BVX700LI not filtering EMI ?

[dynek_apc]

Hello all,

I connected a computer to a 3d printer (USB/UART), and when turning off the light in the room it breaks the UART connection, Linux says "usb 1-1-port1: disabled by hub (EMI?), re-enabling...".
So I bought this UPS (BVX700LI) and expected it to filter EMI, connected both the computer and 3d printer to the UPS but the problem still exists.

I know it's a cheap model, can anyone confirm it's not going to do the job in this situation ?

Thank you

[Teken]

This specific model doesn’t offer any dedicated RFI / EMI filtering besides surge protection. 

Given the error is captured by the computer system there are a few very simple things to do / test.

Grab a really long extension cord and plug in either the PC / 3D printer on a known (opposite) fed electrical outlet.

If you don’t have a means to test for opposite fed circuit. You need only look at the service breaker panel. Every second breaker down the line is the (opposite) side of the single split phase electrical system in a North American home.

Worst case just plug in an item and turn off the breaker until you see an outlet going on - off like a radio / light.

Now turn the light switch on - off and see if you still see the USB error. Another thing you can do is use a higher quality (shielded) USB cable.

Electrical hardware that (may) emit RFI / EMI normally include cables that have a ferrite choke incorporated or attached on one or both ends of the cables.

If it’s incorporated into the cable it looks like a big black circular blob. If it’s attached externally it’s round and looks like two pieces of magnets clipped or snapped together.

As a really ghetto but quick check you can wrap the entire USB cable / power cable in tinfoil. Doing so will show you (IF) the interference is via air vs power line.

If the interference is coming via the power line you’ll need to purchase a plug in filter.

Lets us know what you find and the outcome.

Cheers! 👍

[dynek_apc]

Thank you for the very detailed explanation @Teken !

The light is LED-based, I don't think interference could come from the air, could it ?

That being said, how I was actually able to determine that the interference is coming from the network, is that I have another APC Smart-UPS SMT750I and when both the computer and 3D printer are hooked there, turning off and on the light doesn't have any impact.

The USB cable itself is twisted, shielded with ferrite close to the computer.

I wonder what kind of plug in filter would do the trick or what would be the first price APC to do so (having both filter + battery would be nice).

Thank you for your help!

[Teken]

Per the APC FAQ a (SPD) should not be before and connected to their UPS. The vast majority of RFI / EMI filters incorporate a surge protective device (SPD).

in reality it comes down to quality, make & model SPD. As there are millions of UPS’s connected to outlets, power bars, and generators that incorporate a SPD.

As you stated your choices are to purchase another UPS that incorporates filtering or a third party filter.

They come in outlet form, to plug-in . . .

Lastly, you could simply replace the LED bulb if you believe that’s the root cause! Swap it out for an incandescent bulb or another brand and see the cause / effect.

Probably the cheapest and easiest solution to try - No?

Let us know what you find just changing out the LED bulb.

NOTE: RFI / EMI can absolutely be generated and seen over the air. Hence the phrase Radio Frequency Interference (RFI). EMI is a magnetic field which is always in the air and can be induced into electrical components and wiring.

Think lightning strike . . . Think nuclear bomb (EMP) . . . Think Radio tower or any RF device BLE, WiFi, ZigBee, Z-Wave, Insteon, etc.