Can You Charge a Car Battery While Still Connected to the Vehicle?

Is it necessary to disconnect the battery from the car's installation when recharging the battery with a charger? What are the risks of not disconnecting, and why? It is known for short urban routes in this time of year the battery "has a poverty". It would be good to help him from time to time, but who wants to set the clock and program the radio. I am asking for a substantive discussion. Without remarks like "go to the electrician" or "replace the alternator", cars were not designed to be stuck in traffic every now and then with those idiotic dipped headlights.

I always charge there like this and nothing bad happens. Because why ?? Of course, provided that the charger turns off itself after charging, or I have it under control. In order not to overdo it with this loading

There is risk involved in charging the battery without disconnecting it.
If the rectifier fails and the secondary voltage rises,
you can damage electronic components in the car.
In addition, the clamps must have perfect contact with the battery posts,
there is no good contact the electrodes will oxidize.
Summary ; maybe nothing will happen and maybe ...

The only problem is exceeding the permissible voltage value

I do not know if the low beam headlights are idiotic (?) But I know that the internal resistance of the battery at low temperatures is relatively high, apart from the degree of wear ... temperature of about -15 degrees), so charging the connected battery to the car's installation is rather not advisable.

This can be remedied by using a voltage stabilizer that will not allow a voltage higher than e.g. 15V, it will protect the electronics from being treated with dangerously high voltage ...

Thanks for your opinions. To sum up, nothing bad should happen, the voltage of 17V is not extreme either, it should be able to withstand all this. So where does the opinion come from that the battery needs to be disconnected? And one more question, the battery is bridged by something when welding the bodywork. What? And why is it supposed to prevent it?

When welding, disconnect the battery in order not to damage the alternator

And who and where forbade you to recharge the battery in the car installation? Of course, recharge consciously, that is, with an efficient rectifier and in the prescribed time. We are talking about adding, which is not a very high current of 2-5 A (although it could also be 10 A). Even a not very sophisticated rectifier should have a fuse that will protect it against overloads, i.e. high currents / voltages. And when it comes to welding (electric of course), you should disconnect not only the battery but also the rest of the installation (mainly the ground). Namely, in the installation, voltage may be induced or deposited on the wires, destroying the vehicle electronics. There are special cases, but we will find out about them too late.

The opinion about the need to disconnect the battery while charging is quite widespread. It is promoted, for example, here: http://www.akumulatory.auto.pl/porady.htm#34 Of course, without further justification. The only justification is to scare the client and the advice "come to our station, we will do what you could do yourself and we will delete it accordingly".
Once, I was in a workshop and a guy welded a hole in the muffler with a semi-automatic machine, but by some miracle he bypassed the battery. By the way, I cannot imagine disconnecting the car installation from the ground. After all, the connection to ground occurs at several points in the body, often e.g. under the upholstery.

Hello. When it falls to me to charge the car battery and the charger is in a metal housing, I put it on a rubber squeegee. Best regards.

Hello, I saw a few times, and then I replaced the burned eberspacher heating controller after welding something in the car, so when welding it is absolutely necessary to disconnect the clamp or fasten the overvoltage protection device to the battery,

The rectifier may fail in the event of an increase in output voltages (partial short circuit of the primary windings, breakdown of the insulation between the primary and secondary turns).
The supply voltage of the 230V rectifier can increase to 400V (failure of the power supply / or home substation if it is three-phase /, ) how much will be at the output instead of 12V ??
The electrolyte can burst the casing, if this occurs in the car, the fluid will cause some damage.
Ford Mondeo after charging in the car, lack of power and uneven speed, damaged controller (or on-board computer), work cost PLN 400.
Mitshubisi space, the wagon did not start after charging; no spark, damaged ignition module (here everything is nicely flooded, no interference)
new, over PLN 3,000, the client bought a used one for several hundred zlotys.
These failures may have arisen as a result of charging the battery in the car, or maybe for another reason, but they occurred right after charging.
The question was about the risk of charging the battery fastened in the car, there are always only failures occurring rarely or after some time.
Besides, is there any point in topping up ??
New batteries have a working time of 2-3 years, then winter comes with frost and we may have a problem.
There are cars in which, after disconnecting the battery: we will not start it (Mercedes eyepiece), visit the service (reportedly PLN 4,000), or later its problems with work.

