A lead acid battery consists of lead and lead oxide plates surrounded by an electrolyte made out of water and sulfuric acid. As the battery discharges, the lead plate turns into lead sulfate and the lead oxide plate also turns into lead sulfate, and the sulfuric acid turns into water. Charging reverses this.
Current flowing through the electrolyte (either charging or discharging) causes some of the water to separate into hydrogen and oxygen, just like in the classic high school electrolysis experiment where you take a battery and put wires into water to form hydrogen and oxygen in overturned test tubes.
I also have a portable jump unit. It has a indicator light that will indicate a wrong connection.
I have been within 10 feet of 2 different incidents where battery’s exploded on the mechanic servicing them both came away without any injury, just damaged clothing.
One was while we were working on a RH-200 O&K mining excavator running twin V-16 Cummings. The battery’s were down in a center access hole where the mechanic had 8 large battery’s in a dual bank connecting 4 12 Volts into a 24 volt system and drew a spark(go figure). The machine had been down for other maintenance and chargers running all day.
The battery banks were then mover to the upper deck, as no one else wanted to work down in that pit:smack:
Thank you so much for saying that. When I read that, I KNEW it was wrong, but it actually put a shadow of doubt in my mind and I decided to wait for an expert to come along and make the post.
I also wanted to comment on:
It doesn’t make any difference on which end you’ve reversed the cables. They’re either wrong or right. If one side is reversed, it’s wrong. You have to connect positive to positive and ground to ground. The cables are conveniently marked black and red to try to prevent you from mixing them up, but the colors really don’t matter, as long as the positive has the same color hooked up and the ground has the same color hooked up. (Although the smart thing to do is hook up the red ones to the positive and the black ones to ground.)
I think you’ll find this is not the case with automotive electronics.
They’re safe if used properly, meaning be sure to match the polarity. Effectiveness depends upon their capacity and state of charge. The higher the amperage rating, the more power to do the job. It should be checked regularly and recharged as necessary to get the most out of it.
As to the OP, any damage done was done instantly. The only thing I can think of that might seem to work at first but be later revealed to be a problem is if an alternator diode was damaged, resulting in reduced charging capacity. It might take a number of days (or weeks) for that to become evident. The alternator’s performance can be tested to find out.
I agree that the status of the recipient car is an unknown until it’s provided with a charged-enough battery to put it through the paces.
We went back to the garage today to try and jump his car. No go, so we called AAA. Before trying to tow us, he tried one more jump. Interestingly enough, he hooked up all four posts (no final negative to chassis, iow.) Started right up. Looking at my friend’s owner’s manual, it actually says to hook up all four posts. So, in addition to there being nothing wrong electrically, I’m currently of the opinion that the only thing that saved my buddy’s car from my “help” was the fact that we didn’t make the last connection to the negative terminal of his battery.
How likely is that? Anyways, thanks for everyone’s input.
Not likely, in fact I would say not possible. Electrically speaking, there’s simply no difference between the negative battery terminal and any good ground point on the chassis. The only reason that many jump-starting instructions say to make a connection to the chassis instead of the battery post is to place the last connection’s likely spark some distance from the battery, for the safety reasons already discussed upthread.
The functional word here being “good”. The point selected by the op might have not been a good ground point due to paint, corrosion, a poor connection between the engine and the battery. I have had several occasions over the years where I was able to jump a car where others had failed just by moving a ground clamp.
All consumer grade jumper cables are crap. They’re too thin (can melt easily) and too short (the two cars have to be close together, not always possible).
I went to a shop that sells welding supplies and got 2x5 meters of thick welding cable and two pairs of heavy duty clamps. I have started commercial trucks with these cables with no problem.
Years ago, I bought a pair of “Auto Zone” house brand heavy duty jumper cables. The cables themselves are as thick as the power feed that comes into the back of my house and the clamps will leave teeth marks where it bites into lead battery terminals. They’re about 12 feet long and because of their thickness and size, almost impossible to store in the car because they’re heavy and take up a lot of space.
A couple of months ago, a neighbor of mine was trying to jump start a car and not having much success. I went over to help and his cheap cables looked like they were made of speaker wire and clothes pins. I went to check his connections and fortunately I tapped the clamp with the back of my hand before I grabbed it because it was VERY hot.
I got my good Auto Zone cables and hooked them up and the car started on the first crank.
I agree with the melting of the cables as an indicator of a good ground in this case. What I was trying to point out was the fact that just because it is metal and under the hood, that does not automatically make it a good ground.
I know of one model car where the aluminum intake manifold is rubber mounted on all sides, and therefore is not grounded.
Hi my car (Mazda Demio) had a week or so of flat battery history… Wanted to get it into
have it reviewed/replaced.
A neighbor used my heavy duty jumper cables, and the polarity cap colours differed on our vehicles - so , he ended up with incorrect connections that resulted in big sparks and full burn through the diameter of cable when I turned the ignition on. When I saw sparks, I turned ignition off and said get cables off of batteries. I did not manage to see if he had the final connector onto the chassy, but I think it may have been on the negative pole of my battery.
When he then applied his lightweight jumper cables correctly, my car started immediately. Took it for a long run, but next day car was again unable to be started.
I am retired and have few funds to get this assessed/managed, so would appreciate
some feedback as to the steps I need to take to manage the possible outcomes of
may just need new battery
need auto-electrician assessment before purchase/or if new battery does not solve
the problem. Best process to follow with this, questions I need to ask etc etc?
Hi Barbara, well since you said the battery had been going flat for a week or so before the incident, needing a new battery is a damn good guess.
The fact that the car starts and runs is a very good sign.
You need to have someone check the charging system for output and for AC ripple. The battery will have to be changed before accurate test results can be achieved.
Thanks for that, Rick. I was likely the cause of the original flat battery having inadvertently, during a family crisis, left a door open or a signal flasher on. However I’ve had the car 2+ years, and don’t know how old the battery is, so am not contesting the reason for it being initially tardy.
Am happy to wear the cost of a new battery as the basis fo starting to problem solve. Like you, I’ve been optimistic that no serious damage has occurred to the core computer unit.
So, will ask for the checks you suggested. Assume AC ripple is Alternating Current? Can you please just tell me the reason why I would ask for those two areas to be checked, so I don’t look like a wally to the mechanic?
The device on your car that re-charges the battery is called an alternator. The alternator produces AC which you correctly guessed is alternating current.
You car however runs on DC (direct current). You can’t charge a battery with AC, only DC. So inside your alternator is a series of electrical diodes which convert AC to DC.
The backward jump could have damaged one or more of these diodes. If the diode(s) go open circuit it will effect the charging ability of the alternator. If on the other hand it shorts out a diode the diode will pass AC voltage which will not charge the battery.
Some electrical testers test for AC automatically others have to do it manually.
If all else fails an AC voltmeter across the battery terminals with the engine running, headlights and blower on should read less than 0.4VAC
I hope this helps.
Thanks so much for your replies, Rick. Really easy to understand with your explanations.
Will have more confidence to move forward on this now.
Cheers
Barbara:)
