Charging the car battery? help - Page 2

corning_d3 · 11-02-2006, 02:31 PM

A battery charger puts out AC voltage, as well as DC. AC is bad on electronics built for Low ripple DC..
Plus some battery chargers are poorly regulated, voltage-wise.

UncleBob · 11-02-2006, 05:04 PM

alternators have voltage ripple also. A common failure of an alternator is the diode bridge, which puts large AC voltage into the circuit. I've never seen such a failure do anything other than damage a battery though.

Basically, what you're saying is, some battery chargers are cheap and/or faulty. I still don't see what this will do to the rest of the system though. If a charger isn't regulating the voltage correctly, the battery could very well get damaged whether you have the car cables hooked up or not.

Steel · 11-02-2006, 05:52 PM

There should not be any problem leaving the battery cables on when charging the battery. That's what we did at the dealer with very expensive cars all the time, not waste our time taking the battery out to charge them.
1. if the ignition switch isn't on, the power isnt going to go through most of the circuitry anyway.
2. even if you do leave the switch on, the electronics are only going to use as much power as they always have. The rest of the current is going into the battery.... charging it.

Now. If you try to charge the battery by putting 100 VOLTS to the system, then you'll have problems.

Scrapper · 11-02-2006, 06:17 PM

ok if you say so BOB...you think the dealer ship's going to agree probably not??? if you get a good 1 he'll tell you the truth....BOB......

TheSilentChamber · 11-02-2006, 07:14 PM

I'v never taken them off, and never had a problem. Mine also has a jump start mode, that would be hell-of hard to do with them disconected.

UncleBob · 11-02-2006, 07:27 PM

Quote:

Originally Posted by Scrapper

ok if you say so BOB...you think the dealer ship's going to agree probably not??? if you get a good 1 he'll tell you the truth....BOB......

um, I've worked at dealerships.

I don't want the "truth". I want the "why". Truth is colored by opinions

Steel · 11-02-2006, 07:50 PM

Quote:

Originally Posted by Scrapper

ok if you say so BOB...you think the dealer ship's going to agree probably not??? if you get a good 1 he'll tell you the truth....BOB......

Wow. Great rebuttal. I suggest that anyone who wants to respond to this thread brush up on their basic electrical theory.

Racincc85 · 11-02-2006, 10:54 PM

Quote:

Originally Posted by Steel

There should not be any problem leaving the battery cables on when charging the battery. That's what we did at the dealer with very expensive cars all the time, not waste our time taking the battery out to charge them.
1. if the ignition switch isn't on, the power isnt going to go through most of the circuitry anyway.
2. even if you do leave the switch on, the electronics are only going to use as much power as they always have. The rest of the current is going into the battery.... charging it.

Now. If you try to charge the battery by putting 100 VOLTS to the system, then you'll have problems.

Exactly. The charger may be able to supply 40 amps of current to charge the battery but that doesn't mean it will force those 40 amps through every single piece of electonic circuity in the car. Each individual device will only draw what it needs. If the computer needs to draw .01 amps to retain its memory that's all it will draw regardless of how many amps are available to the entire electrical system. As long as the voltage output of the charger is matched to the electrical system on the car everything will be ok.

Moppie · 11-03-2006, 12:01 AM

Quote:

Originally Posted by UncleBob

ooh....I want to hear the theory on THIS!

I've yet to see a alternator that wasn't switched via the ignition switch.

To be honest, Iv simply always been told to disconnect the Earth.
I can think of two reasons: Yes, there have been cars built where the alternator was not switched off the ignition.
My old Herald based kit car was one, the Herald loom it used was so old (circa 1950's) it didn't even have any fuses. (yes it had an electrical fire, which is how I discovered the lack of fuses, yes this was fixed)).
Now, imagine one of these cars, but its an MG, or a Rover, and has a positive earth because some English engineer wanted to be different?

