How to Become a Hypermiler

Step 4 Reduce Driving Loads

That is, load placed on your engine. Avoid using the following

• Air Conditioning
• Defrosters
• Loud Sound Systems
• Headlights (that means, try driving in the day rather than at night)



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You can't get something from nothing. The greater the load you put on your alternator - the harder your engine has to work to turn it. As a corollary, the more amperage you put into a motor, the greater the torque it will provide...

Comments

[jimmytvf]

I don't agree with the alternator feature. the alternator loads the battery, and doesn't need more power to drive all the electric features, the battery does the job as well. Yes, the faster the alternator goes, the more power generate, and goes to the battery.

[trebuchet03]

Generally speaking - the battery is only used while starting. Alternator output will match the load requirement from all electronics from the car. The alternator is capable of delivering more power at a higher RPM but will not deliver if the load does not exist.

A battery is not an infinite sink of energy storage. You can't add more energy to a "full" battery without damage. Grab an ammeter and measure yourself (I would recommend a clamp on inductive type rather than a shunt ammeter as the current flow during starting will be very high).

If you have the opportunity, I highly recommend auditing an introductory course on electrical engineering at a local university. Particularly lessons on Kirchhoff's Circuit Laws (loops and whatnot). I was Mech engineering but really loved the electrical engineering bits :)

[sthomas28]

trebuchet03 I'm just getting on the scene here, doing some research. I'm giving a lot of weight to your comments. You seem to know your stuff. It looks like you and another poster were speaking around each other. I think the other poster has it mixed up a bit, in that an alternator and typical electric generator/electric motor work a bit differently. Specifically where "Magnets" are concerned. Please correct me if I'm wrong.

If I'm correct, as are you, the increased spinning of the alternator will not increase output. It's not the input spinning that's the factor but the load placed on the alternator. The alternator will meet the load without an increase in the input rotation.

Again, please correct me if I'm wrong. Do know if you'll see this but if you do I'd appreciate your response.

[jimmytvf]

they have some voltage regulators inside that keeps a constant voltage no more than 14v

[jimmytvf]

that's what i wanted to say, when the battery is full, it have enough power to run any electric device you want, and doesn't mean any fuel consumption, because the alternator is always running. I'm spanish and i don't even know to express myself in some ways, and i'm a automotive technician and we learn Kirchoff's law too. Have to take a look, because i have some aspects that i don't remember, 3 years have been passed since that

[trebuchet03]

You're somewhat familiar, excellente! If we were to represent the vehicle loads (computers, lights, valves, etc.) as one single load for simplicity - we could draw the circuit diagram with three components in parallel. Those components are the alternator, the vehicle loads and the battery.

The alternator is source, the battery can be represented as a capacitor as it is near full and the loads can, for simplicity be represented as a resistor (lets not mess with inductance).

Before the car is started, the battery is around 12.5V

When the vehicle is started, current flows from the battery through the loads and bypasses the current source.

Next, the alternator takes over. The voltage off the alternator is higher than the battery (13.8-14.5V or so). Current flows into the load. Because the alternator's voltage is higher than the battery, current can also flow into the battery. As the battery voltage increases (as it will for this chemistry), current slows down until the voltage equalizes and current can not flow. This is why we can represent the battery as a capacitor. When a capacitor is fully charged, it is effectively an open circuit.

From this point on, current flows from the alternator to the load and bypasses the battery (as it is "open").

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Now, an 80amp rated alternator does not always put out 80A. If the load only calls for 10A, the alternator only puts out 10A. We can not have this equation out of balance (energy in must equal energy out + entropy losses). Simply, the current that goes in must be consumed. When the car demands more current, the alternator supplies it and in turn the alternator requires more torque from the engine to turn.

More torque means more fuel consumption. With an instantaneous fuel gauge, this can easily be seen be comparing idle fuel consumption with little electrical load to fuel consumption with as much load as possible (high beams, defroster, vent fan without a/c, brake lights, hazard lights, power windows in motion, etc.)

[jimmytvf]

The amperes become through the resistance of the material (more loops on the alternator), doesn't mean more torque. The engine has the same torque all the time (crankshaft, camshaft, and so on) are spinning with a minimum torque when it starts, the torque is only needed for the wheels to keep on the ground, excessive torque=wheelspining you don't want an alternator do this.

http://automecanico.com/auto2002/alter4.jpg

alternators work like engines, there's minimum friction, only for + and - contacts ( they have to spin to connect the wires obviously)

NOW, what you want to do, is turn, for example, water pump, fuel pump, the engine fan and so on, running electric, that will be less load on the engine and the alternator is capable enough to run all this elements, is designed for this use, A/C, the stereo, airbag control system, fuel injection... everithing is going with current nowadays and brands desing better alternators to handle up this loads. (Toyota prius, for instance, nuff power to pull out their own motors that are the alternators itselves)

[sdfgeoff]

I went driving one day in an older, low powered car. We were towing a caravan, and the car was jjuusstt coping with slight ups and downs. Then, when it got hot (we had started in the cool morning), we turned on the air-con.
Yup, aircon does make a difference. Now we could only tow it on the downhill, and acceleration was pitiful.

