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Thread: New idea for Tank circuit

  1. #1
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    New idea for Tank circuit

    I have done a lot of reading about tank circuits and relays etc, and a lot of people say that the relay in the circuit may not react quick enought in order for the voltage not to drop.

    I have a PX-70 and an ITPS, work superbly, cannot fault it as i wanted a really small footprint and the opus was just too big.

    Anyway here is my idea, have the Yuasa 0.8-12 or similar, have a resistor in between the 12V contonous between my main battery and the tank battery.

    If i decide to stop the car for some petrol, surely i can have a switch instead of a relay which switches the power to the computer to solely run of the tank battery? Basically the switch act before the resistor?

    Would this work? And if so does someone know where in the UK online i can get the right battery and the right resistor?

    Thank you all in advance

  2. #2
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    Oh and i though i better add that the computer will work after i switch the car off, i.e. off of the voltage solely from the battery as i have heard some peeps have probs with ITPS wanting to see 13something Volts.

    Anyway will the 0.8-12v show more than 12V? I dont want to add the diode as i have heard this will drop the voltage and i think the ITPS is right on its limt

  3. #3
    Clover Grayscale's Avatar
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    probably too small of a tank battery. you need a diode to prevent the starter from sucking power from the tank battery when the car is cranking.
    CarPC install is starting to come along again...

  4. #4
    FLAC PatO's Avatar
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    Quote Originally Posted by adrian_uk17
    a lot of people say that the relay in the circuit may not react quick enought in order for the voltage not to drop.
    Worked for me. Tank batt is a 5Ah model from Rat Shack. Standard Bosch relay disconnects power between main batt and tank when starter wire in steering column is charged. It hasn't failed once. Even after running the comp for 1/2 hr, then starting the car.

    Your idea looks good, but the whole manual switch idea is too.... manual. Spend a couple of bucks on a relay and see if it works for your setup.
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  5. #5
    Constant Bitrate cbergeron's Avatar
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    PatO - we have a 12v 4Ah battery that we're trying to use as a Tank. I'm not sure how to create the tank circuit. How should we connect it? How do you recharge your battery when it's not acting as the primary?
    DashPC - The Linux Car (since 1999).

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  6. #6
    Super Moderator. If my typing sucks it's probably because I'm driving.... turbocad6's Avatar
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    You can do it with two relays & no diode, just use the first relay(tank relay) to connect your tank, triggered by crank signal, & have the first relay also trip the second(main interrupt), which momentarily interrupts your main power wire, this double trip covers the latency in the relay switching. The trick is to have the second relay re-engage (main power) before the first disengages. You can do this by having the second relay powered by grounding one solenoid terminal to the accessory lead, which will drop to ground during crank & return to power immediately after releasing the key, & therefore releasing the second relay & restoring main power. The first relay can be delayed with a Pac tr-27 or similar, & you can set it to be delayed for up to 25 min.s & the benefit here is that the delay here will cause the tank to remain connected for that period of time to top off the charge on the tank. this works well with smaller tank batteries that don't need more than that to be charged for the next time, & are really only being used strictly as a tank battery & not an aux power source as well...

    with this there is no voltage drop through a diode, & there is never a time that the pc has even the slightest split second of power loss throughout the transitions. I could draw a diagram, but it would be a pain to upload it, I may be able to next week......but it's pretty simple if you think about it.........whole thing should cost around $35, with the delay timer being around $25 of that, there are ways to use a small capacitor to delay the primary relay release long enough too.........& then the whole thing comes in at $10-$15 tops...........but that won't charge the tank at all. the third way to do this, & the best way if you want your tank circuit to charge throughout the whole ign. cycle each time is to have the first relay latch upon ign, & stay activated throughout the ign cycle, then when the main interrupt relay is activated while cranking & then released the tank relay stays on until you turn the ign. off, you can also use a delay circuit here to allow your pc to run on the tank for a period of time after the ign is turned off if desired....

    I hope this makes sense to you & if I can put a wiring diagram up I will, if there is anyone out there who understands this & has the ability to display diagrams here please feel free to do so.............

  7. #7
    Constant Bitrate cbergeron's Avatar
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    I understand what you're saying for the most part. We're trying to implement a Tank circuit into our DSSC startup/shutdown controller.

    We'd like to get input from you guys on what we should add and how you'd like for us to implement it.

    Your guys' thoughts?
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  8. #8
    Well, He asked for it. WebDog's Avatar
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    Why wouldent a simple setup like this work?
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  9. #9
    FLAC PatO's Avatar
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    Quote Originally Posted by turbocad6
    You can do it with two relays & no diode, just use the first relay(tank relay) to connect your tank, triggered by crank signal, & have the first relay also trip the second(main interrupt), which momentarily interrupts your main power wire, this double trip covers the latency in the relay switching. The trick is to have the second relay re-engage (main power) before the first disengages. You can do this by having the second relay powered by grounding one solenoid terminal to the accessory lead, which will drop to ground during crank & return to power immediately after releasing the key, & therefore releasing the second relay & restoring main power. The first relay can be delayed with a Pac tr-27 or similar, & you can set it to be delayed for up to 25 min.s & the benefit here is that the delay here will cause the tank to remain connected for that period of time to top off the charge on the tank. this works well with smaller tank batteries that don't need more than that to be charged for the next time, & are really only being used strictly as a tank battery & not an aux power source as well...

    with this there is no voltage drop through a diode, & there is never a time that the pc has even the slightest split second of power loss throughout the transitions. I could draw a diagram, but it would be a pain to upload it, I may be able to next week......but it's pretty simple if you think about it.........whole thing should cost around $35, with the delay timer being around $25 of that, there are ways to use a small capacitor to delay the primary relay release long enough too.........& then the whole thing comes in at $10-$15 tops...........but that won't charge the tank at all. the third way to do this, & the best way if you want your tank circuit to charge throughout the whole ign. cycle each time is to have the first relay latch upon ign, & stay activated throughout the ign cycle, then when the main interrupt relay is activated while cranking & then released the tank relay stays on until you turn the ign. off, you can also use a delay circuit here to allow your pc to run on the tank for a period of time after the ign is turned off if desired....

    I hope this makes sense to you & if I can put a wiring diagram up I will, if there is anyone out there who understands this & has the ability to display diagrams here please feel free to do so.............
    Wow. Someone's put a lot of thought into this!
    My setup has one relay - normally closed which connects the two batteries in parallel. It opens when the key turns to the start position. It works for me (and a few others on this board).

    Why it works is another question. Could it be that the two batteries together have enough power that they would normally run a computer during a start? Possibly. However, cbergeron, it may be worth your time to invest a couple of dollars in a relay to test this out in your ride. At the very least, it seems that this concept hasn't been fully explored and your results would help solidify the idea of an ideal tank circuit...
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  10. #10
    FLAC PatO's Avatar
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    Quote Originally Posted by cbergeron
    PatO - we have a 12v 4Ah battery that we're trying to use as a Tank. I'm not sure how to create the tank circuit. How should we connect it? How do you recharge your battery when it's not acting as the primary?
    Using WebDog's diagram, replace the diode with a relay. The circuit should be normally closed - that is, the two batteries will act as one all the time, unless the car is starting.

    In the case of a Bosch (automotive) relay, you'll want to have the 85 going to the battery, 86 going to the starter switch in the steering column, 30 going to the + on the main batt (heavy guage wire), 87a going to the + on the secondary batt (heavy guage wire), 87 open, and the negative on the secondary batt going to ground.

    Then hook your computer up to the secondary batt as you would a primary battery.
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