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Exactly how much does this drain the battery?

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  • Exactly how much does this drain the battery?

    I just picked up the new 2005 Scion tC and I was wanting to put a LCD screen in it, with dvd player, mp3 player, and whatever else I could throw in. Well I stumbled upon this and became very interested. I have been up all night reading about how to do it, and basically picked out everything I would need. (I am a very fast learner)

    But, I have 1 question. Exactly how much more power will this type of system drain for the battery? Will it run the battery down any faster then it would with just a regular dvd player head unit with lcd screen? I wouldn't have the system running without having the car running, since obviously that will drain the battery alot quicker.

    Cliff notes:
    How much more does this drain the car battery from a normal dvd/lcd system?

    Thanks,
    -- Coy

  • #2
    It all depends on a few factors.

    Firstly, what components you decide to use. If you use something like the VIA Epia range of boards, then they are designed for low power usage, so they won't consume as much juice as standard desktop components.

    The other thing that affects it is the power supply you use. The most efficient thing to use is a DC-DC power supply, such as an Opus, or if you have a case with the Morex 55W DC-DC PSU (which will be in most of the "Mini-ITX" cases you can buy) then you can use the Carnetix CNX-P1260, both of which will give you >90% efficiency. This means that of the power that comes from the battery, over 90% of it will be used in the computer, and less than 10% will be "wasted" in the conversion.

    Compare that however to the other option, which is an inverter and a standard PC power supply. Most inverters will be around 75% efficiency, and add to that the PC power supply will be at best 75% efficiency, so using this setup, you'll be pulling over 150% of the power you need to just run the system!

    So, best bet is a DC-DC power supply, and depending on what you use, depends on how long it will last. I would estimate (but it is only a complete guess) an Epia setup will probably pull about the 150-200% of the power that a basic, standalone DVD/LCD will do, because of the nature of running a PC

    However, if the engine will be running, then it doesn't really matter, as the alternater will be charging the battery all the time


    Garry
    Co-Developer of A.I.M.E.E
    www.aimee.cc

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    • #3
      Maybe a stupid question here, but i thought if your engine was running, basic phyiscs suggests that an increase in power requirements from your car pc means that your engine uses more petrol turning the alternator over to generate more current, no? Would have thought most cars would be able to cope with 12V pc, considering some people power 700W microwaves of their engines
      Ben

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      • #4
        damn, you beat me to it lol
        Ben

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        • #5
          Perfect,

          I'm going to use a board in the range of the VIA Epia, 900 mhz, 20 gig hard drive (ill upgrade later), 128mb of ram, etc etc..... and then use the Opus DC - DC. Then use the MediaEngine for interface. Probably modify alittle bit more to fit my needs. And use the Lilliput screen.

          As soon as I get out of planning stage and purchasing, I'll start posting pics and descriptions.

          Should be pretty sweet, the tC already has a nice setup, this will make it perfect.

          Heres the dash, where the screen will go.



          Directly behind that large square silver peice in the center, it folds up and reveals the double din radio. I'll place the screen there. Computer in trunk or somewhere else.

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          • #6
            From experience, I cannot recommend you get yourself a Lilliput screen.

            Get yourself a Xenarc screen, it definately worth the extra money.


            Garry
            Co-Developer of A.I.M.E.E
            www.aimee.cc

            Comment


            • #7
              Originally posted by bathbiggles
              Maybe a stupid question here, but i thought if your engine was running, basic phyiscs suggests that an increase in power requirements from your car pc means that your engine uses more petrol turning the alternator over to generate more current, no? Would have thought most cars would be able to cope with 12V pc, considering some people power 700W microwaves of their engines

              Yes, conservation of energy holds true here as it does everywhere, nothing is free. But the good news is that the change will be slight enough that you likley won't notice it. Now if you had that microwave going 24/7 allong with a cranked 1500W stereo and full size refrigerator it may be more noticable. But i'm guessing those things arn't in your plans.

              PS: if you wanted to do a little expieiment you could track your gas milage for a week and then do the same the next week but drive with your headlights on the whole time. Your factroy low beams are likley about 40W each and the highs are likley 10-15W more so 2 lights on (high or low beams) would be roughly the power consumed by a system running on an opus 90W

              Have fun and good luck with your project.

