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# Backfeeding?

#1
02-03-11, 04:52 PM
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Backfeeding?

ive been told about backfeeding, but it hasnt been explained to me. i know its when current flows in the opposite direction of its natural flow. if im wrong let me know. and i was also wanting to know if there are any symptoms or characteristics that are associated with this subject. and im looking to know mostly about in a dc circuit.
any info will help me a ton.

#2
02-03-11, 05:09 PM
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Last edited by ray2047; 02-03-11 at 09:20 PM.
#3
02-03-11, 05:36 PM
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Basically if you "backfeed" a circuit, like Ray said, a dryer receptacle, the current goes backwards to the grid. If the POCO is stepping down your voltage at a rate of 100:1, then your incoming voltage ahead of the transformer is about 12,000 volts, and you get 120 volts. Backfeed with 120 volts from a generator, and the power grid is being worked on you pass that 120 volts through that same transformer and build it at a ratio of 1:100, or back to 12,000 volts right to the lineman working on the line.

#4
02-03-11, 09:07 PM
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The OP said he is asking about a DC circuit, which leads me to believe this might be automotive-related. Backfeeding in DC is a fault in one circuit that allows current to pass into another circuit contrary to its design. This is usually seen in resistance circuits without diode protection. For example, a bad ground in a tail/brake light circuit can cause all sorts of weird things to happen with other bulbs or devices.. Like when you put on the left turn signal, the dash lights may flash along with it. This is due to the fact that you have two different filaments in the same bulb connected to the same ground point. If the ground is broken, the current from circuit A travels through filament A, then backfeeds through filament B (they are connected together inside the bulb), to seek ground through circuit B.

#5
02-04-11, 05:38 AM
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Thanks Matt.....zoomed right past me. Basically all I saw was "backfeed" and the hair on my arm stood up thinking he was contemplating something.
I bought a new Nissan Hardbody truck back in the 80's and everytime I took a hard right turn the engine would die. After the dealer changed out injector, throttle body, basically a new top engine, a mechanic found a ground wire that was not nutted to the stud, so everytime I turned right, the inertia took the ground off the post and the computer couldn't find one and freaked out. He explained to me it was a form of backfeeding seeking a ground. Not sure if it is the same the OP has. Thanks again.

#6
02-04-11, 07:20 AM
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Originally Posted by tom_finn89
i know its when current flows in the opposite direction of its natural flow. .

Most electrical folks use the term "backfeeding" to describe a condition where the POWER flow is reversed, not really the CURRENT. It may be a fine point, but when talking AC circuits, there is no CURRENT direction change when backfeeding. In a DC circuit, yes, the current will actually change direction.
In a simple DC circuit with a rechargeable battery, one could say that backfeeding is the condition where the battery is being charged, since the current is reversed from the discharge condition.
Not sure I'd bring up "natural flow", either in this context. "Natural" to some folks means related to lightning, static or other "nature" inspired electrical event. Maybe say: "Power flow as designed" is the opposite of "backfeeding".

#7
02-04-11, 05:31 PM
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yes it was meant for automotive purposes but i thought that thisforum is a much more specific area to post it in, sorry if i should have posted in the automotive. so would it be safe to assume that all backfeeding would be because of a bad ground? or is that still to broad of an assumption?

#8
02-07-11, 07:25 PM
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Backfeeding:

1. Feeding power in via an outlet or terminal normally used to draw power from, for example recharging the car's battery by plugging the battery charger's power output into the car's cigarette lighter socket. Or powering the car's electrical system via the cigarette lighter socket after the car's battery has been removed. Household example: Connecting an emergency generator to the breaker panel through a breaker or pair of breakers used for branch circuits.

2. Power energizing a supposedly dead circuit or portion of a circuit using a path through a related circuit that was not de-energized. See JeremyMatt's description above.

#9
02-07-11, 11:34 PM
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Originally Posted by tom_finn89
yes it was meant for automotive purposes but i thought that thisforum is a much more specific area to post it in, sorry if i should have posted in the automotive. so would it be safe to assume that all backfeeding would be because of a bad ground? or is that still to broad of an assumption?
In automotive terms, yes it is very safe to suspect a bad ground first when things start acting weird or show evidence of backfeeding.

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