Battery Equalizer on battery bank

solarking

Does battery equalizer(not to be confused with desulfator) work on a battery bank with different age batteries.

BB.

I am a little confused about your question... "Equalization" tends to be (for lead acid batteries) controlled over charging of the battery (6-24 cells for a 12 to 48 volt battery bank) so that any "under charged cell" (less than 100% state of charge) is brought to 100% by a high charging voltage (typically around 15-16 volts for a 12 volt bank and around 2.5% to 5.0% charging current) that "forces" current through the 100% full cells so that the series connected less than full cell(s) can be brought to full charge too. This can take 30 minutes a month or many hours over several days for seriously unbalanced/poorly performing (low specific gravity industrial/large deep cycle) batteries.

There are battery "equalizers" or battery/cell balancers too. Lead Acid batteries (usually flooded cell) are somewhat tolerant of "over charging" (aka equalization). Other types of batteries (AGM, GEL, various Lithium Ion) are not tolerant of "over charging" (forcing current through a 100% full cell) and can be damaged/ruined by an "equalization" charge.

Instead, what is done by many is to put a "balancing circuit" across each cell (usually done for various Li chemistries). The balancer monitors the cell voltage and when 100% SoC, the balancer "leaks current" around the full cell--which allows other cells to continue charging until they are 100% full too. There are multiple ways that balancing can be done (top balancing, bottom balancing, etc.). Each has their proponents and applications.

And for other folks, Li Ion cells do not go out of balance very fast or very often. And some folks will manual balance the cells (charge individual cells to 100% each, or place a small load across "full cells" to bring them down to the neighbor cell voltages, etc.). And manually balanced batteries can go many months or even years between re-balancing.

The reason for equalizing/balancing cells in a battery--If you have 5 cells at 100% and one cell at 80% state of charge--Then the battery is only to 80% state of "useful" charge... Most rechargable battery chemistries die if the battery is tank to 0% state of charge or the voltage is "reversed" on the terminals (the low charge cell is "reversed charged" by the other cells. It is hard to "reverse charge" a 12 volt battery with active loads as one cell goes dead, the battery voltage drops by 2 volts (say 11 volts to 9 volts) and the loads stop functioning. With 48 volt batteries, if you have on cell go "dead", that is typically 46 volts to 44 volts and the loads will keep functioning (and the weak cell/battery will be ruined).

For various Lithium Ion chemistries, they have maximum and minimum voltages that the cell must not be taken beyond, or the cell will be ruined (and in some chemistries, the cell can explode/catch fire).

For Flooded Cell Lead Acid batteries, equalization does some good (balancing cells, mixing electrolyte, shedding "dead" plate material). However, equalization is also hard on the battery too... Oxygen generated can cause positive grid/plate corrosion, gassing erodes plate material, and gassing (hydrogen+oxygen gas generation) loses water from the electrolyte plus generates heat--Hot batteries have shorter life.

-Bill

jonr

It will attempt to equalize the voltages in a series string of any batteries.    On the other hand, it's unlikely that it can move enough amps to succeed during high charge/discharge rates.

solarking

BB. said:

I am a little confused about your question... "Equalization" tends to be (for lead acid batteries) controlled over charging of the battery (6-24 cells for a 12 to 48 volt battery bank) so that any "under charged cell" (less than 100% state of charge) is brought to 100% by a high charging voltage (typically around 15-16 volts for a 12 volt bank and around 2.5% to 5.0% charging current) that "forces" current through the 100% full cells so that the series connected less than full cell(s) can be brought to full charge too. This can take 30 minutes a month or many hours over several days for seriously unbalanced/poorly performing (low specific gravity industrial/large deep cycle) batteries.

There are battery "equalizers" or battery/cell balancers too. Lead Acid batteries (usually flooded cell) are somewhat tolerant of "over charging" (aka equalization). Other types of batteries (AGM, GEL, various Lithium Ion) are not tolerant of "over charging" (forcing current through a 100% full cell) and can be damaged/ruined by an "equalization" charge.

Instead, what is done by many is to put a "balancing circuit" across each cell (usually done for various Li chemistries). The balancer monitors the cell voltage and when 100% SoC, the balancer "leaks current" around the full cell--which allows other cells to continue charging until they are 100% full too. There are multiple ways that balancing can be done (top balancing, bottom balancing, etc.). Each has their proponents and applications.

And for other folks, Li Ion cells do not go out of balance very fast or very often. And some folks will manual balance the cells (charge individual cells to 100% each, or place a small load across "full cells" to bring them down to the neighbor cell voltages, etc.). And manually balanced batteries can go many months or even years between re-balancing.