The load on the alternator does effect the strain on the engine.


And, if you want to prove it to yourself, grab a cheap DC motor. Spin it, see how easy it turns? Now solder a wire across the two contacts (shorting them). Now it is a lot harder to turn. The wire simulates a huge load, like what radios and air conditioning will place on a cars alternator.

[swander]

you wanna get off the alternator entirely? Just disconnect it. Youll run off the battery for at least 30 minutes and you can just recharge it when you get home. Saves gas but not your battery or your electric bill. A/C Use is also somewhat of a myth as many cars use the A/C system to recirculate cabin air. Even when the car is not using the A/C to cool, its still running. I did a test on my cars mileage computer going to work one day (40 miles RT) with A/C cooling and then no A/C cooling. Same exact mileage. You really want to reduce drag on a motor? use an electric water pump. The water pump is like a mini dyno, the faster the car motor revs, the more power is required to turn the water pump.

[aLLoU]

Is the engine shown in the step 4 from an AE86???

[Outlander]

1). Additional electronic devices NO NOT use more horsepower or electricity. The alternator(the device that supplies power while the engine is one) is on all the time, it can not be switched off and it does not require more effort to draw more power. The magnets inside do NOT increase in polarity. I would love to know who made this myth up about elec. devices using more power. They cause more heat build up and if you draw more power than the alternator can supply or over tax it, it will fail in time, BUT IT DOES NOT TAKE MORE HORSEPOWER AND OR FUEL! An A/C system does(when it is on) because it is switchable and not on all the time, but an alternator is on ALL THE TIME, turning on headlights does not take more fuel economy away. 2).Same thing with defroster wires in the rear window, electronic device, no economy loss. Front defrosters(defogers) on some cars turn on the A/C unit and this can consume horsepower to turn the A/C unit, but this is not on all cars, some cars supply heat from the heater core to defrost/defog the front windshield.

[trebuchet03]

The alternator(the device that supplies power while the engine is one) is on all the time, it can not be switched off and it does not require more effort to draw more power.

On the contrary, the higher the load placed on any generator, the greater torque required to turn it.

The next time you get a chance to - put a load on an alternator that hasn't been installed and then try to spin it... You'll feel a bit of resistance. Then, increase that load - and you'll feel even more resistance. It's not voodoo, it's classical physics (which, in some cases, appears to be voodoo :p). This same experiment can be done on just about any motor ;)

An analogous example would be to say that when you're walking, it doesn't matter how much weight you carry - you're walking anyway and you're not stopping. Anyone that has ever moved house or carried "stuff" can say that walking can be severely restricted when you put a high load on yourself (stuff).

[crickle321]

What would you say the minimum RPM for an alternator test? I have two set aside for the windmill instructable and I have yet to get them a charge. Any advice would be appreciated, Thanks!

[martyjr9]

i beleive an alternator needs 1800 rpm to output full amp rating

[scob89]

At least 300 RPM for all alternators would be a good bet. When a car is at idle it still has to charge the battery so it does not go dead by just idling and the lowest I have seen a car idle at(Not a hybrid) is 200RPM.

[Outlander]

Also note, once the device is energized, this is going to be the total amount of resistance you will feel. Even without a voltmeter, you will know, the alternator(not a generator) will give a tug and it will be harder to turn, this is what the other guy doesn't seem to understand that once the device is spinning and energized, that is the total amount of resistance, or force you will feel, it will increase as RPM goes up(force required to turn it, hence the parasitic drag), but NOT when an additional load is placed upon it. If it is energized and spinning at say 500RPM and producing 14 volts and 30 amps(around 420 watts), then that is all you get, any additional load will heat up the regulator inside the alternator and it will fail. The alternator will need to be spun faster say around 3000 RPM to produce it's maximum output, usually around 100amps. I didn't get my ASE certs for nothing :P

[Outlander]

if you hook a volt meter up to the alternator then doing something as simple as turning the alternator by hand will give you voltage you wont get any kind of current, but you should at the very least see a few volts to around 14 volts. Most modern day alternators need to have at least 12V supplied to them(the alternator shuts off at below 12V to prevent damage to the electrical system of a car) in order for them to be energized and the ignition terminal on, or shorted for it to even start supplying it's own current, without it the alternator just sits there.

