UPS vs DSL modem

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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?
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Check the actual current draw and calculate the time it will buy you.
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On 2/17/2011 8:50 AM, Art Todesco wrote:

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.
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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.
--
Tegger

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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.
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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.
--
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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.
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On 2/17/2011 12:35 PM, jamesgangnc wrote:
in

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.
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That would have shown up in my UPS test.
greg
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Art Todesco wrote:

The ISP?
How does your ISP know when power goes off at your house?
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On 2/17/2011 4:59 PM, HeyBub wrote:

Well, out here in the country, there are very few feed lines. So, if I loose power at my house, chances are, the remote switcher will also loose power. If the batteries are not good, the site will (and has) go down.
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Art Todesco wrote:

Ah, thanks for explanation! I thought for a moment there you were weird.
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Art Todesco wrote:

All the telco remote terminals I've seen have a transfer switch and connection for a generator. The issues are how long with the poorly maintained batteries last and how quickly will the telco dispatch a truck with a generator to the site. I've seen a few larger RTs that do have permanent standby generators, but most do not.
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On 2/18/2011 9:20 AM, Pete C. wrote:

Yah, under Verizon days, we had a long phone outage on a Friday in the morning. It went on until about 9:30PM when V brought a portable generator and restored power. Even after commercial power was restored the next day, the generator stayed there for about 2 months. I think a big company in the industrial park must have squawked. Imagine not have phones all day on a Friday, even. I don't know this for sure, but, I'd bet V left the generator there until they installed new batteries, just to appease that large company. Then again, knowing V, they probably just never bothered to pick it up and bring it to there storage facility!
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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.
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snipped-for-privacy@optonline.net wrote:

in
I Dunno, with a big enough cap something in the wallwart might blow trying to charge up the cap. Though I'd 'spect that the xformer in the wallwart would present a high enough impedance to prevent that.
So, suck it and see.
Jeff
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Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
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On Thu, 17 Feb 2011 09:35:07 -0800 (PST), jamesgangnc
in

The cap will be on the DC output of the wall-wart - where it will store enough power (hopefully) to carry the modem through the transition.
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snipped-for-privacy@snyder.on.ca wrote:

in
Hi, Maybe with a back flow protecting diode in-line?
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On Feb 17, 5:23pm, snipped-for-privacy@snyder.on.ca wrote:

I was replying to this;

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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
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