Disconnecting alternator from car....

"Existential Angst" > wrote in message
...
> to run on battery only....
>
> Any idea on how much gas this would save?
>
> I noticed a substantial increase in my mpg's when my alternator went, on a
> Mazda 929S -- mebbe 15-20%?
>
> If this observation was accurate, it would make sense to hump around a
> spare battery, and operate without an alternator -- heh, a kind of
> hybrid, eh?

Let's jsut assume you have a 100 amp alternator. So at 13.5 volts, you could
produce as much as 1350 watts. This is roughly equivalent to two horsepower
or 85 BTUs per minute. Say your engine plus alternator drive is 10%
efficient, so you need 850 BTU per minute of energy from gasoline to
generate this power. A gallon of gasoline has roughly 115,400 BTUs per
gallon. So to run your alternator, you need something on the order of 0.007
gallons of gas per minute or approximately 0.4 gallons per hour. If your
average speed is 30 mph, then the alternator might affect your gas mileage
to the tune of 0.02 mpg......a lot less than 15-20%.

You need to go back and check your mileage.....

Ed

Don't forget to check the tire pressure.Be sure the brakes aren't
dragging, too much.

The only times I ever mess with the alternator is when/if it quits
charging and I take it to a parts store and trade it in for a rebuilt
alternator.
cuhulin

"C. E. White" > wrote in message
...
>
> "Existential Angst" > wrote in message
> ...
>> to run on battery only....
>>
>> Any idea on how much gas this would save?
>>
>> I noticed a substantial increase in my mpg's when my alternator went, on
>> a Mazda 929S -- mebbe 15-20%?
>>
>> If this observation was accurate, it would make sense to hump around a
>> spare battery, and operate without an alternator -- heh, a kind of
>> hybrid, eh?
>
> Let's jsut assume you have a 100 amp alternator. So at 13.5 volts, you
> could produce as much as 1350 watts. This is roughly equivalent to two
> horsepower or 85 BTUs per minute. Say your engine plus alternator drive is
> 10% efficient, so you need 850 BTU per minute of energy from gasoline to
> generate this power. A gallon of gasoline has roughly 115,400 BTUs per
> gallon. So to run your alternator, you need something on the order of
> 0.007 gallons of gas per minute or approximately 0.4 gallons per hour. If
> your average speed is 30 mph, then the alternator might affect your gas
> mileage to the tune of 0.02 mpg......a lot less than 15-20%.
>
> You need to go back and check your mileage.....

Well, in a subsequent post, I pointed out that a car's mpg's arise from from
maybe 15-25 *regular* hp... mebbe even less. So a 2 hp draw is a
substantial fraction of this, quite in the ballpark of my vague 15-20%
recollection.

And your last set of numbers (which I haven't checked) would seem to bear
this out:
Suppose you drove for an hour at 30 mph, and suppose your mpg's were 30
mpg. That would be 1 gal of gas per hour, right? Your .4 gal per hour is
a whopping 40% of that 1 gal!!!

Ergo my point: The alternator, from a number of calculational
perspectives, seems to gobble up quite a bit of fuel, %-age-wise. Mebbe not
40%, but I'll bet somewhere between 10 and 20%.
--
EA
>
> Ed
>

In message >, Existential Angst
> writes
>Ergo my point: The alternator, from a number of calculational
>perspectives, seems to gobble up quite a bit of fuel, %-age-wise. Mebbe not
>40%, but I'll bet somewhere between 10 and 20%.
In an old car with a Vee belt the belt itself would account for 7% of
the load it is driving, further, if you car is that old it's also likely
that the alternator has a fan which is also labour intensive. Modern
alternators are different, they are driven by Poly-vee belts and don't
have cooling fans owning to better quality of insulation at a higher
temperature. Now this is an interesting point because current in any
wire causes heat and there are many yards of thinly coated wire all
adding heat to the internals without cooling. The only answer can be
that whilst the alternator runs at a sizeable load to put back what the
starter has taken out of the battery, once this is done, (1 to 2 mins)
it only trickle charges the battery, maybe 2 to 3 amps. The only other
load on the alternator is the "Hotel load" which is the items using
electricity, lights, fan etc. The heating is done by hot water from
the engine and cooling is by the compressor driven by the engine. The
total normal load on an alternator under normal conditions wouldn't
exceed 10 amps or 120 watts. The load of an alternator is caused by
the electrical load on itself, very little, I don't think you'd notice
the difference.
--
Clive

