Why PWM?

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Equalize Drifting Battery Cells:
Individual battery cells may increasingly vary in charge resistance over time. An uneven acceptance of
charge can lead to significant capacity deterioration in weaker cells. Equalization is a process to
overcome such unbalanced cells.
The increased charge acceptance and capacity recovery capabilities of PWM pulse charging will also
occur at lower charging voltages. Morningstar’s PWM pulse charging will hold the individual battery
cells in better balance where equalization charges are not practical in a solar system.
More testing will be done to study the potential benefits is this area.
Reduce Battery Heating and Gassing:
Clearly battery heating/gassing and charge efficiency go hand in hand. A reduction in transient gassing
is a characteristic of pulse charging. PWM will complete the recharging job more quickly and more
efficiently, thereby minimizing heating and gassing.
The ionic transport in the battery electrolyte is more efficient with PWM. After a charge pulse, some
areas at the plates become nearly depleted of ions, whereas other areas are at a surplus. During the off-
time between charge pulses, the ionic diffusion continues to equalize the concentration for the next
charge pulse.
In addition, because the pulse is so short, there is less time for a gas bubble to build up. The gassing is
even less likely to occur with the down pulse, since this pulse apparently helps to break up the
precursor to a gas bubble which is likely a cluster of ions.
Automatically Adjust for Battery Aging:
As batteries cycle and get older, they become more resistant to recharging. This is primarily due to the
sulfate crystals that make the plates less conductive and slow the electro-chemical conversion.
However, age does not affect PWM constant voltage charging.
The PWM constant voltage charging will always adjust in regulation to the battery’s needs. The battery
will optimize the current tapering according to its internal resistance, recharging needs, and age. The
only net effect of age with PWM charging is that gassing may begin earlier.