Corroded electrical contacts do not cause more current.

[Bitsyncmaster]

So many people preach that corroded contacts cause more current in the circuit. This is only true when your driving an electronic circuit (like a computer power supply) that regulates the output voltage. When you reduce the voltage to a motor or light bulb the current in that load will drop when the voltage drops.

When the corrosion causes a voltage drop it produces heat at that corrosion point. That heat will make the corrosion process get worse and eventually the bad connection will get so hot it will fail (melt the wires and plastic).

I keep informing people of this simple basic electrical fact but it keeps coming up. Just saw it in a video posted. Not that it changes the important point of keeping your electrical contacts clean. But it drives me nuts seeing this miss information posted.

[NckT]

It makes a refreshing change to read a post like this.

To add, any corrosion at a contact (ie electrical connection) causes an increase in resistance at that electrical point. It is this increase in resistance that causes a measured voltage drop (delta V) across this contact.
A consequence of an increased resistance is an increase in heat at that high resistance.

In a DC circuit, rationalising the circuit and its accumulated connections ie the totalised output Impedance (resistance in DC source) to a single load circuit to "Thevinins Theorem" single load circuit, with a fixed DC voltage source, the current will decrease.

So, keep those contacts clean and use decent electrical connections with solder/ heat shrink, crimps using correct crimp tools.

Do NOT use those "Scotch lock" wire taps......

[David T]

It makes a refreshing change to read a post like this.

To add, any corrosion at a contact (ie electrical connection) causes an increase in resistance at that electrical point. It is this increase in resistance that causes a measured voltage drop (delta V) across this contact.
A consequence of an increased resistance is an increase in heat at that high resistance.

In a DC circuit, rationalising the circuit and its accumulated connections ie the totalised output Impedance (resistance in DC source) to a single load circuit to "Thevinins Theorem" single load circuit, with a fixed DC voltage source, the current will decrease.

So, keep those contacts clean and use decent electrical connections with solder/ heat shrink, crimps using correct crimp tools.

Do NOT use those "Scotch lock" wire taps......

As a common example that most people can relate to I point to when the connections on a car battery get all corroded and cruddy. Eventually it gets to the point where you can't get enough current through the connection to run the starter motor to start the engine. Clean up the corrosion and everything works like new again.

[FABombjoy]

I love explaining this one in person because you get to see the "ah HA!" moment:

"If corrosion on this light bulb connector increases resistance, which increases the current...
if I disconnect the bulb, and resistance becomes practically infinite...
(eyebrow raised) ... the light bulb explodes from the infinite current flowing through it???"

[DMCVegas]

Absolutely true. I couldn't argue with you even if I wanted to.

But just a quick, honest question: The examples spoken of here only appear to focus on the circuit as-is, which is in a serial configuration. Let me explain.

Consider a simple 12V circuit where you have an incandescent light bulb. We have the 12V feed, the positive connection inside of the socket, the negative connection of the socket housing, and then the ground point itself. If we have resistance then obviously we're going to have a problem lighting the bulb. Be it corrosion on the 12V feed (such as the example David T. gives with the bad battery connections), on the positive connection in the socket, the negative connection, and then finally the ground point on the chassis. But still, that is just a serial circuit.

What about when the corrosion becomes so severe that it bridges the negative and positive leads inside of the socket? Now, the bulb still has good contact, so it's going to light up. The amperage draw on it has not been interrupted. However, now we have a secondary Parallel Circuit that has been created by the corrosion. It completely bypasses the light bulb. It isn't a true Dead Short because it has resistance, which is of course transferred into heat. But it is an additional load upon the circuit.

So the question I would pose here is that while corrosion in and of itself does not cause more current, wouldn't sufficient corrosion that creates a secondary, Parallel circuit induce an additional parasitic load? That parasitic load in turn would consume more power, and could overload the circuit and heat up the entire length of wiring. It also would explain the confusion about resistance that many people have.

[Bitsyncmaster]

I have never seen corrosion in a lamp socket that causes a parallel circuit. The oxide is an insulator. Now carbon contamination is another story (in a brush type motor).

By the way, I took an old fan motor, measured the current and then cleaned the carbon from between the brushes and the curent increased. Still don't know why it did that. I was thinking that was causing our OEM fan motors to increase in current as they age.

[NckT]

For a start, a parasitic load is a term to describe the power consumed when an appliance is turned off eg a TV is in standby.

What you are describing in your scenario is a circuit of the corrosion with theoretical resistance in a parallel circuit to the original resistance of the lamp ("light bulb").

In this instance, as the effective resistance is the equivalent of resistors in parallel, i.e. the 'resistance' of the lamp and the 'resistance' of the cortisone you've described. Equating this new circuit back to of the the overall simple circuit to Thevenin would result in an increase in current due to the lower effective overall "resistance".

An example of this is putting a link wire to bypass to cause a short to blow a fuse.

[DMCVegas]

For a start, a parasitic load is a term to describe the power consumed when an appliance is turned off eg a TV is in standby.

