Battery Balancing Systems?

ligwyd · November 2019

Any one had much experience with Battery Balancing Systems?

Just watched a few you tube vids on a couple different products. Without knowing more it sure sounds like an awesome idea. I'm sure the new Lithium batteries have this type of cell balancing electronics built in, however, sure would be nice to add some equip like this to any bank of batteries to keep them bang on for all the obvious reasons. Seems to good to be true?

https://www.solar-electric.com/victron-energy-battery-balancer.html

https://www.amazon.ca/Battery-Equalizer-Balancer-Connection-Protection/dp/B07XYW2J1L/ref=sr_1_fkmr1_2?keywords=Victron+Energy+Battery+Balancer&qid=1574752710&sr=8-2-fkmr1

https://www.youtube.com/watch?v=XMOz-5JeAy0

https://www.youtube.com/watch?v=d7bIwEB3iWk

mcgivor · November 2019

This is not a revolutionary concept, there have been other ballancing systems which shift charging between batteries, but the crux of the matter is it is limited to battery level, not cellular level. This is akin to putting a computer on a Model T Ford, it may help to some degree but the base technology is outdated, perhaps if this could be used at a cellular level it would be of serious consideration.

My personal thought is it would be really advantageous if monoblock batteries had access to individual cells in the form of a small auxillary post to provide a useful means of ballancing at a cellular level, this would be extremely advantageous in the implementation of a true BMS, sadly lead acid is reliant on its laurels of being a robust but somewhat temperamental outdated format particularly in the monoblock arrangement.

ligwyd · November 2019

Un-equal charge and discharge cycling of strings seems to be the main obstacle to overcome. If a battery balancer could effectively ensure equal charge and discharge current from two or three strings of batteries, wouldn't that in it self be providing an invaluable function?

Otherwise this is only done by paying strict and close attention to S.G. and correcting any eventual imbalance manually, which would be time consuming and also would interrupt system usage.

ligwyd · November 2019

Image: https://us.v-cdn.net/6024911/uploads/editor/6o/s5jjtre1t0em.png

mcgivor · November 2019

Definitely it would be an improvement over a parrallel system without monitoring, but it is important to remember the monitor is still looking at a battery as opposed to cells. With monoblock batteries a single cell is possible to fall behind its cell mates which comprises the individual battery, for this reason it would be advantageous to monitor each cell individually. Sadly due to the nature of cell arrangement with lead acid being series first, then parrallel, it doesn't by nature lend itself to fine monitoring of individual cell performance, unlike LiFePo4 where it is the opposite, parallel first then series.

With LiFePo4 cells, or cell blocks, are maintained within mV's of one another, it's a more accurate form of monitoring with safeguards to prevent any variations, assuming that a BMS is used and that it works as it's supposed to. Life is full of supprises, especially in the electronic world.

With lead acid it's still SG that determines individual cell performance, which although is a primitive means, in and of itself, is pretty reliablle if accurate reading are measured, which brings into question the accuracy of the hydrometer and the temperature of the electrolyte, which influence the readings, so many variables to think about.

Just food for thought, not trying to discredit either format, we're all here to learn .

ligwyd · November 2019

Even with carefully monitoring your bank, it would seem a battery balancer would take a lot of the leg work out of the process, would it not?

Also, even if there is a low cell in a battery, that low cell exists whether or not the batteries are wired up in series, parallel, cross-tired, battery balancer equip installed etc..... The only way to bring up the low cell is with EQ - overcharge (which most FLA.s are designed to tolerate regularly as part of the regular charging process voltages)

I was told yesterday by someone who knows a lot more than I, that (yet to be verified) some high end Rolls batteries normally charge at 60V. ie: batteries are regularly being overcharged - balanced as part of their regular charge process. Not hard on the battery at all! Just using a little more water.....

So, a battery balancer does not replace diligence, just makes the job of balancing batters easier, which is all they are designed to do.

I would still be taking regular S.G. readings as necessary, as this is the only method of really knowing whats going in each individual cell.

