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Why not just use a diode between accesory

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  • Why not just use a diode between accesory

    battery circuit? wouldn't the accessory just switch off power to the circuit when cranking, same as having the relay doing it but only faster?
    Iwill ZPCgx 2.4ghz cel, 256mb pc2700, external combo drive, 80gb 2.5 laptop drive, xp pro, usb gps, 7 in Lilliput TS , carnetix CNX1900. All mounted ghetto- still experimenting and tweaking.

  • #2
    How about posting a coherent question?

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    • #3
      Originally posted by HoSS
      How about posting a coherent question?
      Coz crazymadbastard's don't do that!
      Laidback


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      • #4
        Ummm, what type of diode are you talking about, there are MANY types of diodes and if I think I know what you are talking about, you want to keep your stuff on when you turn from acc to crank right???? If so, no, a diode won't work....

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        • #5
          Originally posted by Laidback
          Coz crazymadbastard's don't do that!
          very true!


          These questions are very coherent to those who know what a tank circuit is, and also know why/how they work.

          And these are the same folks I hope would answer instead of n00bs like me...
          Iwill ZPCgx 2.4ghz cel, 256mb pc2700, external combo drive, 80gb 2.5 laptop drive, xp pro, usb gps, 7 in Lilliput TS , carnetix CNX1900. All mounted ghetto- still experimenting and tweaking.

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          • #6
            I'm so tired right now that your question actually made sense....
            Diode's suck the juice. Thus, your tank will never get a full charge. Search. This topic has been covered thousands of times before. Check out the "similar treads" at the bottom of the page.

            Err... wait. Maybe my tiredness made me read your question incorrectly...
            Why the heck would you put a diode between an accessory and the battery?
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            • #7
              Originally posted by crazymadbastard

              These questions are very coherent to those who know what a tank circuit is, and also know why/how they work.
              um, no.
              If you had any idea what u were saying you either; wouldn't need to ask, or possibly you could even string a complete sentence together.

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              • #8
                Originally posted by PatO
                I'm so tired right now that your question actually made sense....
                Diode's suck the juice. Thus, your tank will never get a full charge. Search. This topic has been covered thousands of times before. Check out the "similar treads" at the bottom of the page.

                Err... wait. Maybe my tiredness made me read your question incorrectly...
                Why the heck would you put a diode between an accessory and the battery?
                if you do not put the diode there, when the car is off- the accessories might suck the juice out, when the car is on- it would see power from the accessory.
                You would need a very efficient diode- a "schotke", sure the tank battery would never see full voltage, but it should be enough. This circuit eliminates the relay and the problems with the relays being slow and "complicated".
                Iwill ZPCgx 2.4ghz cel, 256mb pc2700, external combo drive, 80gb 2.5 laptop drive, xp pro, usb gps, 7 in Lilliput TS , carnetix CNX1900. All mounted ghetto- still experimenting and tweaking.

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                • #9
                  Ok, as I said in the first place - If you want a sensible answer, make a clear question.
                  Anyway, reading between the lines...

                  1. ACC circuit id (usually) disconnected when the car is off, so you would not lose power.
                  2. A diode allows current to pass in one direction. If you wire it anode to the load, nothing will flow, If you wire it cathode to the load it will not stop power drain.

                  I suggest that rather than flounder around trying to reinvent the wheel, with little understanding of electronics, you do what PatO suggested & SEARCH for previously descibed solutions.

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                  • #10
                    [QUOTE=HoSS]Ok, as I said in the first place - If you want a sensible answer, make a clear question.
                    Anyway, reading between the lines...

                    1. ACC circuit id (usually) disconnected when the car is off, so you would not lose power.

                    **** my thought here is that the computer would draw
                    power directly from the acc line, therefore ony charge the battery while the car is on so no relay needed.

                    2. A diode allows current to pass in one direction. If you wire it anode to the load, nothing will flow, If you wire it cathode to the load it will not stop power drain.***** The danger here is that the tank circuit is going to power the accesoriers while the car is "off" so the diode serves a purpose this way too. Each car will vary, I am sure.

                    I suggest that rather than flounder around trying to reinvent the wheel, with little understanding of electronics, you do what PatO suggested & SEARCH for previously descibed solutions.
                    **** I guess you are opposed to inovation and should not be on a computer, I suppose you only like to follow the crowd.
                    Iwill ZPCgx 2.4ghz cel, 256mb pc2700, external combo drive, 80gb 2.5 laptop drive, xp pro, usb gps, 7 in Lilliput TS , carnetix CNX1900. All mounted ghetto- still experimenting and tweaking.

