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  • Orderin wiring...

    I am curious what are your thoughts about putting a capasitor on the main power line for the computer and maybe for the monitor? Has anyone done it? Any recomendations on picking one? Do they cause any issues with draining the battery?

  • #2
    Originally posted by DracoPCGuy View Post
    I am curious what are your thoughts about putting a capasitor on the main power line for the computer and maybe for the monitor? Has anyone done it? Any recomendations on picking one? Do they cause any issues with draining the battery?

    My thoughts? Unnecessary.
    Has anyone done it? Probably, you can always find someone to sell snake oil to.
    Don't buy one, that's my recommendation.
    No they won't drain the battery... Who told you that? And while we're at it, who gave you the idea that you would possibly need one?


    Capacitors are a bandaid to fix a broken system that will otherwise fail at some point anyway. If you're not having issues, you have nothing to fix, and therefore nothing to put a bandaid on in the first place.
    Last edited by malcom2073; 04-23-2012, 02:41 PM.
    "stop with the REINSTALLS, what do you think we got some lame-o installer!!!" - mitchjs
    RevFE
    My Shop

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    • #3
      i have recently spent a lot of time pondering this-- why is it ok to have a capacitor in a heavy load device like your home a/c unit, but bad for your car?

      the simple answer comes down to the power supply. at home, you cannot fix poor power problems coming into the house, so if your a/c unit is causing dimming issues, the capacitor is your only option.

      in the car, you have complete control over the power delivery system and the devices that are installed.

      capacitors have their use, but not in a situation that can be fixed by a correctly-implemented power system.

      also, you will not need a capacitor, higher capacity battery, or different alternator if you are only installing a carpc. from what i've seen, you typically need to be above 1,000watts rms before serious power system upgrades become a absolute requirement.
      My OLD 2001 Mitsubishi Eclipse GT:
      "The Project That Never Ended, until it did"


      next project? subaru brz
      carpc undecided

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      • #4
        no one told me it would drain my battery I was just curious. I as far as I have seen no problem with my power in my car...just wanting input on the matter.

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        • #5
          I will eventually have 2 amps, screen and pc installed

          Comment


          • #6
            How much power (RMS) are you planning on the amps being? It wouldn't be a bad idea to upgrade the "big 3" (http://www.the12volt.com/installbay/...TID~73496~PN~1), especially if you are trying to run higher load amplifiers.

            Do you have a work log yet?
            "stop with the REINSTALLS, what do you think we got some lame-o installer!!!" - mitchjs
            RevFE
            My Shop

            Comment


            • #7
              And house AC appliances do not have whopping big batteries attached.


              A car battery is the equivalent of millions (or billions?) of Farads.

              Hence why loads that need "clean" power are often taken direct from the battery.

              A cap would only be added near the load to remove line noise and reduce voltage dips for SMALL loads due to limited wire size.

              The proper way to eliminate voltage dips cause by wire resistance is fatter wires. Then there is no need for the cap. (Bu if you do use one, the rest of the car uses it too - just like most spike suppressors in houses proeect nearby neighbors too.)


              A cap will only drain the battery if it is faulty. They may have a leakage current, but that should be much smaller than the battery's own self leakage.



              PS - I'd argue separate feeds for amp & PC. But that depends on the amp & burp size and resulting voltage drops.
              And big amps should have their own local battery (ie, a BIG cap) which has an automated "battery isolator" to prevent draining the main battery - else a low voltage cutout so that there is enough cranking power left.
              Caps would only be desirable for BIG amps on nearby AGM batteries (eg, >~3kW with only 100AH AGM etc).
              Last edited by OldSpark; 04-23-2012, 09:01 PM. Reason: PS...

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              • #8
                Originally posted by OldSpark View Post
                A car battery is the equivalent of millions (or billions?) of Farads.

                12V 62Ah battery is 12,600 farads. Scary to think there are actually 10kF+ caps out there, but they're 2-5 volts and have really high ESR so they're no better than a battery.

                But yes, everything else OldSpark said :P
                "stop with the REINSTALLS, what do you think we got some lame-o installer!!!" - mitchjs
                RevFE
                My Shop

                Comment


                • #9
                  Hmmm - I thought is was more, but I'm "picturing" someone's quote...
                  I was gonna calculate it myself, but that would involve searching for a simple formula.


