When I looked up how to jump a car battery, they tell you WHAT to do, but not WHY, which is infuriating as it's harder to remember unless you know why.
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First they say the cars shouldn't touch. Why?
Then they said positive first. Why?
Once started, they say remove the negative cable first. Why?
Here, they say adding water damages the batteries. Why?
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And how often do you need to add water? This says to add water after every ten charging cycles? Isn't that like every ten days?
And how do you know how much to add? They say add water to the "splash plate" but what is that?
They say the six chambers produce 2.1 volts each for 12.6 volts? Isn't it more than that?
They say adding water before charging will make it overflow. Does it really change the water level that much from dead to charged?
And what happens if you tap water instead of distilled?
In case there is any hydrogen gas that has developed in the battery and may be still concentrated enough to burn, any spark from completing the circuit should be made at some distance from the battery. That is, but connecting the earth to some metal part of the chassis, not to the battery terminal itself.
The chassis is (usually) negative, which is why that is the first and last contact point.
If there is any ionic content in your tap water, it is likely to precipitate as conductive salts in the bottom of your battery, increasing the self-discharge rate. Here in Sydney, our water is clean enough not to need to bother - any effect on battery life is negligible.
The metal body of a car is connected to the negative terminal of the car battery. In the old days the bumper was chrome-plated steel, but today most bumper are covered with polymer so the metal part of the two cars won't touch anyway.
The metal frame of the car is permanently connected to the negative terminal of the car battery. If you connect the black negative jump cable first, then when you try to connected the red positive jump cable you can accidentally drop the big clip into the engine compartment and cause a fire or battery explosion.
The electrolyte in a lead-acid car battery is sulfuric acid. Normally the battery and the sulfuric acid are separate before the battery is ready for installation. The technician dilutes the pure sulfuric acid with de-ionized water to the proper strength to be used to fill the lead-acid battery.
De-ionized water is purer than distilled water. If you use tap water, then the minerals and ions in the tap water will be conductive and your car battery will self-discharge internally rather than holding the charge for a long time. You can easily prove that tap water is quite a good conductor of electricity by dipping your multimeter test leads into a cup of tap water.
You can normally get de-ionized water from some auto-parts or hardware store.
If you cannot get de-ionized, then distilled water will suffice.
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When you charge the car battery too fast or overcharge the battery, the H2O in the electrolyte will separate into H and O2. That's why there is an air vent to let the hydrogen and oxygen out so that it will not explode. You can fill the depleted H2O with de-ionized water to the same level when you got the battery. It is not exact science. A little more or a little less won't make much difference in the concentration of the sulfuric acid inside.
When your car is running, the battery is being charged so the terminal voltage is higher than the theoretical nominal voltage of a lead-acid battery. If you really want to check the nominal voltage of your car battery, then open the hood to check the terminal voltage with a multimeter after the car has not been used for a day.
Don't buy that for two reasons. Firstly most cars and trucks have the battery in the engine compartment and just opening the hood/bonnet to get to the battery will ensure that any hydrogen under the hood will be long gone by the time you use the jumper leads. Secondly you will always get a spark when connecting the last one anyway.
Presumably the 'logic' for connecting the negative lead to the body of the car with the dead battery is that the spark will be further away from the battery, but as I say, it is a pretty dubious proposition that there will be any hydrogen still around.
A few cars do have the battery in the passenger comparment or the trunk/boot, so many that instruction is to cover that situation.
If you connect the negative first and inadvertently touch any grounded surface you'll get a spark. That's also the reason for not having the cars touching although that advice is seriously out of date. Plastic to plastic contact isn't a problem. The majority of the vehicles any more don't have steel bumpers.
It's a little different situation but the battery on a Harley Sportster is a pain in the butt. The easiest way to get the positive terminal screw tightened is to come in across the engine with a long screwdriver, then snug it down with a 10mm. If you do the negative first you're probably going to have some fireworks.
Because of the danger of touching metal with the positive lead when the two negatives are connected.
This assumes the car has negative ground, although a positive ground is very rare in cars nowdays.
Same reason.
I don't know about damaging, but you dilute the existing liquid, will not have the proper proportions when you start charging immediately. Better wait.
However, if the plates are partially out of the liquid, don't attempt to charge, fill first. The battery may be dead in any case, though.
Also, read about bubbles below.
You find that from observation of how fast the level goes down.
There is typically "something" to show you the level.
As you add water, the level touches the rim of a "tube" and the reflection of the light in the water surface suddenly changes shape. Stop there.
Depends on charge level.
