car performance drop?

**FireWire** · 01-07-2004, 06:00 PM

Hi, sorry if this has been posted already, but I didn't find the topic in the history. Anyway, i was wondering if running a computer while driving impairs the car's performance on the road. Because with my 1.6L '97 Civic LX I noticed turning off the A/C while I pass gives a little "boost" so I think that with a CPU and a screen connected it would be hard to reach 60 mph :P

so have you noticed something similar? if so, is installing a bigger Alt or batt would help?

also, have you tried putting a UPS (backup battery) in your system, so you could turn off your car and still have a few minutes to turn off your pc properly? i think that would solve most "restart" and crash problems

**kami333** · 01-07-2004, 06:20 PM

There's a thread about carpcs affecting gas mileage that should answer your question but the short of it is it shouldn't except for the extra weight. It's using power from your alternator and the alternator has to be on all the time. With AC, when in use the belts need to turn the AC compressor as well, which results in the loss of power.

**Freeman** · 01-07-2004, 06:35 PM

1.6 L.... thats your main problem with reachig 60mph.... not ya PC :P

**Walleye** · 01-07-2004, 07:06 PM

lol... the car creates the power regardless of whether or not your pc is attached to it. the ac compressor is driven by the car's engine, that's why it takes a performance drop. when you turn off the compressor, it declutches from the engine, so it no longer has any effect on it. however, the alternator is always connected back to the battery, and always clutched with the engine (cause it has to supply power to the spark plugs, obviously). it runs at 14 volts, and constantly charges your battery. the battery cleans the power before it heads to the car's onboard computer, and also you draw your own computer off the car's battery. so no, it'll have no effect at all on your car unless you draw more power than you can recharge. and that's determined by your battery. generally, with most modern cars (and batteries) this isnt a problem.

in fact, i cant think of any cars where it would be a problem. maybe one of those 1 liter cars? cant think of any.

**none** · 01-07-2004, 11:57 PM

Wrong.

The alternator will be harder to turn when it is under more load (cranking out more amps.) The difference should be negligible, but a really crappy car with a high draw system (P4 running through inverter with raid and crt monitor, for example) might see a hit.

**Jackso** · 01-08-2004, 12:11 AM

Originally Posted by none

Wrong.

The alternator will be harder to turn when it is under more load (cranking out more amps.) The difference should be negligible, but a really crappy car with a high draw system (P4 running through inverter with raid and crt monitor, for example) might see a hit.

That is correct (mostly). Current is drawn NOT CREATED! That is the first thing you must understand in electronics. The car does NOT create full power all the time. If you have a 100 amp altenator, that means that it is CAPABLE of creating 100 amp without doing damage to itself. An altenator creates electricity by intersecting a magnetic field with a wire. The current is then created in the wire. The problem with that is that any wire carrying current, creates it's own magnetic field. Right Hand Rule will show that these two magnetic fields (the one used to create the current, and the one created BY the current) oppose one another, thus making a "load". The more current that is drawn, the larger the magnetic field that is created by the current, the harder it is to intersect the wire with the original field, thus further loading.

Where NONE is slightly incorrect, is that even a small system will put a heavy load on the altenator. Lets say that you're using a 150 Watt system (DC-DC, DC-AC, doesn't really matter, it's the wattage we're concerned with) to create 150W the altenator must produce 12.5 Amps of current (in a perfect world with no losses). Considering that most cars come with around a 100 Amp altenator (probably smaller on that 1.6L engine), that is 12.5% of the available current capacity. I vaguely remember something from fields that the force is the square of the increase, so if the car before computer were using say 50 Amps of power, increasing the current draw by an additional 1/4 would increase the load 56%, thus affecting gas milage, and performance.

But alas, your real problem is a 1.6L engine.

**none** · 01-08-2004, 01:56 AM

I do know that my system places no noticable load on the electical system of my car, but then I designed it to be low draw

and my car is quite a beast

**Jackso** · 01-08-2004, 02:45 AM

Mine isn't noticable either, but 3 car batteries will do that.

**GingerPrince** · 01-08-2004, 03:57 AM

Originally Posted by Walleye

the alternator is always connected back to the battery, and always clutched with the engine (cause it has to supply power to the spark plugs, obviously). it runs at 14 volts, and constantly charges your battery. the battery cleans the power before it heads to the car's onboard computer

The battery doesn't "clean" the power, it's still the 13.8 or whatever that your alternator chooses to give out. That's why you need a regulator. Your ECU etc will have its own regulator, or be built to tollerate varying input voltages (not sure which).

**MatrixPC** · 01-08-2004, 11:06 AM

More electrical is use in the car, more load to the alternator -> engine. It will affect the car's performance, service life, and gas milleage.
Have you guys notice that when you go up hill (big one), sometime there is always a warning sign "To advoid overheat, turn off AC and RADIO".