Battery drain mystery

[K8MHZ]

Also, perhaps with Brtish roots, called "ignition off drain"
It draws current, which drains the battery.

The tech books usually abbreviate to I.O.D. which works for either.

 

[drcampbell]

When I was the new guy, (age 19) they left an ignition "condenser" on the servicewriter's desk and challenged me to tell them what was wrong with it. I picked it up carefully, by the case only, and looked it over. Then I pushed it down on the desk and touched the case to the center terminal. Loud SNAP and big blue arc. I did it again. Little snap and small yellow arc. And again. Barely audible snap. I did it a few more times, then held the whole thing in my hand, center terminal and all, to their great puzzlement.

"Seems just fine.", said I. "Takes a charge; holds a charge; delivers a charge." They I tossed it to the guy who originally challenged me. He ducked out of the way and let it hit the floor, where it laid for a week before anybody dared to touch it.

In retrospect, I wonder how much internal self-discharge they had, and if ithey would retain a charge for a week.

 

[K8MHZ]

When I was the new guy, (age 19) they left an ignition "condenser" on the servicewriter's desk and challenged me to tell them what was wrong with it. I picked it up carefully, by the case only, and looked it over. Then I pushed it down on the desk and touched the case to the center terminal. Loud SNAP and big blue arc. I did it again. Little snap and small yellow arc. And again. Barely audible snap. I did it a few more times, then held the whole thing in my hand, center terminal and all, to their great puzzlement.

"Seems just fine.", said I. "Takes a charge; holds a charge; delivers a charge." They I tossed it to the guy who originally challenged me. He ducked out of the way and let it hit the floor, where it laid for a week before anybody dared to touch it.

In retrospect, I wonder how much internal self-discharge they had, and if ithey would retain a charge for a week.

What were you using to charge those up with? When in normal use, they only see 12 volts so why would they have to be made to handle enough voltage to make such large sparks? You are talking about this kind of condenser, correct?

 

[GoldDigger]

One common use of a condenser is in parallel with the distributor points to form a resonant circuit with the ignition coil. The ringing waveform provides a better spark current through the spark plugs compared with the point and coil only circuit.
The capacitor needs to be rated at a voltage of several hundred volts even though its steady state voltage is not above 14 volts. Playing the trick requires charging the capacitor from a higher voltage source.
Other uses of such capacitors are as simple filters to keep noise out of sensitive systems. A lower voltage, higher capacitance would be used there.

Sent from my Pixel 4a using Tapatalk

 

[gar]

211018-1614 EDT

K8MHZ:

The capacitor is across the breaker points. When the breaker points open we have a series LRC circuit, and energy was stored in the ignition coil primary prior to opening. You can not instantaneously change the current thru an inductor. Thus, the same current is flowing, and in the same direction after the breaker points open. Much of this energy is transferred to the capacitor, and we get a peak oscillating voltage that is determined by how much of that energy is transferred to the capacitor. Simultaneously a large voltage is generated on the secondary, and on this first half cycle of oscillation a sufficiently high voltage is generated to breakdown the spark gap in the spark plug, and a whole new circuit is created with much of the stored energy going into the spark.

Shunt resistance in the spark plug is an additional problem, and when it gets low enough, like 10,000 ohms as an example, there is not enough energy to get to the spark plug breakdown voltage and there is a misfire. This was a major problem back in the 1950s as compression ratios increased, and we still had leaded gas that deposited shunt resistance across spark plug insulators.

This problem could be reduced by going to a faster rise time with a capacitor discharge system, and low series inductance, or by eliminating lead in gasoline. Gradually over the next 20 years lead was eliminated, and also compression ratios were reduced some because of pollution problems.

GoldDigger:

Your statement --- Playing the trick requires charging the capacitor from a higher voltage source. I would classify as incorrect. There is no higher voltage source. It is the inductor energy being transferred to the capacitor.

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[K8MHZ]

I was taught that the function of the condenser was to reduce the size of the spark across the points to make them last longer.

The capacitor suppresses arcing at the points when they open; without the capacitor, the energy stored in the coil would be expended at an arc across the points rather than at the spark plug gap. The Kettering system became the primary ignition system for many years in the automotive industry due to its lower cost, and relative simplicity.

