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Axpert radio interferences


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My Axpert/Synerji MKS 5k system produces strong radio interferences on HF as well as on VHF. That bothers me since I'm a radio amateur. I attribute it to the MPPT since they disappear after sunset and come on again at sunrise. I tried to block them with a ferroid toroid core around the PV feeder wires but it doesn't help.

Does anybody have a solution?

 

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4 hours ago, Beat said:

Does anybody have a solution?

PV wiring should be inside bosal conduit or a steel trunking, that might be the solution and also earthing the bosal conduit, If that is not possible another option is a 40x40 galvanized channel with a steel cover it should also be earthed. 

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On 2020/10/13 at 4:48 PM, Beat said:

My Axpert/Synerji MKS 5k system produces strong radio interferences on HF as well as on VHF. That bothers me since I'm a radio amateur. I attribute it to the MPPT since they disappear after sunset and come on again at sunrise. I tried to block them with a ferroid toroid core around the PV feeder wires but it doesn't help.

Does anybody have a solution?

 

Is the source of the noise your AC side or HF emissions through air?

My first attempt would be to use a ferrite with wire running some loops through it for wiring (internal to the inverter) going from the MPPT to the Axpert inverter board.  Also are you using multiple loops around the ferrite or just putting it through the middle of the ferrite?

Your inductance will be really low if you just put it through the center.  In which case I would wrap a few turns.

Btw. this increased inductance may have other side effects so best be careful about this.

If the emissions are radiated then I would consider some kind of faraday cage situation around the MPPT connect to the ground of the PV to couple the noise to ground.

If you have noise coming in over AC line, isolation transformer with a shield winding help at all?

Edited by Gnome
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On 2020/10/13 at 9:28 PM, Gerrie said:

PV wiring should be inside bosal conduit or a steel trunking, that might be the solution and also earthing the bosal conduit, If that is not possible another option is a 40x40 galvanized channel with a steel cover it should also be earthed. 

Thank you for your advice.

However it would be very difficult to completely rewire all PV panels. Besides it runs trough a living space where it would appear rather ugly. Actually it's in a 25x16 PVC trunking.

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Sorry, my previous post was probably not the most helpful so I decided to add some more useful info.

As a radio amateur, you should understand that the PV wires (and also the battery wires to some extent, just shorter) make nice long antennas.

The MPPT will typically switch at about 20kHz, meaning that you have a nice big 20kHz ripple on your PV wires and battery wires.

Since this is a buck converter the inductor will cause the current to rise and decay linearly making a triangular wave which will have lots of harmonics, so it will likely cause interference up to some pretty high frequencies. . You should be able to measure this triangular current if you have a scope and a current probe. The battery wires will have additional ripple from the inverter, which will include both 100Hz ripple that will vary with the load and HF ripple.

Adding a common mode inductor on the PV wires may help to some extent (which is what a ferrite core over the wires is, except with a low inductance) but the best is to also shield the wires. A common mode inductor on the battery leads is not really practical due to the currents involved, so shielding is the best option there as well.

Adding some capacitance from each lead (PV+, PV-, Bat+, Bat-) to ground as close to the inverter as possible may also help to conduct some of the HF stuff to ground and reduce the radiation.

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16 hours ago, Gnome said:

Is the source of the noise your AC side or HF emissions through air?

My first attempt would be to use a ferrite with wire running some loops through it for wiring (internal to the inverter) going from the MPPT to the Axpert inverter board.  Also are you using multiple loops around the ferrite or just putting it through the middle of the ferrite?

Your inductance will be really low if you just put it through the center.  In which case I would wrap a few turns.

Btw. this increased inductance may have other side effects so best be careful about this.

If the emissions are radiated then I would consider some kind of faraday cage situation around the MPPT connect to the ground of the PV to couple the noise to ground.

If you have noise coming in over AC line, isolation transformer with a shield winding help at all?

Thank you for your answer.

Yes, interference is transmitted trough air and received by antennas far away from the system. The Axpert itself has a steel housing solidly earthed that constitutes a Faraday cage. I cannot intervene inside the cage between the MPPT and the inverter. Anyway the only power link between the two is the 48V power bar. However I consider to run some loops trough the ferrite  core.

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11 minutes ago, Stanley said:

Adding some capacitance from each lead (PV+, PV-, Bat+, Bat-) to ground as close to the inverter as possible may also help to conduct some of the HF stuff to ground and reduce the radiation.

Thank you for your considerations.

I already sought of that. I'll get me some suitable capacitors.

The inverter seems not to bother since the interference disappears after sunset even with load on the inverter from battery.

 

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8 minutes ago, Beat said:

Thank you for your considerations.

I already sought of that. I'll get me some suitable capacitors.

The inverter seems not to bother since the interference disappears after sunset even with load on the inverter from battery.

Great, but the 20kHz ripple from the MPPT will still be present on both the PV and battery leads so it is still a good idea to shield both.

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Success !

The radio interference is gone. I improved the inductance and added some capacitors.

In order to run several turns trough the ferrite core I went to the motor and transformer winding shop to get some 6mm² winding wire. But they don’t have such. We finally agreed on 2mm² wire that I would use in 3 wire bundles. I bought 10m of it (R40). I also went to the electronic shop to buy 4 0.33µF 310V capacitors (R40).

I first thought to have one core for each polarity. But then I realized that the 30A PV current could saturate the core and reduce the inductance. So I decided to run both polarities trough the same core. The two magnetic fields would then cancel each other and prevent saturation. I managed to run each polarity 3 times trough the core. Since the core can be opened it is easy to wind each half separately. I separated the polarities with a piece of card board. One challenge was to strip the 12 wire ends of the tough isolation varnish. The outgoing bundles are hold together with shrinking tubes. I tightened the two half cores together with a strong cable tie to prevent a gap between the core halves. The finished winding is shown in picture below.

PICT1304.thumb.JPG.2604699f6bf09fa13333c8554ff0ea83.JPG

I had many thoughts how to connect capacitors to the 48V M6 terminals. I finally found the solution shown below. I soldered the capacitor leads to 6X22 washers with a 60W soldering iron. The washers are then installed under the M6 nuts of the terminals.

PICT1305.thumb.JPG.dfabf6a69f114fb5d08a8e17756a7673.JPG

The final installation of inductance and capacitors is shown in picture below. The outgoing leads of the inductance are directly wired to the PV input terminals together with the leads of the capacitors. I had to solder little pieces of installation wire to the capacitors leads because the terminals would not clamp the tiny wire of the capacitors. The other ends are crimped to the earth wire.

PICT1308.thumb.JPG.34fcc5f71629ab6244763756d3a6fa64.JPG

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