"Existential Angst" > wrote in message
...
> "C. E. White" > wrote in message
> ...
>>
>> "Existential Angst" > wrote in message
>> ...
>>> to run on battery only....
>>>
>>> Any idea on how much gas this would save?
>>>
>>> I noticed a substantial increase in my mpg's when my alternator went, on
>>> a Mazda 929S -- mebbe 15-20%?
>>>
>>> If this observation was accurate, it would make sense to hump around a
>>> spare battery, and operate without an alternator -- heh, a kind of
>>> hybrid, eh?
>>
>> Let's jsut assume you have a 100 amp alternator. So at 13.5 volts, you
>> could produce as much as 1350 watts. This is roughly equivalent to two
>> horsepower or 85 BTUs per minute. Say your engine plus alternator drive
>> is 10% efficient, so you need 850 BTU per minute of energy from gasoline
>> to generate this power. A gallon of gasoline has roughly 115,400 BTUs per
>> gallon. So to run your alternator, you need something on the order of
>> 0.007 gallons of gas per minute or approximately 0.4 gallons per hour. If
>> your average speed is 30 mph, then the alternator might affect your gas
>> mileage to the tune of 0.02 mpg......a lot less than 15-20%.
>>
>> You need to go back and check your mileage.....
>
> Well, in a subsequent post, I pointed out that a car's mpg's arise from
> from maybe 15-25 *regular* hp... mebbe even less. So a 2 hp draw is a
> substantial fraction of this, quite in the ballpark of my vague 15-20%
> recollection.
>
> And your last set of numbers (which I haven't checked) would seem to bear
> this out:
> Suppose you drove for an hour at 30 mph, and suppose your mpg's were
> 30 mpg. That would be 1 gal of gas per hour, right? Your .4 gal per
> hour is a whopping 40% of that 1 gal!!!
>
> Ergo my point: The alternator, from a number of calculational
> perspectives, seems to gobble up quite a bit of fuel, %-age-wise. Mebbe
> not 40%, but I'll bet somewhere between 10 and 20%.
> --
> EA

Fantasy figures. You're just guessing.
Why dont you take your alternator and head to Mexico and carefully
monitor your fuel economy. Dont call us...Call AAA

"hls" > wrote in message
...
>
> "Existential Angst" > wrote in message
> ...
>> "C. E. White" > wrote in message
>> ...
>>>
>>> "Existential Angst" > wrote in message
>>> ...
>>>> to run on battery only....
>>>>
>>>> Any idea on how much gas this would save?
>>>>
>>>> I noticed a substantial increase in my mpg's when my alternator went,
>>>> on a Mazda 929S -- mebbe 15-20%?
>>>>
>>>> If this observation was accurate, it would make sense to hump around a
>>>> spare battery, and operate without an alternator -- heh, a kind of
>>>> hybrid, eh?
>>>
>>> Let's jsut assume you have a 100 amp alternator. So at 13.5 volts, you
>>> could produce as much as 1350 watts. This is roughly equivalent to two
>>> horsepower or 85 BTUs per minute. Say your engine plus alternator drive
>>> is 10% efficient, so you need 850 BTU per minute of energy from gasoline
>>> to generate this power. A gallon of gasoline has roughly 115,400 BTUs
>>> per gallon. So to run your alternator, you need something on the order
>>> of 0.007 gallons of gas per minute or approximately 0.4 gallons per
>>> hour. If your average speed is 30 mph, then the alternator might affect
>>> your gas mileage to the tune of 0.02 mpg......a lot less than 15-20%.
>>>
>>> You need to go back and check your mileage.....
>>
>> Well, in a subsequent post, I pointed out that a car's mpg's arise from
>> from maybe 15-25 *regular* hp... mebbe even less. So a 2 hp draw is a
>> substantial fraction of this, quite in the ballpark of my vague 15-20%
>> recollection.
>>
>> And your last set of numbers (which I haven't checked) would seem to bear
>> this out:
>> Suppose you drove for an hour at 30 mph, and suppose your mpg's were
>> 30 mpg. That would be 1 gal of gas per hour, right? Your .4 gal per
>> hour is a whopping 40% of that 1 gal!!!
>>
>> Ergo my point: The alternator, from a number of calculational
>> perspectives, seems to gobble up quite a bit of fuel, %-age-wise. Mebbe
>> not 40%, but I'll bet somewhere between 10 and 20%.
>> --
>> EA
>
> Fantasy figures. You're just guessing.

As are you, if you can't refute specific calculations/estimations.

In fact, CE White's li'l calculation more than agrees with my li'l theory
here, but you haven't said much about that...

> Why dont you take your alternator and head to Mexico and carefully
> monitor your fuel economy. Dont call us...Call AAA

Why would I need to call AAA??
--
EA
>

>
> As are you, if you can't refute specific calculations/estimations.

You are certain of your assertions, but you cant figure out how to
disable your alternator??
Get off the computer...try your theory out for a few tankfuls and let
us know how it goes.
Otherwise you are just playing pocket pool...
Ben

"ben91932" > wrote in message
...
>
>>
>> As are you, if you can't refute specific calculations/estimations.
>
> You are certain of your assertions,

I don't recall expressing certainty. But no one is throwing out numbers,
either, and the one who did wound up supporting my thesis.

but you cant figure out how to
> disable your alternator??