This ignition was developed by Charles Kettering and was a wonder in its day. It consisted of a single ignition coil, breaker points (the switch), a capacitor (to prevent the points from arcing at break)

---From Wiki

 

[GoldDigger]

211018-1614 EDT

K8MHZ:

The capacitor is across the breaker points. When the breaker points open we have a series LRC circuit, and energy was stored in the ignition coil primary prior to opening. You can not instantaneously change the current thru an inductor. Thus, the same current is flowing, and in the same direction after the breaker points open. Much of this energy is transferred to the capacitor, and we get a peak oscillating voltage that is determined by how much of that energy is transferred to the capacitor. Simultaneously a large voltage is generated on the secondary, and on this first half cycle of oscillation a sufficiently high voltage is generated to breakdown the spark gap in the spark plug, and a whole new circuit is created with much of the stored energy going into the spark.

Shunt resistance in the spark plug is an additional problem, and when it gets low enough, like 10,000 ohms as an example, there is not enough energy to get to the spark plug breakdown voltage and there is a misfire. This was a major problem back in the 1950s as compression ratios increased, and we still had leaded gas that deposited shunt resistance across spark plug insulators.

This problem could be reduced by going to a faster rise time with a capacitor discharge system, and low series inductance, or by eliminating lead in gasoline. Gradually over the next 20 years lead was eliminated, and also compression ratios were reduced some because of pollution problems.

GoldDigger:

Your statement --- Playing the trick requires charging the capacitor from a higher voltage source. I would classify as incorrect. There is no higher voltage source. It is the inductor energy being transferred to the capacitor.

.

The "normal" position of the breaker points is closed, so If you remove the capacitor then there will be no voltage on it.. Some fraction of the time when the engine stops the contacts will be open and you could pull off a charged capacitor as long as you used insulated tools to disconnect it.
But if you want to be sure you have a charged capacitor, you would need a separate power supply.

 

[LarryFine]

Playing the trick requires charging the capacitor from a higher voltage source.

The one I mentioned earlier used a 120v test light.

 

[GoldDigger]

The one I mentioned earlier used a 120v test light.

Neon, I presume, so the capacitor could catch a voltage peak?

 

[drcampbell]

What were you using to charge those up with? ... You are talking about this kind of condenser, correct?

View attachment 2558129

Almost. The preferred style for hazing new guys has a spring-steel center conductor, to make it more likely you'll touch both terminals and get zapped. If I recall correctly, it's the Prest-O-Lite style. I heard that they used the Sun machine to charge them up, but don't know exactly how. (and nothing short of catastrophic failure prevents them from exceeding a component's normal voltage rating, which we have no way of knowing anyway; it isn't marked on the case)

I was taught that the function of the condenser was to reduce the size of the spark across the points to make them last longer. ...

It also does that, but that's not its primary purpose. It's there to assure a fat, juicy spark, even when the points are brand new.

 

[gar]

211018-2038 EDT

The primary purpose of a capacitor across the ignition points in an old standard ignition system was to tune the primary circuit of the ignition system to a frequency that optimized the rate of rise of the secondary voltage to produce the fastest and greatest voltage rise on the secondary of the ignition coil. Note: the secondary of the ignition coil also had a resonant frequency resulting from plug and wiring capacitance and coil secondary capacitance. So these resonant circuits and including the effect of leakage inductance were adjusted to optimize the system.

All energy to feed this combination came from the current charge to the coil primary when the breaker points were closed. Upon opening the contacts this stored energy got transferred to various parts of the ignition system. A good deal of wasted energy went into bringing the spark plug voltage up to breakdown.

In general a criteria was that the inductor would get near fully charged 400 times per second. This corresponded to 6000 RPM for an 8 cylinder engine.

The capacitor across the ignition points tended to reduce the build up of contact material from one contact to the other from the unidirectional flow of current. My classmate's father and Henry Ford invented a design that changed the direction of current flow thru the points every cycle. This concept greatly reduced the rate of metal transfer. It was never put in production. Probably as a result of complexity. Later in the early 1950s Ford engineers invented a breaker point design that had a hole in one point. This greatly reduced the rate of buildup of a conical mound on one contact,

The capacitor large voltage buildup in a standard ignition system is the result of stored energy in the inductor that has to go somewhere upon opening the distributor breaker points. The amount of this energy is sufficient to greatly raise the capacitor voltage upon opening of the breaker points.

