Author Topic: An inverter generates horrible RF jamming comms for hundreds of meters  (Read 1958 times)

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Offline FflintTopic starter

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I need some help in my attempt to fix this inverter. It is a solar olinverter, but that really is irrelevant , because the problem is with a  high voltage DC to AC inverter module.

I know it is not a design fault because I have more than one, and only one became an RF jammer. It is a so called "a hybrid "(in quotes as it's not a real hybrid) solar inverter all in one. Its contains the following modules:
- A  bypass relay that can connect AC in to AC out or disconnect them
- A  bi-directional inverter between AC (voltage range 120V to 275V) and a high voltage (430 to 480V) DC bus. It is used to create AC from DC when the grid is down and bypass is opened. It can be used to feed power to the grid when grid is on.  In both cases it synchronises it's phase to the grid.
- a rectifier/booster - this just converts the grid input to high voltage DC for battery charging.
- a 44 to 62V battery charger powered by the HV DC bus
- two solar mppt to HV DC bus controllers.

And that is it. A relatively simple device.

When it is "off" its AC generation is off, but it still rectifiers the grid, maintains the HV DC bus, is able to charge the battery and mppts can be active depending on config. In this state it is not generating any substantial RF.

However when it is switched "on" so the inverter is creating AC it makes horrible RF noise that exits through every single cable including ground as far as I can tell. It generates huge signals at 5Mhz and it's multiples as well as the entire range 24-44mhz (every few kb there is a huge spike 40dB over background).

The inverter design from what I read is very basic. There is no isolation between the HV DC and AC. I believe it just has a bunch of mosfets in parallel and a filter. That is it.

When it initially came to me it seemed to fail to start with "HV DC bus shorted" error, but then after I disassembled it and put it back together it started working . I thought maybe some piece of wire got inside or other thing that caused a short, but now I'm not so sure.

Let's say one mosfet or a diode failed in a bunch. Could it fail open (or it failed almost open and these few jolts opened it fully) and being connected with its neighbours in parallel, can it generate such noise in result?

This noise is practically invisible with an oscilloscope on the ACs signal. It is few mV maybe while the AC is 240V.

I also wonder if there was a cold solder joint in the filter could it result with such RFI?

Thanks in advance for any responses?
 

Offline NiHaoMike

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Re: An inverter generates horrible RF jamming comms for hundreds of meters
« Reply #1 on: January 14, 2025, 04:33:10 am »
Check the "X" capacitors in the AC filter, a common failure mode is for them to go open.
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Offline FflintTopic starter

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Re: An inverter generates horrible RF jamming comms for hundreds of meters
« Reply #2 on: January 14, 2025, 06:56:36 am »
Check the "X" capacitors in the AC filter, a common failure mode is for them to go open.

Thanks. I'll do that when I have it on my bench.

Just to add. A service manual (for a very similar device- they are all clones of eachother differing only in some options, like grid feed in, being enabled or not, and component numbers/quality) shows the inverter as just this:



If it is true there is indeed nothing else there to break other than the capacitors (perhaps a coil can have a short, but that would be visible in the output AC I guess). However, MOSFETS are shown here, elsewhere the manual talks about checking IGBTs in the "Check the INV full bridge on MAIN board", gives types, also shows pictures of drivers as well as optocouplers. So it is really just a conceptual drawing - ah a joy of Chinese manuals....

Same section has nothing about the filtering. It contains various SMD resistor values (which will come handy too).

This is the block diagram of the whole device:



BTW there is a swicth mode power supply fed from the battery and AC there as well. Unfortunately there is no schematic (for this model). I've heard about SPSes having such an effect. I doubt this would be it as the SPS is active even if the inverter is not creating AC and in such state no RF noise is seen.
« Last Edit: January 14, 2025, 07:19:41 am by Fflint »
 

Offline Jeroen3

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Re: An inverter generates horrible RF jamming comms for hundreds of meters
« Reply #3 on: January 14, 2025, 07:13:42 am »
If it's jamming RF, the noise is common mode, typically invisible to probing on the outputs.

Get a TinySA  ;)
The antenna or a set of cheap amazon near fields can probably tell you more.
 
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Offline FflintTopic starter

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Re: An inverter generates horrible RF jamming comms for hundreds of meters
« Reply #4 on: January 15, 2025, 12:45:43 am »
If it's jamming RF, the noise is common mode, typically invisible to probing on the outputs.

Get a TinySA  ;)
The antenna or a set of cheap amazon near fields can probably tell you more.

I have a tinysa. All it tells me is that the noise it all around.

However ,it turns out the inverter is not the source. I was mistaken. So the hunt continuous.

I'll have to make a directional antenna for the tinysa. I saw a small loop online, but i doubt it has a lot of directionality.

I wonder if a ferrite rod antenna could work on 28mhz or is the frequency too high.
 

Offline Jeroen3

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Offline FflintTopic starter

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Re: An inverter generates horrible RF jamming comms for hundreds of meters
« Reply #6 on: January 17, 2025, 04:28:28 pm »
If you suspect an appliance, sniff around with this:
https://www.amazon.com/Magnetic-Conduction-Radiation-Circuit-Antenna/dp/B0CBMN6PY1/ref=sr_1_1_sspa

The noise is way too strong for these, also they are far too broadband.

I built a tiny antenna like this resonant at 29.5MHz:


With this I discovered it is not just one inverter... It's all of my solar inverters...plus Poe switch and the laptop's PSU.

While I can easily filter the laptop PSU and the PoE
Switch uses łan cables as antennas (they respond to 5 turns on a ferrite toroid very well) the solar inverters is a different story.