Appreciate the dialog. Well said. We are all learning everyday.

mcgivor · November 2019

The most common cause of battery problems associated with flooded lead acid is undercharging, battery manufacturers usually base their charging recomendations on ideal conditions, using grid power. PV systems on the other hand are vastly different in that there is a limited window of opportunity usually restricted to ~4 hours give or take at best. For this reason it may be necessary to run batteries at slightly elevated voltages in order to make hay while the sun shines because soon after the peak the output reduces and the battery takes over.

All too often operators are afraid to use an aggressive charging regime in fear that they will cause damage due to overcharging, but in reality they are often causing more damage by undercharging. The other factor is the double edged sorwd of depth of discharge, deeply cycled batteries require more current to replace the withdrawals, this where aggressive charging is needed, on the other hand a shallow discharged bank wouldn't need, nor benifit from, higher voltages and may even cause more harm than good . Each and every system is different, no two are exactly the same, so the one size fits all approach is a recipe for disaster.

String ballancing using ballancers will reduce the inherent problems associated with parallel arrangements, you are correct monitoring SG is still needed, as is the monitoring of water consumption, too high could mean too aggressive requiring a few tenths reduction in voltage, or vice versa. As batteries age they will consume more water and may never terminate charging using end amps, adjustments will probably be required but this will probably occur close to the life expectancy of the battery itself.

FLA batteries are very simple in concept but very complicated when used outside their comfort zone, the Rolls Surrette batteries are high quality but there have been many users having problems using them, most likely due to misunderstanding of their respective needs, which have evolved over time to suit the demand. Many of the requirements are probably applicable to other brands because in essence they are all the same format, or chemistry if you like.

ligwyd · November 2019

Great info. One really would lack critical experience unless you outlived a couple sets of batteries hey?

Sure would gain a lot from working with a battery bank from brand new to end of usable life.

I'm sure once you got it, you've got. Like anything. Seems overwhelming at first until you get a grasp on what going on. Like riding a bike.

The image I posted of the Victron Battery Balancer looks like the negative battery posts (with the exception of the negative battery posts connecting to the negative bus bar) are all cross-wired one the other. Not sure if this is actually high current cable or just small wires to transfer an amp or so of current from high strings to low strings - balance the strings.

Either way, I've read up on a few posts here that cross-wiring is not a good thing. Couple engineers I spoke with both seemed to like the idea and had nothing negative to say of the practice - given the batteries are all new and the same.

I value your guys opinion over design engineers anyway (no offense if any of you are engineers

I work in the trades. Engineers and Guys hands on in the field both have their place, but the guy with the hands on experience trumps it every time.

So is Victron set up in the above image earlier in this thread cross-wired? Not sure I like the idea if using it yet, until I learn more anyway. For now, I'll just keep an eye on the strings and if one get low disconnected from the pack and bring ut back up to par. Hopefully it is not necessary every mth! Every few mths would not be the end of the world. Once a year, totally do-able. We'll see.

BB. · November 2019

Cross wiring is the only way they can use one "set" of battery balancers for a multiple string battery bank. By "laddering" or connecting each battery (or cell)in parallel), then the "one" battery balancer can "manage" the entire parallel string of cells/batteries.

I am not a fan of laddering batteries... If the batteries/cells are all in good shape (for lead acid), then nothing is gained (no current flows in cross connects).

If there is a "bad" or "weak" cell/battery, the other parallel connected ones will "hide" the weak unit. Makes it very difficult to monitor the health of each battery/cell with a voltmeter/current clamp meter. If you have a dirty/loose connection, also difficult to find it as there are parallel current paths around the weak point.

In theory, each series string of batteries should have its own fuse/breaker to protect against short circuits (especially if you have 3 or more parallel strings). With cross connected batteries, there is no place to place a single series protection fuse to protect against shorts.

If you are using a battery balancer--And all is working well--Then cross connecting and using the balancer should work OK...

-Bill

ligwyd · December 2019

Here is an e-mail I received in correspondence on this topic:

Couldn't help but post since it is right in line with this discussion.

Interested to get some feed back on this.