You probably want to find an old generator/alternator, the kind without a built in regulator and only has 1 wire, like on older 1960's chevy's and ford's, that way there is no sensing wire or regulator and it should always be supplying power. Here's a good article for you to read as I'm probably a bit rusty on the subject. http://www.autoshop101.com/trainmodules/alternator/alt101.html

As far as a minimum RPM, there really is none, the faster you turn it, the more power you get, to a point that is.

[static]

But there is a minimum RPM. where the alternator, will start producing the power desired, if I'm allowed to state the obvious. :). For a particular automotive alternator refer to a service manual for a vehicle in which is installed. You should be instructed at what engine speed the charging system tests are to be made with. Armed with that figure, measure pulley sizes to calculate the RPM of the alternator.

[trebuchet03]

Here's a good article for you to read as I'm probably a bit rusty on the subject. http://www.autoshop101.com/trainmodules/alternator/alt101.html''

Interesting link in that it states this...
When charging system voltage falls below this point, the regulator will increase the field current, thus strengthening the magnetic field, which results in an increase of alternator output.

Since voltage is directly and proportionally related to current via ohm's law (V=IR) AND voltage is nominally constant (as a result of stator regulation) - the above is very accurate. Alternator output is generally measured in watts (suitable since a watt is a unit of power) - and to find watts, multiply current by voltage. Voltage, again, is nominally constant. Current must increase in order to increase the aforementioned output. At least, this is a top down (backwards) explanation (trying to attempt an explanation from another angle). <-- as a side note, this is the reason why you can diagnose some alternator issues with a voltmeter and a static/dynamic load. It's also the same reason why batteries shouldn't be tested without a load (it just doesn't tell you much other than it's ability to hold a surface charge).

This can be observed with an ammeter (not a voltmeter) - I highly recommend you give this a shot - just make sure you have an ammeter with a high enough current rating (most cheapo one's have a 10A fuse).

Alternatively, you can look at someone else's measurements (but I still recommend you do the same test to see for yourself). See Here specifically, this chart...
Item...................@ 14.4v

Idling ............... 128w
Rev up to 3500 rpm: .. +35w
Heater fan setting 1: . 55w
.. Setting 2: ......... 98w
.. Setting 3: ........ 141w
.. Setting 4: ........ 189w
Marker lights: ........ 95w
Full lights: ......... 240w
A/C (heater fan
subtracted, but
incl. condenser fan):. 163w
Defroster: ........... 104w
Wipers 1: ............. 48w
Wipers 2: ............. 76w
Radiator fan: ........ 144w

As far as a minimum RPM, there really is none, the faster you turn it, the more power you get, to a point that is.
The diode bridges will have a minimum breakdown voltage that you'll need to overcome before you'll start seeing any output ;) This will vary by design, of course.

[jimmytvf]

you aren't running all this stuff all the time! If you do, i thing will before burn your electric installation for the amperage of this stuff running lol

[trebuchet03]

guy doesn't seem to understand that once the device is spinning and energized, that is the total amount of resistance, or force you will feel, it will increase as RPM goes up(force required to turn it, hence the parasitic drag), but NOT when an additional load is placed upon it.

This is false, please this is fundamental physics - the type that used to be taught in high school. Power generating devices (alternator, generator, etc.) can not put out more current than is being drawn - it needs somewhere to go, this flow is called current - something that is measured with an ammeter, not a volt meter. The torque resistance will be related to the current flowing, not voltage.

I didn't get my ASE certs for nothing

If we're going to throw around pieces of paper.... I didn't get the degree in engineering for nothing either ;) I'm just glad it was paid on scholarship :D

[Outlander]

This is not true, why are you rejecting every truth? You don't know how generators work do you? The load does NOT increase. It is simply a myth. The amount of power you get from an alternator is dependent on the amount of winds in the coils and the amount of magnets. You are simply pushing electrons through the coils to generate power. Electrons have NO mass, and there is NO increase in resistance from the alternator from magnetic force(the magnets spinning by the coils)Heat is generated(from the VRM and RPM of the spin), not resistance. Why do you think a typical V8 can produce an "estimated" for example 150KW(4.6L ford) of power if it was a generator. The little 1 to 2KW(at 12V) alternator does not produce much resistance at all and resistance does not increase with load, once the alt is spinning and producing power, that is all the resistance you get. Lets talk this over on a forum or something since this does not seem to be the place for a heated discussion.