What you are describing in your scenario is a circuit of the corrosion with theoretical resistance in a parallel circuit to the original resistance of the lamp ("light bulb").

In this instance, as the effective resistance is the equivalent of resistors in parallel, i.e. the 'resistance' of the lamp and the 'resistance' of the cortisone you've described. Equating this new circuit back to of the the overall simple circuit to Thevenin would result in an increase in current due to the lower effective overall "resistance".

An example of this is putting a link wire to bypass to cause a short to blow a fuse.

Right! Even if it was not emulating a Thevenin circuit with the resistance substituting for ground/earth, it may have been either iron or even suspended water inside of the rust allowing it to complete the circuit. But yes, it wasn't hindering the flow of current to the bulb, but was bypassing it to create an additional pathway to ground.



I have never seen corrosion in a lamp socket that causes a parallel circuit. The oxide is an insulator

You're correct. Oxide is an insulator and should cause a reduction in current, and not an increase. Prime example was taking a wire brush and cleaning out all but one of my bayonet sockets. You could look inside, particularly with the rear light boards, and see the oxidation.

But let me give you a little background information here.

Get into my car one night, and the lights will not turn on. I pop the Headlight Switch out, and I find that the copper connectors inside the assembly wipes against have sunk into the plastic as it melted. Scrape the plastic off, lights work for a while, but the problem returns. Switch has the same problem, but now it's deformed. I grab a wire bayonet socket brush. A little bit of scrubbing later, the connections were clean, save for one. The clearance light on the left front fender. But the light still works! So since I'm in a hurry, I just shove a spare fan fail jumper wire I have into the headlight switch socket and away I go. Lights all work fine. I burned the hell out of my fingers pulling the jumper out! That wire was HOT!

So the reason I never cleaned the socket on the fender marker was because it was rusted solid. I could not pull the bulb out. The rust fully encapsulated the entire space between the bulb and the socket and fused it in. Turns out the gasket was cracked on top, and standing water had been sitting inside of the bulb housing for some time. You could see the water stains inside. So I order a replacement socket from Grady that I spliced in. New light bulb looks just as bright. But now the jumper wire in the headlight switch is cool when the headlights are running.

So the pure oxidation by itself was not increasing the load on the circuit, but either iron or water content inside of it was indeed acting as a bridge to create an alternate pathway around the lightbulb. Hence it increased the load on the circuit enough to melt the headlight switch.

I should have the bulb in storage somewhere. Once I dig it up, I'll post pictures and hit it up with a multimeter to do a side by side test on it with a clean bulb and socket.

[David T]

Everything will become obvious if you understand Kirchoff's Law. The sums of all currents going into a point must equal the sums of all currents coming out. In this case it is easy because it is a DC circuit. AC circuits are much harder to understand.

[NckT]

http://www.dummies.com/education/science/science-electronics/circuit-analysis-for-dummies-cheat-sheet/

Back to the original post. .. keep the connections clean ;)

No scotch locks !

[Elvis]

Thanks Dave for starting this thread,
I read so much wrong stuff about electrical things here - and so often...

Glad others see it, too and want to help to correct it.


Where is the "I like" button ? :-)

[Rich_NYS]

This morning while watching YouTube, I found myself reviewing Ohm's law in my head and thinking: "I=V/R....HTH is current increasing when it's inversely proportional to resistance???"

[NckT]

V=I x R

I = V / R

For a DC circuit, for constant voltage (engine running approx. 13.5 to 4.5v), increase Resistance, Current decreases. ..

Increase resistance, the current will reduce. ....

[Elvis]

I can't beliebe Bob is telling us the current of the fan goes up when the connector corrods :-(

https://www.youtube.com/watch?v=rbpxOi1bgFI


...
And I have never seen door lock solenoides that failed because of rust.
...
And whatch out with those silicone hoses that easily fail / are cut when using the wrong clamps...

and corrsion in the headlights causes the light switches to fail ???? ouch !!!!!

[Bitsyncmaster]

I can't beliebe Bob is telling us the current of the fan goes up when the connector corrods :-(

https://www.youtube.com/watch?v=rbpxOi1bgFI


...
And I have never seen door lock solenoides that failed because of rust.
...
And whatch out with those silicone hoses that easily fail / are cut when using the wrong clamps...

and corrsion in the headlights causes the light switches to fail ???? ouch !!!!!

That is the video I saw that started this thread. There was also a lot of comments on facebook that stated that bad grounds increase the current. I did not bother correcting the facebook thread since I did not want to start an argument.

A new rule for me:
Never discuss politics, religion and now electrical grounds with friends and family or on facebook.

[Elvis]

and remember - saving standby-current is useless, bad and stupid !

:mallet:

[Bitsyncmaster]

and remember - saving standby-current is useless, bad and stupid !

:mallet:

Yes that face book thread was about a large battery drain when not running. I really had to "bite my tongue" to not correct bad grounds causing the battery drain.