Will running engine stationary charge up battery?

It will charge eventually, but if it is completely flat it will take quite a while. You also run the risk of burning out the alternator, as it will be producing a hefty current, and will have little air flow due to slow fan speed.

Don't believe it.

With poly v drive belts, alternators capable of over 100A, water cooled alternators and smart alternators this current is possible.....believe me.

G

Chris Whelan ( snipped-for-privacy@prejudicentlworld.com) gurgled happily, sounding much like they were saying :

Why? WHY? Why...?

I guess they've not moved to a 42V system yet - that would reduce the current requirements. I believe MB and BMW have done so on the top models.

The message from Chris Whelan contains these words:

My brother had one for a year or so - and flogged it 'cos he didn't like it. Bought a Honda instead.

The message from Adrian contains these words:

Same reason dogs lick their balls. Because they can.

The V10 TDi needs two 70Ah gel batteries connected in parallel just to be able to crank. Other variants have an electrical water heating system. There is an electrically driven compressor for the adaptive suspension, the tailgate close-assist system is electrically driven ... I'm sure you get the picture! The load requirements for vehicles of this type is huge!

The starting price for this range of vehicles is 30k UKP, the V10 starts from about 53k UKP. How many 2CV's would that buy :-)

Chris

Chris Whelan ( snipped-for-privacy@prejudicentlworld.com) gurgled happily, sounding much like they were saying :

Ludicrous. Absolute madness.

53,000...

Yep! Imagine trying to get your friendly local garage to fix it. (Or even your VAG one come to that).

LOL

Doesn't matter what the maximum output is, but putting 90 amps into a battery doesn't make any sense - unless it has some form of temperature sensing built in.

But there's a big difference between voltage and current! The voltage is controlled by the regulators. It should remain constant.

The regulators control the voltage, not the current.

battery doesn't make any sense - unless it has some form of temperature sensing built in.

It is on smart charging ....... the PCM assumes that the intake air temp is similar to the electrolyte temperature, when you look at Battery Electrolyte temperature on live data you are actually looking at IAT. Calcium batteries also accept a higher input charge when cold.

clever eh

Lol - I've got a fuel driven heater!

Constant voltage charging is only used for SLA batteries. Gel types.

Explain how voltage has no relation to current in a battery. The internal resistance of a battery in good condition remains fairly constant - otherwise it wouldn't be able to deliver several hundred amps when starting the engine. So the way the charge current is controlled is by the voltage applied.

The terminal voltage whilst a battery is being charged is nominally 2.2V per cell or 13.2V for a 12V battery. During this charging state you can pump in a whole lot of current and the voltage will stay nominally the same. As you reach full charge so the charging voltage creeps up. If the voltage is limited say to 13.8V then the charging current will start to fall as the battery approaches full charge. If you kept delivering current to the battery the voltage terminal voltage would rise significantly and can go to

17-20V. Apart from blowing bulbs and loss of electrolyte, irreparable damage would be done to a battery.

Therefore for a lead acid battery, a constant voltage source is required with some form of current limiting. An alternator fulfils these things!

Slip rings - commutator - same thing really. Still have brushes which wear out eventually.

I was taught that the reason for being able to run it faster because in an alternator it's not the windings that are rotating. The dynamo was limited in it's rotational speed because the windings tend to separate under centrifugal force.

Steve

[...]

I'm sorry, but that is rubbish! They are not the same thing at all!

A commutator consists of a number of pieces of copper held in place by an insulating material. Centrifugal force is trying to make those pieces fly outwards. (...and sometimes succeeds.) Only the insulator is holding it all together. This seriously limits the maximum rotational speed possible before it all flies apart. I've seen this happen many times on series-wound DC motors that have lost their mechanical load. Because they have no self-regulating characteristics they go runaway. Eventually they fly apart internally. Nine time out of ten, the commutator fails first. I have also seen it happen when the commutator segments have worn down too much. This was a common reason for failure of Lucas car dynamos in the 50's and 60's.

There is almost no way that a slip ring could be damaged by the speed of rotation. It is almost certain that something else would fail first.

Because the segments of a commutator are copper, the brushes used have to be soft to prevent commutator damage. The gaps needed between the segments have a scraping effect on the soft brush. Slip rings are made of a much harder material than commutator segments. Consequently much harder brushes can be used. There are also no gaps on the slip ring to have a scraping action on the brush. The brush wear rate on a like for like basis with a commutator will be much higher that on a set of slip rings.

Chris