Gas bubbles form inside when charging. If you do fast charging, they can be big. Those bubbles inside the liquid make its volume bigger, and it may overflow. A car battery is designed considering that the vibrations of the motor will release the bubbles fast, before they become big. A battery designed to be on a room has more space between plates so that the bubbles release easier without vibrations.
So, if the level is too low (close to the plates) add some water, but not the maximum.
Damage.
In chemistry, you only use distilled water, for every reaction. You do not want extra chemicals.
Two common types of treated water are distilled and deionized water. Here are some similarities and differences that are key to understanding them:
Both distilled and deionized water are fit to drink.
Deionized water is purer than distilled water.
Distilled water conducts electricity, while deionized water does not.
IIRC when cars had metal bumpers and people didn't have such good jumper cables, they would touch the bumpers together in place of the negative cable. And then maybe it could leave damage on the chrome from sparking. ??? Now all the bumpers are covered in plastic or rubber and it makes no difference. But the warning is still there.
The second goes with the first, so that making/breaking is with the negative cable, but that leaves the origial question. The correct answer seems counter-intuitive. I used to know the answer and it's not obvious. It had to do with accidentally ....aha it had to do with accidentally touching both cables to the frame of the car. Say you've hooked it up to the car with the good battery, and then you connect the negative first. Then while you're trying to connect the positive (and sometimes that's not easy. It has a cover or it's tucked away, or you can see it but can't get the clamp on, you touch the metal body or engine or frame of the car. Now you have both cables touching the frame while at the other end, at the car you are using to jump your own, they are connected to a good battery. Big spark. Thing you are touching it to gets damaged. If you manage to clamp or hold it on, cables get hot, insulation melts.
If you connect the positive first, you know you have that cable in the right place, and then the ground cable would have to accidentally touch specifically the positive terminal to be a short circuit. Anything else it touches would be okay. In fact they also urge people to connect not the negative battery post but to some other body or frame part, so that that spark is away from the battery where the hydrogen is generated.
I suppopse hydrogen must have been a problem at least one time in history -- a spark will ignite the hydrogen, and the flame could spread, I suppose, to the hydrogen still in the battery, which would cause the battery to explode and burst which will ruin the battey and spray acid all over the place. But as Rod said, hydrogen is light and disperses quickly and iirc it's only made when the battery is charging (wrong. See below) and is also (so this is wrong too:) discharged enough to take a charge, and your dead battery lately, unless it has been and ylu got interrupted and have to put the cables back on. And the good car battery has enough alternator voltage to charge all the time, but it's probably fully charged and not making any hydrogen anyhow.
So to correct myself, it makes hydrogen when the battery is discharging. I suppose by the time you go find someone to jump the car, there has been loads of time for the hydrogen to blow away. Maybe the explosion happened in a testing lab where they were all set up and they discharged the battery and then recharged it immediately. ?????
So this is less likely to be a problem and I still use my negative battery post for a jump, but the first question, negative on last, makes sense. Even though I know where to put the cable, eventually I will touch something I shoudln't so it's better to go in that order.
Very rarely, unless the charging voltage of the alternator is too high, because the regulator isn't working right. These things continue to get more reliable.
Or ten trips??
I don't know what they mean by charging cycle, but I check maybe once a year. If I needed more than a little bit of water, I'd would plan to check again in a month or two. Doesn't mean I would do so. I've been sluggish and actually checked only once in the last 5 years. Two years ago. I did need quite a bit of water.
When the water looks flat, it needs water. When the water reaches the right level, it touches the bottom of the tube-like thing that is the filler for the chamber and you can see the meniscu, where the water curls up at the edges, so when you look, it's not flat everywhere. It's curled at the edges like water in a glass is where it touches the glass. That means you've put in enough water.
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Water forms a concave meniscus. Maybe liquid mercury forms a convex one. Oh, yeah sure enough, that's what it says. You can see it in any glass of water, although I think soap keeps it from forming.
Never heard that term but they must mean what I just said.
No. Charging voltage is intended to be 13.4 or something like that because if you only have 12.7 it will charge too slowly to recharge what it lost during starting or running lights while the engine is off.
I'm sure they didbn't make this up, but I don't worry about timing like that and I've never noticed it overflow. OTOH, I have had shmutz on the top of the battery, white crud, and that is from the acid in the battery. Plus even if you don't see white crud, if you pour some baking powder on the battery and then add water (this is to the outside so it doesn't have to be distilled) and you see bubbles, that means there is acid on top of the battery. When the bubbling ends, all the acid has been neutralized. There very often is some. (Even sealed batteries have a vent iirc, but maybe not). does it get there because of evaporation and then condensing, can acid do that? or did the battery overflow when I was driving. I very rarely overfilled even one of the six chambers, and even then there is room for expansion. You have to overfill a lot before it's near the top. .
