Change language:   es   de

Equalization of flooded batteries

Tuesday, September 22nd, 2009

August, 1995 (rev B), ©2000 – 2010 Xantrex Technology Inc.

Equalizing or conditioning batteries refers to a method of charging deep cycle wet- cell batteries and is intended to restore battery capacity, revive battery efficiency, and extend battery life.
The process involves periodic application of a controlled overcharge cycle to batteries. This type of charge cycle requires that certain procedures and precautions be followed.

While a battery is being discharged, sulfuric acid in the electrolyte reacts with the lead plates in a chemical reaction that produces electricity and lead sulfate. When the battery is re-charged, electricity flows back into the battery and causes a reverse chemical reaction that turns the lead sulfate back into lead and sulfuric acid.
However, with each discharge and recharge cycle, a small amount of lead sulfate will remain on the plates. Using a three-stage charger, the amount of residual sulfate left on the plates will be less but some will still accumulate with each discharge and recharge cycle.
If this sulfate is left in place for very long, it will harden or crystallize and eventually reduce the battery’s capacity, increase its internal resistance and destroy the battery’s ability to produce an adequate amount of power.
When this occurs, even an equalize charge can not remove the sulfate and the battery becomes useless except as a recyclable item. (Recycling batteries is recommended to reclaim the lead and prevent contamination of the environment.)

Over time, the electrolyte tends to stratify into layers of acid and water with higher concentrations of acid near the bottom of each cell and more diluted electrolyte near the top. This causes uneven specific gravity within a cell and further reduces its capacity and efficiency.

An equalizing charge is a controlled overcharge cycle that performs several actions within the battery and provides certain benefits. During equalization, the voltage is raised to approximately 2.7 volts per cell, or about 16.2 volts for a 12-volt battery.
The current output of the charger should be limited to about 5% of the battery’s capacity. In other words, a 200-amp hour battery should be allowed to accept no more than about 10 amps of current. This will help prevent overheating.
The equalize cycle is timed to be between 4 and 8 hours depending on the features of the charging source, but the cycle can always be terminated early if necessary.
The particular battery manufacturer’s recommendations for equalization time should be followed.
This elevated voltage results in a vigorous charging action to take place within each cell that has several effects on the battery. First, much of the residual sulfate is forced to re-combine with the electrolyte in the form of sulfuric acid. Crystallized sulfate that will not re-combine is broken loose from the plates and falls harmlessly to the bottom of the battery.
Deep cycle batteries have additional space beneath the plates intended to collect this material. This action cleans the plates exposing fresh lead to the electrolyte and restores battery capacity.

The vigorous bubbling action that occurs during equalization stirs up the electrolyte and restores it to a consistent mixture of acid and water. The equalizing process also causes all cells in a battery to reach their maximum idle potential of 2.1 volts.

It is best to check with the battery manufacturer’s recommendations before equalizing since each manufacturer has slightly different suggestions on how often and how long to equalize their batteries. But, as a general rule, it is a good practice to equalize batteries after every 10 or 12 deep discharge and re-charge cycles. For batteries in constant discharge and recharge usage, this would mean about every two weeks. For periodic users, it would mean about two or three times a year.
For seasonal users, this could mean at the beginning and end of the season.

Again, check with the battery manufacturer’s recommendations, but as a general rule, the following steps should be observed:
1. Only attempt to equalize wet cell deep cycle batteries. Never equalize gel batteries or maintenance free batteries.
2. The batteries should be fully charged and near ambient temperature before beginning an equalize charging cycle.
3. There should be a sufficient amount of electrolyte in each cell to cover the plates, but do not top-off each cell until after equalizing. Since there is some heating of the cells during equalization, the electrolyte will expand and could overflow the cells if they were topped-off before equalizing. This would not only make a mess, but force you to terminate the equalize cycle too early to gain maximum benefit and would result in diluted electrolyte when it came time to add water.
4. Leave the caps on each cell. The caps are vented, and when left in place will prevent splattering of electrolyte onto the top of the battery when the bubbles pop. It is a good idea to lay a paper towel over the caps. This makes it easy to spot a cell that may start spitting electrolyte, and will soak up the liquid when this does happen.
5. Since the batteries will give off significant quantities of explosive hydrogen and oxygen gas during equalization, and produce moisture that will contain some amount of corrosive sulphuric acid, it is imperative that sufficient ventilation be provided.
Avoid smoking or generating sparks or flame near the batteries during this charge cycle.
6. All DC loads on the batteries should be turned OFF and disconnected. Since the battery voltage will be higher than normal during the charge cycle, some DC equipment could be damaged if left ON. These loads would draw current from the charger that should be available to the battery instead.
7. Equalize only one bank of batteries at a time.
8. During the equalize cycle, periodically check the batteries for any spitting cells and if this begins to happen, terminate the equalize cycle early. Do not start an equalize cycle and then leave the batteries unattended.
9. After equalizing, turn OFF the charging source, and allow the batteries to cool to ambient temperature before resuming normal float charging. After the batteries cool, it is a good time to check the specific gravity in each cell. They should all be 1.265 +/- .050 at 80 degrees F.
11. Refill each cell with distilled water up to the FULL indicator.

End ©2000 – 2010 Xantrex Technology Inc.

Equalization charging can be done with your PV system if your array is large enough, or with an engine generator.
Most PV Solar charge controllers and inverter-chargers have battery equalization functions.

