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Thread: Someone please advice.

  1. #1
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    Someone please advice.

    This is the setup on my tank battery.

    http://imagepaste.nullnetwork.net/viewimage.php?id=805

    Can anyone comment on it?
    Will it work fine?
    Tank battery is a 7.2Ah battery, and car battery is a 70Ah battery.
    Thanks

  2. #2
    Variable Bitrate rEegLer's Avatar
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    I have a similar setup. I have an auxiliary battery that supplies power to my carPC when it is in standby. Your load will draw power from whichever source has the highest voltage or if both if one source cannot supply the necessary current. In your pic you have your Ignition running your CarPC, not sure if you mean this is coming straight from the battery or if you literally mean the ignition 12v+ source. This typically is low power and cannot power your PC.

    Hope this helps! Check out my build to see my setup.
    Love

  3. #3
    Maximum Bitrate bes51659's Avatar
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    Agree. Connect relay switch to battery instead. (if you go with that solution)

    To avoid your tank charging the car a diod could be a good idee. More likely situation is however that you will have a current rush to the tank when turning on ignition. I would suggest some kind of current limiting, but I cannot think of anything else than a simple resistor.... If not you will melt the relay.

    One neater solution is to separate the two batteries at all time, letting the PC run on tank only. Then add a charger to the tank when car is running (not when ignition is on).
    How to ashieve this I am not completely sure... A standard car charging relay?

    Edit:
    Oh, and you probably better have some sort of supervision on the tank battery. You do not want it to be completely flat, so a relay to cut it off completely would be a good idee.

  4. #4
    Variable Bitrate rEegLer's Avatar
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    The problem with having the relay switch the two sources is that the PC has to be off when the relay is switched or else it will turn the PC off when switched. I have the car battery switched with a relay and it works fine. I have a high current rectifier stopping the auxiliary battery from 'charging' the car battery. I do have a relay hooked up to my Fusion brain that measures the voltage of the auxiliary battery and charges it when it drops below a certain point.
    Love

  5. #5
    Maximum Bitrate bes51659's Avatar
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    I did not find your connection diagram unfortunately, reegler.

    However, I would suggest something like this:



    As you can see I have left out the starter battery. I suggest keeping it separate for two reasons.
    1) Difference in battery capacity. You will have balance problems for this reason alone (lifelength issues of battery)
    2) Normally when starting car and you have been using the PC (and soundsystem?) the tank battery needs charging. You want to charge it from the alternator and not the starter battery, aspecially when you have just turned on the ignition

    This circuit will work so that tank is connected to PC as soon as ignition is turned on. The PC can then enable its own power with the second relay that can be connected to a fan connector on the mobo, and then stay on even if ignition is turned off.

    When the ignition is off and eventually the PC shutsdown, the voltage on the fan connector will go away, and the relay will fall disconnecting the tank battery from your entire PC system including DC/DC converters, audio poweramps and what have you.

    Charging relays can be found new at 40$ or so, and will ensure that your tank battery is charged properly without affecting the starter battery too much. Yes, I know, alternator voltage is not that easy to connect to. Sorry.

    BUT.
    1) Will the relatively small tank be sufficient for a PC _and_ a proper soundsystem?
    2) You will have to monitor the tank voltage and shutdown the PC when low. Manually or automatically with fusion brain or what ever.

    BUTTT.
    Next step is to use some kind of microcontroller system. That will enable you also to turn on the system even without ignition. That is the route I took.

    BUTTTTTTT (edit)
    I forgot. You obviously need protective diods on the relay coils! (not on drawing)

  6. #6
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    more info

    The way ign on comes from cigarete ligther that only powers up when car is runing or ignition on....switchs off during crank....

    The idea is that when car is running realy closes connecting tank to cigarete lighter and chargin battery....but as soon as car is off, tank battery is completely disconnected from main battery, allowing me to run my pc from the tank battery and so that when engine cracking cant draw power from my tank battery as its not connected...

    Now apart from diodes accross coil of relay for clamping, what else do i need to modify?
    i do have fuses on the initial connection to the (IGN) lighter, and one directly on the battery...
    any more sugestions?

  7. #7
    Variable Bitrate rEegLer's Avatar
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    Yea I don't have a neat paint diagram for my build, just hand drawn ones . I just have pictures of the circuit i built and a description of how it works.
    Love

  8. #8
    Maximum Bitrate bes51659's Avatar
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    Quote Originally Posted by brukutu View Post
    The way ign on comes from cigarete ligther that only powers up when car is runing or ignition on....switchs off during crank....

    The idea is that when car is running realy closes connecting tank to cigarete lighter and chargin battery....but as soon as car is off, tank battery is completely disconnected from main battery, allowing me to run my pc from the tank battery and so that when engine cracking cant draw power from my tank battery as its not connected...

    Now apart from diodes accross coil of relay for clamping, what else do i need to modify?
    i do have fuses on the initial connection to the (IGN) lighter, and one directly on the battery...
    any more sugestions?
    I might have missunderstood the purpose of the tank battery, but anyway; I would not connect batteries as on your drawing.

    I would get a PC power supply that is not affected by power surge. I do not think voltage to cigarette lighter is turned of during cranking. It is just very low.

    btw. You have not connected the PC to the cigarette lighter, have you? That was just a joke was it?

  9. #9
    Raw Wave
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    Paralleled batteries - bad (usually; when not charging).

    See my (first) reply in How to hook up extra battery? - that overcomes all the above issues.
    That only connects the tank battery when the vehicle is charging (easy if you have a normal alternator with D+ or L charge-lamp output).

    Later I mention the MW728 low voltage cutout to protect the aux/2nd battery.


    PS - avoid high current diodes; they are rarely if ever a good solution!

  10. #10
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    Quote Originally Posted by bes51659 View Post
    I might have missunderstood the purpose of the tank battery, but anyway; I would not connect batteries as on your drawing.

    I would get a PC power supply that is not affected by power surge. I do not think voltage to cigarette lighter is turned of during cranking. It is just very low.

    btw. You have not connected the PC to the cigarette lighter, have you? That was just a joke was it?
    I have on in the boot, rated at 10A.....

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