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How routers work ?

To chose a good router, you need to know how they work.

Routers are using a mix of Zero-Cross Detection system and Phase Control system to control the voltage curve in order to reduce the voltage and send a reduced power to the resistance, and then consequently prevent the Linky from recording a consumption more than what the solar excess is. Depending on how the router is built, this phase control system can be done in a different ways and with different hardware.

Phase Control System

This method can use a TRIAC-based device to chop the voltage curve to reduce the voltage and consequently the power. Phase Control System can be achieved for example with:

  1. Robodyn AC Dimmer: a component able to do both ZCD and PC
  2. Zero-Cross Detection circuit (ZCD) + Random Solid State Relay: a fast switching relay which is able to do PC

They can both chop the voltage curve by letting the load pass at a specific time.

The ZCD circuit is able to detect when the voltage curve crosses the Zero point. Here is an oscilloscope view of how a ZCD circuit works:

Dedicated ZCD circuit Robodyn ZCD circuit

When the AC voltage curve crosses the Zero point, the ZCD circuit sends a +5V pulse (assuming it is powered with 5V DC) for about 1 millisecond. Thanks to this pulse, we can decide to activate the Phase Control system at the right moment depending on the wanted power.

Here are 3 different views from an oscilloscope of the voltage and current curve at the dimmer output, when using a Robodyn AC Dimmer set at 20%, 50%, 80%, and at full power (without dimmer), for a nominal resistive load of 600W:

20% 50%
Oscillo 20% Oscillo 50%
80% 100% (Bypass)
Oscillo 80% Oscillo Bypass

We can see the effect of the TRIAC on the voltage curve, and the resulting current curve, which is chopped at the wanted level. A TRIAC is like a switch that can be opened and closed at a specific moment of the voltage curve, thus reducing the consumed power.

Now, let’s see the effect of the TRIAC on the voltage and current curves, both at the output of the dimmer, and at the input of the router:

Image Description
At Router output, no dimmer involved, full nominal power of ~600W (230V, 2.7A)
At Router output, dimmer set at 20%, ~160W (97V, 1.7A). Current curve hidden by voltage curve.
At Router input, dimmer set at 20%, current at ~1.7A, voltage is normal

Hardware used for measurement:

All measures are done with the Owon HDS2202S portable oscilloscope with a 10x probe (yellow curve) and the Owon CP024 current clamp (100mV/A) to measure the current (blue curve). The resolution of portable oscilloscopes is not as good as a lab oscilloscope, so the RMS values is not highly accurate, but the curves and values are good enough to see the effect of the TRIAC.

Burst Modulation

Burst modulation will let a complete or half complete voltage curve pass or not, and this control is done at the zero point. 50Hz current has a voltage curve with a period of 20 ms decoupled in 2 half-periods: one positive, one negative, so the zero voltage is crossed twice per period. So during 1 second, there are 100 half-periods which can be “turned” on and off.

This method can use a simple Zero-Cross Solid State Relay: a relay that will only close or open when the voltage curve is at 0. So there is no load at that time of switching. Switching at Zero-Cross point is clean because it does not cause harmonic and is recommended for a resistive load. Several methods could be used: burst mode (we allow complete periods per burst), or some more customized method.

The goal is to beat the grid utility meter so that it does not record any excess or consumption. For example, the Linky is looking at the voltage curve each 20 ms but is doing an aggregation over a longer duration of 1 second. In order to beat the Linky, we allow within this window a correct sequence of half periods so that the Linky does not record any Watt (in consumption or excess), or just a few.

Here is an example of what Clyric’s router is doing:

Burst mode (20% and 50%) at the top and an adapted version from Clyric at the bottom:

  Burst mode Clyric’s version
20% Burst 20% Clyric 20%
50% Burst 20% Clyric 50%


Router Issues and Solutions

The biggest issue with routers is harmonics, when using a Phase Control system that is chopping the voltage curve. Chopping the voltage curve by allowing a current at a specific duration creates some harmonics which can impact other appliances if not filtered. These harmonics gets bigger when the Phase Control system activates with a higher load. And filtering these harmonics for such use is difficult so most commercial routers do not even filter them out, or just a few expensive ones, like Eddi from Myenergi and Fronius Ohmpilot. Harmonics generated by a solar router can impact or even damage other appliances, typically those which are more sensitive like inductive loads (motors), UPS, devices with clocks bases on voltage frequency, electronic devices like EV car charger, etc.

Harmonic examples:


How to reduce harmonics ?

According to EN 61000-3-2, a Solar Router is a Class A device because the dimmer is not integrated inside (the resistance is in the water tank). We can read in the study below, page 5, that a Class A device for resistive load that is dimmed should be limited at around 750W in order to keep harmonics at a level accepted by the regulation.

Here are the things you can do to optimize your installation and reduce the effects of harmonics:

Installation and wiring:

Routing configuration:

In any case: try to route as little power as possible, use steps, and make sure the router does not have any priority over the other appliances.

What about the Burst method ?

When using a a Phase Control system that is using the Zero-Cross point to open and close, there is no harmonic issue. The problem is that it can allow too much load to pass at high power and at the opposite can open the relay for a long time, which will create some excess. For this system to work properly, it needs to know how the utility meter is working internally in order to beat it, if it can.

It has some limitations:

Overall this method is quite new and seen in only 1 router so far, and seem to offer good performance regarding harmonics suppression, but in my opinion is not perfect and has some limitations.