts?
 
john61ct said:
AKA "non-protective BMS"

I would not leave a balancer hooked up.

The one I use has a claimed quiescent current consumption of 20 microamps or less. Given that it will spring into action and level voltage imbalances as they occur, that seems like an inherently more protective gizmo than a BMS that stealthily drains just a few cells whenever you're not using the battery. You just need to have a system outside the battery that automatically won't run it below minimum voltage (like a controller with LVC), a charger that can't overdo it on the top voltage or charge rate, and a battery that will support more that your maximum load. What else does a full featured BMS do anyway?
 
BMS is just shorthand for a collection of functionalities.

Balancing does nothing to protect a pack, it's just to occasionally get the varying capacities "mapping" between voltage and a given single SoC point in alignment

the weakest lowest capacity cells will always dictate pack capacity, only solution to that is replace them.

The core purpose of a BMS is the HVC and LVC, usually bases on cell voltage level.

Displays, alarms prior to or instead if cutoff maybe.

Trying to calc SoC%, rarely accurate

Sometimes OCP, and/or temperature.

That's about it. None of these functions are essential to all use cases. All of them can be implemented without "a BMS", often more safely and reliably if done right.

I would always want any such circuitry easily removed / replaced, parasitic draw being a minor issue even if large NP once you're aware.

A good BMS draws its power evenly across the whole pack voltage.

BMS do not necessarily include balancing, which 99% do very poorly.

You do not want balancing to be done at any SoC point other than the **one** you select, throwing away lots of energy otherwise.

With the purpose-designed single function balancer devices they should only be needed for a few short sessions per year, maybe once a month.

Circuits fail cause pack failure, only use them when needed KISS any unnecessary complexity just reduces reliability and longevity.


 
E-HP said:
My charger has a very low balancing current, so it takes forever to balance even if cells are just a tiny bit out of balance.
So disable that. For example, never charge above the start-balance voltage set point.

> I was going to try keeping the equalizers in place all the time

No do not do that.

> just bulk charge the lipos, and let the equalizers take care of balancing.

So you want to keep top balancing? You now have the freedom to select a different SoC/voltage point to do so, no reason to associate it with the charging process.

Only do so when the cells actually get out of balance.

______
You still need to make sure no single cell goes higher than your stop-charge point, that is separate from "balance charging".

And I would advise having a failsafe cutoff active for when the charger's regulation circuits fail, that's how fires usually start.



> The effect on balancing current varying due to the delta is really my main question, since I could see frying the equalizer, if the delta grows when cells sag under load.

No, all such devices have effective current limiting.

What you usually want is for the balancing session to get done quickly, 5-10min maybe 30 worst case.

It is IMO silly to buy a balancer where the rate gets slower and slower as the gaps close, an active balancer should keep the rated balance current up as rated from start to finish.

 
i liked the thinking behind the "expensive" one Vortecks used.
bluetooth to see voltages
on/off button to activate.

if you cant turn it off a whole pack could be destroyed in a month.

if 1 cell goes bad in a group, it will take out the entire group but with the balancer all it does is transfer energy from 1 group to another group
Pack voltage stays the same, just energy is transfered but one cell goes bad and the entire energy of the pack gets consumed by 1 bad cell????
 
That's a great example.

Just like "equalizing" lead banks with "intelligent" chargers - do not let anything like that be automatic.

Explicit intentional maintenance procedure, done better on **your** schedule, "manually" in the sense of keeping an eye on it yourself.
 
goatman said:
i liked the thinking behind the "expensive" one Vortecks used.
bluetooth to see voltages
on/off button to activate.

if you cant turn it off a whole pack could be destroyed in a month.

if 1 cell goes bad in a group, it will take out the entire group but with the balancer all it does is transfer energy from 1 group to another group
Pack voltage stays the same, just energy is transfered but one cell goes bad and the entire energy of the pack gets consumed by 1 bad cell????

Actually when I said I'd keep them connected all the time, I really meant when in use (riding, charging), not when storing them.
 
And to be clear, my reco is never "leaving it attached" at all, except for when you are specifically performing that maintenance procedure.

So maybe for a total of a couple/few hours per year, given a good balancer and a pack in decent shape.
 
john61ct said:
the weakest lowest capacity cells will always dictate pack capacity, only solution to that is replace them.

That tells me a device that can deliver 1A of balancing current per cell could in effect add up to 1 Ah to a badly imbalanced pack if the battery has an hour of run time. You don't want to have a messed up pack like that, but this is a way to use one, and a BMS that balances at 20mA and only at 4.2V/cell isn't. My pack is a module of automotive cells that have never been separated, so that's probably not a factor.

At sub 20 microamps drain when it isn't actively balancing, I don't think being able to shut it off or not is even a factor. If my math is correct, my 20Ah pack contains one million hours worth of resting current for that device. Anyway, there's a ribbon cable and I can unplug mine if I have to do a prison term for sedition or something.