                  And it wouldn't surprise me if the other figure included the "farads" below 12.4V or 11.6V etc... Oh hangon, they do that with caps anyhow... LOL! (IE, you may have a 10F cap, but it only "discharges" down to the battery/supply voltage).
                  I think I'm confusing my battery surface charge capacitance calcs. (If a battery has a surface charge of ~13.6V and it takes headlights several minuted to remove that to get to ~12.7V, how many Farads is that? (Heaps!) That also reduces a cap's usefulness since it's only useful discharge if from the alternator voltage of ~14.4V (if that), hence they are only good for a 0.8V discharge.)
                  But let's not confuse me... I mean, those capsters any more...


                  But thanks malcom!
                  The point is it doesn't take a big battery to swap the effect of a BIG cap.

                  Or would you suggest I use 1,260 10F caps instead of a battery?
                  After all, caps don't have the 30% inefficiency of a battery, so I might save some petrol....
                  And think of my improved acceleration (ignoring the wind resistance of the tonne of caps...)

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                  • #10
                    I am trying to compile a list of parts to order next week…I am using crutchfield just for research…I haven’t decided where to get everything yet.

                    Starting with the battery – currently I have a battery with a top post being used for my car but also has the side post holes. So I am thinking - http://www.crutchfield.com/p_211BASM...L.html?tp=2681

                    I was planning on using a stretch of 2 gauge to go to the rear of the van from the battery. The entire length of the van is just about 16 feet (bumper to bumper) and it is 6 feet wide. At most I would need 22 feet and that’s probably over kill. Most kits are 15-19 feet on Crutchfield. Maybe if I got a 18 foot kit that had 2 gauge and added the rest from a piece cut from a spoll? IN this I will need 1 fuse. So I might be able to get a kit and then a small section of 2 gauge to make the full length I want.

                    Now the next part I was thinking is this - http://www.crutchfield.com/p_211DBX4...4.html?tp=3001 – I have heard people say on other sites that going down in gauges can cause problems is this true at all? I have done it before on just amp installs and never had problems that I know of but maybe I am wrong.

                    Now this gets me to the rear of the van. Only thing really missing is the fuse from the battery to the power splitter. What gauge ground wire should I make my ground. I always used the rule of the ground should be the same size as the power line. Maybe a 2 gauge fron the ground to a splitter then 4 gauge to each device?

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                    • #11
                      Originally posted by DracoPCGuy View Post
                      Now the next part I was thinking is this - http://www.crutchfield.com/p_211DBX4...4.html?tp=3001 – I have heard people say on other sites that going down in gauges can cause problems is this true at all? I have done it before on just amp installs and never had problems that I know of but maybe I am wrong.
                      it depends on what kind of problems they are talking about. assuming whatever you downgrade it meets the requirements of the device, there is no issue there. the only issue i can possibly see is that cutting the cable adds a failure point-- if one of the bolts were to come loose, etc.

                      Originally posted by DracoPCGuy View Post
                      Now this gets me to the rear of the van. Only thing really missing is the fuse from the battery to the power splitter. What gauge ground wire should I make my ground. I always used the rule of the ground should be the same size as the power line. Maybe a 2 gauge fron the ground to a splitter then 4 gauge to each device?
                      yes. it should always be at least as large, if not larger then the power input wire.
                      My OLD 2001 Mitsubishi Eclipse GT:
                      "The Project That Never Ended, until it did"


                      next project? subaru brz
                      carpc undecided

                      Comment


                      • #12
                        Thankyou for your feed back...on both there. I have done Amp installs before and did the 2 gauge to the 4 gauge after a spliter and never had an issue but for the first time I was doubting myself after a couple people said they heard that would cause issues. I don't see why it would but I thought maybe I was missing something.

                        I have always used atleast the same gauge ground as the power. maybe to make it easier I will take a good ground point(usually i used a bolt down spot for a seat) run a spliter off that and distribute to everything that way there is a 2 gauge being split to 4 gauges. This would make it the same as the powe then. What do you all think?

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                        • #13
                          sounds good.
                          My OLD 2001 Mitsubishi Eclipse GT:
                          "The Project That Never Ended, until it did"


                          next project? subaru brz
                          carpc undecided

                          Comment


                          • #14
                            I'm a bit late, but...

                            FYI - 2G = 0.1563 Ohms/1000, hence R = 3.4mR (milli-Ohms) for 22'.
                            V = IR (Ohm's Law).
                            Hence a voltage drop of 340mV = 0.34V over 22' at 100 Amps.
                            That IMO is quite reasonable for 100A. (Or rather, I try for well under 0.5V drops in power circuits...)
                            Plus relay and fuse and connector drops...