[Joenavy85]

look up counter electromotive force, that will explain it to you. i know this is late but hopefully you will read it and it will help you understand. when the electricity (that is generated) flows through the coils it creates a magnetic field, this counteracts the permanent magnet's field and causes drag, the more current drawn through(the greater the load) the greater the field strength and the greater drag. i didn't get a bachelors in mechanical engineering and in electrical engineering by the age of 24 by being dumb, so just take my word for it and look it up.

[theRIAA]

electrons have no mass.. what?

[Ritsuki]

I think you may be confused as to what the author of this article is referring to. He means that the more electrical load you put on your electrical system, such as electric defrosters (where there is a grid of wires on the back window that heat up), the more load there is on the alternator. The alternator, while it is on all the time, isn't always putting out 70A or whatever it's rated for, since there isn't anything using all that available power. If you were to hook up an ammeter between the alternator and the rest of the electrical system, you would see the load increase when you turn your headlights or defroster or other electrical load on. The alternator's purpose is to maintain the charge in the battery, and to power accessories. If you don't have anything electric turned on in your car, and the engine is running, all the alternator has to do is keep the battery charged, and power the electrical and fuel systems for the engine. In this state, the alternator takes very little power from the engine. If you turn on your headlights, that adds an electrical load to the system. The load on the alternator goes up, and it takes more energy for the engine to rotate the alternator. If the alternator took as much energy to turn it as it is capable of producing, it would put a much greater load on the engine. If you hooked up a device that consumed as much current as the alternator was capable of consuming, and had it on while you were driving, you would get a significant drop in fuel mileage, as much as or perhaps even greater than having the AC turned on. This follows one of the most basic laws of thermodynamics. You seem to be confusing the amount of current *available* (current that the alternator is capable of producing without overloading), and the amount of current it produces at any given time. Your logic states that an alternator is always putting out it's maximum amount of current, and therefore the parasitic load on the engine is always the same. In fact, if you use your defroster (think electric heating coils on your back window, not your AC compressor) all the time, and leave your headlights on and plug a inverter into the cigarette socket to power your laptop, the alternator will require more horsepower to turn it. Not more than it is capable of producing, but more than it was already using, which is almost nothing if you don't have any electrical loads.

[yourcat]

Well said.

[trebuchet03]

Ritsuki, Thanks - that was a fair bit more eloquent :) I'm a hands on explanation sort of guy, a problem when communicating textually :p

[trebuchet03]

Lets talk this over on a forum or something since this does not seem to be the place for a heated discussion.

I hope you're not getting heated - I'm certainly not ;)

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So here's the results of a quick google search...
U of V - How things Work - ask a physics question

As for how the current varies with load: the more current the load permits to pass through it, the more current will pass through the generator. Assuming that the generator is well built and has very little electric resistance, the load will serve to limit the current. The generator will then deliver just as much current as the load will permit. If the load permits more current, the generator will deliver more. As a result, the wires in the generator will waste more power as heat, the magnetic fields in the generator will become more complicated, and the device powering the generator will have to work harder to keep the generator turning.

[iwilltry]

Power in (torque * rpm) * Efficiency = Power out (Voltage * Current)
You don't get something for nothing. If you draw 2KW of from your alternator you will require twice as much torque to turn it compared to drawing only 1 KW at the same rpm. The additional torque may not be very significant compared to what the engine is capable of, but it is definitely there.

A common example: On older vehicles without idle speed control the idle speed will decrease when you turn on the headlights or defrost circuit. This is exactly because more torque is required to turn the alternator (or generator).

[ryanaghdam]

We've all come to the agreement--as all sane people should--that saving 17 cents is better than using air conditioning in mid-August heat. However, to eliminate some of the discomfort (which is frankly a small price to pay), you can affix aluminum foil to the rear windshield as well as all side windows to reflect sunlight. As mentioned earlier, headlamps use a massive amount of energy. If it is absolutely necessary to drive at night, you may replace the headlamps with reflectors. This will save you money in two ways--first you will eliminate the need to power your headlamps, and secondly, you will reduce the overall weight of your vehicle. A few plastic reflectors weigh less than the lighting fixtures. Weight can be reduced in removing the following superfluous items: -Back seats (Have children? Use packing tape to secure them to the floor) -Windshield-washer fluid. (A few gallons ads roughly 15 pounds!) -Your left leg--only the right one is needed to control the accelerator and brake. A method of driving that has been overlooked is the very effective "Don't Stop Until I Have to" method. Smart (simply more-evolved and sophisticated) drivers should stop only when ABSOLUTELY necessary. This means running a red-light when there's no body around. Children at the crosswalk, beep the horn (but only once, wouldn't want to waste too much energy using it) and barrel on through. Practicing this technique reduces the waste in accelerating from a stop. I hope this comment has helped others achieve maximum MPG! I will soon post my first Instructables article when I chronicle my latest attempt at obtaining better fuel economy when I add a sail to my Toyota Prius.

