What`s the real story on disconnecting the negative terminal all the time?
01-05-2012, 10:43 AM
#22
Le Mans Master
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Paul, thanks for putting it in those terms, makes a bit more sense. I had read something to that effect but could not remember enough to post a rational statement. I believe I also heard that lightning - not sure if it's ALWAYS or SOMETIMES - actually jumps UP from earth, not DOWN from the clouds. It happens so fast the eye does not catch the difference and since we're raised with the idea that it comes down, the brain "sees" it that way. At least that's what the article claimed IIRC - I read it quite a while ago.
P.
01-05-2012, 12:43 PM
#23
Drifting
THANK YOU, Paul! When I was in college, I was taught pos-to-neg. When I shared that with my dad who had founded 2 very successful tv repair shops, he gently corrected me and explained why it was really neg-to-pos. This started my lifelong habit of "questioning authourity". My next exposure to that neg-to-pos flow of electrons came at Ma Bell. I must say, you put it in such easy-to-grasp terms! This one's for you! 
P.S. "your mileage may vary..."
P.S. "your mileage may vary..."
Last edited by SQUIRMIN VERMIN 84; 01-05-2012 at 12:45 PM.
01-05-2012, 05:20 PM
#24
- 1986 Original Owner -
Paul, Where did you go to B double E school? I did my Electronics, A and C school at GMS Dam Neck after sub school. Of course that was in the days of wooden ships! Your reply was one of the best I've read on this Forum in a very long time.
01-05-2012, 07:02 PM
#25
Le Mans Master
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I got my start by studying physics in college, but it was Uncle Sam that introduced me to electronics; FTA school at Great Lakes, and various ad hoc C school classes at Treasure Island while the "boat" was in an extended yard upgrade. After the Navy, I went back to school in San Diego and later came full circle and taught electronics at San Diego State to Navy personnel for a while.
I love Corvettes, especially the C4s. Love to help folks with our passion whenever I can (and try not to give anyone a "bum steer"
)P.
01-05-2012, 07:33 PM
#26
Pro
NOT that it matters, but up until the the invention of the CRT (cathode ray tube - the display used in radars and TV picture tubes, etc) "conventional flow" (aka positive flowing to negative) was thought to be the case. Nobody could actually "see" current (i.e. electrons) flow, so the "convention" was current flowed from positive to negative. (To this day, when you look at a circuit schematic the "arrowheads" on diodes and depicted in transistors, etc, point in the direction of positive flowing (to negative potential).)
The CRT shoots a beam of current from the base, which is steered by parallel vertically and horizontally placed magnets to bend or steer the beam, to strike a fluorescent screen creating a visible spot of light. But, when applying a positive potential to the anode (at the base of the CRT) and negative potential on the screen, nothing happened until (what the hell?) someone swapped polarity, and walah!! It must have been quite a "shock" to the scientists standing around when they suddenly realized current flowed from negative to positive (giving way to "electron flow" i.e., negative to positive as opposed to "conventional flow" i.e., positive to negative). And, now I can imagine how the concept of current flowing opposite to what you thought...is causing you too to ponder the logic of what you have said.
My point? My point is the battery can be thought of as the "pump" in a closed circuit network - providing the force to move current around the components, and returning to the battery. So, regardless of whether you subscribe to "electron flow" (negative to positive) or "conventional flow" (positive to negative) if you remove either pos ro neg cable from the "pump", current stops...Well, almost.
Someone made the (excellent) point there are capacitors associated with various modules, e.g., the ECM, etc - think of them as the equivalent of mechanical springs. When voltage is applied, the capacitors are charged (the equiv of compressing springs). The battery (pump pressure) can be removed, but the capacitors remain charged - for a time - until current leakage around the capacitors depletes the charge until "the pump" is reapplied, a la connecting the cable(s) to the battery.
However, until the capacitors have a chance to bleed off the voltage, if the positive cable was disconnected and then came in contact with the frame, there IS a chance of the reverse flow from the capacitors to ground could do harm - especially in sensitive computer circuits.
If readers are still with me, (you poor bastards
) all of this to say because of the location of the positive post in our cars being the convenient one, I (and most of us) will remove the positive cable. That's OK, but just take precautions to avoid shorting the terminal to the chassis with the wrench, and keep the exposed connection from coming in contact with a ground e.g., the chassis somewhere.
