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Forum Index : Electronics : EMI
| Author | Message | ||||
renewableMark Guru  Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Just saw a vid on EMI and wondered if a 4 layer board would help an inverter project. https://www.youtube.com/watch?v=crs_QLuUTyQ When I pull into the garage the radio if set on AM goes bonkers the closer I get to the inverter. Cheers Caveman Mark Off grid eastern Melb |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Would be a marginal improvement if any, most of the RFI you are picking up on the AM radio would be coming from the mains wiring in the garage, the battery cables to your bank. As the inverter + electronics is mounted inside a metal box, one would think this is shielding it from the outside, however with the very heavy fast switching currents the localized EMI is induced into any wires and cables in\out of the box. From a safety aspect the inverter case must be connected to mains earth, unfortunately this is not going to do much for RFI as the earth cables go all over the house and quite long with lots of series inductance, so high impedance for RF signals, legally a MEN switchboard can only have a single earth stake ground connection, so you cannot bang another ground rod into the earth beside your inverter and connect the case to it in order to reduce the RFI. A good mains filter will help. You could double skin the inverter box, one metal layer connected to a ground rod, the other to mains earth (both isolated from each other). Radiation from the battery leads can be minimized by tying long parallel runs of +- cables together so their magnetic fields cancel somewhat, or shielding them with an earthed braid. Cheers Mike |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Thanks Mike Cheers Caveman Mark Off grid eastern Melb |
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wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
Mark, I think looking around your circuity with a good CRO is essential to finding the source of the EMI. Fast, high enery switching transients create harmonic wavelengths that spread from DC to Light (well nearly.....) If you have used them, it may even be the smaller DC/DC converter modules that power the 5 & 12v & isolated gate drives? Is it just one AM station or is the interference trashing the whole AM band? Excessive HF ringing after each cycle may be the cause and extra FET snubbing is required. Surely others must have identified this as an issue, or did they just gave up on AM as an acceptable trade off for being off grid ? If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Thanks for the reply Wiseguy, it doesn't effect the house, just the vehicle when I pull into the garage, maybe within 2 metres, probably nothing to worry about, but when I saw that video I had the idea it may help. What I was actually thinking was the brownout issue the Oz/Mad inverters both had. The on/off cable appears to pick up some crap and cause the totally random restarts, the extra caps connected to the on off switch (thanks Oz) sort this out and I found that clip on ferrites also solve it without using the caps. But if an issue can be addressed before it became an issue that might be a better option. Cheers Caveman Mark Off grid eastern Melb |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Ok just tested it, that's interesting, close to 1278 (3aw) it goes bonkers, 774 just fine and some others higher than 1278 work fine. I was more interested in the possible hidden gremlins that may effect the rest of the inverter than the radio though. Cheers Caveman Mark Off grid eastern Melb |
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| tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 438 |
Reminds me of testing to MIL-STD-461. Of course the test lab setup and equipment are more sophisticated. In the oz control board schematic, I've been thinking about that EG8010 pin 6 start/stop signal. It seems that currently an SPDT is used. The way I understand it Start connects pin 6 to +5v and Stop connects pin 6 thru the RC network and then to gnd. Since the switch is mechanical, when it is operated, pin 6 will float momentarily as the common contact moves from one position to the other. This happens also when the contact bounces. To prevent the momentary float, maybe it is better to permanently connect pin 6 to the 'pull-down' RC network. Use an SPST switch to pull pin 6 to +5v for the start condition. In the schematic, jumper J1-2 to J1-3 and connect the SPST switch between J1-2 and J1-1. This way the RC network will also filter the contact transition, bounce, and chatter. This is just my theory and I have not tested this. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Thanks Tinyt, that specific problem can be fixed with either the caps or ferrite clip on, I was just wondering as a general idea would it be beneficial to make 4 layer boards as per the video to lessen the chances of any unforeseen issues arising. Cheers Caveman Mark Off grid eastern Melb |
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| wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
The reason for asking about a specific station issue is that it gives a hint of the offending frequency generator. If it trashes the whole band it is usually broadband noise and may be difficult to cure. If it is a specific station it can be due to harmonics from a frequency source that has a harmonic affecting the station of interest (or 455kHz away from it). So you either have a "ringing" that needs to be snubbed or a noisy dc/dc converter that also needs filtering/snubbing/shielding. Of course as a last resort you could also just find a different radio station..... I know you are a "if it aint broke leave the bastard alone guy" so that might have to be the best solution. If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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