The reason for equalizing/balancing cells in a battery--If you have 5 cells at 100% and one cell at 80% state of charge--Then the battery is only to 80% state of "useful" charge... Most rechargable battery chemistries die if the battery is tank to 0% state of charge or the voltage is "reversed" on the terminals (the low charge cell is "reversed charged" by the other cells. It is hard to "reverse charge" a 12 volt battery with active loads as one cell goes dead, the battery voltage drops by 2 volts (say 11 volts to 9 volts) and the loads stop functioning. With 48 volt batteries, if you have on cell go "dead", that is typically 46 volts to 44 volts and the loads will keep functioning (and the weak cell/battery will be ruined).

For various Lithium Ion chemistries, they have maximum and minimum voltages that the cell must not be taken beyond, or the cell will be ruined (and in some chemistries, the cell can explode/catch fire).

For Flooded Cell Lead Acid batteries, equalization does some good (balancing cells, mixing electrolyte, shedding "dead" plate material). However, equalization is also hard on the battery too... Oxygen generated can cause positive grid/plate corrosion, gassing erodes plate material, and gassing (hydrogen+oxygen gas generation) loses water from the electrolyte plus generates heat--Hot batteries have shorter life.

-Bill

No Bill I am not talking about the equalization charge. I am talking about the device usually called as battery equalizer which equalize battery voltage in series connection. For eg.In a 48v battery bank batt1 is 13.2v, batt 2 is 13.5v, batt 3 is 13.6v and batt4 is 13.1v,  battery equaizer will prevent the lower voltage battery in a battery bank from getting overcharged.

mvas

solarking said:

No Bill I am not talking about the equalization charge. I am talking about the device usually called as battery equalizer which equalize battery voltage in series connection. For eg.In a 48v battery bank batt1 is 13.2v, batt 2 is 13.5v, batt 3 is 13.6v and batt4 is 13.1v,  battery equaizer will prevent the lower voltage battery in a battery bank from getting overcharged.

Is this device, that you speak of, called a Top Charge Balancing circuit?
Typically, this device is used on a "per cell" basis inside Lithium Battery Packs, as part of the BMS.
Do you have a URL LINK to this Lead Acid Balancer?

It is OK, to slightly over-charge one Lead Acid Battery, to get the entire Series String to 100% SOC.
So, we do not use a Balancer Circuit with a Series Bank of Lead Acid Batteries
We do not normally mix old & new batteries.
If you have batteries of different age, then most likely they will have different voltages.

Bulk Charging can supply way more amps than the Balancer Circuit can by-pass,
so how does the Balancer  prevent over-charging ???

Estragon

As I understand it, these essentially charge each of serially connected batteries individually. That might help if entire batteries need individual charging, but they don't charge individual serially connected cells. Your 48v bank is 24 cells connected in series. The equalizer charges in groups of 6 instead of 48.

You could do the same thing by hooking up a 12v charger in turns to batteries 1 and 4. That may be easier on batteries 2 and 3 than doing a normal EQ, which as Bill points out, can be hard on batteries.

Will it work on old and new batteries mixed in a bank? I suppose, but I don't know that it will do much to prevent the new batteries from aging prematurely.

BB.

A 12 volt balancing circuit still is balancing 6 cells in series--So, i am not sure how it is much better to have these for 24/48 volt battery banks. I have always wondered if 2 volt balancers for lead acid batteries are more trouble than they are worth (49 wires to balance 24 cells in a 48 volt battery string--And even more if you are have several parallel strings.

And thought of a bluetooth or wifi enabled battery monitor module--You clip to the smallest battery unit in your system (12/6/4/2 volt) and it watches for high/low voltage units so you can investigate/equalize the bank when needed (detect hidden failures in long series strings of batteries without having to go out with a mutimeter every week or four).

There are 12/24 volt battery balancers. These are used, for example, in a 24 volt bus that has 12 volt house loads. The balancer is an isolated DC to DC converter that (in some models) is bidirectional. It can take charging from 24 volts and supply 12 volt loads, or even take 12 volt charging and recharge the "upper" 12 volt battery bank. These are "high power" devices that can run the 12 volts directly from the "high 12 volt" battery too (basically moving power between batteries):

http://www.dan-marcrvparts.com/vo12vobaeq.html

I guess, if you are looking to mix old/new 12 volt batteries (or series pairs of 6 volt, etc.) together in the same series string, a 12 volt based balancer circuit will "make up" for the higher self discharge that is present in older batteries.

