Charging the car battery? help

[Moppie]

Originally Posted by UncleBob

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.

Because one can spike at over 240volts, and the other can't?

[UncleBob]

ah. And what do 200 amp capable car alternators peak at in AC voltage?

it really doesn't matter. They prefer to avoid damage to the system(s). So we are left with considering the likelyhood of it. I don't think it's likely with a remotely modern charger or alternator. They design fail-safes into them even if they fail. They don't like being sued.

[Moppie]

Did you have a worse Friday than I did?

Originally Posted by UncleBob

I don't think it's like with a remotely modern charger or alternator. They design fail-safes into them. They don't like being sued.

Ahh, now this is an interesting point.
In the states or UK that might be an issue, in the rest of the world its pretty mute. I would have hard time suing my chargers manufacturer, not only do my own country's laws make it difficult, the charger was made in China, and their laws are totally different again.

[corning_d3]

Originally Posted by UncleBob

ah. And what do 200 amp capable car alternators peak at in AC voltage?

Anything more than .5 AC volts and an alternator is considered defective. An average battery charger puts out waaay more than ten fold this number.

[Scrapper]

you are correct.....

[UncleBob]

let rephrase it then.

I've been a full time mechanic for 12 years. I've never worked at a shop that worried about disconnecting the battery first. I've never seen any failure that wasn't improper use of the equipment. Some days I'll personally charge 3 or 4 batteries.

Thats a lot of batteries I've charged on a very wide variety of chargers. Never had a single issue.

[SR Racing]

Originally Posted by UncleBob

ah....CURRENT is higher? Current to what? To the computer? How?

Actually he is correct. Depending upon the charge rate and how he is charging it. The voltage at the charger connections can be much higher than 12.6 (a fully charged battery) And the computer is connected (along with a few other devices) so, it is law that I = E/R. The load remains the same, the voltage is higher and thus the current to the computer is higher. Nothing secret about this. However, the risk while finite, is small. The manufacturers were well aware of this and the ECM can handle it fine. There is also some remote possibilty of large voltage spikes due to inductive loads in the circuit. This can occur when connecting and disconnecting a charger. (It doesn't matter whether you disconnect the negative or positve terminals first.) However, the manufacturers also prepped for this with decoupling capacitors in all the high impedance devices like the ECM. So it is also a very small risk.

If current is higher to the computer, its higher to everything else in the circuit. So IF thats the case, then everything else is at risk.

And it is., albeit a small risk.

I'm leading you. I want to see a better answer. What is the REAL risk here, and what causes it, specifically.

I just gave it to you. AND, all other things being equal... it is not a bad idea to disconnect the battery when charging. But almost not worth the effort.

Jim
EE/ME

[UncleBob]

Originally Posted by SR Racing

Actually he is correct. Depending upon the charge rate and how he is charging it. The voltage at the charger connections can be much higher than 12.6 (a fully charged battery) And the computer is connected (along with a few other devices) so, it is law that I = E/R.

The very next line of my post that you quoted said all that, without being specific.

I was trying to cut through the mystical beliefs and get someone to actually say what can cause dangerous currents to the computer.

Which is simple: too much voltage. In otherwords, improper voltage regulation. Either due to a faulty charger, or due to operator error. The latter being far more likely IMO.

[KiwiBacon]

There are some very bizarre concepts being pushed around this thread.

So I'll throw in some of my own.

Chargers provide voltage, the current through the battery is the result of this (not the cause).

Chargers and alternators all push a similar voltage to charge the battery, 14.2-14.7v is the range for all the vehicles I've tested.

Car electronics are safe to beyond this level and will not be damaged by a healthy charger. Of course a dodgy charger could kill anything (including you)!

The only times I've bothered to disconnect a battery for charging were:
1. When the power cord wouldn't reach the car.
2. When I have had electrical leakage (the cause of the flat battery).

You can even jump modern cars without problems, my jumper leads have a capacitor between the wires, damps out voltage spikes.

[SR Racing]

Originally Posted by KiwiBacon

Chargers and alternators all push a similar voltage to charge the battery, 14.2-14.7v is the range for all the vehicles I've tested.

Car electronics are safe to beyond this level and will not be damaged by a healthy charger. Of course a dodgy charger could kill anything (including you)!

Yep

my jumper leads have a capacitor between the wires, damps out voltage spikes.

Few do. (if any)

To the contrary, some use a pulsed DC to supposedly break up sulfation.
However the battery is, for all practical purposes, a capacitor and it tends to filter spikes.

Try running your car radio off the charger alone without the battery. On most chargers all you will get is a loud hum... That's because it is a 1/2 wave 120cycle pulsed voltage. (No filtering caps.)

You will often see this same effect when the car has a totally bad (open) battery.

The main point to this thread though... If you are real anal, pull the battery to charge it.
If you are pretty normal, charge it while connected.

Jim

[KiwiBacon]

Originally Posted by SR Racing

Try running your car radio off the charger alone without the battery. On most chargers all you will get is a loud hum... That's because it is a 1/2 wave 120cycle pulsed voltage. (No filtering caps.)

My charger cost less than $US20 and it produces good DC. But I can see why others would take the cheapest way to charge a battery.

I have used my charger to run a car radio before. I pulled the radio to sell it and realised there was still a CD in there. Connecting up the charger was enough to wake it up and eject the CD.

Big relief.

[sracing]

Originally Posted by KiwiBacon

My charger cost less than $US20 and it produces good DC. But I can see why others would take the cheapest way to charge a battery.

I have used my charger to run a car radio before. I pulled the radio to sell it and realised there was still a CD in there. Connecting up the charger was enough to wake it up and eject the CD.

$20 US? You can't get much cheaper than that. I think you have a trickle charger there. (Or a wall wart DC power supply).

Most real chargers put out either a pulsed DC or a ripple DC. They charge better in theory at least.

BTW, pulsed DC or ripple DC would still eject your CD. However if you tried to play the audio it would probably be just a hum...

[bob5918]

i learned my lesson. i put my charger on boost to charge my battery not taking cables off. went to start my car and had a puff of smoke come out of air vent. car started but i toasted by radio. had to buy another radio for my car. if your driving a newer car take charger off after battery is charged when cranking car .