Absorbent Glass Mat batteries differ from regular lead-acid models in special production technology: liquid electrolyte is absorbed by microporous material (fiberglass). Thanks to such structure, the battery can be placed in any position, used in cars and trucks, boats, motorcycles, scooters, special equipment, backup or emergency power sources.
Quite often, web users write that AGM units do not require maintenance. This is an erroneous statement. To ensure stable and long-term operation, first of all, it is necessary to acquire the best AGM battery charger and adhere to some rules when exploiting it.
Types of suitable chargers
Most devices available on today’s market are of the inverter type. With their help, you can charge units that have not been used for a long time. Pulse chargers are compact and lightweight. Such models are more expensive than transformer analogs. But both options prove reliable and durable.
You can opt for automatic or manual charging. Automatic chargers have the following advantages:
- they diagnose the state of the battery and control the power supply
- automatic shutdown preventing the possibility of overcharging
- a buffer function storing the info about the remaining charge and the latest operating parameters
- capacity is being restored by cleaning sulfate deposits by pulsed electric current
Human intervention is minimal. It boils down to visual control, while the system sets operation parameters.
The consequences of improper charging
Striving to attract buyers, marketers often do not mention the most dangerous property of AGM batteries – the tendency to get into thermal dispersion mode. An increase in the temperature of the electrolyte leads to an influx in the charging current, which can result in a short circuit.
Normally, the electrolyte is kept in a “bound” state preventing its free mixing. Thermal dispersion can occur due to the lack of electrolyte in cells and weak diffusion (mixing).
Oxygen release during electrolysis oxidizes the negative electrodes. The heated electrolyte has less resistance. Accordingly, a stronger charge current is received, which in turn leads to an increase in the amount of oxygen (and hydrogen) released. This is how a self-accelerating heating process (thermal dispersion) occurs.
Batteries with an absorbent glass mat should be charged in special conditions and with suitable chargers. Under no circumstances, shall your vehicle be started from another car.
Before charging, unscrew the plugs and make sure the glass mat is not dry. Otherwise, it should be wetted with distilled water. Dry glass mat will heat up when charging.
In addition to conventional charge control methods:
- do not allow the voltage to exceed 14.4 Volts
- do not allow the charge currents to rise above 1/10 of the nominal battery capacity
- closely monitor the temperature
A common sign signaling that thermal dispersion is starting is the simultaneous decrease in charge voltage and increase in charge current. In such a case, stop charging and take a break for slow diffusion. Let the charged and uncharged electrolyte with different current resistance mix in the glass mat.