Proper equalization technique

kab69440

In another recent thread, the subject of pack equalization has come up. For the past five years, I have started a second charge the day after a recharge. I do this maybe once a month or every other month. The end result has been pretty favorable(sp.? That doesn't look right?).

So, my batteries are five years old (give or take) and running a dual motor 4x4 conversion I have roughly an hour and fifteen minutes of straight "pedal on" time in stop and go driving to deplete the pack to 36.5 volts. Granted, this level of discharge is very rare, but one day I took my meter with me to get an idea of just how far I could push them. I am talking about neighborhood stop and go driving, not stop at the Speedway to grab a slurpee and hot dogs, stop at the park and shoot baskets kind of stuff. Continuous driving from pull out to park.

I do my best to take good care of the NAPA batteries I bought brand new. I keep a close eye on water levels. I don't allow dust to sit on the tops. I charge as soon as I am done crusing for the day. My terminals have a nice thick build up of wax from repeated treatments of protectant. I believe that for the amount of draw this system must be consuming, my battery life is close to phenomenal.

The other thread just got me wondering about my equalization routine. Could I be doing a better job than that? If I have the cart long enough to warrant yet another pack replacement, could I change my routine to squeeze more life out them?

BGW

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Volt_Ampere

The way that our FLA batteries get equalized is by overcharging them. The weak batteries get to full charge first and they gas more than the stronger ones. This is why it's never a good idea to replace one battery in a series pack.

sunking

OK first off an Equalization Charge or EQ for short is just a controlled over charge. There is a right way and wrong way to perform it, and only a specific time to perform it.

EQ is unique to lead flooded lead acid batteries (FLA) as they are about the only battery you can EQ. There are a couple of AGM that can be EQ under very specific conditions, but most AGM wil void the warranty if you EQ them.

Why EQ a FLA? It is part of routine maintenance to correct two characteristics of FLA batteries. 1 is to dissolve soft lead sulfate crystals that build up on the pates before they harden. Lead sulfate crystals begin to form as soon as the battery begins to discharge from 100%. Just letting the batteries sit and they begin to self discharge at a rate of 10 to 15% per month. The deeper you discharge the batteries, the process accelerates. Once you go below 50% DOD the soft crystals begin to harden. Once hardened they cannot be dissolved and the damage is permanent. The accumulation of lead sulfate crystals raise the battery internal resistance which prevents or slow down the battery ability to accept a charge and give up its charge. When you notice your battery performance does not accelerate the way it use to, or get the range it use to. See if this rings a bell. You go to charge up your battery, and the charger shuts off quickly and indicates your battery is fully charged. Then you go try to use it and nothing or extremely sluggish and the voltage collapses. You now have a new boat anchor, you battery has sulfated and is dead.

2 The other reason and thus as the name implies is to equalize the specific gravity between cells, and to some extent equalize the cell voltages. Over several charge/discharge cycles the batteries become unbalanced and is normal. The cause of that is no two cells or batteries are truly equal in resistance and capacity. After multiple cycles the unbalance builds up enough to affect performance as the weakest cell give out before the stronger cells. Allowed to go and it will destroy the weaker cells prematurely.

OK now that we know why to EQ we need to know when to EQ. As stated a EQ charge is a over charge, and any over charge causes permanent damage in the form of plate corrosion. As the plates corrode, they flake off and either come to rest in the bottom of the battery jar, or lodge in between and can short out a cell. FLA batteries have two failure modes. They will either die for sulfation (90% of all failures) and the remaining 10% from plate corrosion or over charging. OK to answer the question of when is real easy to answer. Only when required.

OK how do you know when it is required. Only your temperature corrected battery hydrometer tells you when it is required. To some extent a volt meter can tell you when you see cell voltage are unequal but, and I strongly emphasize, the HYDROMETER readings is the deciding tool. Voltage is only a clue to indicate you might have an EQ problem.

Just about every battery manufacture including Trojan only recommend EQ when the cell specific gravity reading of a fully charged battery vary more than .030 points from the lowest cell to the highest cell. Then and only then do you EQ. How often depends on how much you use the battery but as a rule of thumb roughly 20 to 30 cycles. FWIW only a Hydrometer with a Temperature Correction can accurately measure a batteries true state of charge. Voltages are only ball park and can only be used on a well rested battery.