"Ok I read through what others had said about cross-tying in the links you provided. All the cons I can make out are in reference to either a weak/old bank near failure, or the added work or complexity in understanding what’s happening during troubleshooting. In my mind, the biggest reason TO crosstie is to prevent the bank from going there. True, in a perfectly-balanced set of strings, you wouldn’t have any current flowing in the cross-tie wires, and one person commented “you only have a few hundred mA flowing even under heavy load” from which was inferred an insignificant benefit – but what that person isn’t considering is the cumulative effect over time of that small correcting current. The cumulative effect, if uncorrected, causes weaker batteries to be cycled more extremely, and stronger batteries to “atrophy”.

If one cell in one string fails, and it’s cross-tied in to another, true you have failed cells pulling down other cells that they wouldn’t otherwise, but it’s just a case of WHICH other cell(s) get(s) stressed, not a case WHETHER other cells get unduly stressed. This example represents a bank near end of life anyway (or a defective cell).

Manufactured batteries have probably about a 1% or 2% tolerance in their actual capacity vs nameplate.

If by dumb luck, 2 cells are paralleled that have either the highest or lowest capacity, that offers the least benefit. But, when high and low capacity cells get paralleled, they will both operate in the same voltage window as the average battery. In this way, you help mitigate the “one bad cell bringing down the whole bank.”

Writer, to be credited.

Dave Angelini · December 2019

The easy way is to never use anything but 2V cells in a bank with one string for offgrid. If you need more capacity you buy the next bigger cell size. This can get 10 to 15+ years of service with good maintenance in FLA. This may not be an old subject for you and it is good to understand the concepts, but, it is a really old subject offgrid. Good Luck!

BB. · December 2019

I don't want to beat a dead horse... But, this is my reasoning.

Anytime you try to make for "redundant systems", I like to make sure that the redundancy does not hide failures, or make diagnosis and repairs more difficult, or in the worst case--Make for more spectacular failures.

The list below is probably a bit pedantic... But covers the major issues:

I suggest that every series string of batteries/cells should have its own fuse or breaker to protect against short circuits causing wires to overheat/start a fire. With cross connected batteries, there is no single current path where a fuse/breaker can be installed.
If there is a shorted or cell/battery with high self discharge, it will simply discharge the rest of the parallel connected batteries/cells. Granted it will be "better supported" by the cross connected current paths. But it makes it almost impossible to quickly find/isolate a shorted cell/battery with just a voltmeter. Typically bad SG readings will help find the problem, but for AGM and other sealed batteries--No SG readings. Also, when you have high self discharge (typically >~2.5% rate of self discharge), your cell/battery runs the risk of overheating or even fire. Using an IR thermometer for FLIR camera can help here too and isolate hot spots. Bad cable connections (corrosion, loose, etc... There is very little voltage drop because of the cross connecting buses).
If there is an open cell or battery, again cannot quickly use a voltmeter to find the open cell (typically higher voltage than rest of cells/batteries in string). No big safety issue with an open cells and cross connections. And, it is possible that cross connections will keep the voltage across the open cell "low" when you are looking at >>48 volt battery banks (less chances of internal arcing). One issue with series connected open cell/battery, the rest of the batteries don't get charged or discharged--So if you are not monitoring, the other batteries can sit and eventually sulfate if not checked weekly/monthly.
In the case of open cells, the battery bank is reduced in total AH capacity by the open cell (4x 200 AH strings, open cell gives bank 300 AH of capacity because of the open cell/circuit). With shorted cells/batteries, the cross connected batteries can also be discharged by the one bad cell/battery... And cause early sulfation there too.

So, for me, my issue with not being able to diagnose weak cells/batteries without disconnecting the cross connects (with a voltmeter), cannot easily measure and understand current flow (with current clamp meter), and cannot use a fuse/breaker per string to reduce the chances of fire--I just do not see the "advantages" of cross connecting and the added expenses (lots of heavy cross connected cables, more connections, etc.).

If all "goes well", then cross connecting does not do anything.

If a cell/battery goes bad, we still lose the "same" bank capacity, cross connected or not (you only have 3 parallel connected "working" cells/batteries and one bad non-working).