I guess you are asking about this type of unit?:

https://www.amazon.com/ZHC-Equalizer-Lead-acid-Batteris-Balancer/dp/B01JJ3UKDU

It looks to have a 5 amp rating... That should be good for upwards of a 500 AH rated battery bank (assuming 1% rate of charge transfer--should be "good enough" for batteries in good shape). Batteries that are "failing" will show upwards (and over) 2% rate of self discharge (and can run hot/fail).

I do worry about added complexity / points of failure--The more wiring and circuits added, the more chances something will go wrong.

-Bill

jonr

A balancer is statistically advantageous, even if you only have one connected every 6 cells.   And cells within the the same package/battery are more likely to be balanced anyway.

A 5A balancer operating during a 30A charge will certainly help, but imagine the case where one 12V battery is fully charged and the other (in series) isn't.  The former will have to boil away ~360W of  excess energy being applied (not good for the battery).    Should help to put the temperature sensor on the weakest battery.

littleharbor2

Or is this the type of equalizer the op is referring to. This is for tapping 12 volts from a 24 volt battery. It monitors usage and switches from one side to another as power is drawn.

solarking

I was referring to sukam 48v battery equalizer

Marc Kurth

jonr said:

A balancer is statistically advantageous, even if you only have one connected every 6 cells.   And cells within the the same package/battery are more likely to be balanced anyway.

A 5A balancer operating during a 30A charge will certainly help, but imagine the case where one 12V battery is fully charged and the other (in series) isn't.  The former will have to boil away ~360W of  excess energy being applied (not good for the battery).    Should help to put the temperature sensor on the weakest battery.

Curious about this comment. A fully charged battery will draw very little current, often in the range of 0.05% of the C/20 capacity - resulting in very little wattage being dissipated by the fully charged battery.

Will a battery eventually overcharge if left at its absorb voltage long enough? Yes, of course! With fairly healthy batteries, they tend to balance out when given adequate time to charge. This is always the danger with PV systems with a weak ratio of PV to battery bank size. With Concorde and Fullriver AGM's, adequate time at Float voltage on a regular basis will keep them close.

In my experience, you will see a voltage rise across the batteries that are full, while the other(s) catch up.
Again, in my experience, the batteries that "charge" first are done accepting current because they won't accept as much capacity as the others. If this is due to sufation, the voltage rise will perform a mini-equalization bringing that battery more in line with the others.

Watching individual batteries can tell you a lot.

Marc

mvas

Marc Kurth said:

jonr said:

A balancer is statistically advantageous, even if you only have one connected every 6 cells.   And cells within the the same package/battery are more likely to be balanced anyway.

A 5A balancer operating during a 30A charge will certainly help, but imagine the case where one 12V battery is fully charged and the other (in series) isn't.  The former will have to boil away ~360W of  excess energy being applied (not good for the battery).    Should help to put the temperature sensor on the weakest battery.

Curious about this comment. A fully charged battery will draw very little current, often in the range of 0.05% of the C/20 capacity - resulting in very little wattage being dissipated by the fully charged battery.

Will a battery eventually overcharge if left at its absorb voltage long enough? Yes, of course! With fairly healthy batteries, they tend to balance out when given adequate time to charge. This is always the danger with PV systems with a weak ratio of PV to battery bank size. With Concorde and Fullriver AGM's, adequate time at Float voltage on a regular basis will keep them close.

In my experience, you will see a voltage rise across the batteries that are full, while the other(s) catch up.
Again, in my experience, the batteries that "charge" first are done accepting current because they won't accept as much capacity as the others. If this is due to sufation, the voltage rise will perform a mini-equalization bringing that battery more in line with the others.

Watching individual batteries can tell you a lot.
Marc

In my example below, a fully charged battery can still have 30 amps flowing through it ...
 
The OP's example was ... four (4) batteries in series, with a mix of old and new.
When the Charger is in Bulk Mode, all four (4) batteries must have 30 amps flowing them.
If there is a significant mismatch between batteries, then one battery can get to 100% SOC and start gassing way too soon.
This battery will lose more water through electrolysis.
The other batteries can never "catch-up" with normal charging.
Bulk Mode should get all four (4) batteries to an equal ( +/- 85% SOC ) but it cannot.