Cell balancing is protection, no doubt about it. Say you have a charger that only delivers 4.05V per cell, like mine does. And say your bike has a controller that cuts off at 3.33V per cell, like mine does. Would you be willing to use an entirely unprotected pack in that situation? I hope not. But would you be willing to use a pack that only had active cell balancing? I can't see why not.
 
lets do some math :D

20ah/20micro amps= 1 million hours
1million hrs /24=41,666.67 days
41,666.67/365= 114 yrs, im not worried about the leap year calculation

sedition in the USA carries a maximum sentence of 20 years
https://legal-dictionary.thefreedictionary.com/sedition#:~:text=A%20person%20found%20guilty%20of%20seditious%20conspiracy%20or,Governments%20have%20made%20sedition%20illegal%20since%20time%20immemorial.

yep, i agree an active balancer is the way to go :thumb:
 
Is there any reason why you can't use several of these unit together to cover a larger pack. For example 3x4s units for a 12s pack. It seems that you could stick one in middle of a pack without issue as there is no reference to the battery's actual negative.
 
Balmorhea said:
john61ct said:
the weakest lowest capacity cells will always dictate pack capacity, only solution to that is replace them.
That tells me a device that can deliver 1A of balancing current per cell could in effect add up to 1 Ah to a badly imbalanced pack if the battery has an hour of run time. You don't want to have a messed up pack like that
You assume your balancer is using capacitance balancing methodology as opposed to resistance or shunt based.

There lie huge gross inefficiencies.

The point of balancing is **not** to try to counteract that "law", it's a fool's errand, see that pretty-boy's YT videos from last year, not knowing what to test for.

Balancing should never be done while the pack is in use, only while fully isolated from loads.
 
kdog said:
Is there any reason why you can't use several of these unit together to cover a larger pack. For example 3x4s units for a 12s pack. It seems that you could stick one in middle of a pack without issue as there is no reference to the battery's actual negative.
There are several balancers designed to be modular, either one device per cell/group, buy as many as you like,

or daisy-chain multiple xS units together to cover a higher-voltage pack.

Doing so with products not purpose-built for that feature could get risky, in several ways.

Do not expect help for even normal operations from the Chinese sellers, much less non-standard use cases.
 
Balmorhea said:
At sub 20 microamps drain when it isn't actively balancing, I don't think being able to shut it off or not is even a factor
I was very clear, vampire load discharging is not the reason for my advice.

But you say you will make it easy to disconnect the device, and that is all I'm saying, only connect it when a balancing session is required.

Unless this is for a stationary House bank, or in a boat or something, I'm not sure why you'd want to unnecessarily subject such a sensitive and expensive piece of gear to shock and vibration when it may only be needed 30min per month.

Not to mention, one balancer will take care of dozens of packs, not like you need to buy one for each!


> Cell balancing is protection, no doubt about it

Not so long as HVC and LVC are based on the per-cell voltage of the "weakest link".

Otherwise, going out of balance is just a minor annoyance, creeping loss of functional capacity.

The actual voltage settings of your charger or LVC are not relevant.

Having a **protective** BMS act as a failsafe backup to your primary control circuits is IMO a **very** good idea.

No balancing gear will provide those functions any more than protect against shorts / over-current, or temperatures being too high or low.
 
john61ct said:
Balancing should never be done while the pack is in use, only while fully isolated from loads.

All the more reason for it to sleep with one.

The only practical drawback I can even see to using an active balancer is that it would disguise underlying weakness in individual cell groups that you'd otherwise be able to discover. But it's easy enough to run the pack through a cycle with the balance board unplugged.
 
I am not in any way saying an active balancer is not the way to go! How do you define that term BTW?

The term "active" refers to the balancing methodology used, certainly nothing to do with the question of how often the balancer is hooked up to a given pack.

Determining the SoH of a given cell or group is an entirely different maintenance procedure involving different gear.
 
And I would advise having a failsafe cutoff active for when the charger's regulation circuits fail, that's how fires usually start.
Hi could you show an example of a failsafe cutoff to buy? maybe a drawing . When you write charger's regulation circuit fail, concretely does that mean when a charger keeps on charging above the maximum capacity of the cells?
thanks
 
Circuits fail cause pack failure, only use them when needed KISS any unnecessary complexity just reduces reliability and longevity.
by circuit fail, are you talking specifically about the active balancercuircuitboard?

Is there a way to install an active balancer in a battery in such a way that you can access the wire and plug of the active balancer so that you leave it unpluged and only plug it once a year ? WHen unpluged, do the active balancer drains energy or not? or maybe having loose wire out of the pack and plug it outside of the battery?

thank
 
Last edited:
AKA "non-protective BMS"

I would not leave a balancer hooked up

just use when balancing is needed, with a good healthy pack might be only one cycle out of 50 or even less frequently

Key specs

what is the actual balancing current? does that vary depending on the delta?

can choose any SoC / voltage to start balancing at? (pick one point and use that consistently, do not balance at say 3.5V and then also do so at Full SoC after charging)

Make sure if your protective BMS also has a balance function, that that is disabled.
Hi are you saying to only use one at the time ex: put the bms balance fct off use the active balancer and one it has done its job unplug it and put the bms balancing fonction back on?
 
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