(quoted from article below by Windy Dankoff, well worth a read on this link)
© 2006 by Windy Dankoff – Home Power Magazine

although it sounds technically difficult, equalization is quite simple to do
Just remember to check your electrolyte (distilled water) level is topped up to the correct level after the equalization. Just as paramount is to check the levels before hand, to ensure that there is sufficient electrolyte is covering the lead plates. If you are in doubt, refill and wait a couple of charge cycles (days) before commencing the process. This is specially important in the hot summer months, as the equalization process will drop the water level a bit.

With our two preferred MPPT regulators there are different ways to “skin the cat”.

The Xantrex XW60, supports the equalization programming in 3 easy steps, and keeps timing of the process. You can even activate the process without having reached full state of charge. The regulator will abide its time and initialise the process at first given opportunity.
The Xantrex is programmed to equalize for 1 hour. This is often not adequate, so get your specific gravity meter out (you have one don’t you?!!) and go check the cells before you start the process.
Repeat the equalize command 4 to 6 times in a row to achieve the desired amount of hours of equalization.
Remember that the batteries has to be fully charged before the equalization is initiated.
Measure the specific gravity of the battery acid on at least two cells in each mono bloc battery. Make sure that you take measures of the extreme + and – terminals of the entire bank, as these two cells will see the most action during use.
If you bank needs equalizing the cells will show slightly different values. If the values are more than 0.05 apart you will need to repeat the 1 hour process several times to achieve equilibrium. As soon as the Xantrex is done with the charge reset the yolk and do it all over again. Sometimes this is needed for 3 to 4 times, so make sure to limit your discharge the night before. This way you will have all afternoon to repeat the equalization until the cells check out.

Charge……………….Specific Gravity

When you check the gravity meter, you should position the top of the fluid level with your eyes. Take the reading from the lowest part of the level (the acid will make a slight depression in the Centre of the cylinder, clinging a bit higher on the sides, creating something that looks like two levels).

The MPPT500, does not support equalization readily, but that should not prevent the vigilant solar user from “boiling up the batteries” once in a while.
You will simply have to monitor the process yourself. The equalization should be performed for 3-4 hours every 40 to 80 days depending on your usage of the system. Solar systems on daily discharge needs equalization more often than holiday homes. (better give me a call on 6299 47701 before you set off the first time)

You will need a small flat head, and one medium sized Phillips head screwdriver to perform the operation.

Choose a bright sunny day, after a relative restrained power consumption the night before, to ensure that you see the red FLOAT LED (located on the front plate) blinking at mid morning.
This indicates that the regulator has sensed 90% charged batteries, and therefore has gone into FLOAT CHARGE.

Now you unscrew the four Phillips head front screws on the regulator to access the print plate behind. You unhook the data cable and remove the front plate entirely for eased access. On the print plate you will see the another FLOAT LED blinking away.
Right below this indicator there will be two small yellow adjustment screws, the higher will have “FLOAT ADJ” (float adjust) printed next to it.
Use the small flat head screwdriver to carefully turn the float adjust to fully clockwise position. (absolutely no force allowed, you are virtually screwing on/with a print board!)
Reinsert the com cable and select battery Voltage on the front plate display. You will now see the Voltage rise to about 15V. This voltage is a bit low for a 12V system equalization (15,6V is more ideal), but you can compensate by over charging for a longer time.
Keep an eye on the clock, and let the batteries overcharge for 3-6 hours.
Readjust the float level to 14.1 Volts referring to the Voltage display on the front plate. Refit the front plate and put a note in you calender for next equalization date.

Two words of advise.

While inside the regulator, you are able to short quite powerful DC terminals. Keep away from the cable lugs with any metal object. The adjustment terminal is placed well away from these, so it should not be a problem.

If the desired Voltage level of the float adjustment is unreachable, there is another way. Wait for the FLOAT LED to light steady, then disconnect the solar panels (PV +/-) first never disconnect the battery cable before the PV current is shut down (or you will fry the regulator!)
Also make sure to clearly mark the PV and Battery +/- cables, before removing them from the regulator terminals, to avoid reverse polarity by accident.
1. Switch your PV breaker to off (you have one don’t you?! if not fit one immediately, a single pole thermo magnetic 220VDC switch is enough. Just make sure that the Amp capacity is well above your maximum current rating from your total panel output)
2. Battery breaker or battery 50 Amp Fuse disconnect, meaning battery is disconnected on the + line.
3. Connect PV+ cable to Battery+ cable via sturdy cable assembly bloc (obviously connect on the regulator side of the battery fuse or breaker point – this fuse or breaker ensures your safety and will work as a switch to start and stop the equalization)
3. Connect PV- cable to Battery- cable via sturdy cable assembly bloc
4. Reinsert master battery fuse or flip battery breaker to on.
5. Turn the PV breaker on (this establishes connection to the batteries directly from the panels.
You are now equalizing on full voltage capacity
Use a Voltage meter to monitor the process (you can take the readings at the newly established connection). If the voltage exceeds 16V disconnect PV Breaker or battery breaker/fuse for a little while. The Voltage will drop quickly and you can reconnect and continue the equalization.
Keep it up for 3 hours, Disconnect the PV breaker + the battery breaker/fuse. Then reconnect the regulator.
It is recommended to wait a good hour before re connecting the regulator. This enables the batteries to cool down to ambient temperature.
Make sure to establish battery connection before turning on the PV breaker
The MPPT500 will make an audible click and show values in its display as soon as battery connection is established.

I disclaim any responsibility for supplying this information.
If you fry up your system – don’t come crying to me, but ….. equalization is a very important part of maintaining your battery store healthy and its not very complicated to do. Just take your time, work slow and methodically, and you will be all right.
Alternatively call me for a house call (60 Euro charge in a 30 Km perimeter from Lanjaron)