effect of electrical loads on mpg - Fuelly Forums

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Old 09-20-2006, 06:26 PM   #1
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effect of electrical loads on mpg

Does anybody know how much electricity affects mpg. Like blasting the radio, rear window heater, high beams, fan... has on mpg.

I no alternator had a 10% advantage thanks to metro

http://www.gassavers.org/showthread....ght=alternator

But I would like to know the affect of more normal use vs. high eletrical use.
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Old 09-20-2006, 06:48 PM   #2
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Quote:
Originally Posted by kickflipjr
Does anybody know how much electricity affects mpg.
Yes. Follow the links in this thread:
http://www.gassavers.org/showthread.php?t=1798

BTW: Because an alternator is just an electrical generator (converting mechanical energy into electricity), and all such generators need to put more drag on their power source (in this case the car's engine) when you have a larger load, you will save gas by using less electrical power in the car, even if you leave the stock alternator in! And if you are planning to remove the alternator completely, you also benefit (in terms of more range) by also getting the electrical load down. So getting the electrical systems in your car more efficient is helpful in any event...
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Old 09-22-2006, 07:20 AM   #3
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A typical alternator can put out about 80 amps, but I'd guess that the average is probably more like 40 amps. 40 amps x 12 volts = 480 watts output.

Belt drives, alternators & rectifiers are inefficient, say 60% total efficiency, so this bumps engine drag to about 800 watts, a little over 1 horsepower. This may not seem like a lot in a 100 HP engine, but auto engines rarely use all their power. Road HP on a level road might be 20 HP.

I'd guess that eliminating the alternator might improve mileage by about 5%.
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Old 09-22-2006, 08:52 AM   #4
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I'm sure my stereo is hurting my FE some. I wonder how much though?

I have just one 12" sub with a 400watt amp. But if I bump while the car is idleing the RPMs drop with loud bass hits. lol
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Old 09-22-2006, 10:43 AM   #5
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That sounds about right! But the 5% if you are running at 20hp . . . if you are running at 10HP then it is a 10% hit but chances are you don't have a 40 amp load for very long unless you have all the lights on and are holding down the brake with the A/C Blower on full and the wipers running.
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Old 09-22-2006, 03:36 PM   #6
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this is why I like stock... and i need to convert my brake lights to LED -_-

also this is why i never use my accessories... maybe the defrogger once in a while to keep the A/C lubed up.
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Old 09-25-2006, 03:05 AM   #7
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In my metro I have the stock radio and no rear window defroster. I use rainx on the windshield so I rarely need to use the windshield wipers. Since my car is a 1994 US model it does not have daytime running lights. I am guessing that my biggest electrical load is headlights when driving at night and the starter which I use frequently because of engine off coasting. 3Tech makes an aftermarket pully for Geo Metros that is 25% smaller than the stock pully that drives the alternator and water pump. That results in fewer turns of the alternator (and the water pump). Do you think there is any FE advantage to that? It seems to me that in the end it will take just as much energy to charge the battery it will just be extracted over a longer period of time. Would there be any disadvantages? Do they make LED headlights yet?
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Old 09-25-2006, 06:07 AM   #8
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The metro engine turns slow enough with its tall gearing as it is and any lower rpm will result in not charging at idle and yeah you are right it takes the same power from the engine to generate the output and actually will be a little more efficient at a higher RPM because it will require less field current to generate the required power.
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Old 09-28-2006, 08:54 PM   #9
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Quote:
Originally Posted by philmcneal
this is why I like stock... and i need to convert my brake lights to LED -_-

also this is why i never use my accessories... maybe the defrogger once in a while to keep the A/C lubed up.
I see you're in BC... When I see people saying how easy it is not to use the A/C, invariably they aren't in SE Texas.... Here if you don't use your AC, then you show up to work drenched in sweat. It isn't merely comfort, it's a requirement unless you work at a gym where being drenched is OK. Going without AC in a Texas Summer is like going without heat in a North Dakota Winter - nearly suicidal.

As far as the electrical loads... I believe that the biggest loads are two things, lights and fans(AC/Heat). Lights you cannot avoid, as you'd be blind at night without them! AC/Heat, you can avoid climate permitting. Heavilly amped stereo systems may very well put a huge load as has been pointed out too, but honestly, I don't see how anyone needs thousands of watts. I like a little more than stock, but that's it.
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Old 09-29-2006, 05:59 PM   #10
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when your on your brakes your not on the throttle anyway.....the gas saved from lowering the electrical load from the brake lights is completely nill. the running lights are a different story though.
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