Do you put the heater on in the car?

Strider590

adouglasmhor wrote: »

The voltage may not change but the current can.

I didnt mention a load, you can't have current flow without a load.

But yes, of course under load a higher RPM will give a greater load capacity. I think I mentioned that wayyyyy back somewhere.

johnnyroper

Strider590 wrote: »

I wrote a huge reply, the forum went tits up and now I really can't be arsed.....

Alternator runs at the same speed as the engine, for example it produces a potential 30A @ 12v @ 2000rpm and maybe 70A @ 12v @ 8000rpm... The faster the engine speed the greater that potential (up to it's maximum output), the only time you'd have a problem is if you overload the alternator at any given RPM, in which case there may be a magnetic flux produced that could place a small load on the engine.... However!!! the auxileries belt and the cam belt are not meant to withstand additional or abnormal mechanical loads to the sort of extent to which you (and im not sure who has the opinion V who's jumping on the band wagon) seem to infer. If this was the case, we would have auxiliaries chains and not belts.

As soon as you increase RPM the alternator is capable of more current and any overload problem disappears. So moving back to topic, under normal driving conditions you won't increase fuel consumption by switching on your lights, your heater, or pretty much anything for that matter and EVEN if you did, the battery would compensate for that additional electrical load before any problem was encountered.
The very reason (or one of) that manufacturer's are moving over to electrically driven PAS and Aircon etc etc is because doing so removes the additional mechanical load these used to place on the engine.

As for people talking about ECU's compensating for this that and the other, it's just not a valid point..... Nothing has changed since way before anyone had ever heard of ECU's. You have always had that slight judder from the engine when turning on electrical elements of the car. The reason being "inrush current" where electrical devices briefly draw abnormal amounts of current when first turned on.

gave up reading after first sentence because if that is wrong i dare say the rest is,alternator does not run same speed as engine pulley on crank is far bigger than alt so alt is driven at approx 3-4 times engine rpm.
please only post if you have an idea what you are talking about.
more electrical load put on will increase fuel use as alt works harder fact.as i said earlier fuel use minimal and barely noticeable when using heater but still slight increase non the less.

hueknight1969

Stop feeding the troll !!!!!!!!!!!!!

pwllbwdr

Strider - you do know that at a given RPM the effort required to turn an alternator (and hence the power it takes from the engine) depends totally on the electrical load on the system don't you? The effort required to turn an alternator at low load is not big, but when the coils are energised (when the system detects high load) the drag is much more. RPM on its own is not a way of judging how much effort an alternator needs to be turned.

molerat

Strider590 wrote: »

Alternator and generator are two subtly different things.

What is an ac generator then ?

optimus_primera

All i know is that the higher the load on a genset, the faster the engine turns.

Zanzibar

"The alternator does not place any addition mechanical load on the engine, no matter how much electrical power you use."

It does. The alternator shaft is harder to turn under increasing loading due to the magnetic field interaction between the rotor and stator.

"To suggest that the alternator somehow applies an additional mechanical force when you use more power, is totally illogical"

Only to the terminally daft.

"The alternator does not directly place an addition mechanical load on the engine dependant on power usage.... It just DOESNT."

Yawn, yes, it does. That is EXACTLY why extra electrical load DOES increase fuel consumption.

"The change in engine tone is down to the dip in voltage when you switch on a device, it the same way that turning on your kettle causes the lights in the house to dim for a split second."

Good gravy. The sound is the engine revs changing in reaction to the higher alternator loading on it. Go LOOK at the RPM change when you turn say the rear heater on at idle. Go on - do it now - go to your van and DO IT. EDUCATE yourself. It has nothing to do with kettles.

"The alternator over produces electricity, this electricity is used to recharge charge the battery, but once that is fully charged the electricity being produced simply goes to waste."

The alternator powers car electrics and charges the battery. Its output is regulated with reference to load - its not constantly at full power output - it does not 'over produce' anything. The battery is only used to start the car, excite the alternator and as a supply during transient power load events and... why am I even bothering?

"..... But you seem to be suggesting that the alternator physically grabs the engine and slows it down. Which is utter non-sense."

Except that's exactly what it does. As electrical load on an alternator increases so does the torque required to turn it - is this Groundhog Day or has this been mentioned before...


You have a fundamental misunderstanding of automotive electrics. Get a book on it and read it as I'm not sure if anyone could demonstrate less knowledge on a subject. Stating people are sheep for quoting fact is classic.


Baahhh.

lozzaman

optimus_primera wrote: »

All i know is that the higher the load on a genset, the faster the engine turns.

This isn't true either, otherwise the AC frequency changes. The engine is working harder though - it will need to generate more torque.
Petrol generators will often sit at 3000rpm, Diesel at 1500rpm.