April 2002 — By Capt.
The Tao of Power
|Part 3: Gassing Point|
Most of the charge is delivered in the bulk stage. Once this limit is reached, the charger enters the acceptance phase, reducing the voltage. Finally, with the float charge engaged, the charger maintains battery voltage at a lower level appropriate for long-term battery maintenance.
The important factor in charging a battery is making sure it reaches its gassing point, the voltage at which the battery begins to generate significant amounts of oxygen and hydrogen gas when fully charged. Not to do so will mean a battery below a full charge. A charger can take the guesswork out of all this with automatic temperature-compensation sensors.
But no matter how carefully you monitor charging cycles, some sulfate deposits will remain on the plates. Equalizing or conditioning is used to not only remove the residue from lead-acid batteries but also restore battery capacity, revive efficiency, and extend operational life. You should not equalize your gel-cells due to their vulnerability to overheating. Instead, check with your battery manufacturer if you feel they should be equalized.
Basically lead-acid equalizing involves a controlled overcharging cycle that raises the voltage of a 12-volt battery to 2.7 volts per cell. Given the voltage requirements, and as this is not an automatic function of the charger, you must take care during this process. In fact, if you’ve never done this, I strongly advise checking with your battery manufacturer first. Additional battery care involves inspecting cable connections for corrosion and wear, replacing if necessary, and always using distilled water when adding liquid.
A few words concerning gel-cells. A gel-cell is nothing more than a lead-acid battery that is pressurized and sealed using special valves and a gelled electrolyte. Gel-cells are recombinant batteries, meaning the oxygen normally produced on the positive side recombines with the hydrogen at the negative plate. This produces water that was lost during operation. Therefore, they are "maintenance free."
Due to their chemistry and construction, gel-cells present unique problems. First, they recharge inefficiently when deeply discharged. Second, most of the charge current produces heat rather than the chemical reaction necessary for recharging. And when discharged to more than 80 percent of their capacity, they are susceptible to damage from two sources: high temperature and an excessive charge rate. High temperature causes a gel-cel’s thinner plates to degrade, and overcharging can destroy the battery by raising the internal temperature during gassing. With nowhere to go, the hydrogen and oxygen gas escape from the release valve, and since you can’t add liquid, electrolyte is irretrievably lost. That’s why if you’re thinking about getting gel-cells, you need to make sure you’ve got them matched with the proper charging unit.
You can keep your batteries healthy and working properly if you take care of them on a regular basis. Doing so will enable you to have years of reliable service and trouble-free starting. It’s not so mysterious after all.
This article originally appeared in the January 2003 issue of Power & Motoryacht magazine.