Power used by demist, headlights &c?

Here in the UK we have been experiencing the slow onset of wintry
weather along with earlier nightfalls and I have been noticing an
interesting variation in my car's fuel consumption. That it is a
Prius is probably not very important; but it does keep me advised
on consumption figures, which have set me wondering.

When it was new in early August, I was getting 58-60mpg(UK). The
weather was mainly warm and dry and most driving was in daylight.
So equipment such as headlights and electric rear window demister
were not used seriously. OTOH, the electric a/c ran often.

With temperatures down to around 3-4 C and rain on many days, the
demister had heavy use, along with headlights, and mpg(UK) dipped
to 54 or so. When the car is still cold, I think windscreen heat
comes from the battery, which must be replaced (if indirectly) by
the petrol engine, thus using fuel; this last is a guess, though.

Lower temperatures led to drier air, with waste engine heat being
enough to demist. But mpg(UK) still went through a 50-ish period
from which we seem to be recovering slowly (up to 52+).

The general driving style and routes have not varied much. Where
they have varied, mpg have tended to go in the "wrong" direction:
ie, up when they should go down, and _vice versa_.

Tyre pressures have been watched carefully. I have not driven in
snow, or more than token coats of mud and/or water on the road.

This leads to two technical questions:

1) Typically, what sort of a load (in KW) do a full set of night-
lights (headlights plus sidelights) plus the rear window demister
cause in a medium-sized Toyota? (Prius, if it matters.)

2) Assuming I go to the same garage and fill up with what is sold
as the same basic grade of unleaded fuel, what percent variations
in calorific value are likely? Would +/- 9% be improbable? I go
to a big UK supermarket chain (Sainsburys) selling its own brand.

Am interested to hear thoughts on this.
--
Andrew Stephenson

[color=blue]
> 1) Typically, what sort of a load (in KW) do a full set of night-
> lights (headlights plus sidelights) plus the rear window demister
> cause in a medium-sized Toyota? (Prius, if it matters.)[/color]

Well your headlights are gonna take 110W, sides probably 5-10W, demister -
maybe 10-15w. Car may take longer to get up to temp so the ECU may keep the
fuel rich for a tiny bit longer at startup.

Shouldnt see more than 200w usage extra IMO. My mpg has dropped from 320
miles to a tank (62 litres) to 260 so count yaself lucky lol - dont think
thats weather related though. Seriously though, 9% is about the figure I
used to get on my other car. Dont think fuel calorific value varies much at
all.

J

On Mon, 28 Nov 2005 19:20:24 GMT, [email]ames@deltrak.demon.co.uk[/email] (Andrew
Stephenson) wrote:
[color=blue]
>Here in the UK we have been experiencing the slow onset of wintry
>weather along with earlier nightfalls and I have been noticing an
>interesting variation in my car's fuel consumption. That it is a
>Prius is probably not very important; but it does keep me advised
>on consumption figures, which have set me wondering.[/color]

Snip a significant drop in fuel mileage when it got cold.
[color=blue]
>This leads to two technical questions:
>
>1) Typically, what sort of a load (in KW) do a full set of night-
>lights (headlights plus sidelights) plus the rear window demister
>cause in a medium-sized Toyota? (Prius, if it matters.)[/color]

Headlights are 55W or 60W each, Stop lamps and turn signals (both
ends) are 32W each, the CHMSL is in the 32W range if it's an
incandescent, and the tail lights, side marker, license lamps are
anywhere from 1W to 2W each. Overall, not that much. For
headlights, tail lights, instruments and markers, 150W constant (12 to
13 amps) is a nice round number to work with.

Hit the brakes and you throw another 100W of load on, and turn
signals would average about 40 - 50W when you figure the duty cycle.

Change any of those 'other than headlights' loads from incandescent
to LED lamps, and you cut the load by (educated guess) 60 to 75
percent.

The heater blower is going to be under 100W at full load, so that
won't change too much. Same blower for air conditioning. The AC
running during the Defrost cycle (for dry air) will add another 100
watts between the compressor clutch and the condenser fan.

Add it all up, and a small fuel mileage drop is to be expected.
[color=blue]
>2) Assuming I go to the same garage and fill up with what is sold
>as the same basic grade of unleaded fuel, what percent variations
>in calorific value are likely? Would +/- 9% be improbable? I go
>to a big UK supermarket chain (Sainsburys) selling its own brand.[/color]

If they put an oxygenate additive in the fuel such as ethanol or
MTBE or such in the winter "for smog reduction", that additive drops
the BTU per gallon of the fuel up to 10% - California fuel mileage
numbers took a big hit when the US Federal Government started
insisting on an oxygenate additive.

