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[skyeci]

Hi,

Just wondered if its ok to connect a standard apc ups to provide power backup for my modem. We have had a number of mains issues lately and now my cabinet is sorted I want to provide some power to the modem in the event of a drop out to try and protect the sync.

I know its probably over kill but is it ok to use a normal 240v ups and connect a modem to it with the aid of IEC C14 plug adapter.

many thanks

[PhilipD]

Hi

No problem at all, I use a APC UPS Backup Pro 550, and in a recent 6 hour power cut it powered the modem/router for all that time and was fine.

Regards

Phil

[William Grimsley]

Best thing to do if you want is to have the UPS going, but do a manual power down and up of the router in that time, you'll thank me.

[skyeci]

Ok thanks all. Cheers

[PhilipD]

Hi

Best thing to do if you want is to have the UPS going, but do a manual power down and up of the router in that time, you'll thank me.

Well it depends on what they are already sync'ing at, for me on 80/20 I couldn't get any more speed when we had an area wide power cut and so I was likely the only person connected, but SNR went up by around 10db during the power cut, so that is what cross talk is costing me.

Depending on the amount of cross talk, re-syncing during a large area power cut may get you a lot more speed, but it's only going to be short lived, as once power is back on and cross talk returns, any large gains in SNR will go causing the modem to drop and resync.

Regards

Phil

[William Grimsley]

True, but if you look at my most recent thread, you'll see that it won't just always drop out, my line has been stable at a 4 dB SNR Margin.

[roseway]

It's a gamble, so you might end up with increased speed while still stable, or you might end up with an unstable connection. As Phil said, it depends on circumstances, it certainly isn't good general advice.

[underzone]

I would like to see how anyone could fit a new UPS without causing a re-sync 

The modem/router is going to have to be unplugged from the wall socket and then plugged into the UPS 

[PhilipD]

Hi

I would like to see how anyone could fit a new UPS without causing a re-sync 

The modem/router is going to have to be unplugged from the wall socket and then plugged into the UPS 

Yes you will have a resync when you first connect up via the UPS but that's before any power cut, it then remains connected ready to kick in when the power goes down without the equipment noticing the change.  So at the time of any power cut, assuming that power cut is affecting the local area and the cab is supplying just residential homes, the chances are the person with a UPS is most likely the only person with a UPS and so connected at the cab for the duration of the power cut, so gets to see the effect of cross-talk* versus no cross-talk.

* it also removes any mains derived electrical interference of course having a wide area power cut so the difference between sync/SNR pre and during a power-cut isn't necessarily just a difference caused just by cross-talk.

Regards

Phil

[William Grimsley]

It's a gamble, so you might end up with increased speed while still stable, or you might end up with an unstable connection. As Phil said, it depends on circumstances, it certainly isn't good general advice.

Couldn't agree more, most of my advice is as you know, not brilliant, but it's worth the gamble!

[Weaver]

I recommend mains filtering on the output of the UPS, in case the output is a synthesised square wave one. I use an APC UPS on my three modems, but I have two levels of filtering on the output, from a Belkin PureAV unit and a Tacima unit.

[jid]

Couldn't agree more, most of my advice is as you know, not brilliant, but it's worth the gamble!

I personally wouldn't advise everyone to try this - especially if they have a poorer line than William's. This could cause some severe instability and possibly DLM intervention.

[PhilipD]

Hi

I recommend mains filtering on the output of the UPS, in case the output is a synthesised square wave one. I use an APC UPS on my three modems, but I have two levels of filtering on the output, from a Belkin PureAV unit and a Tacima unit.

Snake oil I'm afraid 

A square sine wave poses no problems for the switch mode supplies of the type used on these devices.  Before anything happens the AC square wave hits a bridge rectifier, gets turned into DC and then fed into a big smoothing capacitor, the actual low voltage is then derived from a DC-DC converter from a DC source of around ~320 volts.   

The switching noises involved in these types of supplies dwarf any rough and ready noise from a typical UPS power supply.

You can get issues with square waves with PFC computer power supplies, but not for power bricks of low wattage, they don't use power factor correction.

Regards

Phil

[burakkucat]

I have always considered the conversion of 240V AC to 12V DC (incoming mains supply to the UPS battery), then 12V DC to 240V AC (UPS battery to a "protected" AC output), then 240V AC to 12V DC (typical switching mode PSU for a typical modem/router) to be both inefficient and convoluted! 

If I should ever have a need for an interruptible power supply for a modem/router I would probably consider using a SLA battery to provide 12V DC to the device and employing a sufficiently capable PSU to keep the SLA battery trickle-charged. When the mains input is absent, the SLA battery supplies the load. Essentially the SLA battery is floated across the PSU output (and due to the low impedance of such a battery it would also provide smoothing of the PSU output).

[William Grimsley]

I personally wouldn't advise everyone to try this - especially if they have a poorer line than William's. This could cause some severe instability and possibly DLM intervention.

How can you "try" it? What happened to me wasn't planned, I didn't plan the power cut.