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Thread: second battery setup for powering M2-ATX and Inverter

  1. #1
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    second battery setup for powering M2-ATX and Inverter

    Any Ideas/thoughts on this plan for my carputer power setup in my 07 Impala?
    The Vehicles battery is isolated via the isolation diode and also through relay #1 which only allows charging of the secondary battery while the vehicle is running. Relay #2 is basically an on/off switch for the power inverter so it is only on during engine operation also.
    The Ignition signal to the M2-ATX is provided through 2 redundant sources. To sidestep WOL issues with a non supported pcmcia wireless nic I decided to just let the remote start on the vehicle boot the computer, which will also be great for making sure it's up and running when I enter the car. I choose the 12v fuel pump feed wire as this is hot any time the engine is running (during remote start) and it runs through the rear compartment harness so it is an easy target. When I stop at a destination I often need to enter and/or obtain info from my computer before I leave the car so I wanted the computer to stay on until I exit the vehicle. This is the purpose of the redundant feed coming from the retained accessory power relay, the shut down process will not begin until I open the drivers door. both circuits have an isolation diode to prevent feedback into each other.

    I have an old burnt out Inverter I hope to use to house the electronics in, it has two 110 plugs I plan to remove and replace with the relay connectors, so in the event of a failure of one of them, they can be replaced without disassembling the unit. This should be a little more aesthetically pleasing than a mass of wires and relays laying in the trunk.

    I am guessing that a deep cycle type marine battery would be best to use for this along with a marine type battery box to prevent any leakage in the rear compartment.

    This is my first go-round with a dc-dc PSU, I just built my first actual carputer, up until now I have been using my laptop in a docking station using an inverter. Any advice would be welcome.
    Thanks
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  2. #2
    Maximum Bitrate JimmyFitz's Avatar
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    Post Battery in trunk requires vent tube

    Quote Originally Posted by jimp View Post
    Any Ideas/thoughts on this plan for my carputer power setup in my 07 Impala?
    The Vehicles battery is isolated via the isolation diode and also through relay #1 which only allows charging of the secondary battery while the vehicle is running. Relay #2 is basically an on/off switch for the power inverter so it is only on during engine operation also.
    The Ignition signal to the M2-ATX is provided through 2 redundant sources. To sidestep WOL issues with a non supported pcmcia wireless nic I decided to just let the remote start on the vehicle boot the computer, which will also be great for making sure it's up and running when I enter the car. I choose the 12v fuel pump feed wire as this is hot any time the engine is running (during remote start) and it runs through the rear compartment harness so it is an easy target. When I stop at a destination I often need to enter and/or obtain info from my computer before I leave the car so I wanted the computer to stay on until I exit the vehicle. This is the purpose of the redundant feed coming from the retained accessory power relay, the shut down process will not begin until I open the drivers door. both circuits have an isolation diode to prevent feedback into each other.

    I have an old burnt out Inverter I hope to use to house the electronics in, it has two 110 plugs I plan to remove and replace with the relay connectors, so in the event of a failure of one of them, they can be replaced without disassembling the unit. This should be a little more aesthetically pleasing than a mass of wires and relays laying in the trunk.

    I am guessing that a deep cycle type marine battery would be best to use for this along with a marine type battery box to prevent any leakage in the rear compartment.

    This is my first go-round with a dc-dc PSU, I just built my first actual carputer, up until now I have been using my laptop in a docking station using an inverter. Any advice would be welcome.
    Thanks
    My Thunderbird has the main battery in the trunk. There is a vent tube which comes from the top side of the battery and exits the compartment to the outside. I was warned by others on Thunderbirdnest.com that putting a substitute battery that didn't have the vent system built in would be an explosion risk. In normal operation, you wouldn't notice the difference. If a condition of the battery or alternator failing causes an overcharging condition, the result would be a discharge of hydrogen gas into the confined space of the trunk. One spark could mean disaster. So be sure to use an appropriate type of battery for you application.
    ~Jimmy

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    Quote Originally Posted by JimmyFitz View Post
    If a condition of the battery or alternator failing causes an overcharging condition, the result would be a discharge of hydrogen gas into the confined space of the trunk. One spark could mean disaster. So be sure to use an appropriate type of battery for you application.
    A very good point, I have seen this many times as I spent 25 years as an auto tech, the possibility of an explosion I think would be minimal (the rotten egg smell would most probably alert me well ahead of time) but I also wouldn't want the mess or smell in the car. I think most quality automotive batteries are sealed and have a vent tube, so it wouldn't be a bad idea to attach a hose and put a grommet in the floor (or strut tower) to allow it to pass outside.

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    Variable Bitrate billmee's Avatar
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    I used a two battery setup for several years before the (second) battery would no longer take a charge. It was a sealed lead acid Yuasa.

    Rather than replace the batt I decided to eliminate the batt and improved my shut down circuit.
    Now I run for 1 minute after the tail light is turned off ( I prefer this over the Acc signal ).

    When I need to keep things going on the Pc I just keep the lights on. ( parking brake turn off headlights on VWs )
    If I get out with the lights on I get an audible signal that the things ( lights, pc ) are still on.

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    The tail lamp circuit was my other choice being in the trunk harness and also hot during remote start, but I figure that if I ever need to get something from the car and use the key fob to unlock it then the pc will boot, thats why I am opting towards the fuel pump circuit.

  6. #6
    Variable Bitrate billmee's Avatar
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    I like the fuel pump idea.
    Most posters stick with the tried and true; new ideas, new options.

    Example, I've seen some posts where some have used the security pulse to boot the pc.

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    I am in hopes that the fuel pump circuit will work with no problems, I do have a couple concerns with it. I am not sure exactly what the M2-ATX does with this circuit, I am thinking it is simply a discreet sense line to the M2's logic telling it that it has 12 volts, and that no current flow actually takes place. The fact that they send it with this colossal 12 gauge wire and it connects to that huge spade connector sort of makes me wonder though, I certainly don't want any voltage drop on my fuel pump feed. The other thing that Ive thought of is the fact that the fuel pump is an electric motor with windings like all have and I am not sure how sensitive the M2 would be to any AC noise on the line caused by the motor, but am hoping the isolation diode will also help with this.

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    Well I haven't gotten around to shopping for a battery or the relays, but since I was trying to beat the weather I went ahead and wired it to run from one battery for now. The fuel pump circuit seems to work fine, the computer boots as soon as I hit the remote start, and the RAP circuit keeps it alive tell I open the drivers door to exit. I did have a bit of a scare when I got finished wiring it all up, double checked everything then went to plug in the harness to the computer and sparks went flying. Still not sure why, I rechecked every thing with my meter and all was fine so I plugged it back in with no issues! I did find the fuse in the filter for my lilliput was fried when the monitor wouldn't power up so I just cut it out of the circuit since I am powering it from the M2 now.

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