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Author Topic: Why does having the car radio on increase fuel consumption?  (Read 12945 times)

Offline DoctorBeaver

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Offline chris

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Why does having the car radio on increase fuel consumption?
« Reply #1 on: 24/06/2008 19:20:53 »
Switching on the car radio consumes electrical energy, which is provided by the alternator. To make up for the increased consumption by the radio the alternator applies increased drag (load) on the engine. This in turn slows down the engine, so the driver presses the accelerator slightly harder to compensate, thereby burning off more fuel.

To be honest, unless you are powering a 2 kilowatt ICE (in car entertainment) system on par with a nightclub, the average radio will make a negligible difference to engine economy. The air-conditioning, on the other hand, is a different matter entirely.

Chris
 

Offline RD

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Why does having the car radio on increase fuel consumption?
« Reply #2 on: 24/06/2008 20:34:33 »
Listening to the music could affect driving style and consequently fuel economy.

Changing gear at the wrong rpm can reduce fuel economy.
If the music was so loud that you couldn't hear the revs until they were very high,
this could cause you to change up a gear a little too late, which would reduce fuel economy.


[a banging in-car sound-system :) ... http://www.dailymotion.com/video/x3z0d_blaupunkt-pimp-my-ride_ads]
 

Offline DoctorBeaver

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Why does having the car radio on increase fuel consumption?
« Reply #3 on: 24/06/2008 21:42:18 »

To make up for the increased consumption by the radio the alternator applies increased drag (load) on the engine.


How?

The alternator is driven by a belt. No matter how much electrical power is being drawn, that belt is turning the alternator all the time at a speed governed by the engine revs. The only way I can see that it could increase the load on the engine is if the friction increases. I don't believe that is the case.
 

Offline Pumblechook

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Why does having the car radio on increase fuel consumption?
« Reply #4 on: 24/06/2008 22:23:03 »
You think the radio takes no energy to power it???

 

lyner

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Why does having the car radio on increase fuel consumption?
« Reply #5 on: 24/06/2008 22:28:29 »
The engine does work in turning the alternator.  The work done in turning the alternator depends upon the force (or, in this case, torque)  used to turn it times the speed. The torque needed will increase as you take more current from the alternator.  You choose the speed according to how fast you want to go, so taking more current will need more work done (power) and this will require more fuel into the engine to maintain that speed.

When you try to turn the handle of a demonstration dynamo, how can actually feel how much harder you need to push when a couple of bulbs are being lit, compared with the no-load condition.
 

Offline Pumblechook

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Why does having the car radio on increase fuel consumption?
« Reply #6 on: 24/06/2008 22:35:37 »
The extra power required is very small though...around 0.1%.

Think of power stations where alternators have to run at constant speed because the frequency is fixed at 50 or 60 Hz.  A light loaded alternator will need far less energy from its driving turbine than one which is heavily loaded.  Think of a car going uphill at 30 mph compared to one on the flat or going down hill at 30 mph.
 

Offline chris

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Why does having the car radio on increase fuel consumption?
« Reply #7 on: 24/06/2008 22:42:10 »
The best evidence of how this works is to look at the UK grid frequency. When demand is high the load causes the rotors to slow down slightly at the power station, lowering the frequency.

http://www.dynamicdemand.co.uk/grid.htm
 

lyner

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Why does having the car radio on increase fuel consumption?
« Reply #8 on: 24/06/2008 22:48:43 »
The air con takes far more than the radio; it's a significant item.
Also to rear windscreen heater - listen to the note of the engine change, on tickover, when you turn the heater on - that's the energy being used!

Frequency / phase control on the National Grid is a serious issue. They have to 'make up' for lost revs during periods of light load by speeding up a bit. Over a 24hr period, the total number of cycles is kept 'right'. It used to be a real issue when electric clocks were all synchronous motors and relied on the 50Hz standard.
Also, if you want to connect another power generating set to the grid, its frequency and phase have to be matched extremely closely or it can "jump off it's bed" - to quote my Dad, when you throw the switch.
 

