Current Draw Limits - 5V DC Expansion Pin
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  • Derek,

    What are the current draw limits on the 5V DC expansion pin (Pin 14) of the CBT 18-pin expansion header?

    We're connecting a device that draws an average of 155mA, with a peak at 215mA. We can drive it perfectly from other Arduino devices but when connected to the CBT the external device powers up but the CBT shuts down and the power LED turns off.

    Disconnecting the device instantly brings the CBT back to life - so we assume the issue is the device is drawing more power than the CBT can supply.

    The CBT is connected solely to USB power for testing - would it matter if we used the 12V supply from the CAN line instead?

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  • Hey @jamesatfish,

    i'd try the same with 12V Powered via Pin 2 and 1.
    The car battery should give you the power you'll need.
    The PCB shouldn't take any damages, because you could power it with 16V.

    Give it a try ;)
    Greets Fry

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  • P.S.

    And remind that USB gives max. 500 mA. From this state 215 mA is a lot of power.

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  • Thanks for the suggestions @Fry2412‌ - but it seems like a limitation of the CBT not the power source.

    Connecting an Arduino Uno via USB and hooking up the same 215 mA device to the 5V regulated power from the Uno works perfectly, so it's not a limitation of the current draw on a USB power connection.

    We tried today with the CBT wired to the 12V from the car with no success - the CBT turns off when the external device is connected.

    In the end we've just worked around it by grabbing 12V from the car, regulating it ourselves to 5V and powering both device and CBT from that regulated supply.

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  • administrators

    The CBT linear regulator is good for up to 250ma at 5v. At 250ma it's going to make some heat.

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  • administrators

    It also has over current shutoff, so that is probably what you're seeing when you hook up your external device.

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