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My question is, can a simple small UPS provide a solution for power dips? Both from before and after the UPS?

I don't need the UPS to run the machine for hours, just for catching the power dips. Having juice for a save shutdown in a power outage is just a bonus. Would a UPS be fast enough to handle power dips? I could imagine it takes time for the machine to detect a dip and switch to battery. I would imagine a capacitor would be faster.

Background information

I've got a 3d printer in a 70 year old building. Wiring is, let's say, not optimal. And my printer disconnects quite regular from the print server (Octoprint). I've done all I know to keep the serial connection going. I have shielded USB with ferrite beads. I have isolated the 5V on the USB to prevent back powering. I am using a big enough power supply for the Raspberry Pi, powered USB hubs for the camera's. And so forth.

I notice the LED, connected to 230V, flickers when the stepper motors move. The machine disconnects on many factors, turning a light on or even off, the coffee machine, etc. I also notice the power dips in other electronics like crackling in the radio speakers.

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Would a UPS be fast enough to handle power dips?

Well, the basic AC waveform alternates (dips if you like) 50 or 60 times per second so, finding a switching mechanism that is capable of dealing with dips shorter than ten or 20 milli-seconds is unnecessary because that is what the AC waveform does all the time.

I could imagine it takes time for the machine to detect a dip and switch to battery.

I think you broadly misunderstand how a UPS works; the battery is nearly always active all the time and is recharged by the incoming AC (rectified and processed). So, a small dip in the charging process is what it handles and is designed to handle.

The battery then feeds the output stage that reconstitutes the AC voltage for feeding on to whatever appliances are connected to the output. No need to worry about suddenly bringing into play a battery because it is used all the time: -

enter image description here

Image from here. Of course, some types of UPS may have a slightly different topology but, switching between one source and the battery source can be done in microseconds with modern electronic parts. However, if you are looking for product recommendations, then these are off-topic.

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  • \$\begingroup\$ Thanks, that's elaborate. Would this also mean that getting a small, say, 500Va version would support he dips when using a 230V 750W machine? And what would be the referred topology in a case like this? I've seen stand-by and line-interactive from the brand I was looking at. \$\endgroup\$
    – Tim
    Aug 1, 2021 at 9:45
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    \$\begingroup\$ @Tim - the devil is in the detail and it's impossible to generalize about whether a 500 VA UPS could handle unspecified dips to any load. Your load is more than 500 VA i.e. it is 750 VA so, it's unlikely that it's sensible choosing a 500 VA for a 750 VA load. Then, there is the case that 750 watts might actually mean 900 VA due to the load's power factor. This is a design site and that means that details in the form of clear schematics and clear specifications are the backbone of any definitive answer. \$\endgroup\$
    – Andy aka
    Aug 1, 2021 at 9:50
  • \$\begingroup\$ Thanks for pointing that out. I think I have enough pointers now. \$\endgroup\$
    – Tim
    Aug 1, 2021 at 9:59
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Normally, power supplies are designed to store enough energy for a 1 cycle dropout as power switching occurs daily. If you do not have such a good supply, there can be mechanical switched off load transients that propagate thru to DC.

So the characteristics of both the disturbance and supply tolerance affect this. A simple UPS can only respond within a 1/2 cycle best case to switch outputs.

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  • \$\begingroup\$ You say "a good supply", what would define that? I mean, I guess you mean a certain technique, what would that be named? Where to look for \$\endgroup\$
    – Tim
    Aug 1, 2021 at 14:18
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    \$\begingroup\$ PC PSU's are designed for 1 cycle min storage time would be an example, but I overlooked you have EMI issues too \$\endgroup\$ Aug 1, 2021 at 14:23

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