(And now we have MTBE in the ground water from the filling station
tanks and pipes leaking, but that's another discussion...)

On a Prius, the engine will be running a bit longer at startup in
cold weather to warm up before it will go into "Stealth Mode" in city
traffic, and run a bit longer to get the BTU's for heater output. And
it does need to enrich the mixture a bit more for a very cold startup
(probably below 0 Celsius), but that shouldn't affect overall mileage
that much. (Yes, I know it's a totally different combustion cycle,
and they spin the engine up good and fast before turning on the fuel,
but there are some things you can't change.)

Does the new Prius still have that 'bladder in the gas tank' setup?
It cuts down on evaporative emissions, but the older Priii ;-) are
reported to have been temperamental, and the tank will take several
liters more or less on a fill from day to day - depending on whether
the bladder lets you fill it to the brim or not. This can confuse the
mileage calculations when done on a per-tank basis, though figuring
the average over several tanks should even those variations out.

--<< Bruce >>--

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

"Andrew Stephenson" <ames@deltrak.demon.co.uk> wrote in message
news:1133205624snz@deltrak.demon.co.uk...[color=blue]
> Here in the UK we have been experiencing the slow onset of wintry
> weather along with earlier nightfalls and I have been noticing an
> interesting variation in my car's fuel consumption. That it is a
> Prius is probably not very important; but it does keep me advised
> on consumption figures, which have set me wondering.
>[/color]
Snip


Personally I would use better quality fuel than supermarket stuff.

The Prius keeps its water hot in a sort of thermos flask, so if you leave
the car for several days then that gets cold and reduces the mpg.

Any power use is ultimately produced by petrol, so the more of one you use,
the more of the other is used.

Slowing down recharges the battery, so the worst use you can give the prius
is long steady motorway use, around town is far better (economically)

My friend has an 05 Prius in the uk (Essex), his economy has also dropped a
little to 52 - 53 recently, usually it is more like 58.

So your figures are just as I would expect.

mrcheerful

mrcheerful
. wrote:[color=blue]
> The Prius keeps its water hot in a sort of thermos flask, so if you leave
> the car for several days then that gets cold and reduces the mpg.[/color]

Is that the case? Thats pretty interesting - didnt know that! Doesnt
the fractional decrease in time-to-warm get outweighed by the extra
weight of carrying round a significant quantity of extra water?
J

"Coyoteboy" <coyoteboyuk@hotmail.com> wrote in message
news:1133275975.147410.293890@z14g2000cwz.googlegroups.com...[color=blue]
>
> mrcheerful
> . wrote:[color=green]
>> The Prius keeps its water hot in a sort of thermos flask, so if you leave
>> the car for several days then that gets cold and reduces the mpg.[/color]
>
> Is that the case? Thats pretty interesting - didnt know that! Doesnt
> the fractional decrease in time-to-warm get outweighed by the extra
> weight of carrying round a significant quantity of extra water?
> J
>[/color]

apparently it gets pumped there and out again, so that the engine warms
quicker. so there probably isn't much extra coolant, but lots of bits to
make it happen !

mrcheerful

In article <dmfpvq$19a$1@nwrdmz01.dmz.ncs.ea.ibs-infra.bt.com>
[email]coyoteboyuk@hotmail.com[/email] "Coyoteboy" writes:
[color=blue]
> [estimates][/color]

Thanks. See other replies for extra remarks.
--
Andrew Stephenson

In article <9qano1hrfadrk0f5s3o7f9pjl8tvh2k7gk@4ax.com>
[email]blPYTHONbergman@earthlink.inva[/email]lid "Bruce L. Bergman" writes:
[color=blue]
> [discussion of power ratings and fuel additives -- suggesting
> 150W for steady lights, 100W for heater blower, 100W for a/c,
> plus maybe 40W (from another reply) for the demister][/color]

IOW just tootling along with night running lights, windscreen fan
blowing a/c'd air and rear electric demister should give an extra
load of around 390W. Estimating the car's essential power use is
tricky but suppose a guess-average of 60KW (slightly over 80HP),
then the extra load represents 390/60000 or 6.5% extra power use.
[color=blue][color=green]
> >2) Assuming I go to the same garage and fill up with what is sold
> >as the same basic grade of unleaded fuel, what percent variations
> >in calorific value are likely? Would +/- 9% be improbable? I go
> >to a big UK supermarket chain (Sainsburys) selling its own brand.[/color]
>
> If they put an oxygenate additive in the fuel such as ethanol or
> MTBE or such in the winter "for smog reduction", that additive drops
> the BTU per gallon of the fuel up to 10% - California fuel mileage
> numbers took a big hit when the US Federal Government started
> insisting on an oxygenate additive.[/color]