For what it is worth, I was first taught "electron flow" in the US Navy, prior to fussing with missile and gun fire control radars and computers, etc. But, like you, I since converted to "conventional flow" theory because it made reading electronic schematic diagrams much easier: when they discovered the truth about "electron flow", they never changed the symbols (the "arrowheads") that indicated the flow direction of "conventional flow". The difference is when you look at a schematic, you can almost envision the current flowing and spreading out across the circuit, guided by all the "arrowheads". In "electron flow", current flows against the arrowheads - kinda like steering a car by looking in the rear view mirror. As long as I don't try to apply a positive bias to the anode of a CRT, it's all good.
Bottom line...
Disconnecting either cable will open the circuit - preventing current flow**.
Removing the negative cable is arguably safer because if the wrench comes in contact with the chassis in the process, there will be no danger.
Removing the positive cable** will open the circuit, but precautions need be used to avoid the tool used from shorting against the chassis, AND the open connection needs to be isolated from the chassis to avoid inadvertently discharging the capacitors (in the ECM, etc), at least until the "caps" potential has time to bleed off.
Your mileage may vary.
P.
The CRT shoots a beam of current from the base, which is steered by parallel vertically and horizontally placed magnets to bend or steer the beam, to strike a fluorescent screen creating a visible spot of light. But, when applying a positive potential to the anode (at the base of the CRT) and negative potential on the screen, nothing happened until (what the hell?) someone swapped polarity, and walah!! It must have been quite a "shock" to the scientists standing around when they suddenly realized current flowed from negative to positive (giving way to "electron flow" i.e., negative to positive as opposed to "conventional flow" i.e., positive to negative). And, now I can imagine how the concept of current flowing opposite to what you thought...is causing you too to ponder the logic of what you have said.
My point? My point is the battery can be thought of as the "pump" in a closed circuit network - providing the force to move current around the components, and returning to the battery. So, regardless of whether you subscribe to "electron flow" (negative to positive) or "conventional flow" (positive to negative) if you remove either pos ro neg cable from the "pump", current stops...Well, almost.
Someone made the (excellent) point there are capacitors associated with various modules, e.g., the ECM, etc - think of them as the equivalent of mechanical springs. When voltage is applied, the capacitors are charged (the equiv of compressing springs). The battery (pump pressure) can be removed, but the capacitors remain charged - for a time - until current leakage around the capacitors depletes the charge until "the pump" is reapplied, a la connecting the cable(s) to the battery.
However, until the capacitors have a chance to bleed off the voltage, if the positive cable was disconnected and then came in contact with the frame, there IS a chance of the reverse flow from the capacitors to ground could do harm - especially in sensitive computer circuits.
If readers are still with me, (you poor bastards
) all of this to say because of the location of the positive post in our cars being the convenient one, I (and most of us) will remove the positive cable. That's OK, but just take precautions to avoid shorting the terminal to the chassis with the wrench, and keep the exposed connection from coming in contact with a ground e.g., the chassis somewhere.For what it is worth, I was first taught "electron flow" in the US Navy, prior to fussing with missile and gun fire control radars and computers, etc. But, like you, I since converted to "conventional flow" theory because it made reading electronic schematic diagrams much easier: when they discovered the truth about "electron flow", they never changed the symbols (the "arrowheads") that indicated the flow direction of "conventional flow". The difference is when you look at a schematic, you can almost envision the current flowing and spreading out across the circuit, guided by all the "arrowheads". In "electron flow", current flows against the arrowheads - kinda like steering a car by looking in the rear view mirror. As long as I don't try to apply a positive bias to the anode of a CRT, it's all good.
Bottom line...
Disconnecting either cable will open the circuit - preventing current flow**.
Removing the negative cable is arguably safer because if the wrench comes in contact with the chassis in the process, there will be no danger.
Removing the positive cable** will open the circuit, but precautions need be used to avoid the tool used from shorting against the chassis, AND the open connection needs to be isolated from the chassis to avoid inadvertently discharging the capacitors (in the ECM, etc), at least until the "caps" potential has time to bleed off.
**I only mention removing the pos terminal because the POS terminal is very accessible on the C4, whereas the NEG is not so much. Being aware of the concerns should be enough to avoid any problems...in this case.
Your mileage may vary.
P.
Being taught as an EE (engineer), we always analyzed and troubleshoot circuits using the conventional current flow model ~ to the negative.