[Turboelf]

The Toyota Prius might be a good plan if anyone intends to use your driving strategy. The braking system will fail, negating the ability the slow down and the accelerator will over rev causing you to barrel on thru the kids at the crosswalk (if the little beggars even walked to the crosswalk) - don't worry about the horn, you can just blame it on Toyota. When you sue, you get mega-bucks = free gas therefore free motoring! (the kids might only lose a leg in the accident (if you aim correctly) and they'll get a payout from Toyota too! - free gas money for them and reduced motoring costs!)

[cash68]

Driving in the day instead of night? Screw that.

Nighttime= less traffic, and colder air. Less traffic= a more constant speed. Colder air= denser charge of air, sucking into your engine, which results in more power. Also, when it's warmer out your tires will be slightly softer, so colder asphalt and colder air should result in less rolling resistance.

[trebuchet03]

Cold air does mean more power (typically).... but who the hell wants more power available while cruising? Warm air, on the other hand, reduces power at a given throttle opening. But the power necessary to maintain a certain speed (or accelerate to a given speed) doesn't change. So you must open the throttle more. This results in less pumping losses while operating closer to peak load (nearer to most efficient). Road temperature is an interesting point... Can you link us up to info saying colder means less rolling resistance? Softer isn't necessarily a bad thing, considering high efficiency tires are much softer than the high mile warranty counterparts...

[Derin]

and asphalt is blck so heats up

[ironsmiter]

from how i understand it, cold air means more power, but more power means MORE FUEL, in most cases. The denser air means, you can add more fuel, and still get complete combustion... and therefore more power. If you already have plenty of leftover horsepower(only 15 out of the 55HP are actually "needed" for cruising at 55MPH) so in theory, a WarAirIntake would provide better mileage. Provided you could keep your pedal off the sheet metal(what, you mean you HAVEN'T ripped out all that heavy carpet yet? :-) I have my doubts about the air temperature effecting tire temperature much. Once they start rolling, no matter how cold it is, the friction will heat them up. and they stay nice and toasty till you let them sit(warm enough to melt through a 1/4 inch layer of ice after a highway trip.) but if you have the data to back it... I'll listen! Perhapse the benifits colder tires outweigh the alternator drag caused by needing to run headlights?

[ogorir]

I think more importantly is the lack of traffic around. also, around here, the lights switch to blinking yellow/blinking red, so you don't have to stop in as many places after 11PM or midnight.

[Derin]

same here according to a traffic handbook: blinking yellow means yield sign and blinking red means stop sign

[trebuchet03]

I have my doubts about the air temperature effecting tire temperature much.

In auto racing, I have heard that argument... But that plays a roll in static friction (traction)... Rolling resistance is a little different :p It's not so much the air - but the surface ground temperature that's colder. On highways with a lot of traffic, it's probably not so much of a concern as all of those tires are warming up the road. Rural roads, however, def. are cooler.

Here's a link with no alternator - also has a chart with electrical loads Metrompg site. Note that full lights is more than running the engine itself o.0

[wi-fi astronomer]

The real kicker is the A/C. It imposes two loads, one the load for the electric clutch AND the pulley load to spin the compressor in the first place... and the system adds in the fast idle to add insult to injury. But don't get overzealous about driving without A/C. First reason is that opening windows at full speed creates aerodynamic drag greater than the A/C loads. The second reason is that you'll be accused of bad hygiene like the bane of bicycle users in workplaces without showers. I get hot easy so going A/C free is a non-starter just for this reason alone outside of discomfort. My workplace is normally kept hot enough that it's a big problem unless you're one of a hot climate ethnic group, which I'm not. Going sans alternator requires homeownership unless your SUV has a flat top for solar panels. You need to be a homeowner to plug it in, just like the electric car. Being a condo owner normally won't cut it unless your deeded parking space is by a plug to steal electricity from.

[trebuchet03]

All good points I personally will dress light when driving to keep from sweating - but if that doesn't work well for the workplace and you're a sweaty type of person - a compromise must be made.. Which is basically what all of this is about, compromise for better or worse fuel economy :p If you live in an apartment of condo etc. that doesn't allow you to bring power to your car... And you're determined enough - you could carry the battery to the charger in your home... I've used 12V "security" batteries to keep my presets, clock and keep the computer alive :) The "off" draw is typically very low - but I wouldn't use power locks and such on a tiny battery like that :)