If something goes bad, a quick voltmeter and current clamp meter measurement will quickly isolate the fault(s) on a non-cross connected battery system. Simple voltage/current checks on a cross connected system need further investigation (disconnecting cables, checking SG, etc.) to drill down and find the fault.

And if all seems to be going well, using a DMM and Clamp DMM, can do very quick and safe sanity checks to confirm that all is well.

Do I see advantages to BMS for lead acid batteries... Sort of, if you have a weak cell, a BMS can detect it and/or support the weak cell with additional charging current... But that is only postponing the inevitable failure.

Another advantage to battery/cell level BMS--For "12 volt systems", losing 1x cell drops the voltage to 10 volt--And "obvious failure". For a 48 volt system, a loss of a single cell can reduce to a "46 volt battery bus" system. Not near as obvious (need to pay close attention to see a "small" voltage decline). For a very high voltage system like 140 to 380 volts--A single cell failure is not obvious at all, and the failed cell could cause a fire/explosion if not caught in time.

If not cross connected, then need a single BMS for each string of batteries. If cross connected, then only need a single BMS for the whole bank... So a definite cost savings there.

-Bill

Dave Angelini · December 2019

Pedantic huh... Less is more offgrid and the last thing I would want for my clients would be to, as you said Bill, add onto a redundant system new modes of failure.

Save the electronics for the battery designer who knows the modes, can warranty the system, can be there in the long run, and is listed for residential use.

One of the major attributes on FLA if designed correctly, is it is mostly immune to electronics failure.There are none! For Offgrid this is the Holy Grail. The user failure will always be there with most anything. We read it often on this forum.

If the OP wants to be a hobbyist and get nerdy with this, go for it.

ligwyd · December 2019

So far, I'm thinking of not using the balancers and just monitoring each string closely, like I would be anyway even if it was 24 - Two volt cells.

If S.G. of all cells stays where it should be I'm happy! Not gonna get to hung up on .1 of a volt difference under load from one string to another.
Sure appreciate the feedback. As always love this forum

ligwyd · January 2020

Anyone aware of a battery balancer that can balance three 48 volt batteries? At this point, I am not sure if such a product exists. EQ charge could aid in balancing each of the three strings like any other string of FLA,s but just wondering if there is a way to balance the charge/ discharge to each string at the bus bars?

Technically, I have three, 48 volt batteries, consisting of four - 12 volt batteries each.

I know this has already been discussed in some detail on this post, however, I'm still doing a little digging on the subject.

Appreciate anyone's input on the subject as to the best approach to do balance three strings aside from simply charging up strings individually from time to time as required. How often that is required will decide for me whether to invest in battery balancing equip or not.

BB. · January 2020

Are the 3x 48 volt battery blocks connected in series (144 volt battery bus), or in parallel (48 volt battery bus)?

-Bill

ligwyd · January 2020

Hi Bill,

Yes, the three strings are connected in parallel (48 volt - blue seas bus bars - positive individually fused).

Image: https://us.v-cdn.net/6024911/uploads/editor/6s/n1zleukdpo82.jpg

Maybe the following pic, using a set (3) Vicrtrons is the only way to "somewhat automatically" do this? Albeit the rats nest of cabling and extra fusing as previously discussed on this post?

Image: https://us.v-cdn.net/6024911/uploads/editor/8d/0gui8jhjy8xx.png

mike95490 · January 2020

If your three strings are wired well (good crimps, solid connections) you should not need to balance them. Your monthly EQ should take care of that. You might want to insure you get a good full charge on them, either with lots of solar, or running the generator once a week to bulk them and let solar finish a good full charge.

ligwyd · January 2020

I hope that is the case and definitely the easiest, however the more I read about battery balancing the more I like the idea. Undercharge is no good but overcharge, although rare, is also hard on the batteries.

Even with periodic EQ as required, wouldn't a "low string" still become lower as a "high string" becomes higher?

EQ is a best attempt, without battery balancing equip, to balance strings by overcharging some batteries/ cells, to allow time to bring up low batteries/ cells,....correct?