Second reason, what would happen if you were to start the car, while it was connected to a charger? It dosn't sound like it would be healthy for the alternator or the charger?

I work on the theory that until its proven safe to leave it connected, its safer to disconnect the earth from the battery when hooking up a charger.

I would rather to something I know causes no harm, that something I don't if it could cause harm. Flux capacitors are expensive and sensitive to current flow.

UncleBob · 11-03-2006, 12:06 AM

some rather....extreme examples. I'm just guessing here, but the original poster of this thread doesn't have a pre-50's era car, and it has fuses and all that fancy jaz.

as for the car starting with the battery charger connected....I don't know if you've bought a charger since the 50's....? But most of them have a switch for "starting". Its a high amp circuit to help get enough amperage to the starter when theres a dead battery in the circuit.

They don't put that feature on the chargers in hopes of you foolishly believing it so that they can catch your car on fire.

I'm all for the "I've always done it this way and it works" method. But you are operating off of a belief with no "why".

Lets really tear up this thread. Lets get some dialog going here.

Lets hear a story about an attempt to charge a battery, and something bad happened. I want to hear what has happened when uneducated poor saps didn't follow such beliefs. Hopefully, we'll get some gory details.

UncleBob · 11-03-2006, 12:15 AM

granted....I can tell you all sorts of stories about people jumping batteries incorrectly, hooking up batteries backwards, etc. then trying to get it covered under warranty (not!). But I don't count those.

I've personally never seen a "failure" from charging a battery on the vehicle.

Now I CAN relate one story, where my battery charger helped me diagnose a problem. I had a Jeep Cherokee that was giving me fits with a problem. I can't even remember what it was, as far as symptoms. But the battery was low on charge. We have an ancient charger at work, it does not regulate voltage. (probably from the 70's). I accidently put it on too high of a setting and so a puff of smoke come out of the junction box. I traced it and found the problem that was causing all the other symptoms. A bad terminal connection on the ASDL relay. But no harm was caused by the charger....only a small puff of smoke on a pre-existing bad circuit. The voltage spiked to over 20V

corning_d3 · 11-03-2006, 12:16 AM

Ever measured the voltage produced by a charger on the boost setting? I've seen 18-20 volts on most 200 amp boosters. Makes all the lights bright as hell! I'm not worried about current biting my electronics, just voltage...and spikes. Every service manual (Ford, GM, Chrysler, Honda, etc..) I dug up today said to at least disconnect ground, preferrably both cables if possible. I just don't leave anything to chance..

UncleBob · 11-03-2006, 12:22 AM

not all chargers are the same. As I mentioned, most "modern" chargers are much better at regulating voltage. It really depends one what charger is in question.

If you have an ancient charger from WW2, then I agree. Be worried. Anything that smells vaguely like "electronics" will be smarter than the operator. Liability has a habit of causing such corrections in application

Moppie · 11-03-2006, 12:24 AM

Quote:

Originally Posted by corning_d3

I just don't leave anything to chance..

Exactly.
Iv seen a PC blow up because the transformer in the back of the power supply decided life was no longer worth living. It fried everything in the PC, even destroyed the HDD controller board.
Iv seen a house worth of electronics written off because of a voltage spike from the mains.
Imagine either of those two things happening while your car battery is on charge? How are you going to go to the shops to spend the insurance money and buy a new TV and PC?

UncleBob · 11-03-2006, 12:56 AM

Quote:

Originally Posted by Moppie

Exactly.
Iv seen a PC blow up because the transformer in the back of the power supply decided life was no longer worth living. It fried everything in the PC, even destroyed the HDD controller board.
Iv seen a house worth of electronics written off because of a voltage spike from the mains.
Imagine either of those two things happening while your car battery is on charge? How are you going to go to the shops to spend the insurance money and buy a new TV and PC?

so....why do you believe your alternator is safer?

Why is one form of charger not a concern, and another is?

I dont' mind the anal level, but lets be consistant.

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