If you've got more of those ferrite cores lying around try putting one around the AC line going to the VFD. It could be sending a lot of noise back into the AC mains.
I did move the ferrite core there and no change, but I think it is pretty clear there is back EMI fed into my entire shop AC supply by the VFD because of the earlier test isolating the wall wart to a different shop circuit and cable still creating interference.
As a test you could try some batteries at the end of the cables in place of the switcher- if it works then you know the supply is suspect. If not then you know the emi is being picked up directly by the cables, acting like antennas
Thanks for this suggestion. I had forgotten I had this auxiliary battery pack for mobile phones given to me several years ago. I don’t think I’ve ever used it but when I was rooting around for wall warts and cables and saw a 5vdc battery source with two USB ports, I knew what to do with it. It certainly looks the part.
I couldn’t find an old transformer style 5vdc wall wart laying around but I don’t think it matters because I’ve all but convinced myself the problem is the power cables that plug into that wart are probably unshielded antennas and I literally have four feet of those two cables taped side by side with the DRO control cables. As further aggravation, there is an additional two feet of the power cables coiled up in the electrical enclosure in a 3” diameter coil which may be a good receiver.
So I charged it and plugged in the power cables while holding it in my hand and used a loose cable to connect to the DRO away from the VFD and cables. It powered them fine with and without the VFD powered up . Same thing when I connected the cables in the cabinet without the VFD powered up but as soon as I powered up the VFD down went the DROs. The odd thing was, even when I disconnected the barrel jacks at the DROs, they still were scrambled unless I disconnected the battery at the other end. So then I plugged the cables back into the battery and started changing the position of the power cables in the enclosure and when I pulled the battery and 3” coil of excess power cable out of the electrical enclosure, the DROs recovered, but I still could not plug the barrel jacks into the DRO and run them off the remote battery through the cables.
This is more of an intellectual curiosity, but does the cable radiate more when it’s also energized…..even with just 5vdc? Because when the battery is disconnected and the cables inside the enclosure, they don’t broadcast enough to take down the DROs.
So, a number of options here, but I may need to decide how much effort I want to put into solving an EMI problem for what may not be much of a battery problem. I’ve done more for less…..but not recently
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- I could remove the additional two feet of power cable coil by either cutting it out or just move it to the other end at the DROs, shield the power cable with braided sleeve, and/or simply route the power cables separately from the control cables instead of tightly joined to them. There may still be a conducted problem with the wall wart if I do that. I have a 12vdc to 5 vdc converter typical of what’s used for cars, RVs, ATVs, etc and I suspect my little 12vdc power supply has a relatively clean dc output. I see a small onboard transformer and that tachometer circuit has no issues. Not sure I want to resort to circuit board surgery. I don't have fine soldering equipment.
- I bet I could power those DROs a long, long, time with that battery pack, and just mount it on the backside of the DRO displays with a short stub cable to each DRO. Problem would be if I could remember to turn it off…LoL.
Best,
Kelly