Maybe this will explain it better;
Electrons are negatively charged particles and the flow of electrons (not to be confused with current) is from negative to positive, due to the attraction of the negative charged electrons to the positive terminal. However, current flow is always opposite to the direction of electron flow, and hence it flows from positive to negative in a circuit outside the cell / battery. Within a battery, however, current flows from negative to positive. Got It! or are you all more confused?
Or maybe this explanation is clearer;
Electrons flow from negative to positive. Electrons are negative charges and are attracted to the positive side of the circuit. The current flow, or the flow of holes as described below is to the negative.
Look at it this way (over simplified). The positive side of the battery has a bunch of positive ions. When you connect a wire, an electron moves into the battery leaving a hole behind. The hole is filled by an electron further down the wire. That leaving a hole to be filled by another electron and so on.
The holes move from positive to negative, the electrons move negative to positive.
Military taught electron flow and universities taught hole flow. Be prepared to deal with either way. You will hear both.
Last edited by mako41; 09-04-2016 at 09:26 PM.
01-05-2012, 07:42 PM
#27
Race Director
01-05-2012, 10:41 PM
#28
Drifting
I remember hole-flow. Thanks to you and Paul for explanation of both schools, each with their distinctive perspectives of the same phenomenon. It was always a real brain-bender for me.
01-05-2012, 11:22 PM
#30
Team Owner
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St. Jude '03-'04-'05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16-'17-'18-‘19-'20-'21-'22-'23-'24
Of course the rule-of-thumb has always been negative first for safety.
Good write-up BTW
01-06-2012, 06:18 AM
#31
Le Mans Master
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I recall a thread here where it was discussed the pros and cons of pulling just the neg or pos cable when storing for the winter. It seemed pointless to me since pulling the battery off line is accomplished with either removed.
Of course the rule-of-thumb has always been negative first for safety.
Good write-up BTW
Of course the rule-of-thumb has always been negative first for safety.
Good write-up BTW
w/ the rule-of-thumb.Veering off topic a little, and not that you asked, but the electrolyte (H2SO4) in a resting car battery will react with the lead plates, forming a lead sulfate film on the lead plates. The sulfate is non-conductive and as it grows, it effectively reduces the exposes area of the lead plates, resulting in the diminishing of the battery capacity by approx a percent or so per week, much less in a DD, however.
A modern battery charger has a "de-sulfate" mode that will dislodge at least some of the buildup, thus restoring some or most of a battery's capacity. However, if storing a battery for winter, it is by far better to keep one of the "smart chargers" (e.g., Battery Tender) on it as the battery will not sulfate as long as there is some charging current flowing at all times.
The "smart chargers" have circuitry aboard that will sense when the battery is fully charged and fall back to a little pulse mode to retard/prevent the sulfate from forming. And, with such a charger on line, there's no need to disconnect the battery.
The battery in my wife's C3 is 7 years old, the battery in the ZR-1 is at least 4 yrs old (age unknown as it came with the car when I bought it), both cars have 11:1 compression motors, and even after soaking in sub-freezing temps, the batteries whip dem starters like rented mules! So, for me, disconnecting the battery over the winter is something I never worry about - long as the "BT"s are running (one is 7 years old, runs constantly - never been shut off).
That's my story, and I'm stickin' toit!
P.
01-07-2012, 10:33 AM
#32
Drifting
Another way of learning.....very fast.... work under a dash with a metal watch band and DON'T disconnect the battery...... I had watch band scars for a month on my wrist where the band instantly heated from shorting out something....I was 18...I have disconnected batteries ever since and removed watches and rings....
01-07-2012, 03:52 PM
#34
Race Director
01-07-2012, 04:38 PM
#36
Burning Brakes
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And some MGs.
The rule is first take off the side of the battery that's connected to the frame,
which today is the negative side, but wasn't always.
Chuck
The rule is first take off the side of the battery that's connected to the frame,
which today is the negative side, but wasn't always.
Chuck
01-07-2012, 06:49 PM
#37
Safety Car
01-11-2012, 03:32 AM
#39
Drifting
Nearly all early 6-volt systems were positive ground. In the 50's when everyone was converting to 12-volt systems, negative ground became the standard.
01-15-2012, 08:42 PM
#40
Drifting
Another way of learning.....very fast.... work under a dash with a metal watch band and DON'T disconnect the battery...... I had watch band scars for a month on my wrist where the band instantly heated from shorting out something....I was 18...I have disconnected batteries ever since and removed watches and rings....
I wound up with blisters under the very hot watch band.