Offline RD

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Why does having the car radio on increase fuel consumption?
« Reply #9 on: 24/06/2008 22:56:28 »

To make up for the increased consumption by the radio the alternator applies increased drag (load) on the engine.


How?

The alternator is driven by a belt. No matter how much electrical power is being drawn, that belt is turning the alternator all the time at a speed governed by the engine revs. The only way I can see that it could increase the load on the engine is if the friction increases. I don't believe that is the case.

Increasing the current drawn from a dynamo will increase the magnetic forces of repulsion within it*, increasing the force required to turn the rotor, increasing the load on the engine.  The additional energy consumption would be minute, a 200Watt sound system (full on) would use 1/3rd of a horsepower.

*Lenz law video demonstration ...http://msdaif.googlepages.com/demo_lenz
« Last Edit: 24/06/2008 23:01:51 by RD »
 

Offline DoctorBeaver

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Why does having the car radio on increase fuel consumption?
« Reply #10 on: 24/06/2008 23:04:50 »

To make up for the increased consumption by the radio the alternator applies increased drag (load) on the engine.


How?

The alternator is driven by a belt. No matter how much electrical power is being drawn, that belt is turning the alternator all the time at a speed governed by the engine revs. The only way I can see that it could increase the load on the engine is if the friction increases. I don't believe that is the case.

Increasing the current drawn from a dynamo will increase the magnetic forces of repulsion within it*, increasing the force required to turn the rotor, increasing the load on the engine.  The additional energy consumption would be minute, a 200Watt sound system (full on) would use 1/3rd of a horsepower.

*Lenz law video demonstration ...http://msdaif.googlepages.com/demo_lenz

Now that's what I was after... the reason why. Thank you RD.
 

Offline Pumblechook

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Why does having the car radio on increase fuel consumption?
« Reply #11 on: 24/06/2008 23:11:52 »
I would think the widespread use of video recorders and now PVRs has reduced the 'kettle effect'.   Power stations have to fire up extra generating capacity in time for millions of people putting the kettle on after a popular telly prog. 
 

Offline DoctorBeaver

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Why does having the car radio on increase fuel consumption?
« Reply #12 on: 25/06/2008 07:38:30 »
I would think the widespread use of video recorders and now PVRs has reduced the 'kettle effect'.   Power stations have to fire up extra generating capacity in time for millions of people putting the kettle on after a popular telly prog. 

Wasn't the biggest peak during half time at some football match a while back?
 

Offline Andrew K Fletcher

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Why does having the car radio on increase fuel consumption?
« Reply #13 on: 25/06/2008 11:22:14 »
Depends what station you are listening to. Some are definitely a drag, specially with Terry Wogan at the helm :)

It is interesting though, even having an indicator on if you listen carefully you can hear the engine alternating it's revs in tune with the indicator.

Guess it boils down to the conservation of energy converting increases in magnetic friction from the extra load on the alternator into electricity. When the vehicle is running with out demand say as in a diesel where no spark is required and a manual fuel pump is fitted the alternator would be at rest placing minimum load on the engine. Add the radio to cause the alternator to begin returning electricity to charge the battery rather than just covering the small amount of power for the radio but the radio provides the stimulus for the recharging of the battery and we have sufficient drag to cause a noticeable drop in revs. So although we associate the radio with the change in engine pitch, the radio serves to cause the alternator to recharge the battery also?
 

Offline Alan McDougall

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Why does having the car radio on increase fuel consumption?
« Reply #14 on: 25/06/2008 20:29:53 »
Yes it does but so minutely that it really does not matter. Your fuel consumption would increase by about one ounce in 10 000 kilometres

Alan
 

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Why does having the car radio on increase fuel consumption?
« Reply #14 on: 25/06/2008 20:29:53 »

 

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