yes or no

[Rustinho]

I dunno how true it is but when I was a kid I was told by my dad not to charge a battery still wired into the vehicle cos it can damage the alternator. I've never really thought about it to consider why it could do this. I've just always kinda gone with it out of habit cos of what my dad told me all those years ago.

[Voodoo-Child]

That must be where I got it from...My old man used to be AA patrol, back when the AA was the fine establishment we learnt to trust, not the shambles it is now. Also.....connecting a car up to another car vis jump leads can also cause late model vehicles to lose infromation in ecu's etc....wheres the damping effect of the dead battery when this happens?

[yoshie]

Comfy chair found, continue please.

[Apache]

Really cant think how it could.

Here's a rather small load dump waveform. (The transient seen when a large load such as a bank of spotlights on your roof bar is suddenly switched off - and your battery is disconnected so the transient isn't absorbed by the capacitive effect of the battery)



This is only just over 70V and the energy is only significant for about 25uS. The most common commercial automotive standard 2004/104EC, and Def-Stan 61-5 call for 174V for a longer duration, and vehicle electronics MUST survive that to be marketed in Europe.

Modern vehicle electronics are tougher than you think!

(I did destroy a gearbox ECU and blow all the headlamps on a Mastiff with the load dump test, but that's 'merkin )

Re. AA - I wouldn't trust them, or the RAC within a few miles of automotive electronics. It's a very complex subject. They aren't (and shouldn't be) specialist enough.

[Voodoo-Child]

I see your complicated post and raise you a packet of 10 amp fuses....you must be right......cos I dont understand....!

[Apache]

'tis what I do for a living. Fix what the designers of auto electronics get wrong before it goes to market.

You weren't to know

[Voodoo-Child]

pmsl

[Rustinho]

Electronics has always been my Achilles heel!

I presume that an alternator will have something like a diode to prevent current flowing into it while charging the battery? The only thing I can think of that might conceivably cause damage would be the coils of wire in the alternator doing something (good old Flemings left & right hand rules fighting it out?!).

It's too late at night for me to think too deeply about it! lol

[Apache]

I presume that an alternator will have something like a diode to prevent current flowing into it while charging the battery?

Your presumption is correct. An alternator produces AC, so the output is rectified by the diode(s) you mention. The alternator is connected to the 12V from the battery, so fact that it sees the ~14.4V from the charger matters not.

Fleming uses his right hand rule mainly - he just uses his left hand rule when he wants it to feel like someone else.

[Voodoo-Child]

hahaha ...I have to sit on mine for that

[Rustinho]

Your presumption is correct. An alternator produces AC, so the output is rectified by the diode(s) you mention. The alternator is connected to the 12V from the battery, so fact that it sees the ~14.4V from the charger matters not.

Fleming uses his right hand rule mainly - he just uses his left hand rule when he wants it to feel like someone else.

Cheers for that Mr A. I knew there was a reasonable explanation for it that I just couldn't quite put my finger on. It's bl00dy awful when I have a smart kid in the class running rings around me on stuff like this! lol

[Voodoo-Child]

Cheers for that Mr A. I knew there was a reasonable explanation for it that I just couldn't quite put my finger on. It's bl00dy awful when I have a smart kid in the class running rings around me on stuff like this! lol

That happens to me when I go to get the kids from school....they're all smarter than me in there!! haha

[flounderbout]

That happens to me when I go to get the kids from school....they're all smarter than me in there!! haha

This is becoming increasingly obvious.

[Voodoo-Child]

Clever people say clever stuff all of the time...no-one expects any less from them....Stupid people say stupid stuff....but when they say something profound/intelligent....it's a revelation. I'm waiting for my lightbulb moment......

[TonyN]

...... I'm waiting for my lightbulb moment......

No one's turned you on yet?