Changing battery with alternator running

[Kb27]

...is a no no.

 

If your workshop is still doing this, you are well advised to find another.

 

And the reason is something called "Load Dump"

 

Depending on certain conditions, a high voltage of up to 120V can be sent to your ECU.

If it survived, you're lucky. If it's crippled or dead, oh well..

 

According to wiki:

http://en.wikipedia.org/wiki/Load_dump

 

In automotive electronics, it refers to the disconnection of the vehicle battery from the alternator while the battery is being charged. Due to such a disconnection of the battery, other loads connected to the alternator see a surge in power line. The

peak voltage of this surge may be as high as 120 V and the surge may take up to 400 ms to decay.

[Picanto]

oh, the mech told me if done this way, the radio and clock do not need to be reset. the mech is fong from autosaver

[Tcx607]

Based on the electrical circuitry, there is a bridge rectifier in the alternator still limiting the voltage generated for the car.

If you have a voltage stabilizer, it will help to prevent voltage surge above recommended value.

 

Of course, this is not the correct procedure to change battery while your car engine is running. This is a lazy way and subject to human error i.e short circuit and damage other components. Usually, the mech should use a back up battery and insert in the 12V jacket to support and supply 12V voltage during battery change. It is only a small work but many choose not to follow this procedure. Finally, you are the customer you can decide if you want them to replace the battery.

[Kb27]

Based on the electrical circuitry, there is a bridge rectifier in the alternator still limiting the voltage generated for the car.

If you have a voltage stabilizer, it will help to prevent voltage surge above recommended value.

 

 

Those voltage stabilizer are mostly capacitors. Capacitors do not prevent voltage spikes.

In fact, it get damaged if voltage spikes above their ratings. A 25V rated capacitor will be zapped by 100V and starts leaking.

 

MOVs, varistors are the kind of surge protectors you need, usually found in better grade of PC power supplies and they have to be rated correctly. Whether these are found in your expensive ECU, is a question mark.

 

But yes, a 12V backup battery is the way to do a battery change.

 

Never start an engine, while changing battery.

[Jumpmanz]

yeah. i believe this has been discussed in some battery threads.

even got graphics and engineers inputs

[TVT]

Sorry for to ask a noobie question:

 

What about in the case of removing the battery during a car repair? Meaning the engine is off, after the repair the same battery is put back, and reconnected. Only the radio frequency and clock settings are gone, but nothing else is damage.

 

If changing a new battery couldn't we just off the engine, and change the battery?

[Friendstar]

Guys. anyone know if DACB is doing the correct way? I'm going to use him soon

[Spinelli_ck]

Sorry for to ask a noobie question:

 

What about in the case of removing the battery during a car repair? Meaning the engine is off, after the repair the same battery is put back, and reconnected. Only the radio frequency and clock settings are gone, but nothing else is damage.

 

If changing a new battery couldn't we just off the engine, and change the battery?

 

yes, the engine needs to be off prior to removing the car battery. the battery serves as a voltage stabiliser to protect voltage-sensitive circuits, according to autoshop 101 manual.

[Fcw75]

Yes, this should never be the recommended method. Those workshop that insist in doing it this way, walk away!

 

I asked DACB before and he said he don't use this method.