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Quote: Originally posted by MartyM on 18/6/2008

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You wont get less mpg when the fridge is switched on while driving, the alternator is turning whatever,

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Sorry Marty, not true. The alternator will require more energy to produce more energy. Next time you are are sat in your car in a car park with the engine warm, put the headlights on with the engine on tickover, you should see the revs drop for a second or two before the engine management system increases the tickover to compensate.

I used to love school semolina.

Martin

Well, I expect poor Jenny has lost the will to live by now!

Take my advice, find your nearest Bailey dealer and ring them. They should be able to tell you what to do. It's generally a matter of changing a switch from one setting to another.

Have a nice weekend!

June.

Hi Flossy 12,

Did you try the advice of switching to 12V (Battery Sign) on the Fridge and switching the 12V master on? This works for us in or 2007 Ranger.

Just to add my tuppence worth, it will use more fuel with the fridge on. Probably a very minor amount, and I always have my fridge on for the convenience of it but it will use more fuel.

Incidentally, the analagy of the air con using more fuel isn't a very good one as the main reason the air con uses more fuel is that the belt driven compressor has to run which increases drag and reduces fuel consumption.

Cheers

Chris :)

Quote: Originally posted by MartyM on 18/6/2008

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You wont get less mpg when the fridge is switched on while driving, the alternator is turning whatever,

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Hi,

Sorry don't agree, listen to the engine on tick over and then switch on main beam and screen heaters. the engine note changes as the load on the alternator increases.

You don't get owt for nowt in this life. (Flemings left hand rule or was it Maxwell?)

Mr U-M

found this . . . its about a discharged battery but same principal

The physics of the thing are quite simple. A discharged battery has a lower voltage than a charged one. If or when you get the engine started, the alternator begins to produce electricity (nominally 14.4 volts dc).

The difference between the alternator output and discharged battery voltage could be as much as 10 volts (as a realistic scenario). The alternator is trying to bring the battery up to 14.4v whilst the battery is trying to pull down the alternator voltage to whatever its discharged voltage has fallen to (for argument's sake, 4v because you parked-up and left your lights on all day!).

The net result is that energy (in the form of electricity) is being delivered to the battery, which translates into a high current (amps) to bring the two into balance.

The alternator is an electromechanical device that takes rotational energy from the engine to produce electricity. The more electricity it has to produce, the harder it has to work. The harder the alternator has to work, the greater the rotational energy it needs from the engine to convert into electrical energy. It doesn't take long to recharge a discharged battery that is in otherwise good order.

A steady run of about 15 to 20 minutes would be ample. The initial current might be in the order of 30 to 40amps, but will begin to fall almost immediately as the battery begins to recharge. Eventually, as the battery voltage rises to near that of the alternator, the current will fall to as little as 0.5 to 1amp, (assuming no other load is applied, i.e. wipers, lights, radio etc.) just enough to maintain an OCV (operating circuit voltage) of 13.8v to 14.4v.

This increased energy demand is 'seen' as increased load on the engine, and is compensated for by your right foot!

I used to have half a day to explain this to students, so be aware this is a VERY, VERY, abridged version!!

In reality, the extra load is short lived, and the amount of extra fuel used is neglegable, but if you were to run a set of controlled tests in laboratory conditions you would see a small but measureable increase in fuel consumption.

On a vastly larger scale, we used to use a dynamomter based on an alternator in the order of 100KVA (about 100,000 watts at 240v AC). To test an engine's performance you would, little by little, increase the load, in form of shunt resistors (in effect, big electric heaters!). The more shunts an engine could sustain at a given throttle opening, the greater it's power output, measured in BHP. (brake horse power).

Although, it is much smaller, the same principal applies to your car's alternator - similarly, just turning on your lights will increase your fuel consumption, but again, only by an almost immeasurable amount, but bear in mind, modern car alternators can put out as much as 1.5Kw (1,500 watts) and can account for as much as 3 to 5 BHP load on your engine! - an extreme example perhaps, but in a car with heated seats, heated windscreen, heated rear window, heated mirrors, ABS, quad HID lighting, air conditioning, etc. etc. you can begin to see how power can get gobbled up without your even being aware of it!

Not a definitive, nor an exhaustive explanation, but then I don't have half a day to take you through it!.

Source(s):

Quote: Originally posted by MartyM on 18/6/2008You wont get less mpg when the fridge is switched on while driving, the alternator is turning whatever,

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"Wow - I can't believe this topic has been resurrected after nearly a year!"

It's a good thread though

Thanks for all the detailed explanations as well all. It's easy to assume that the alternator will turn with the same resistance whatever the load but when you remember that it will also act as a large electro-magnetic braking system under heavy load it all makes sense!

Hope the OP found the correct switch position too lol 

Cheers

Chris :)

Quote: Originally posted by Niall24 on 19/6/2009

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Stanley knife anyone?

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