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Old 16th June 2008, 18:58   #1
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Default A 2 second UPS?

Our apartment building has generator backup.
So when power goes, the PC modems shuts down, and then after a couple of minutes generator starts, and the modem switches on and connects.
So far so good.
The problem is when power comes back.
they do a changeover during which the voltage drops for half a second before coming back. This hangs the modem.
Now if power went and came back, it wouldn't matter, but modem hanging means I have to turn it off and on,
Is there a cheap DIY way of making myself a UPS which gives around 2 second backup.
Easily availability of parts for this DIY is important.

If I put a cheap 10 mF capacitor in series, will it do? I am gravitating towards the capacitor solution. I will connect the DC output of the adaptor to capacitor, so it will charge. Then when power dips it will cushion against the inverted spike.

Last edited by tsk1979 : 16th June 2008 at 19:00.
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Old 16th June 2008, 19:03   #2
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I assume you are talking about the Dlink Modem,It uses an AC-AC adapter and resets even on UPS switchover.
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Old 16th June 2008, 19:16   #3
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Nope, its not dlink and it has AC-DC adaptor. Its a Beetel ADSL modem
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Old 16th June 2008, 19:24   #4
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Suggest pick up a small capacity UPS - will be a clean install & use.
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Old 16th June 2008, 19:32   #5
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Can I get a 200W UPS somewhere?
I would like to power my laptop and modem with that.
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Old 16th June 2008, 19:33   #6
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A cap will be a cheap and good try. But put a bigger value. It will restore some energy when there is a dip. Atlest 1000-2000 mF.
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Old 16th June 2008, 19:34   #7
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Wouldn't 10 mF be too little? What's the DC supply for the modem? What's the mA rating on the adapter?
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Old 16th June 2008, 20:08   #8
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isnt the cap supposed to be in parallel?
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Old 16th June 2008, 20:16   #9
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Quote:
Originally Posted by greenhorn View Post
isnt the cap supposed to be in parallel?
Of course you're right!
Everybody seems to have missed the fact that tsk has written 'series'!
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Old 16th June 2008, 21:09   #10
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I think he is using as a filter but DC will not pass.
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Old 16th June 2008, 21:12   #11
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Quote:
Originally Posted by low_bass_makker View Post
I think he is using as a filter but DC will not pass.
As a filter for what?
He's clearly said he wants to 'augment' the DC storage!
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Old 17th June 2008, 00:03   #12
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Quote:
Originally Posted by anupmathur View Post
As a filter for what?
He's clearly said he wants to 'augment' the DC storage!
To clean the spikes in the DC out put of the ac-dc converter
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Old 17th June 2008, 00:07   #13
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boss,

dekho before you try a cap soln, please visit nehru place. you will get junta selling old UPSes for 250-400 bucks (seen it meself).

These ones are typically with a gone case battery that only last a few seconds.
but from what you say - few >> 2.

QED
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Old 17th June 2008, 00:18   #14
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Quote:
Originally Posted by low_bass_makker View Post
Atlest 1000-2000 mF.
L_B_M paaji, 1000mf? or uF? 1000mF = 1F which is a huge cap value.

If you can spend like 1000 odd bucks you should get a wipro or a proview one.
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Old 17th June 2008, 00:53   #15
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I had the same problem years back with a Sony cordless phone! I had used a 10000uF capacitor, but even that was not a fool-proof solution.

It is better that you use a small UPS, especially like what @phamilyman described. The electronics part of the UPS doesn't cost much, the battery is the killer - you can get a new UPS for the retail cost of a battery.

I have a 1992 vintage 0.5KVA UPS that powers my modem & LAN switch at home - had replaced the batteries a while back. Must check the backup time with the current load some time.
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