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Author Topic: Dect phones on a non-inverted off grid 12vdc supply  (Read 1021 times)
Cornishwoodsman
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« on: September 07, 2015, 05:38:25 PM »

Just wondered if anyone else has tried to run a cordless dect phone without inverting the supply from a 12v system? I don't want to use a mobile all the time, and we have a landline connection to the house.
Last time I spent time on this I got as far as a very buzzy line, though I did get the system to give me a dial tone, the noise was such that calls were not possible.
I would love someone to point out a ground loop type noise isolator etc. etc. and a phone that runs on 12vdc (many dect actually seem to run on low voltage ac)
Whilst we have coped with a wired phone, the ability to wander around the house would be a definite benefit!

Thanks
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merkland
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« Reply #1 on: September 07, 2015, 08:35:56 PM »

Our Dect phones have plug in chargers which output 5.5vdc at 500ma. All you need is a suitable socket connected to your 12vdc circuit and plug in a suitably rated car satnav/mobilephone charger.

merkland.
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Cornishwoodsman
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« Reply #2 on: September 07, 2015, 10:14:20 PM »

Charging the handset is not the problem- it's the signal and supply for the base unit- this is where the interference comes in.
Do you have a dect phone working without an inverted or mains power supply?
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jonesy
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« Reply #3 on: September 07, 2015, 10:25:19 PM »

I run my dect phones off 12v.  You have a ground loop.  The telephone line is nominally grounded at the exchange.  Devices connected to a phone line must incorporate an isolation transformer.  To save money this is frequently done with the mains adapter rather than a line transformer.  Your battery will be getting earth either directly or indirectly.  By wiring the phone off the battery you are now creating an earth loop as there is no longer isolation.
I achieved the isolation with a 1000v isolation dc/dc converter.
You could prove this by taking any 12v battery not connected to anything else and run the phone.  There should be no buzz!
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merkland
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« Reply #4 on: September 07, 2015, 10:25:46 PM »

Our base unit plugs into the mains and the phone line. The mains supply could be replaced in the way I described and the base unit should work normally.

merkland.
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200w wind turbine grid tied, 1x175w PV grid tie or to batteries,
2x55w PV to batteries, 24vx440ah battery bank. 3.5Kw grid tie (14xSanyo 250w facing 160degrees at 80 degrees inclination, Aurora 3.6 inverter), 2xflat panel water heating (for over 30 years )
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