If that's the case, then I can well understand how mpg could nose
dive. I don't know if UK petrol suppliers bother with any major
winter formulations. For diesel, it's quite likely, as (believe
it or not) we do sometimes get serious weather (compared with our
usual relaxed not-too-cold-not-too-hot setup). I'll see if I can
find out, next time I fill up.
[color=blue]
> [warming up in the Prius -- and that thermos flask for coolant][/color]

The effect of the coolant storage bottle is quite evident, both
in how the engine attains its median efficiency faster even after
a stop of 3-4 hours in zero-ish (C) weather, and in how the cabin
warms. (Prius doesn't yet have heated seats as an option. I did
ask but it looks like Toyota expect the bulk cabin heater to take
care of it -- which it seems to, sort of.)
[color=blue]
> Does the new Prius still have that 'bladder in the gas tank'
> setup? [...][/color]

Don't know. In practice, calibration of the segmented dashboard
gauge and the litres one ends up putting into the tank are a good
fit with each other. They may have fixed those bugs. <g>

One dim trick the system pulls is to zero the ongoing mpg figure
if you add more than about 10 litres. :-( That may be a hangover
from older bladder problems. Hints exist, here and there in the
design, that Toyota are feeling their way on the best way to do
some things, so you are apt to find minor (NB) options that don't
make sense. For example, locking with the remote uses one click
to do the basic locking, and a second click for "double" locking.
Could they not have done full locking with the first click? I'll
be interested to see how such details evolve.

FWIW, a full tank is about 45 litres, or roughly 12 US gallons.

Wouldn't mpg be calculated by measuring the output of a fuel flow
meter and road wheel revolutions, and therefore be independent of
what's happening in the tank?
--
Andrew Stephenson

In article <OBXif.17783$Lw5.3641@text.news.blueyonder.co.uk>
"mrcheerful writes:
[color=blue]
> "Andrew Stephenson" <ames@deltrak.demon.co.uk> wrote in message
> news:1133205624snz@deltrak.demon.co.uk...
>[color=green]
> > [using supermarket fuel][/color]
>
> Personally I would use better quality fuel than supermarket
> stuff.[/color]

I truly don't know how good or bad Sainbury's fuel is; but, going
by their overall attitude to quality (for example, several orders
of magnitude better than ASDA, now owned by Wal-Mart), I find it
easy to trust they're not selling rubbish. OTOH, your scepticism
may be well founded. It'd be interesting to learn the truth.
[color=blue]
> My friend has an 05 Prius in the uk (Essex), his economy has
> also dropped a little to 52 - 53 recently, usually it is more
> like 58.[/color]

Interesting. Thanks. The service dept of my Toyota dealer said
most of their Prius owners get around 55 mpg(UK); but it was then
warmer weather; or maybe he meant "over a full year".
--
Andrew Stephenson

In article <1133275975.147410.293890@z14g2000cwz.googlegroups.com>
[email]coyoteboyuk@hotmail.com[/email] "Coyoteboy" writes:
[color=blue]
> mrcheerful wrote:
>[color=green]
> > The Prius keeps its water hot in a sort of thermos flask, so
> > if you leave the car for several days then that gets cold and
> > reduces the mpg.[/color]
>
> Is that the case? Thats pretty interesting - didnt know that! Doesnt
> the fractional decrease in time-to-warm get outweighed by the extra
> weight of carrying round a significant quantity of extra water?[/color]

Overnight is enough to let it cool. The benefit is mostly within
the same working period with pauses of a few hours being covered.
My guess(NB) is the flask is a sump, into which coolant drains.
Must ask, when I next can.
--
Andrew Stephenson

"Andrew Stephenson" <ames@deltrak.demon.co.uk> wrote in message
news:1133205624snz@deltrak.demon.co.uk...[color=blue]
> Here in the UK we have been experiencing the slow onset of wintry
> weather along with earlier nightfalls and I have been noticing an
> interesting variation in my car's fuel consumption. That it is a
> Prius is probably not very important; but it does keep me advised
> on consumption figures, which have set me wondering.
>
> When it was new in early August, I was getting 58-60mpg(UK). The
> weather was mainly warm and dry and most driving was in daylight.
> So equipment such as headlights and electric rear window demister
> were not used seriously. OTOH, the electric a/c ran often.
>[/color]
snip
[color=blue]
> Am interested to hear thoughts on this.
> --
> Andrew Stephenson
>[/color]

