Equalization Charge Type

I am asking… because I don't know.:D

What is the correct type of charge for battery equlalization? Constant current? Would a basic taper charger work?

My situation:
I have two 12 volt 180 ah batteries in series and I bought a 12-0-12 15amp transformer; put three 6amp rectifying diodes on each + output. When I put this on the batteries after a normal charge and the batteries are at capacity will it work as a battery equalizer? Or do I need to invest in a constant current charger?

Thank you

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,321 admin
    Re: Equalization Charge Type

    I guess the answer is C/20 or 5% of the batteries 20 Hour capacity is a good current for equalization. Only perform the equalization after the battery is fully charged. Monitor the cells and once the specific gravity stop rising (1/2 - 1 hour between measurements) stop the equalization.
    • 180 AH * 0.05 = 9 Amps equalization charge
    You will have to check your charger--not all chargers can reach high enough voltage for equalization--or may have too much/too little current.

    Equalization is not something that should be done every week... But once every month to six months. When specific gravity becomes unbalanced, or low in one or more cells, or for tall cells -- to mix the acid (stratification--dense acid sinks, water rises).

    Here is a good thread talking more about the equalization issues.

    AGM's and other sealed batteries should never have a full "flooded cell" equalization performed (an "extended" full charge a couple times a year may be helpful for AGM/Sealed batteries--see mfg. specs. for details).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: Equalization Charge Type

    A transformer with rectifiers only is called a battery killer.

    When battery gets fully charged the voltage from a 12vac transformer with rectifiers will rise to over 16 vdc which will overcharge battery.

    If you watch it, or put a timer on it you may help the situation.
  • jprokosjprokos Registered Users Posts: 8
    Re: Equalization Charge Type
    RCinFLA wrote: »
    A transformer with rectifiers only is called a battery killer.

    When battery gets fully charged the voltage from a 12vac transformer with rectifiers will rise to over 16 vdc which will overcharge battery.

    If you watch it, or put a timer on it you may help the situation.

    Yes, it has to be watched; the battery temperature monitored, etc. It works fine for the poor person who has more time than money on his hands. I have read that equalization should be performed every 10 charge/discharge cycles or when the voltage between cells differs more than .2 volts. Is that correct?
  • BB.BB. Super Moderators, Administrators Posts: 29,321 admin
    Re: Equalization Charge Type

    No, do not equalize unless the cells s.g. is miss-matched or one or more cells are low s.g. while the rest are high.

    Equalizing once every one-two months as a starting point should be OK.

    Remember, equalization is pretty hard on a battery bank and really should only be performed when conditions warrant.

    Here is a thread on Specific Gravity versus voltage. And, the voltage difference of 0.2 volts between cells is probably way to high... That is probably almost the difference between a "full" and a "dead" cell's voltages.

    Form the above link, the formula for specific gravity to voltage is:

    • Specific gravity = single-cell open-circuit voltage - 0.845
    • (example: 2.13v – 0.845 = 1.285)
    • Or:
    • Single-cell open circuit voltage = specific gravity + 0.845

    If we use the Trojan value of SG 0.030 difference in Specific Gravity between cells as a point at which to equalize--that would be 0.030 volts between cells.

    From Trojan's battery manual (PDF):
    Equalizing (flooded/wet batteries ONLY) 3.4.2.

    Equalizing is an overcharge performed on flooded/wet batteries after they have been fully charged. Trojan recommends equalizing only when batteries have low specific gravity, below 1.250 or wide ranging specific gravity, 0.030, after fully charging a battery. Gel or AGM batteries should never be equalized.
    • Confirm that the batteries are flooded/wet
    • Check electrolyte level to make sure plates are covered with water before charging
    • Check that all vent caps are secured properly on the battery before charging
    • Set charger to equalizing mode
    • The batteries will gas (bubble) during the equalization process
    • Measure the specific gravity every hour. Discontinue the equalization charge when the gravity no longer rises
    WARNING: Do not equalize gel or AGM batteries

    I like Dave Sparks' post:
    I learned this strategy from Dave Surrette (Rolls) in the late 70's. Pretty much the bible on how I design my systems for off-grid.

    Assume that the system will never reach more than a 90% state of charge.
    Try not to go below 50% SOC, ever! Complete absorption over 90% of the year

    Use the energy stored from 70% to 90% SOC for your daily cycles.
    Save the energy from 50% SOC to 70% SOC for aging to get long battery life.

    I know Surettes has changed their recommendations over the years but I also know they are in the business of selling batteries! If you do the above you will get 10 to 15 years on their batteries with decent maintenance.

    The OP is making it complicated by mixing battery types and not really stating a lot of information that would allow decent specific advice.

    Oh yea, I am really happy that Surrette and Trojan are making L16's with 1000 AH capacities @20HR. Been bugging them for many moons to do batteries less than 125LB's!

