Bell Canada → Re: Treadmill start = modem crash (interference)

While arguing sementics, you ignore the bottom line. A UPS output is so 'dirty' as to be potentially harmful to electric motors and power strip protectors. That same 'dirty' electricity is also ideal perfect for all electronics. Stick with the facts. Electrics are so robust as to make even 'dirtiest' power from a UPS irrelevant. Also so robust that voltage is ideal when incandescent bulbs dim to 50% intensity.

Why would anyone buy a UPS to fix a trivial and slightly lower voltage? Or to clean mains power when mains power is typically the 'cleanest power'.

Again, you say, "the cheapest UPS that APC makes, for $50, claims noise filtering." And again you are making subjective claims. Subjective claims can prove anything. Where is the number? APC has near zero noise filtering. Just enough above zero so that you will promoting it as 100% filtering.

Noise filtering alread inside every modem is so good as to make irrelevant increased harmonics, noise, and other anomalies.

Meanwhile, with all this discussion of expenisve miracle boxes has made impossible a discussion of why a modem would lose synch. A suspect list includes more than just noise on AC mains.

The modems I have taken apart have little to no noise filtering on their power supply input. They have a tiny HF choke, some decoupling capacitors and those directly feed DC-DC converters within the modem. Little more than the bare minimum necessary to avoid radiating EMI through their DC power cable, definitely not enough to filter junk power from the AC adapter. The AC adapters are either "iron lump" types with no filtering whatsoever or self-oscillating inverters with little more than EMI filtering, nothing that would protect the load or the adapter itself from any junk on the line.I would not bet the farm on that.

Most of today's consumer electronics are designed with cost-cutting and disposability in mind which means much thinner tolerances if not engineered for timely failure (just after warranty expiration) outright. If you take apart consumer electronics, most stuff hard-wired for 120V only has line-facing components rated to 200V which are likely to get damaged from any sort of exposure to 600V if not immediately destroyed. If you step up to universal PSUs with APFC, most of those have components rated for 400-450V so 600V peaks would still be quite likely to cause some permanent damage even if MOVs eat the brunt of it.

A product designed with such obsolete technologies would, so obviously, cost too much. Nobody uses those obsolete designs. Therefore costs are lower AND electronics are more robust.

Obviously, denials are from one who thinks that tiny device is a choke. That choke would be much too tiny to accomplish any useful filtering. Why would they spend so much for a choke that does nothing? They don't. The mythical choke is something completely different. A device that means electronics easily exceed 600 volt spec. As defined by the APC salestool.

Is APC lying when citing design standards from 1970? Of course not. Only problem is one who has no idea how easily power is conditioned inside electronics. And therefore cost less to build.

All these denials do nothing helpful for the OP or the topic. Does not address other more likely reasons for that modem cutout. Numbers, even from an APC salestool, say why modems can operate just fine even with 'dirtiest' power - from a UPS.

Which 'obsolete' designs would those be? They are all still in use today. For devices like routers and modems, brick-style iron-core transformers are still very common but plug-style oscillator or SMPS designs are becoming more popular. All three options provide some degree surge protection simply from line-load isolation but are not surge-protected themselves. A 600V spike of any significant duration (say one cycle) would likely destroy most semiconductor-based AC adapters I have dissected since the only "protection" they have is a fuse between line power, their rectifier bridge and 200-250V cap. They also have an EMI choke but those don't do squat against surges since EMI is common-mode noise while surge is differential.You would already have the answer to your question if you actually read the message: EMI filtering to prevent the modem's switching regulator noise from going out on on the adapter cable. These things only have a few uH of inductance. Enough to block most of the switching regulators' EMI and ineffective against surges from the AC adapter.Proper filtering of 60Hz line power uses up lots of space, there is no miracle work-around to that.

Unfortunately, the new energy efficiency regulations in many areas have forced manufacturers to stop using the iron-core transformer style power supplies and start using SMPS designs.

We have several thousand modems in the field, and note that occasionally power disruptions will confuse the switch mode devices, requiring them to be unplugged for a few minutes to allow the capacitors to drain and the circuit to re-set in order to function again.

Very annoying.