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Old 02-17-2009, 06:48 PM   #1
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12v DC ground to chassis ground of a 120V appliance?


I'm running a 10 gauge wire from a remote car battery to a ~4 amp 12VDC UHF radio. Do I need to run a separate ground, or can I hook ground up to my household ground or, say a screw on the chassis of my UPS or computer which is grounded to my household ground?

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Old 02-17-2009, 07:24 PM   #2
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12v DC ground to chassis ground of a 120V appliance?


If you are asking can you use the AC system ground as your negative DC connection then ABSOLUTELY NOT.

The DC negative is NOT the same as an AC ground.

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Old 02-17-2009, 07:36 PM   #3
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12v DC ground to chassis ground of a 120V appliance?


I guess I was trying to figure out if the chassis of my UPS (which has a 12vdc battery in it) would that be an adequate 12v dc ground? or what, if anything i could do to get that ground without running another wire from the battery.

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Old 02-17-2009, 07:38 PM   #4
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12v DC ground to chassis ground of a 120V appliance?


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I guess I was trying to figure out if the chassis of my UPS would that be an adequate 12v dc ground?

Your going from the battery to the radio... thats it
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Old 02-17-2009, 07:38 PM   #5
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12v DC ground to chassis ground of a 120V appliance?


The radio power cord should be two wire with a fusible link/inline fuse.
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Old 02-17-2009, 07:41 PM   #6
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12v DC ground to chassis ground of a 120V appliance?


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Originally Posted by pcampbell View Post
I guess I was trying to figure out if the chassis of my UPS (which has a 12vdc battery in it) would that be an adequate 12v dc ground? or what, if anything i could do to get that ground without running another wire from the battery.
Why don't you just use an AC/DC converter?
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Old 02-17-2009, 07:50 PM   #7
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12v DC ground to chassis ground of a 120V appliance?


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Originally Posted by pcampbell View Post
I'm running a 10 gauge wire from a remote car battery to a ~4 amp 12VDC UHF radio. Do I need to run a separate ground, or can I hook ground up to my household ground or, say a screw on the chassis of my UPS or computer which is grounded to my household ground?
Test it.
First measure any DC or AC voltage between the grounds.
Then put a 4w 120v incand. lamp between the grounds and measure the voltage across and the current though it.

If all readings are zero you're OK.
If not, you still may be OK, I don't have specs for such a thing.

The problem is there are currents running in the ground, mostly 60 Hz and harmonics, maybe even DC.
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Old 02-17-2009, 07:56 PM   #8
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12v DC ground to chassis ground of a 120V appliance?


sound like i will be running a separate wire.

as for why not just get a power supply. i need for it to work when the power goes out (the ups is for the computer) and already and setup with a small solar panel that charges a battery.

thanks for the replies.
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Old 02-17-2009, 08:17 PM   #9
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12v DC ground to chassis ground of a 120V appliance?


What's the radio for? Ham?
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Old 02-17-2009, 08:32 PM   #10
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12v DC ground to chassis ground of a 120V appliance?


If this is a remote battery, and you only run one wire, you can ground it 100 times to every AC system in the neighborhood and it still won't work cause there is no complete circuit back to the battery. Every circuit requires at least two wires.
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Old 02-17-2009, 08:36 PM   #11
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12v DC ground to chassis ground of a 120V appliance?


Unless I am missing something here From your remote battery to whatever you need to supply you need 2 wires one will be positive, one will be negative.
They both need to terminate at the battery to complete the circuit.
The negative will have to go back to the negative post of the battery that is supplying the power.

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Old 02-17-2009, 08:44 PM   #12
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12v DC ground to chassis ground of a 120V appliance?


It is a GMRS radio - a old police cruiser Motorola radius M100 I have pointed to a repeater with a Yagi antenna I built, just a few miles away up on a hill at about 800 feet (it's highest point around here for 50 miles, and it'll go about that far), so I've got the power turned way down (hence only 4 amps) - no need for any more.

My wife's car will get the same radio in her car (got a pair of them for 90 bucks) with the power turned up and an NMO mount antenna


OK that makes sense, with regard to completing the circuit. Thanks.
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Old 02-17-2009, 09:24 PM   #13
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12v DC ground to chassis ground of a 120V appliance?


Well it's nice to see someone else using GMRS as it was intended. Not just kids yelling and singing into bubble pack radios.
I got my GMRS license in '05 which led to my tech in '07.

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