How to you EQ? Well there are a couple of different ways. Slow or Fast with slow being the kinder gentler way. EQ is just a Constant Voltage charge of a higher voltage than Float Voltage. Slow would only be slightly higher than Float, and Fast would be significantly higher than Float voltage. Let's use Trojan line up as it pretty much applies to any manufacture. If you look at Trojans manual Float is 2.2 volts per cell and EQ is 2.6 vpc. Note here any voltage over Float is considered an EQ charge, Trojan is giving you the highest voltage or the fastest method. Universally 2.45 vpc is the industry standard voltage which is slower, kinder, gentler. If you want to know the voltage for 36 volt packs multiply by 18, and for 48 use 24.

If you use the high method means you are going to have to stay withing eye shot of the batteries and measure specific gravity very 15 minutes. Additionally the danger in using the higher voltage or fast method is going to boil the electrolyte rapidly and it may boil over and spill out electrolyte. If that happens you are fooked Laddy because you cannot put it back in. Don't fool yourself into thinking all you have to do is add water because that is dead wrong. If you add water all you are doing is diluting the acid and will never get those cells back to 100%. So if you see that is about to happen, lower the voltage down to a nice gentle simmer.

When you see the specific gravity back to within tolerances, terminate the charge, replace the fill caps, and call it a day. Let them rest several hours and check the voltages and specific gravity, they should be roughly EQUAL with a SPG reading or 1.227 and cell voltages of 2.122.

Last note. You only EQ a battery that has the correct water level and has been fully charged up and allowed to rest. Personally I EQ slow at 2.3 volts and it can take up to 24 hours.

branson

am I correct in assuming that a DPI charger will equalize the batteries automatically

kab69440

That is good info. Thanks for the effort, sunking! Looks like I need to buy a hydrometer. I am more than curious to find out how my pack measures up.

sunking

OK you don't have to spend a fortune either on a hydrometer. Deka makes a decent Temperature Compensating Hydrometer for less than $10. Check Amazon and you should get a hit

like this

like this

.

You don't have to worry about Temperature Compensation while you EQ the battery because all you care about is that all cells are within acceptable range of less than .030 points. Once you are done or say after running for a day or after charging and you want to know the State of Charge, then you will need to apply the correction to obtain an accurate measurement.

kab69440

Dumb question removed. Nothing to see here.

JohnnieB

No, the DPI does not have an equalization mode, but it uses dV/dT technology to "fully" charge all of the cells in the series string and keeps them at 100% SoC with float charging, so about the only time inequalities have a chance to manifest themselves is while you are out and about on the cart.

I measure and record individual battery voltages every time I check the electrolyte level, which is about once a month, and so far (2+ Years) they are staying well within 0.1V of each other.

sunking

That is correct. The best charging algorithm is a pure Float Charger that has a EQ stage. Float Chargers hold the batteries to 100% SOC. Once the battery is fully charged up a Trickle Current continues to flow which eventually brings the lower cells up to match the stronger cells. Batteries will still need to be EQ once in a while but far less frequently which means extended battery life. The only down side to a Float Charger is it can take up to 16 to 24 hours to recharge a fully discharged battery which you should not be doing.

Most chargers that come with Carts are essentially Float Chargers on a timer, but the voltage is higher than Float at what is called Daily Charge. It is fast but not accurate and does have tendency to over charge batteries depending on the model.

JohnnieB

FWIW: The DPI Accusense charger I use, goes into float charge after the regular charge cycle ends, so the "charge" time is on par with other golf cart chargers.

The regular charge cycle consists of 4 phases.
1. 5A constant current to see if battery pack while take a charge and to bring severely discharged batteries up to 1.75VPC before going to full power.
2. Constant current in the 18A-20A range until a preset voltage is reached (preset voltage is from 2.35VPC to 2.50VPC depending on battery manufacturer selected).
3. Constant Voltage at the preset voltage until current flow decreases to about 2A
4. Constant current at ~2A until dV/dT decreases to the specs for the mode selected.

Then the charger goes into a constant voltage float charge from 2.19VPC to 2.22VPC depending on mode selected.

In addition, if the charger has been in float charge for 28 days, a regular charge cycle is initiated.