Repost: Using a 2-cell LiPo battery (7.4V) for battery input

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This topic contains 1 reply, has 1 voice, and was last updated by  akiba September 11, 2017 at 2:43 pm.

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  • #481

    akiba
    Keymaster

    [Reposted from old forum]
    “Got my boards in last night and got them assembled and talking with the example. I have a quick question on the battery power circuit. What voltage ranges can it handle? I’m looking to drive a solenoid off the battery pack and so I need to use some lithium batteries. Using 2 of them the voltage should be about 7.4V. Can the battery circuit handle that voltage or is it going to be too much? I’ll be driving the solenoid directly off the batteries through a dedicated driver circuit so I won’t need to worry about pulling the drive current through the board’s battery power circuit.

    Thanks,

    Ryan

    Akiba
    FreakLabs Open Source Wireless
    Twitter: @freaklabs
    Facebook: https://www.facebook.com/freaklabswireless

  • #482

    akiba
    Keymaster

    Hi Ryan.
    I just tested the system using a 7.4V input. You will mainly be bypassing the boost circuit and powering the system off of 7.4V (minus one schottky diode voltage drop ~0.3V) so almost 7V. Unfortunately, the design assumption is that you will be going in at less than 5V and the boost regulator would handle the voltage regulation. There is no regulator to bring that down in case the battery input is higher than 5V. There is a radio for the 3.3V side of the system so the radio and anything else on 3.3V is safe. The problem is that the MCU maximum supply voltage is 6V so at 7V, you will be outside of spec and could potentially cause a failure. I’d recommend bypassing the battery input and going straight into the DC jack instead. The DC jack expects higher voltages and goes to the onboard 5V regulator. In that case, being at 7.4V is no problem for the system.
    Hope that helps.
    Akiba

    Akiba
    FreakLabs Open Source Wireless
    Twitter: @freaklabs
    Facebook: https://www.facebook.com/freaklabswireless

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