I could if I could goddamm see it/the wiring. No clear fuse for it either,
tried a few things. That was going to be my next Q.
This is not the 1960s or 1970s, where **** is obvious, or even meant to be
fixed.
You do know that many parts are now RFID'd, so you cain't even change many
of your own pats, without the dealer.


> Get off the computer...try your theory out for a few tankfuls and let
> us know how it goes.

Actually, if I could disconnect the alternator, I could tell you almost
immediately, because I have a ScanGauge that will read mpg's realtime.


> Otherwise you are just playing pocket pool...

You seem to miss the point of (attempted) intelligent discussion.
--
EA




> Ben

"Existential Angst" > wrote in message
...
>
> but you cant figure out how to
>> disable your alternator??
>
> I could if I could goddamm see it/the wiring. No clear fuse for it
> either, tried a few things. That was going to be my next Q.

Go to the library, if there is one in your town. You will find that there
are some subtle differences between generations and manufacturers of
alternators.. Most are minor differences, but you will at least get a
schematic
which will lead you through your research.

> This is not the 1960s or 1970s, where **** is obvious, or even meant to be
> fixed.
> You do know that many parts are now RFID'd, so you cain't even change many
> of your own pats, without the dealer.

That occurs with some things but is a copout in this case. Replacement
parts for most alternators are widely available at well stocked parts
stores....


>> Get off the computer...try your theory out for a few tankfuls and let
>> us know how it goes.
>
> Actually, if I could disconnect the alternator, I could tell you almost
> immediately, because I have a ScanGauge that will read mpg's realtime.

Well, it will give you a number anyway. Those things are not so very
accurate in my experience. If they are reproducible enough, even if they
are not accurate, they might be helpful in your quest.



>> Otherwise you are just playing pocket pool...
>
> You seem to miss the point of (attempted) intelligent discussion.
> --

So now the pot is calling the kettle black?

"Existential Angst" > wrote in message
...
> "C. E. White" > wrote in message
> ...
>>
>> "Existential Angst" > wrote in message
>> ...
>>> to run on battery only....
>>>
>>> Any idea on how much gas this would save?
>>>
>>> I noticed a substantial increase in my mpg's when my alternator went, on
>>> a Mazda 929S -- mebbe 15-20%?
>>>
>>> If this observation was accurate, it would make sense to hump around a
>>> spare battery, and operate without an alternator -- heh, a kind of
>>> hybrid, eh?
>>
>> Let's jsut assume you have a 100 amp alternator. So at 13.5 volts, you
>> could produce as much as 1350 watts. This is roughly equivalent to two
>> horsepower or 85 BTUs per minute. Say your engine plus alternator drive
>> is 10% efficient, so you need 850 BTU per minute of energy from gasoline
>> to generate this power. A gallon of gasoline has roughly 115,400 BTUs per
>> gallon. So to run your alternator, you need something on the order of
>> 0.007 gallons of gas per minute or approximately 0.4 gallons per hour. If
>> your average speed is 30 mph, then the alternator might affect your gas
>> mileage to the tune of 0.02 mpg......a lot less than 15-20%.
>>
>> You need to go back and check your mileage.....
>
> Well, in a subsequent post, I pointed out that a car's mpg's arise from
> from maybe 15-25 *regular* hp... mebbe even less. So a 2 hp draw is a
> substantial fraction of this, quite in the ballpark of my vague 15-20%
> recollection.

That was the maximum the alernator could ever draw with worst case
assumptions piled on for good measure. Usually in the real world an
alternator will be drawing much much less - just enough to run the fuel
pump, engine control system and accessories once the battery reaches full
charge. Probably most of the time it is pulling less than 0.3 hp (unless you
are constantly running a 1000 watt stereo).

> And your last set of numbers (which I haven't checked) would seem to bear
> this out:
> Suppose you drove for an hour at 30 mph, and suppose your mpg's were
> 30 mpg. That would be 1 gal of gas per hour, right? Your .4 gal per
> hour is a whopping 40% of that 1 gal!!!

Again, that 0.4 gallons per hour is using worst case assumptions with the
alternator at maximum draw. For normal running it is a fraction of this
(less than 0.05 gallons per hour).

> Ergo my point: The alternator, from a number of calculational
> perspectives, seems to gobble up quite a bit of fuel, %-age-wise. Mebbe
> not 40%, but I'll bet somewhere between 10 and 20%.

Likely less than 5% if you are driving 30 mph. And if you are really worried
about that draw, then don't run the radio, heater, A/C, use the power
windows or seats, leave off all lights all the time, and push start the car.
Get it down to where your only draw is the fuel pump and the engine control
system.....then you probably can get the alternator draw to under 2%. If you
really want to know, you should put a ammeter on the main alternator power
feed. I bet once the battery is charged it won't exceed 15 amps most of the
time. 15 amps at 14 volts is 210 watts (about 0.3 hp).

Ed