Does air con really eat your fuel?

skiddlydiddly

The electricity generated isn't "free" but its produced in excess of what is used the majority of the time, as we don't drive around using every electrical option on the car 100% of the time.This means that some of electricity is wasted, these electric air con motors are just using that normally wasted electricity by the sounds of it.

Also, comparing current draw on an engine that is idling is producing far less power than one with load on it so its not really a good comparison.

I'm no mechanic/electrician but it seems common sense to me.

retrocircles

I have a 1.2 Chevrolet Kalos & I have less power using air con, as in it's slower off the mark.

Probably just because it's a 1.2... you probably wouldn't notice it in a more powerful car.

johnnyroper

Strider590 wrote: »

The rear electric window is different kettle of fish, they draw nearly 20 amps current!!! that's more than 240watts when the engine is running (battery voltage 13.8volts)!!
Short of the starter motor itself, the rear demister is probably the most high power device in any car and should never be left turned on for extended periods.
The reason that makes a difference is because your pushing the output capacity of the alternator, therefore having a negative effect on coil/spark voltage....

I simple low friction DC pump will use hardly any current at all!! and if you convert that DC into say 30v AC, to run a small AC motor (as in an EPAS unit), you can supply well in excess of 100 AC amps with no negative effects.

I must point out that I was the lead technical engineer on 2 EPAS projects in my previous employment........

Belt driven equipment is being driven by the crankshaft or camshaft, if you drove the wheels directly from the crankshaft they'd spin extremely quickly but you'd have practically no torque whatsoever.
Anything attached to this point is going to sap engine power and therefore efficiency will suffer....

i disagree,if it was a simple as you make out why do the major car makers persist with belt driven set up and not go to the "super efficient electric motor" you describe.
not a car i know but an example of an electric set up,on a train the air con is driven by electric motor but to achieve this they do not use the 24volt battery supply there is a seperate alternator either mechanically driven off engine or hydraulic motor.the alternator puts out 3 phase 480vac.on older stuff the compressor is driven by hydraulic motor and trust me whatever system is used it puts a big load on 350-400hp diesel engines even under power at speed you can notice the compressors kicking in.
so to run electric motor capable of driving A/C compressor off 12 volt supply is going to put load on the engine equal if not more so than a belt driven type.

Gloomendoom

skiddlydiddly wrote: »

The electricity generated isn't "free" but its produced in excess of what is used the majority of the time, as we don't drive around using every electrical option on the car 100% of the time.This means that some of electricity is wasted, these electric air con motors are just using that normally wasted electricity by the sounds of it.

OK, assuming that laws of physics, as we currently understand them, are correct, they dictate that energy can be neither created nor destroyed, only converted. So, in that case, where does this wasted electricity go when it's not being used to power the air con?

ariba10

You get nothing for nothing.

A generator not producing power needs a lot less effort to turn it than one that has a high demand.

Some people think that the same amount of effort is needed to turn the generator, no matter what the demand is.

Gloomendoom

Eggszackerly... which is why the engine revs drop when you turn on the heated rear window.

On a cold day I could stall my old Metro just by turning on the HRW.

bryanb

skiddlydiddly wrote: »

The electricity generated isn't "free" but its produced in excess of what is used the majority of the time, as we don't drive around using every electrical option on the car 100% of the time.This means that some of electricity is wasted, these electric air con motors are just using that normally wasted electricity by the sounds of it.

Also, comparing current draw on an engine that is idling is producing far less power than one with load on it so its not really a good comparison.

I'm no mechanic/electrician but it seems common sense to me.

So you don't know how an alternator works either!

ariba10

There was a thread on here a couple of days ago about keeping cool in the warm weather and one suggestion was to use a dehumidifier.

The assumption being I should imagine, that as it has a cooling circuit, it would cool the room.

Ignoring the fact that the heat generated would far outweigh any cooling produced.

skiddlydiddly

Gloomendoom wrote: »

OK, assuming that laws of physics, as we currently understand them, are correct, they dictate that energy can be neither created nor destroyed, only converted. So, in that case, where does this wasted electricity go when it's not being used to power the air con?

Charging the battery and heat.Thats my best guesstimate.

As all alternators I have seen are clutchless,once the engine is running they're constantly generating electricity regardless of whether its used or not, so its inevitable there will at times be surplus energy to requirement.

Like I said, I'm no expert in this but this is the best way I can explain my thoughts.

As there already seems to be a (claimed) expert on this matter in the thread, I'm sure he/she can explain it much better than myself .

ariba10

They may be turning but not necessarily producing electricity.