Do you put the heater on in the car?

lozzaman

johnnyroper wrote: »

what a load of bo11ox as more demand is placed on alternator to service electrical loads like heaters etc then the engine load is also increased.
why do you think the idle speed is affected the more electrical loads are switched on?

As has been stated here, the load increases on the engine and the ECU compensates. This is why the revs briefly decrease when a high load is applied (and increase when the load is removed)
This is more notable on a small boat diesel with some rather larger loads (inverter) powered by dual 165 amp alternators.
The car heater doesn't draw much at all as it uses waste engine heat, so the fan on hot or cold (with AC off) will draw the same amount of power.
The AC costs money but it's not an electrical load, rather an additional mechanical load on the compressor.

lozzaman

An alternator is just like an electric motor, except there's a mechanical input rather than output. Stryder seems to be suggesting that an electric motor wouldn't use more power to spin at the same speed when more load is applied to it either.

Strider590

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.

lozzaman

Yes, the forum was playing up earlier. Very, very slow.
While it is true the amount of current the alternator can produce increases with load, you seem to be inferring that with zero load (not possible in practice) or a full 70AMP load the engine load is the same? I'm going to build some rig with thousands of 70 amp alternators on as it's free electricity.

Most alternators are producing full output by the time the engine is up to around 2000rpm. No one drives at 8000rpm for any extended period.

lozzaman

Why is the engine tone changing with load on this?
http://www.youtube.com/watch?v=THShu7X9pbY

OK, so it's not a car engine but something is changing within the alternator to cause the engine speed to change.

Strider590

^^ bat voltage dropping below 13v = overload conditions, because the alt should be able to hold at around 13.8+

Once you start dipping into the battery, your asking for problems. This is something I covered in my last post

lozzaman

The battery voltage is dipping because the load on it is higher than the input from the alternator. The alternator is becoming loaded, thus slowing down the engine.
Or do you have another explanation?

True, you could fit a governor to the engine to keep the speed of the alternator up to stop it from slowing down (within reason) but the fact that the throttle has to be adjusted to compensate is indicative of the fact the load is higher.

The energy has to come from somewhere. Generators use more fuel at full load than idle, as one would expect.

Strider590

But this was my point..... Normally you'd not overload the alternator and thus this whole topic of using more fuel is null and void.

lozzaman

Even a 1 watt increase is an increase in engine load. The generators in the link I gave are not being overloaded and yet they are using more fuel with increased load. The engines will be governed in speed to keep the mains frequency constant, so what's causing them to use more fuel under load?

jackieb

Mark_Hewitt wrote: »

You usually don't need the fan on for heating either, certainly in my car you can have the fans set to off and the air will still come through the vents, just blown by the motion of air through the engine, so you don't really notice unless you're on the motorway.

In any case, having the heater on is completely insignificant, so much so it can be regarded as zero cost. Without the heater you're much more likely to be cold and not concentrating and have a crash! Which would cost much more than the 2p's worth of petrol per year it costs to run.

I usually have my heater on but if i'm driving very early in the morning (I sometimes have to leave at 4.30am and drive for 2 hours) I tend to have it turned off so I don't get sleepy. Too warm can be a danger too. If the side windows begin to mist up I just blast the blower on - it takes seconds to clear. My parents car however mists up all the time if it's cold outside, even with their heater on.