Does using pc's in your vehicle cause increased fuel use?

TiTUS · 09-17-2003, 10:16 PM

Just wondering?

TiTUS

osirisdon · 09-17-2003, 10:26 PM

TiTUS · 09-17-2003, 10:39 PM

That must be my shortest question ever.. and that is the shortest answer I've ever seen!

I just figured it might increase fuel usage, with the extra load on the engine and alternator...

TiTUS

osirisdon · 09-17-2003, 10:41 PM

nope

pcman · 09-17-2003, 10:43 PM

it would slightly

extra weight
extra load on alternator

miniscule difference tho i dont think anyone would notice it you would prolly get worse fuel econemy driving around with the windows open creating drag lol

cheers
pcman

Seraph · 09-17-2003, 11:16 PM

It should not but I am going to have my alternator rebuilt so that I get more amp. Just in case.

bgoodman · 09-18-2003, 12:02 AM

you lose about 1mpg per every 200 pounds of weight

fluffy2097 · 09-18-2003, 02:19 AM

Quote: Originally Posted by bgoodman

you lose about 1mpg per every 200 pounds of weight

So I shouldn't try and put an ENIAC in my car?

frodobaggins · 09-18-2003, 03:30 AM

Quote: Originally Posted by fluffy2097

So I shouldn't try and put an ENIAC in my car?

you might could get PART of it in this..

cproaudio · 09-18-2003, 04:25 AM

This type of question is almost the same as "will remote start worsen your gas mileage?" Yes it does but not because of weight or extra load on the alternator. The time you spent setting up your PC for the trip that you're about to take while the engine is still running. That's what increases fuel use when you're running your PC.
For example, during remote start for engine warm up, the engine usually takes about 3-4 minutes to warm up to a driveable status. Remote start usually runs the engine for about 15 minutes before shuts off. People who use remote start often leave their car running while doing quick stops at AM/PM and also quick bathroom breaks. I notice when I use my remote start to do all the above, I got 14-15mpg. I would always have to refuel my little 13 gallon tank after 185 miles of driving. I noticed the same thing when I'm using my PC. I would park and let my engine run with AC on while I setup songs, copilot, read some emails, and before I know it, I spent 30 minutes with the engine running and got 14 miles to a gallon. What I do now is I set everything up and running before I start my truck. Now I get about 18 mpg. My carpc, stereo and tonneau cover weighs about 400lbs. EPA rated my truck at 17 city and 21 hiway. I'm getting 18 city and 25 highway, 29 if I drive at 65 with AC on. For some reason my truck's gets better gas mileage with the AC on even though the windows are rolled up. I dont think the 200lb/1mpg is not very accurate. My parents sienna with 7 passangers and luggage adds about 1000lbs and it only loss about 2 mpg compared to the empty load.

Linus · 09-18-2003, 08:57 AM

Can anyone attach some numbers to all this so it makes more sense to me?

A low-power carputer uses something like 40W when on, right? For comparison's sake, about how much power do headlights require? How many amp hours (Ah) does a typical start take? What about the climate control fans on high? For that matter, what about a high-powered head unit?

It seems to me that the alternator would hit your fuel economy pretty hard when it kicks on, and a carputer (combined with high-power head unit) would require it to do that more often. The carputer might only cost you $10/year at the pump, but it's gotta cost you SOMETHING.

98explorerxlt · 09-18-2003, 09:04 AM

i thought alternators were belt driven why would it mater how much your puter was using unless your car compensates for electrical load sorry i dont know much about cars

Linus · 09-18-2003, 01:37 PM

Quote: Originally Posted by 98explorerxlt

i thought alternators were belt driven why would it mater how much your puter was using unless your car compensates for electrical load sorry i dont know much about cars

As I understand it, the alternator kicks on and off to keep the battery within a certain voltage range. It is belt-driven, but has more resistance when on than off, requiring a little more oomph from the engine, and hence impacting gas mileage (slightly). Someone correct me if I'm wrong.

MeanGT · 09-18-2003, 02:23 PM

Quote: Originally Posted by Linus

As I understand it, the alternator kicks on and off to keep the battery within a certain voltage range. It is belt-driven, but has more resistance when on than off, requiring a little more oomph from the engine, and hence impacting gas mileage (slightly). Someone correct me if I'm wrong.

Yeah, you've pretty much got it, although rather than cycling on and off, most alternators can alternate (hence the name) their amount of output to match the amount of electricity being used by the car's electrical system and to recharge the battery.

And technically yes, it would decrease gas mileage although you would probably never notice the difference. This is because the alternator adds a little more resistance on the drivetrain by upping its output to compensate for a running computer. But that little extra resistance is probably equivilant to an extra drop or two of fuel per mile.

cproaudio · 09-18-2003, 03:47 PM

Time for Ohms law. power is measured in watts. Current is measured in amps. Voltage is measured in volts. Power = voltage X current. Voltage = Power / Current. Current = Power / Voltage, 1 horse power = 746 watts. 746 watts / 14 volts = 53+ amps. It would take an electrical drain of 53 amps for your engine to loose 1 horse power. If you have a high power stereo system of 750 watts RMS (amps are 50% efficient the other 50% turns into heat) it would take your engine 2 horse powers to power your alternator. Is 188 horse power gonna use more gas than a 190 hourse power engine? I dont think so, not enough to notice the difference. Your AC probably use 10-15 horse power to power it. It's been proven that using AC with windows up saves more gas than no AC with windows down. Power steering takes about 5 horse power. Fans attached to the water pump and the pump itself take another 5 horse power. You do the math.
Headlights are usually 55 watt bulbs. High power ones are probably 75 watts. high beams could use as much as 100 watts.
CarPC usually pull anywhere from 4 amps to 20 amps if you're using an inverter. The worst case sinario is that you have a 2000 watts RMS super bad *** but affordable system and you're running a P4 3.2ghz with 4 HDD, 2 CD drives, 3 GPS receivers, Wifi, all running on a 400 watt regular ATX PSU with a 500 watt sustained inverter, and 10 LCD screens, 5 cell phones all charging at the same time, 4 indash DVD players, 4 KC lights on the roof bar. You're probably gonna loose 1/4 miles to a gallon. You can make it up by driving a couple of miles per hour slower on the freeway. So instead of driving 95mph try 90 instead. The point is your Car PC uses VERY VERY VERY little power.

Edit: do you guys notice the gas mileage between driving in the day time as apose to night time?