                            Re going to smaller wires... (Relax and bear with me for two lines...)
                            Oh yes, big problems because the +ve ions hit the "reducing wall" and bounce back, hence building up in the battery until it explodes.
                            Meanwhile the returning electrons suffer decompression which splits them apart. Now if you've seen a hydrogen atom splitting (H-Bombs) trust me - you do NOT want to see an electron split.
                            Okay - the above is total bullsh.
                            That's right, the H-bomb is a fusion bomb - there is no splitting involved (that's the Uranium fission bomb).
                            But the rest is true... well it is when someone else says they read it on the net....
                            The 2nd & 3rd line in this block are complete bullsh, but I occasionally like doing what others so often do (but not on mp3car - yay!). I'm so tempted o say how it flattens the battery because in actual fat the returning electrons combine with the bounced +ve ions ad cancel out, hence the battery increases its output etc etc...
                            Why did I write this? It reflects the crap else misunderstanding I so oft read in webland. (And the occasional sanctioned legit book/reference!)



                            Now, re going to smaller wires...
                            Assuming the wires are sufficient gauge and protected, then no problems.
                            Protection may be physical - ie, maybe no fuse, but a short "is guaranteed" not to occur.
                            (EG - the 2G is fused at its battery end (with a "2G" rated fuse) but the DistBlock cables are smaller and not fused.)
                            Besides, in practice, a smaller gauge (4G, 8G etc) will (most likely) still blow a 2G fuse if short circuited because fuse ratings are to protect cables from excess heat (ie, current overloads) as well as the much greater short-circuit current. (Is that clear & sensical?)

                            Also if the small gauges are short, they may get hot but the ends may conduct that heat away sufficiently (eg, the DistBlock & other cables, and the amp/load connections) hence allowing the cable to be over-driven. (But if its insulation does melt... That's where its physical protection is important - heat-poof sleeves, or being sufficient distance from other conductors even when hot and expanded.)

                            Big to small is often used simply to reduce the voltage drop - ie, reduce the resistance.
                            EG, 5G may be sufficient for the load. But 5G has double the resistance of 2G (0.31 vs 0.16 Ohms/1000'), hence using 2G for (most of) the run halves the cable voltage drop.
                            The 2G cables fuse (battery end) should be to protect the 5G cabling at the far end (eg, ~120A instead of ~180A), but if the 5G is short etc as I described earlier, it could be higher.

                            Sure, the smaller cable section may have increased resistance (per length), but it's only a relatively small resistance at the end - it shouldn't add much to the overall path resistance.
                            And although conductor changes can effect high-frequency AC circuits (wave theory), this is DC. (Though noise is AC, but we eliminate that don't we? Unless it's not a problem, ergo, we are talking about DC.)



                            Not that I recommend nor endorse running cables above their rating, I am merely mentioning practical options and considerations.
                            Done incorrectly, loss of vehicle and life could result...
                            Click image for larger version

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                            (The "Car Toaster" pic courtesy of 2k1Toaster. Brilliant man, and IMO a brilliant pic.)

                            Okay, that pic is about using cig-sockets, but the idea is the same - heat causes fires or explosions etc.


                            I hope I've provided some demystification. It's just a pity about the resulting confusion (LOL).



                            And no matter what the situation, remember to occasionally check or feel for heat - whether wires, connectors etc - BUT beware fuses - they are often normally quite warm to hot!!
                            And that goes for ANY wiring etc.
                            Connectors age and build up resistance, hence heat, and may eventually melt or flame.
                            And loads can be added to cables, or cables may degrade (especially at joins).




                            PS - the resistances I used for the 2G & 5G (from powerstream's Wire Gauge and Current Limits may be at room temp as opposed to engine-bay temps. (Resistance increases with increasing temperature.) Not that many seem to worry about that... (Possibly reflecting the extra margins used when rating quality cables.)
                            Last edited by OldSpark; 04-25-2012, 11:14 PM. Reason: PS...

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                            • #15
                              I haven't read the entire last post yet because I am running out the door as We speak...but I can say all the lines will be fused also...so any branches from the splitter box will also be fused before going nto the device taht it is powering. I guess my confusion then is this...if you can't safly step down gauge(the basic jist that the above post is telling me right now) then how can you hook computer power supply into any line? every power supply install I have seen look like it has a 16 gauge wire powering it from the 4 gauge wire fro the battery. Like i said I never had any problems stepping down an amp..but want to ask you guys before I assume on a PC its all good.

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