I think that due to sloppy / damaged battery terminals there may be more problems with electrical / electronics than by charging even with a faulty rectifier, and it is often the case that if someone disconnects the battery, then the terminals do not "connect" as they should.

Well, buddy Robson, what is this "surge protection device"?
And with the possibility of a short circuit in the rectifier windings or a mistake of the installers on the network, it is probably a slight exaggeration. You should also park under a cloud because the garage roof may collapse (and what can't?)
Problems may be when charging with some kind of impulse rectifier or some new invention, but an ordinary rectifier should probably do nothing.

When reading reviews on the subject and many others, you should not touch the vehicle because anything can happen. Dread to think what will happen when the alternator is connected to the circuit. After all, a complete overvoltage may appear similar to that when connecting a rectifier. And if lightning strikes nearby, it's just undoing and exorcisms. And what should the user say, to whom the driver also goes bust while driving? Whom to blame? I repeat that everything should be done wisely and I am not saying that everyone must be able to operate the car to the full extent.

Some time ago I received (for repair) a dozen or so damaged chargers for charging batteries. All from a reputable company and with a certificate. In addition, with the description that you can charge the battery with this charger without removing it from the car without risking damage to the electronics in the car. With such a certain shyness, I looked inside, expecting technology straight from StarTrek. Unfortunately, until today I am disappointed with what I saw . Well, the system is an ordinary comparator on the LM741 + thyristor control system and, of course, the thyristor itself. And the reference voltage system is also included. That's all. So let's not exaggerate with theories about the harmfulness of charging (overcharging) the battery in the car.

And I wonder why this battery should be recharged in general, today's alternators have such power that it is enough for basic receivers even at idle speed [unless someone drives a large Fiat, then you can go ahead and unplug it, because it will not erase anything there] and if the battery does not require it, it means that it's time to replace it no chya that someone drives once a mess, in this case it would be cheaper for him to rent a taxi

In my opinion, it is enough in this topic. It starts off somewhat offtopic
I close

Gentlemen, but in such Scandinavia they have cars connected to the network for the night - there is an engine heater, electric cabin heater and 12V3A charger, temperature sensor, programmer, etc. For a few days I have a decent winter, yesterday and today -20, I have a golf 4 1.9sdi aku 6 years old, lit yesterday without any problem, today I have not tried yet Yesterday I was going to connect the rectifier, but I came back late from the fish on the ice, so I did not want to pull out the battery for the night, and the tin was not heated, so I also gave up leaving the rectifier for the night, and I have such an old Polish to 15A and so I thought whether to connect for the night of 12V chargers, would something help? but the charger manual says that it is intended for 2A-17A batteries and the power is 8W?

stomat wrote:

Is it necessary to disconnect the battery from the car's installation when recharging the battery with a charger? What are the risks of not disconnecting, and why? It is known for short urban routes in this time of year the battery "has a poverty".

If you don't do 300 meters to work, it's no problem.
And I had a lady what Seicento used to commute in winter. Windshield with water blower full, rear window heating. And there was no chance of a top-up. If you have a good rectifier with automation, you can not disconnect it, but the opinion of the rectifier manufacturer is important. How old is it better not to risk, especially if you want to leave it overnight. Because all devices are rated at 12V, and they are calculated at max 16V, after exceeding this voltage, there is no guarantee that they will not be damaged. They tolerate a small excess, but not always greater. So that's the only danger there.

goldwinger wrote:

When welding, disconnect the battery in order not to damage the alternator

I have already seen battery explosions, long ago in the times of ordinary welding machines, that is, in the 70s and 80s. And nowadays. Some electronics, in later times.
Therefore, you need to remove and connect them with the clamps. There are also special devices.

100 times nothing will happen, and once something goes wrong and the electronics have to be replaced. If someone likes that ... his business. Rectifiers are powered from 230V and especially impulse ones are prone to breakdown. If 230 goes to the installation, there is nothing to collect. In my opinion, a question of choice.

Moderated By robokop:

However, I would propose to leave my opinion for myself. And not to sow more heresy writing about things you don't even know the faintest.

waran3 wrote:

If 230 goes to the installation, there is nothing to collect. In my opinion, a question of choice.

Do you know what is galvanic isolation? Show at least one rectifier legally traded that would not hit.