TapHome

Power Limiting with PWM Groups

PWM groups on TapHome Bus output modules (12 DO, 16 DO and others) keep the total power of electric heating outputs within a set limit by staggering their PWM cycles.

Power limiting keeps the total power of several electric heating circuits within a limit, for example the capacity of the main circuit breaker. The outputs share one group: the module staggers their pulse-width modulation (PWM) so that the outputs switched on at the same time never exceed the group’s limit. It applies only to outputs set to Pulse-width modulation and added to a group; an ordinary switched digital output is never limited.

Which modules support it

PWM groups are available on TapHome Bus modules with digital or universal outputs that support PWM: the 16 DO, 4 LED OC, 6 LED OC modules and the Core from their first firmware, and other modules, including the 12 DO, from firmware 27. A module has as many groups as outputs minus two, at least 1 and at most 7, so both the 12 DO and the 16 DO have 7 groups.

Setting up a group

  1. Settings → Hardware → TapHome Bus → tap the module.
  2. Set each heating output to Pulse-width modulation.
  3. In the Power limiting section, tap Add new group and then the new group.
  4. Save the module page; the group is saved with it.

The group page shows its labels in English in every language of the app:

  • Total resources — the limit of the group, a number without a unit. Use any unit (W, A), but the same one for the outputs.
  • Pulse width (interval) — the common PWM period of the group, 600 to 7200 seconds for digital outputs, 0.5 to 7200 seconds for universal outputs.
  • Outputs → Add new output — offers the module’s outputs set to PWM that are not in another group. Tap an added output to enter its power; a value larger than Total resources is rejected with the message “Resource can’t be more than total resources!”.
  • The order of the outputs is their priority: the top output gets power first. Drag the rows to change it.

How the module limits the power

The module runs the limit itself, without the Core. All outputs of a group start their PWM cycle together. During the cycle, an output is on while it still has on-time left and the outputs already on, plus its own power, stay within Total resources; the outputs with higher priority are served first. An output that does not fit waits, and on-time it has not used by the end of the cycle is lost. A heating circuit can therefore get less power than its thermostat requests when the whole group needs more than the limit; the app does not report it.