Why are my batteries wet on top?

[bash11]

Thanks guys. All your comments make sense. I truly appreciate your willingness to help me out.

Bash11

[JohnnieB]

Technically, a lead-acid wet-cell battery isn't fully charged until the SG (Specific Gravity) of the electrolyte ceases to rise while a charging current is passing through it. Since the On-Charge voltage tracks the SG of the electrolyte, the On-Charge voltage can also be used to determine when the battery is fully charged.

Chargers that use dV/dT (Change in Voltage over Change in Time) technology to terminate the charge tend to fully charge the batteries, while chargers the use a predetermined voltage to terminate the charge tend to undercharge the batteries because the voltage selected is one that is below the on-charge voltage older (aged) batteries reach when they are fully charged.

Electrolysis of the water in the electrolyte occurs whenever there is current flowing through it, so some gassing exists during both charge and discharge. However the highest gassing rate occurs during charge when the On-Charge voltage reaches 2.37VPC (Volts per Cell) and climbs above it.

By design, the chargers typically used by most cart owners transition from bulk charge to absorption charge around 2.37VPC to minimize gassing.

[bash11]

Originally Posted by Volt_Ampere

The main reason we get so much gassing is that our chargers are designed to overcharge. This is necessary because we charge our battery packs in series. If the charger isn't designed to overcharge the pack will get imbalanced over time due to the variability of the battery capacity from cell to cell.
By the way this is a big problem with lithium packs because you can't overcharge them even a little or you destroy the cells.

Has there been any thought to balance charging like they do with some lithium packs, or is that just too expensive?

[JohnnieB]

Originally Posted by bash11

Has there been any thought to balance charging like they do with some lithium packs, or is that just too expensive?

It is already being done, but mostly at the battery level rather than at the cell level. It is called bank charging.
Basically, groups of cells (aka a battery) are charged individually and discharged in series.
The FLA (Flooded Lead-Acid) in some industrial applications use individual 2V cells or batteries with exposed straps connecting the group of cells connected in series that form a battery, so the individual charging can be done at the cell level, but in the batteries typically used in golf carts, the straps between cells are not exposed, so the individual charging is limited to the battery level and variances can exist between the cells within the battery.

Fortunately, FLA batteries don't catch on fire and release toxic fumes (or explode) like lithium batteries do when overcharging occurs, so they can be balanced (equalized) by taking them to a higher On-Charge voltage or just using the normal On-Charge voltage for a longer period of time. This is known as an Equalization Charge and technicians that maintain industrial battery packs have been using the process for decades.

I'm not aware of any six bank or an eight bank 6V chargers that would work for 6 x 6V and 8 x 6V packs, but I believe there are some forum members using NOCO GEN3 and GEN4 12V bank chargers connected to pairs of 6V batteries.

[sportcoupe]

Speaking of NOCO bank chargers, I believe they charge in succession, meaning bank #1 charges then finishes, next bank #2 charges and finishes and so on till all banks are charged. Seems this would greatly increase downtime charging and you really couldn't go anywhere till it was finished since the batteries would be so far out of balance. Not a great idea in a golf cart.

[JohnnieB]

I get the impression they charge all banks simultaneously because they give Amps per bank and Total Amps in their specs, but they don't make it clear one way or the other.

I agree that they would be next to worthless for a golf cart application if they charged the banks sequentially.