Starting in 1955 I worked on a University of Michigan contract from Chrysler to improved the automotive ignition system from the perspective of firing fouled spark plugs. This took us in the direction of a capacitor discharge system to get a high rate of rise. Unfortunately this got canceled in December 1957 because cars were not selling and were piling up in lots all over. This was the start of the very severe recession of 1958. We made made good progress on our stated goal. I got transferred to a secure communication project and the ignition system project was never restarted.

.

 

[Little Bill]

Almost. The preferred style for hazing new guys has a spring-steel center conductor, to make it more likely you'll touch both terminals and get zapped. If I recall correctly, it's the Prest-O-Lite style. I heard that they used the Sun machine to charge them up, but don't know exactly how. (and nothing short of catastrophic failure prevents them from exceeding a component's normal voltage rating, which we have no way of knowing anyway; it isn't marked on the case)

View attachment 2558130

It also does that, but that's not its primary purpose. It's there to assure a fat, juicy spark, even when the points are brand new.

Sun Machine was what the mechanic used where I worked at (Coca Cola plant) just out of high school. Of course I was a victim before I ever saw the trick. Then it was on...........I learned how to charge and handle them. I remember one of the route drivers was at the check-in station where they counted the money collected for the day. He had on baggy pants and the opening to the pockets was rather large due to carrying a lot of coins. I eased up beside him and dropped the condenser into his pocket, knowing he would reach in to get out his coins. What I didn't expect was when the condenser zapped him he had a handful of coins. His reaction was quickly pulling out his hand, with the coins, and coins went flying all over the place. Probably $10 worth of coins!
I had to steer clear of him for a while!

 

[GoldDigger]

Almost. The preferred style for hazing new guys has a spring-steel center conductor, to make it more likely you'll touch both terminals and get zapped. If I recall correctly, it's the Prest-O-Lite style. I heard that they used the Sun machine to charge them up, but don't know exactly how. (and nothing short of catastrophic failure prevents them from exceeding a component's normal voltage rating, which we have no way of knowing anyway; it isn't marked on the case)

View attachment 2558130

It also does that, but that's not its primary purpose. It's there to assure a fat, juicy spark, even when the points are brand new.

Apparently the original ignition condensor (capacitors) were metal foil with paper insulation, sealed against moisture, with a value of roughly .25 microfarad at 600 volts. Enough energy for a very noticeable shock, but not dangerous unless the discharge goes between your hands.

Capacitors in Ignition Systems

www.smokstak.com

 

[RichB]

RFI or EMI might interrupt a modern brain-box's shutdown sequence, causing it to drain the battery, but it's more than a bit of a stretch and it doesn't jibe with the owner's claim that it's been that way for years.

I would first verify the owner's observations & claims. There's a huge difference between draining a battery so it won't start an engine and killing a battery so it won't accept a charge. The voices of Click & Clack, asking "Did you learn that from your dad?", are echoing in my ears.

But there may well be some truth embedded in there. Perhaps it's a popular spot for battery thieves, who put an old, dead battery back in its place to avoid being discovered by recycling too many batteries too often.

I'm reminded of the popular old myth that if you leave a battery sitting directly on concrete, it will lose its charge because concrete is conductive.
(there's some truth in that: Concrete is conductive, especially when it contains moisture or rebar, and if you leave a flooded lead-acid battery sitting dormant for two years ... )

or you have the old wood cased batteries that allowed a small drain to flow through the saturated wood to the concrete

 

[drcampbell]

If so, that would be one seriously-durable piece of folklore.
When was the last wood-cased lead-acid automotive battery made? A hundred years ago?

 

[Fred B]

If so, that would be one seriously-durable piece of folklore.
When was the last wood-cased lead-acid automotive battery made? A hundred years ago?

Saw one in an old barn. There was also an old wooden box plunger for explosives. Owner didn't know what they were but didn't want to let them go. They were just tossed on the barn floor in a corner with a bunch of other junk.