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                    • #11
                      Maybe I am missing something, WHY do you need a tank circuit?
                      are you trying to isolate the computer from the battery when the car is off?
                      the Acc circuit is only live when the key is on ACC or RUN


                      what I thing you are talking about is correct in an AC circuit
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                      • #12
                        Originally posted by Twopoint
                        Maybe I am missing something, WHY do you need a tank circuit?
                        are you trying to isolate the computer from the battery when the car is off?
                        the Acc circuit is only live when the key is on ACC or RUN


                        what I thing you are talking about is correct in an AC circuit
                        Whenever you start the car, the amount of power available will drop and may cause your computer to hang or shutdown.
                        A tank circuit will keep the voltage from dropping while you crank the car, it "feeds" the power to your computer while your car cannot provide the "juice".
                        Iwill ZPCgx 2.4ghz cel, 256mb pc2700, external combo drive, 80gb 2.5 laptop drive, xp pro, usb gps, 7 in Lilliput TS , carnetix CNX1900. All mounted ghetto- still experimenting and tweaking.

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                        • #13
                          CMB - would you please sketch this circuit out for us? I think we're having trouble visualizing what you're describing.

                          Just as a note of caution - don't run your computer directly off the ACC line. That circuit is not rated for such a large load. Hence, why most people use a relay of some sort.
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                          Ne1 recognize the avatar?

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                          • #14
                            Originally posted by PatO
                            CMB - would you please sketch this circuit out for us? I think we're having trouble visualizing what you're describing.

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                            • #15
                              Wow, so much rubbish in such a short thread. And give the guy a break - he's asking a perfectly intelligible question if you actually know anything about the subject.

                              Let's see if I can address some of it.
                              How about using a diode between accesory and the tank
                              battery circuit? wouldn't the accessory just switch off power to the circuit when cranking, same as having the relay doing it but only faster?
                              1. Yes, you can do this. It's exactly what I'm going to do. The acc line is turned off by an existing relay in the car - but it only turns off power to the acc line (at least in my car), it doesn't isolate your tank circuit from the rest of accessories.
                              ACC circuit id (usually) disconnected when the car is off, so you would not lose power.
                              2. In my car, the accessory is disconnected from power when the ignition is off (and during crank). It is *not* disconnected from your accessories. So my tank battery (without the diode) would happily keep the windscreen wipers going, the radio on and the dial illumination going.
                              Diode's suck the juice. Thus, your tank will never get a full charge. Search. This topic has been covered thousands of times before. Check out the "similar treads" at the bottom of the page.
                              3. It will cause little to no effect on charging - certainly a lot less than the voltage drop across a current limiting resistor (if you want to keep totally within battery charging specs). Use a schottky diode. Digikey.com has a 20A, 0.25V forward voltage drop for about $1.40. It's what I'm using. I have no issues fully charging the tank - the output from the alternator is more than high enough even with a fixed 0.25V drop. You need to ensure you won't totally discharge the battery or the huge charge current will cause difficulties. This a long thread on a circuit with a current limiting resistor, if you can't guarantee the tank will never get fully discharged.

                              4. The diode will prevent any current drain the accessories both when the car is off and when the tank is feeding the computer during the crank.
                              **** my thought here is that the computer would draw
                              power directly from the acc line, therefore ony charge the battery while the car is on so no relay needed.
                              5. You can't have the acc line powering the PC directly since that will bypass the diode. But perhaps I'm misunderstanding your description.
                              I suggest that rather than flounder around trying to reinvent the wheel, with little understanding of electronics, you do what PatO suggested & SEARCH for previously descibed solutions.
                              6. That won't help much - there are few people doing this and locks of people who should know better telling them (incorrectly) it won't work and telling them to search. Trust me, I've been through this forum with a fine tooth comb for the last 6 months looking for ideas and experience doing this.
                              um, no.
                              If you had any idea what u were saying you either; wouldn't need to ask, or possibly you could even string a complete sentence together.
                              7. Then you probably don't know about what he's asking about and should leave answering to people who do. His question is totally understable.
                              **** I guess you are opposed to inovation and should not be on a computer, I suppose you only like to follow the crowd.
                              8. Right on. This forum is full of people like that. They like to follow the crowd without understanding if/why that's a good idea, but better still like to lecture everyone else to do the same.
                              You would need a very efficient diode- a "schotke", sure the tank battery would never see full voltage, but it should be enough. This circuit eliminates the relay and the problems with the relays being slow and "complicated".
                              9. It doesn't actually eliminate relays as such - it just eliminates the need for having one in your circuit (for this specific purpose). The car itself uses a relay to disconnect the acc line from power. Also, there might be other reasons you'll still end up with relays in your tank circuit (I probab;y will have several as part of a cheap and simple shutdown controller).

                              10. You still have to worry about full draining the tank battery - just as you would otherwise worry about draining the main battery. Obviously your car still runs in the worst case with the tank circuit, but your tank battery might be totally ruined. And you might blow fuses due to unacceptably initial high charging currents.
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