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PWM controllers

A PWM controller (Pulse Width Modulation) switches the battery panel on and off at high frequency to control the charge. It is the simplest and most cost-effective solar regulation technology, and still has its place in small-scale installations where the cost of the equipment is a greater consideration than performance.

When is it better to use PWM rather than MPPT?

When the panel voltage is close to that of the battery. A PWM does not convert voltage: it forces the panel to operate at the battery voltage, so if the panel has 36 cells —with an operating voltage of around 18 V— and the battery is 12 V, the loss is acceptable.

If the panel has 60 or 72 cells, PWM wastes a significant proportion of the available energy, and that’s where a MPPT controller It recovers between 20 % and 30 % more output.

Rule of thumb: for panel power below 200 W and with modules rated at 12 V, use PWM. Above that, or with grid-connected panels, use MPPT.

What types of PWM controllers are there?

  • BlueSolar PWM-Pro 12/24V: Basic version, from 5 A to 30 A, with automatic voltage selection.
  • BlueSolar PWM-LCD and USB: with a built-in display and USB output for charging devices, from 10 A to 30 A.
  • BlueSolar PWM DUO: Two independent battery outputs, designed for caravans or boats where there is a service battery and a starter battery.
  • Remote panel: to check the status without accessing the controller.

What panel power rating does a PWM controller support?

The limit is set by the current, not the watts. Divide the panel’s power by the battery voltage: 200 W in a 12 V system is around 16 A, so you’ll need a 20 A regulator with a margin.

Always allow a margin of 25 % on your calculations: on cold, clear days, a panel may exceed its rated current, and a regulator operating at its limit will overheat and have its lifespan shortened.

All models are from Victron Energy and are compatible with lead-acid and lithium batteries with configurable profiles. Not sure whether to choose PWM or MPPT for your installation? Drop us a line.