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              • #8
                Originally posted by StationRocket
                Your factroy low beams are likley about 40W each and the highs are likley 10-15W more so 2 lights on (high or low beams) would be roughly the power consumed by a system running on an opus 90W
                Do not forget that if you are using an Opus 90W you might not actually be using 90W - that is it's maximum. I should be around 30W

                you might find this useful:

                http://www.mini-box.com/powersimulator.html
                Ford Focus MP3 : www.stevieg.org/carpc Blog Updated 29 January 2009!
                Car PC Status: Complete - Undergoing Software Redevelopment

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                • #9
                  My system draws at most 10A (90w) but never 100%. How's that for efficiency? ANd that's with DVD drive, screen, computer all running.
                  Mine needs to be updated.

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                  • #10
                    Originally posted by bathbiggles
                    Maybe a stupid question here, but i thought if your engine was running, basic phyiscs suggests that an increase in power requirements from your car pc means that your engine uses more petrol turning the alternator over to generate more current, no? Would have thought most cars would be able to cope with 12V pc, considering some people power 700W microwaves of their engines
                    Not true! The alternator produces the same amount of drag on the engine no matter how much current is required by electronics. It is electrical and not mechanical. There is no physical connection inside the alternator itself to produce electricity.

                    The only thing that will happen if you go over the output of your alternator/battery combo is you'll lose power or fry your alternator because it will try to produce more current when it can't.

                    Air conditioning, power steering pumps are both mechanical and use more gas. Alternators do not!
                    www.natchezss.com

                    God Bless America and Our President!

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                    • #11
                      10 amps is a lot... and thats more than 90 watts at 12v
                      CarPC install is starting to come along again...

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                      • #12
                        Originally posted by NorthGaVigor
                        Not true! The alternator produces the same amount of drag on the engine no matter how much current is required by electronics. It is electrical and not mechanical. There is no physical connection inside the alternator itself to produce electricity.

                        The only thing that will happen if you go over the output of your alternator/battery combo is you'll lose power or fry your alternator because it will try to produce more current when it can't.

                        Air conditioning, power steering pumps are both mechanical and use more gas. Alternators do not!
                        this is incorrect, the alternator will produce more strain on the engine if you are drawing more current, if there is more current being produced it is harder to turn the coil inside the alternator, i cant remember who's law this relates to, the air conditioning will however use more power because when it is not in use it is not attatched to the engine.
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                        • #13
                          Originally posted by Nic
                          this is incorrect, the alternator will produce more strain on the engine if you are drawing more current, if there is more current being produced it is harder to turn the coil inside the alternator, i cant remember who's law this relates to, the air conditioning will however use more power because when it is not in use it is not attatched to the engine.
                          And it's harder to turn the coil becuase of an electromagnet? I think, however my searches on google and making me more enlightned. I know when the cars idling and I turn my lights on the RPM goes up which must mean there is more load on it. It must do something with the load, because the one time the car almost stalled when I switched on all the electrics when it was cold!
                          Ford Focus MP3 : www.stevieg.org/carpc Blog Updated 29 January 2009!
                          Car PC Status: Complete - Undergoing Software Redevelopment

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                          • #14
                            Originally posted by NorthGaVigor
                            Not true! The alternator produces the same amount of drag on the engine no matter how much current is required by electronics. It is electrical and not mechanical. There is no physical connection inside the alternator itself to produce electricity.

                            The only thing that will happen if you go over the output of your alternator/battery combo is you'll lose power or fry your alternator because it will try to produce more current when it can't.

                            Air conditioning, power steering pumps are both mechanical and use more gas. Alternators do not!

                            I'll also go on record saying that this post is incorrect. I don't have time to explain motor/generator theory right now but i'll say that the forces felt are a due to magnetic fields which are generated by flowing current. More current, more magnetic field density, more resistance to rotation.

                            If anyone really wants hear the whole drawn out explination bug me later and if i've got time i'll pull out some of my notes and do it right.

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                            • #15
                              Just asked my old man about it (He knows things like this and suitably dumbed it down for me) and apparently the reason it increases load is because the more current it needs to generate, the more charge is set on the electromagnets inside the alternator, thus acting as a brake. The more charge in the electromagnet the more current generated.

                              But from what I can gather my little car pc on it's 5A fuse isn't losing me much MPG!
                              Ford Focus MP3 : www.stevieg.org/carpc Blog Updated 29 January 2009!
                              Car PC Status: Complete - Undergoing Software Redevelopment

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