    And, my two cents... If your batteries are using a bit of distilled water per month--you are probably OK. If you are using none, or a lot per month--then you are probably under or over charging.
    • Undercharging and operating for long periods (below ~75%) is damaging to lead acid batteries.
    • Overcharging is less damaging to flooded cell batteries (at the cost of distilled water and wasted energy).
    • Overcharging sealed batteries (AGM, Gel, VRLA, etc.) can be fatal to those types (venting electrolyte).
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Equalization Charge Type

    i don't think you guys have answered his question. i believe he is asking if it is a constant current or a constant voltage. i don't even know for sure on eq charging and i have never even used eq. my guess is it may be a combo of the 2, but i'll let somebody chime in that has designed them to answer how they approach it.
  • BB.BB. Super Moderators, Administrators Posts: 29,321 admin
    Re: Equalization Charge Type

    Constant current of C/20 or 5% of 20 Hour Rating.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Equalization Charge Type

    bill,
    is there not also a higher fixed voltage?
  • BB.BB. Super Moderators, Administrators Posts: 29,321 admin
    Re: Equalization Charge Type

    I guess you could use around 15-15.5 volts -- but you need to monitor the current and temperature of the battery bank to prevent overheating.

    An issue is that not many run of the mill battery chargers let you set the equalization current--so you are kind of stuck with voltage and temperature compensation... As the battery temperature rises, the battery voltage will fall and increase current acceptance. Potentially leading to thermal runaway.

    But not that many run of the mill AC battery chargers have temperature compensation either...

    So then you need a timer or manual intervention... At C/20---you probably are looking at 2-4 hours of equalization--so a timer can help prevent damage.

    Even the "good stuff" AC chargers -- few have even a minimum amount of what we are generally recommend here and is found on many of the MPPT type charge controllers and some of the combination inverter/chargers.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jprokosjprokos Registered Users Posts: 8
    Re: Equalization Charge Type
    niel wrote: »
    i don't think you guys have answered his question. i believe he is asking if it is a constant current or a constant voltage. i don't even know for sure on eq charging and i have never even used eq. my guess is it may be a combo of the 2, but i'll let somebody chime in that has designed them to answer how they approach it.

    Thanks Niel for clarifying my question. That's exactly what I was asking. I do appreciate the other information as well since I am just entering this game.
  • sub3marathonmansub3marathonman Solar Expert Posts: 300 ✭✭✭
    Re: Equalization Charge Type
    BB. wrote: »
    At C/20---you probably are looking at 2-4 hours of equalization--so a timer can help prevent damage.

    -Bill

    I keep thinking that equalization should be longer than 1 hour, but that seems to be all the XW6048 will allow for its equalization charge. Is there a way to set it to allow a longer equalization time?
  • BB.BB. Super Moderators, Administrators Posts: 29,321 admin
    Re: Equalization Charge Type

    Since an equalization charge is based on the battery's physical differences in SG between cells--you should only have the equalization last just as long as the SG is rising in the "low cells".

    Presumably it would be better to have the equalization stop and manually restarted based on cell condition than to just push current for a longer period of time when the cells do not need the current and you can really be damaging the bank from over charging.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bryanlbryanl Solar Expert Posts: 175 ✭✭✭✭✭
    Re: Equalization Charge Type

    If you consider the post about using between 70% and 90% SOC and that the bank really never gets above 90% for a constantly in use battery bank, you can see what equalization is all about and why it is needed on occasion.

    If the bank is only in periodic use where it has an opportunity to be fully charged, like in typical RV service with a decent charger and maintainer, then the need for equalization is minimized.

    The issue is that last 10% of battery charge for continuous use banks and making sure that all cells in the bank are fully and truly charged. That is what an equalization charge is all about. Batteries not at top charge tend to sulfate and that is not good. That little bit off top charge may only cause slow sulfation but, if it's not addressed, the batteries will suffer. Differential sulfation between cells can also become a problem. Equalization charges work against this process by making sure all cells have a full top charge to keep them all at equal states of function.

    You need current to charge a battery and that means whatever voltage is necessary to provide that current.

    How much current is the issue. A trickle charge is designed to be a safe level but can take a long, long time to do any charging. The C/5 rate is usually considered a good trade-off between battery heating and time but needs more careful attention to avoid excessive overcharging. Note also that higher currents mean higher charge voltages and those voltages might be a problem for any equipment attached to the battery bank.

    It should also be noted that the last 10% of charge takes time. A proper lead acid battery charge can take 8 to 12 hours in normal circumstances to get a full top charge and a lot of that time is that last 10%. An equalization charge is a remedial effort for when that sort of charge isn't feasible as a routine thing.

    When you check your battery bank and find some cells that are not on par with the others, then you know it is past time to act to get them back in line. That often means applying a charge current through other battery cells. That means you need to carefully monitor heat and electrolyte levels. It also means you need to be aware that you are overcharging those other cells and accept what that does to them. That impact can be minimized if you catch the imbalance early and take due care as prescribed.
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    Re: Equalization Charge Type

    EQ is Constant Voltage, once the target Veq is reached. At Veq, the Ieq tapers off slowly, at least for a good battery bank. Doing an EQ from PV input, the current limiter is the array's Imax for the Solar input, temp etc. Veq rises to the target value, with the charge source limiting the current. It behaves like a Bulk/Asorb cycle, just at a higher voltage.

    Ideally, a CC with EQ mode should be used. I have used a Variac controlled transformer/Rectifier to EQ a secondary bank, but this requires monitoring, and manual compensation of Veq as the bank temp rises.

    Normal precatuions should be used, as EQ liberates quite a lot of Hydrogen, and so on.

    Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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