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Topic # 81871 19-Apr-2011 15:34
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I have a linksys PAP2T connected to Saturn cable via a linksys router, and plugged into one analogue phone connection is a Panasonic cordless phone base-station model KX-TCD430NZW. With the devices powered from their own mains adaptors, everything works.
But if the mains power goes off, I loose all communications.
So the plan is to use a 12v battery to power the cable modem, the router, the voip adaptor and the cordless phone. The voip adaptor and the cordless phone run off 6volts, so I made an adaptor to provide 6v from the 12v battery.
With either the voip adaptor or the cordless phone powered from the 6v adaptor, everything still works, but when both the voip adaptor and the cordless phone are both powered from the 6v adaptor, off-hook is not recognised, i.e. I don't get dial tone, and the voip adaptor still shows on-hook, idle.

I have tested for continuity between the power connections and the phone connections with a multimeter, and there is no connection on either device, so I can't see why running off a common power supply should make any difference.

Any ideas anyone.

Smiffy

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  Reply # 460534 19-Apr-2011 15:41
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Not enought watts output to run both devices at once




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  Reply # 460538 19-Apr-2011 15:47
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connecting devices designed to operaye off isolated powersupplies together seldom works how you want.

I would just get some isolated dc-dc converters rather than stuff around more, but you may find that swapping the phoneline polarity helps. but it could make it worse.




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  Reply # 460549 19-Apr-2011 16:18
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This is an interesting thread for me as I am wanting to set up a similar short term emergency back up if we get power failure. I am not concerned to get immediate kick in but would like to know I can power up for a few hours if the power goes out. I was planning to just buy a 300w inverter from Dick Smith and run of the car power socket. I would be powering a 3G router and ata and a cordless phone. Any other ideas for a back up system would be appreciated too.



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  Reply # 460552 19-Apr-2011 16:20
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coffeebaron: Not enought watts output to run both devices at once


Thanks.
Voltage is stable when none, one or both are powered, so that's not the problem.
Smiffy



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  Reply # 460574 19-Apr-2011 16:50
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richms: connecting devices designed to operaye off isolated powersupplies together seldom works how you want.

I would just get some isolated dc-dc converters rather than stuff around more, but you may find that swapping the phoneline polarity helps. but it could make it worse.


The phone polarity line idea seemed hopeful, but it made no difference.

I have a cheap DC-DC converter, (15-24 volts out), but that has continuity between negative in and out, so something like that would be no good, as you said it would need to be properly isolated.

Smiffy

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  Reply # 460581 19-Apr-2011 17:12
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when a friend needed to sort out isolation between the supply for the rf amp and ir repeaters that used the coax a cheap module from either rs or farnell did the trick. i have seen similar looking ones on ebay. im on mobile so cant really go looking but i think it was about $20 and was good to about 4 watts or so.




Richard rich.ms



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  Reply # 460921 20-Apr-2011 13:20
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I had a look at the voltages when both are being powered from their own mains adaptors. The voltage between the two negatives sits around 40v when the phone is on-hook, and close to zero when the phone is off-hook. No wonder they won't work together with a common supply.
I can't isolate the phone line from the DC as low DC resistance is what signals off-hook (if I remember correctly), so I will have to keep the power supplies isolated.

Given that I intend to connect up four things, and I already have a 12VDC to 220VAC inverter, it would seem foolish to spend more money on isolated DC-DC converters.

Thanks for your ideas, but I'll go with the messy and inefficient but cheap solution.

Smiffy

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