For some reason they generate most noise even when doing absolutely nothing. There is a tiny switch mode PSU in them. I suspect the actual inverter modules are well designed.But that PSU may have been an afterthought.

Also, I tried to find out which cables emit the most RF and very weirdly it is theDC cables to the batteries. I measured -47dB with this antenna touching and tinysa (lna on). (despite not using the battery at all! Inverters are in AC pass through mode for most of winter and neither charge nor draw much current from the battery. Maximum of few amps )

Then it's the AC neutrals with its -51dB, then it's AC live out  at -52dB and AC live in at -53dB. Finally solar wires are around -57dB and ground is around -71dB  (background is -120dB).

Ive ordered quite a few of material 31 ft240 cores to test . But now I wonder if my DC battery wires will not just saturated these ferrites.  The current there cab be in the hundreds of amps (150 charging per each of 3 inverters, discharge up to 250A per inverter).

I searched "entire Internet" and I've not found how to calculate a one turn saturation current on aFT240-31 amidon core. If anyone knows let me know please .
 

Online jbb

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Re: An inverter generates horrible RF jamming comms for hundreds of meters
« Reply #7 on: January 19, 2025, 12:27:23 am »
You know, the noise coming out over those battery wires could be common mode noise (ie same current from each wire). You could try putting a single ferrite ring around both the positive and negative battery wires together.
 

Offline nctnico

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Re: An inverter generates horrible RF jamming comms for hundreds of meters
« Reply #8 on: January 19, 2025, 12:22:16 pm »
Maybe there is a recall on the inverters. But solar inverters are problematic for RF reception. The Tetra system used in the Netherlands by the police, fire brigade and ambulances lost about 10% of the coverage due to interference of solar inverters. Actually there is a building called 'World Forum' in The Hague where they have to switch off the solar panels in case there is an event in the city. With the panels on, the Tetra radio system doesn't work well enough. Appearantly due to optimisers / micro-inverters used on the panels.
« Last Edit: January 19, 2025, 12:24:21 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline FflintTopic starter

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Re: An inverter generates horrible RF jamming comms for hundreds of meters
« Reply #9 on: January 20, 2025, 09:04:21 am »
You know, the noise coming out over those battery wires could be common mode noise (ie same current from each wire). You could try putting a single ferrite ring around both the positive and negative battery wires together.

Yes, it's possible. I'll try when my cores arrive. If this really is common mode noise I'll need lots of these cores.

Also I'm thinking what else can I do about grounding. I'm already running the shortest, the straightest possible wire (it is still about 2~4m long - ideal to radiate on the band I'm getting interference on) and I read ~-70dB of noise on it (30dB less than dc wires).

Perhaps I can tune this out somehow?

I though placing ferrite cores on grounding wires is a no-no as it prevents "shorting of the rf to the ground". But I saw some commercial rfi filters that have a common mode choke for all 3 wires (live, neutral, grounding).

Anyone has any advice on this?

Maybe there is a recall on the inverters. But solar inverters are problematic for RF reception. The Tetra system used in the Netherlands by the police, fire brigade and ambulances lost about 10% of the coverage due to interference of solar inverters. Actually there is a building called 'World Forum' in The Hague where they have to switch off the solar panels in case there is an event in the city. With the panels on, the Tetra radio system doesn't work well enough. Appearantly due to optimisers / micro-inverters used on the panels.

Chinese language has no word for recall :-D

Wow, this info from the Hague is amazing. If a big institution can't buy equipment free from EMI issues what hope a normal person with their normal budget has?
 

Offline Whales

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Re: An inverter generates horrible RF jamming comms for hundreds of meters
« Reply #10 on: January 20, 2025, 10:00:15 am »
For some reason they generate most noise even when doing absolutely nothing.

Most SMPS (including inverters) enter a "pulse skipping" mode at low loads.  This mixes lower frequencies into the emissions profile, often low enough you can hear them by putting your ear nearby (please don't do this on an exposed inverter PCB!).

Many pulse-skipping implementations introduce a wide, unstable selection of frequencies.  This makes them sound like a crowd of people hoarse-throat screaming rather than a single tone/note.

You may or may not actually be getting more radio interference emissions power at these low loads, but the changed frequency spectra of them might make them easier to notice.

Offline FflintTopic starter

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Re: An inverter generates horrible RF jamming comms for hundreds of meters
« Reply #11 on: January 20, 2025, 11:13:36 am »
For some reason they generate most noise even when doing absolutely nothing.

Most SMPS (including inverters) enter a "pulse skipping" mode at low loads.  This mixes lower frequencies into the emissions profile, often low enough you can hear them by putting your ear nearby (please don't do this on an exposed inverter PCB!).

Many pulse-skipping implementations introduce a wide, unstable selection of frequencies.  This makes them sound like a crowd of people hoarse-throat screaming rather than a single tone/note.

You may or may not actually be getting more radio interference emissions power at these low loads, but the changed frequency spectra of them might make them easier to notice.

I think that may very well be happening with the main inverter module. But I think the tiny SMPS that powers the logic runs at all times when it gets any power. However , there is huge difference between it running from DC and AC.

See my short video below. Where it says AC input on I flip the breaker to supply AC to the inverter (it is set to not use the battery to power outputs). Then it enables it's AC output and the main inverter I suppose goes into this "idle" mode. Where it is synced with the AC phase and ready to take over in under half a cycle if AC in fails.

Then I switch off AC in and it switches off (you can see caps discharging as EMI drops)

https://youtube.com/shorts/Zvgo2B5zP1w?si=vVTr46ks7GX8mnY3
 


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