UPS vs DSL modem

[Art Todesco]

I have a computer and DSL modem tied to an old UPS (with new batteries). When I have a power failure, the computer keeps right on ticking, but I always have to restart the DSL modem. I've even restarted the modem while running on the UPS and after its restart, all was fine. I am assuming here that the switch over time is killing the modem. I looked at the modem and its walwart. It says

12 VDC. I was wondering if putting a few thousand micro farad cap across the 12 volt line might help. Anyone have any experience with something like this?

[jamesgangnc]

Check the actual current draw and calculate the time it will buy you.

[George]

The whole point of a UPS is to prevent the very issue you are describing. There shouldn't be any "switch over time". Sounds like the UPS has issues.

[Tegger]

Art Todesco wrote in news:ijj941$bqu$1 @speranza.aioe.org:

The UPS is probably switching in too slowly for the modem's logic circuitry.

The need to restart the modem is a giveaway that it's losing power for the tiniest moment, just enough for its logic to /begin/ to die, but not enough for it to die /all the way/ and thus do a complete reset on the new power- up.

I think you need a newer UPS.

[jamesgangnc]

The cap if it works would be a whole lot cheaper solution. I'm not familiar with smaller ups' only the big ones. I assume the smaller ones keep costs and heat down by not running the power through a power supply and inverter 100% of the time. Thus they have to switch sources.

[Tegger]

jamesgangnc wrote in news: [e-mail]:

Correct. They feed line-voltage until that voltage fails to meet certain pre-defined criteria. At that point the battery/inverter is switched-in. The switching time is on the order of milliseconds, short enough that the gap isn't noticeable to the equipment.

Maybe older UPS's used caps to bridge the gap if the switches were too slow to be invisible to the equipment. I'm guessing here.

[Pete C.]

I would agree that you probably could use a newer / better UPS with a faster or no switching time. It is also possible that the DSL modem's cheap power supply has inadequate filter caps, or they are cheap and have failed. A new power supply may solve the problem, or adding a big cap as you indicated should also allow it to ride through a few cycles of outage while the UPS switches.

[N8N]

What you describe is a "true online" UPS and they exist, but generally cost about 5-10x that of a typical consumer grade "line interactive" UPS of the same VA rating.

nate

[jamesgangnc]

[e-mail]:

You can't use a cap cause how would that work? Caps don't store ac. The inverter isn't on until it decideds to switch.

[jamesgangnc]

Yes, I remmeber the first one of those I worked with back in the

80's. Our facility had offices in front and a warehouse in the back. There was this small room back in the warehouse so we took it over and put the ups in it. Day one we figured out that it was hot as hell in that little room. Noisy too. Fortunately it was on an outside wall so we made a hole inthe wall and added an ac.

[zek]

Create your own power failure by unplugging wall, and see if you have the same result.

greg

[zek]

Clarify, unplug power to UPS for a few seconds.

greg

[A. Baum]

I'd try a 1.5 farad cap used on auto power amps. Usually can pick one up for 10+ bucks. That should buffer the source more than enough and would be much cheaper than a new UPS.

[zek]

Seriously, We don't even know the voltage of the supply except its suppose to be 12 at rated current output. Its easy to fry something. Unregulated outputs go up over 16 volts.

As I said, pulling the plug on the UPS will narrow down the problem better. I'm worrying some other telephone line problem can occur during a power failure, up setting the modem. Many devices also warn of reconnecting a wall-wart supply while still active.

[clare]

Using a cheap stand-by "almost" power converter?? (that's what APC stands for)? Many of the cheap standby units have lousy transfer times. Short of changing UPS units, the large 25 volt capacitor wouls likely be the most effective solution. Don't whimp out and use a 12 volt. 16 would be OK, but a 25 will last a whole lot longer (you are looking at unfiltered rectified ac, not clean DC on those power warts).

[clare]

Even a lot of the "larger" UPS units work that way. There are "standby" units (the cheap kind with switch-over drop-out), Line interactive (which switch over very quickly, using zero crossing switches or similar tech) and there are the genuine on-line, or "dual conversion" units the have absolutely no change-over or drop-out - and you pay accordingly.

[clare]

And a "line interactive" is still head and shoulders above the cheap old "stand-by" UPS. In old APC parlence there was the cheap "Back-ups" and the interactive "Smart-ups".

[Art Todesco]

innews: [e-mail]:

Well, actually, I can, because the wallwart puts out 12VDC and the cap would be across that 12 volts. I agree with one poster that measuring the current and then calculate the time gained by a particular cap. But, I think I found the real reason. I think it's the ISP. I'll post more later.

[trader4]

[e-mail]:

I would work because he's talking about putting the cap across the 12V DC output of the wallwart that powers the modem. Sounds like a reasonable solution to try. On the other hand, I suspect the UPS isn't working correctly because the whole purpose of the UPS is to do what it doesn't seem able to do.

[jamesgangnc]

ide quoted text -

I have a few wall warts with switching power supplies but many are still transformers. It's easy to tell, the ones with switching circuits instead of transformers are usually lighter and have a higher current rating. Another giveaway is that many of the switching ones accept anything from 100vac to 220vac.