Extreme Example
==============
Bulk Mode = 30 amps until 59.2 Volts =  14.8 Volts per battery x 4 batteries
 
Old  Battery #1 = 16.0 Volts  <<< This battery is already 100% SOC in Bulk Mode and is already creating excessive gas
New Battery #2 = 14.4 Volts  <<< This battery never reaches 14.8 Volts in Bulk Mode, only +/- 75% SOC 
New Battery #3 = 14.4 Volts  <<< This battery never reaches 14.8 Volts in Bulk Mode, only +/- 75% SOC
New Battery #4 = 14.4 Volts  <<< This battery never reaches 14.8 Volts in Bulk Mode, only +/- 75% SOC
======================
Total                  = 59.2 Volts 

Battery #1 is fully charged but still has 30 amps flowing through it.
When the "Smart" Charger hits 59.2 Volts, it assumes all 4 Batteries are at 14.8 Volts - which is wrong.
And now the "Smart" Charger will switch to Absorb mode, which is way too early for Batteries #2, #3 & #4.

In Absorb Mode ...
a) Battery #1, which is already at 100% SOC, will continue to generate excessive gas.
b) The amps will drop below 3% way before Batteries #2, #3 & #4 can ever get to 100% SOC.

In this scenario ...
Battery #1 is habitually over-charged.
Batteries #2, #3 & #4 are continuously in a "Partial State of Charge" - PSOC is a very bad idea for Lead Acid batteries.

This is why we do not mix old batteries with new batteries.


I do believe that a Voltage Equalizer can help with a mix of old new and new batteries
What if, during Bulk Mode the Voltage Equalizer was able to get all four batteries to 14.8 Volts, at the same?

The $64,000 question is ... Does "Equal Voltage" mean "Equal SOC" for both old and new batteries?
Maybe not "equal SOC" but good enough SOC?

Battery Equalizer
=============
Bulk Mode = 30 amps until 59.2 Volts =  14.8 Volts per battery x 4 batteries
 
Old  Battery #1 = 14.8 Volts = 85% SOC
New Battery #2 = 14.8 Volts = 85% SOC
New Battery #3 = 14.8 Volts = 85% SOC
New Battery #4 = 14.8 Volts = 85% SOC 
======================
Total                  = 59.2 Volts 

With mixed age batteries ...
a) The Voltage Equalizer appears to prevent over-charging of the old batteries
b) The Voltage Equalizer appears to prevent under-charging of the new batteries

A Voltage Equalizer that can transfer the charge from the higher voltage battery to the lower voltage battery is more efficient.
A Voltage Equalizer that just puts a load / resistor across the higher voltage battery just wastes the power!

Some other questions ...
1) How do you determine the correct size ( amps ) of the Voltage Equalizer, for your Battery Bank
2) Is the price of the Voltage Equalizer worth the cost vs buying all new batteries?
3) Does the Battery Equalizer consume a significant number of watts?

bill von novak

solarking said:

I was referring to sukam 48v battery equalizer

That sort of device ensures that voltages are the same across batteries.  With lead acid batteries that does not ensure they are at the same state of charge; voltage at a given load is only a rough indication of SOC.

jonr

Note that there is a big difference between "what is the SOC" and "are the SOCs equal".   The latter is much less error prone and voltage might be the best available way to measure it (I haven't seen data either way).

Some people use SG, but:

"The specific gravity of fully charged deep-cycle batteries of the same model can range from 1.270 to 1.305.  ... Inaccuracies in SG readings can also occur if the battery has stratified..."

http://batteryuniversity.com/learn/article/how_to_measure_state_of_charge

My question:

With matched batteries, does battery voltage balancing increase life (less under/over charging) enough to pay for the cost and complexity (a few extra wires).  My guess is it's important with AGM and nice to have with flooded.

http://www.linear.com/solutions/5673

mvas

littleharbor2 said:

Or is this the type of equalizer the op is referring to. This is for tapping 12 volts from a 24 volt battery. It monitors usage and switches from one side to another as power is drawn.

This particular device is only applicable when you need both 12V Loads and 24V Loads, connected to a single 24 Volt Battery Bank.
Which is an interesting subject, but it is not really the subject of this thread.
This device is missing 1/2 the functionality of the Sukam 48v Battery Equalizer.
This device will only make sure the voltage of "lower battery" is never below the voltage of the "upper battery".
This device will do nothing, if the voltage of the "upper battery" is below the voltage of the "lower battery".
"lower battery" and "upper battery" per the schematic diagram.
This is the proper device when you need to support 12V Loads & 24V Loads simultaneously.

mmaritz

Many of us in South Africa have had great success with Chinese made HA01 and HA02 battery balancers (discussed here).

Mid points are measured using a Victron BMV 702 and even people with huge battery banks have had success bringing banks into better balance (eg. here).

Regards
Mark