Tap water has minerals and they would combine with the sulfuric acid without generating electricity, or maybe with the lead itself. Something like that. They'd get involved in the chemical reactions and slightly lessen the power of the battery. Pb + H2S04 -> PbS04 + H2, when discharging**, and the reverse when charging, or something like that. The reverse is tricky because the PbS04 should release the lead and it should go back onto the plates. If you charge too fast it does but it gets covered by some other compound, probably PbS04, and it makes "spongy lead". then the surface of the plates isn't entirely lead and the battery isn't as powerful as it originally was. Also some lead etc. drops into the bottom, which is empty for a half inch or an inch, so the junk in the bottom doesn't short out the plates. Not easy to build a good car.
**Oops This would mean that hydrogen is made during discharging, not charging like I said.
As to sealed batteries, even non-sealed batteries pretend to be sealed now. They don't have 6 screw on caps. They have 2 wide flat plastic plates you can pry off, that look similar to sealed batteries. IIRC they hoped car charging systems would all work so well that sealed batteries would be fine, but it didn't always work out that way and people still had to add water and they were annoyed when they coudln't, so non-sealed made a resurgence, but they try to look like sealed so the police and border guards won't stop and interrogate them.
Indeed it does say that, but it doesn't give much in the way of reasons. Pretty much proof by assertion.
OTOH, my googling yielded contradictory results!!!!
I haven't read them yet, or looked for tie breakers, becusae I think it's worth reporting the mere fact that it has contradictory results:
Here is my search
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not counting the Q&A part, these are the first two hits.
Water that has been purified of dissolved minerals and salts through a process called deionization is recognized as the best choice for maintaining lead-acid batteries. Deionization eliminates more impurities from water than distillation or conventional filters. The Perfect Solution for Maintaining Your Lead-Acid Batteries
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articles energy-management
vs.
Can you use Deionized Water in Batteries?
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news articles can-you-use-... Oct 12, 2021 Whilst deionized water is not as pure as distilled water; it is perfect for industrial battery watering. It is a cost-effective method
Plainlly, the second article was written by a Brit, or someone from the Commonwealth. As an American, I should favor the first article, but I don't, so I will control my patriotism and wait for more information.
If the only ions in distilled but not de-ionized water are hyrogen, oxygen and/or hydroxide ions, I don't see how they would cause a probem in a battery. Doesn't any water in a lead acid battery ionize into those very ions? And how could there be other ions than those three in distilled water? Maybe the answer is in the articles, but I've already spent a lot of time on this thread, so I'll either wait until you guys resolve this, or I'll come back later with renewed energy.
People have the wrong impression that "distilled water" is the purest form of water but that's not true. Common distilled water is obtained by boiling water and collecting the condensed steam. The condensed steam is not 100% pure H2O because there are chemicals in the water with lower boiling point than H2O that will come over in the distillation process.
The best way to get deionized water is to start the deionization process with distilled water because there will be a lot less impurities to remove, and distilled water is cheap and easy to get.
People have the wrong impression that "distilled water" is the purest form of water but that's not true. Common distilled water is obtained by boiling water and collecting the condensed steam. The condensed steam is not 100% pure H2O because there are chemicals in the water with lower boiling point than H2O that will come over in the distillation process.
The best way to get deionized water is to start the deionization process with distilled water because there will be a lot less impurities to remove, and distilled water is cheap and easy to get.
You don't get pure H2O by using a home water deionizer in your water pipe using resin beads because most of the impurities will still pass through the resin beads.
You can tell deionized water is purer simply by the price. I can get a gallon (4L) of distilled water from a supermarket for about $1, but I have to go to an auto-parts store to get deionized water for about $6.
Read the product description of that deionized water for "topping up car battery":
Turbo Power Deionized Water, 3.78-L
Turbo Power Deionized Water helps provide protection against the damaging effects of scale build-up and corrosion often caused by the use of regular water. Ideal for topping-up cooling systems, topping-up car batteries when battery acid level is low and diluting concentrated radiator antifreeze/coolants.
"Deionized water and Distilled water are both types of extremely pure water, but they are produced in two distinctly different ways. Depending on the source water, distilled water can be more pure than deionized water – but that doesn't necessarily mean that it's better. There are pros and cons to using deionized water vs. distilled water for particular processes, particularly when it comes to cost and efficiency."
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"The main difference between these two types of water comes in the form of purity. Deionized water is the purest form of water available and, in some cases, can be considered a type of synthetic water. However, distilled water does not contain any impurities and therefore has fewer contaminants than deionized water."
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