Does not seem like an ideal situation..............

Even now, in one string of four - 12 volt batteries, after a full charge/ EQ, while still in float for several hours, I've got one of the batteries at 14.91V and another battery in that same string at 14.75V. My volt meter is out a bit, but differentiation in voltages simply serves as a comparison.

When I add up all 4 voltage readings in each of the three strings, the average values are 14.8075V, 14.8075, and 14.8050V. All pretty much bang as far as voltages are concerned. Even when I check the S.G., all bang on. 1.255-1.265 (full for my batteries)

BUT,...... if I have a differing voltage of 14.91 and 14.75 in two of the batteries in one string, won't that spread increase over time, or the high battery be continuously overcharged, when EQing, to drag along the lower battery, leading to shorter battery bank life?

Now here is where, from what I can see from research, albeit not 40 years off grid experience, where a battery balancer would add value, in keeping all batteries at a level playing field all the time, without always having to over charge strong batteries for weaker ones?

Just a bunch of thoughts at this point. Sure appreciate the experienced feedback.

Dave Angelini · January 2020

You are overthinking. Do the EQ long enough to get flat SG's and do something else with your time. Take a walk or something. This is very old mature technology.

ligwyd · January 2020

Ha ha. Yep, I always take it way too far, at least a couple times over. Reason is, not many are excited about 3 strings and I want to have confidence in a product I have to do with. Any time I leave stones un-turned I get burned. Just like to be annoyingly thorough. Wife calls it OCD:)

Thanks for the peace of mind.

ligwyd · February 2020

Thought of a couple more questions the other day.

1. If a string begins to become low, will adequate EQ slowly bring up the low string (provided that there is not a problem with the low string) or will it compound the problem.

2. At what voltage deviation from one string to another or S.G. deviation would you manually correct the imbalance?

Dave Angelini · February 2020

This is the problem with too many strings. Too much time to get them balanced.

You may have to separate the strings and charge longer the low string.

You can measure SG right? If so do not bother with voltage, measure SG.

divideoverflow · May 2020

I've actually ordered two of these devices, one for each string of 4 -12v batteries for my 48V bank of AGMs. (Just getting it out of the way, others mentioned in another thread that they didn't think these type of batteries are suited for solar. The manufacturer claims 1500 cycles at 50% discharge, and that they are designed to handle cyclic applications, they are rated for 190ah in both C10 and C8 rates...and I got them super cheap)

My plan is to use the balancers in lieu of an equalization charge, since AGMs don't tolerate the higher voltages. Per my battery manufacturer, 2.4vpc is what should be used for high frequency cyclic operation, as well as for a periodic "freshening charge". Float voltage recommended is 2.29vpc.

So what I'll be setting the balancers up with quick connect terminals, so I can take them in and out of service as desired. This way, I can use them to balance for a few days a month (in lieu of an eq charge), and then disconnect them to save the parasitic drain. So I'm basically using them as an alternative to hooking a separate 12v charger up to the individual batteries periodically to balance them.

Once I get a few months of data recorded I'll try to remember to report back.

ligwyd · May 2020

Yes, would be curious to know how you make out with your balancers.

Dave Angelini · May 2020

I would like it also but after more than a few months. It takes many years to do this and that is why there is so little useable data. As a designer you just have to say no to battery stringing.
As a user, well, Good Luck

BB. · May 2020

The AGM balancer for 12 volt batteries, you still have 6 cells in series. So I am not sure what a 12 volt battery balancer really buys us.

If you had 2 volt AGM, then a per cell balancer could be nice... But that is even more connections because of 2 volt cells vs the 3.7 volt Li Ion cells.

Holding the charging voltage of 2.4 volts per cell for AGM is still a "soft" EQ (hold for 8+ hour?).

And Concorde Life Line batteries do have a high voltage EQ that they support... So it is possible.

Bill

Gin83 · September 2022

And in general, those batteries that are not balanced, according to what scheme should they be swapped ...? Because I noticed that in the chain of accumulators there is always a weak

Battery Balancing Systems?

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