You might like to read through all the info here: Masses of prius info:
[url]http://john1701a.com/[/url]

mrcheerful

In article <1133287542snz@deltrak.demon.co.uk>
[email]ames@deltrak.demon.co.uk[/email] "Andrew Stephenson" writes:
[color=blue]
> IOW just tootling along with night running lights, windscreen fan
> blowing a/c'd air and rear electric demister should give an extra
> load of around 390W. Estimating the car's essential power use is
> tricky but suppose a guess-average of 60KW (slightly over 80HP),
> then the extra load represents 390/60000 or 6.5% extra power use.[/color]

!!do'h!! That's what you get for counting on your fingers too
fast. "390/60000" should be rather smaller -- more like 0.65%.
So those extras do not, on their own, look like major villains.

If anyone troubled to set me straight, thanks for the effort. <g>
--
Andrew Stephenson

In article <NO6jf.18388$Lw5.6623@text.news.blueyonder.co.uk>
"mrcheerful writes:
[color=blue]
> "Andrew Stephenson" <ames@deltrak.demon.co.uk> wrote in message
> news:1133205624snz@deltrak.demon.co.uk...
>[color=green]
> > Am interested to hear thoughts on this.[/color]
>
> You might like to read through all the info here: Masses of
> prius info: [url]http://john1701a.com/[/url][/color]

Thank you.
--
Andrew Stephenson

On Tue, 29 Nov 2005 18:36:29 GMT, [email]ames@deltrak.demon.co.uk[/email] (Andrew
Stephenson) wrote:[color=blue]
>In article <OBXif.17783$Lw5.3641@text.news.blueyonder.co.uk>
>"mrcheerful writes:[color=green]
>> "Andrew Stephenson" <ames@deltrak.demon.co.uk> wrote in message
>> news:1133205624snz@deltrak.demon.co.uk...[/color][/color]
[color=blue][color=green][color=darkred]
>> > [using supermarket fuel][/color]
>>
>> Personally I would use better quality fuel than supermarket
>> stuff.[/color]
>
>I truly don't know how good or bad Sainbury's fuel is; but, going
>by their overall attitude to quality (for example, several orders
>of magnitude better than ASDA, now owned by Wal-Mart), I find it
>easy to trust they're not selling rubbish. OTOH, your scepticism
>may be well founded. It'd be interesting to learn the truth.[/color]

The "Supermarket Stuff" isn't going to be bad, it just might not be
the very best. It probably works the same way in Europe as it does
here - there is some "Branded Gasoline" that uses a special formula
and is made by the brands's refineries especially for their stations,
and it is transported specially through the pipelines to the local
distribution tank farms.

But most of the fuel out there is "commodity gasoline" that can be
made by any refinery (and blended into one big commingled batch) as
long as it meets the specifications for hydrocarbon composition,
octane, BTU content, vapor pressure, etc.

(The special blends for high altitudes and/or pollution control
complicate that, but not too much. Just like the low and ultra-low
sulfur Diesel that is required in some areas and not others.)

You'll have to ask one of the managers at that supermarket chain to
find out who they get their fuel from in your region.

One regional tank farm might supply a half-dozen different branded
stations - The only thing special about most gasolines at the
brand-name stations is the detergent and additive package added to the
raw gasoline. Chevron Texaco's is Techron, and the other refiners
have trade names for theirs.

The base gasoline all the retail stations use is (or can be) a
market traded commodity, the detergent and additive package is added
at the "rack" when they fill the delivery tank truck headed for the
filling station. If it is going to a Chevron branded station they set
the meter to add their special Techron additive, if it's going to a
small outlet they use the generic detergent additive.

That's about as short as I can edit it and still make sense.

--<< Bruce >>--

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

In article <tr6qo19m1e0l0fvgo4k6gna8jeosbfnoed@4ax.com>
[email]blPYTHONbergman@earthlink.inva[/email]lid "Bruce L. Bergman" writes:
[color=blue]
> [discussion of what commercial car fuel is][/color]

Interesting, ta. It's really a very basic business -- forget all
of that BS about how each company carefully builds its fuel, just
for _your_ car. ;-)
--
Andrew Stephenson