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Battery packs for mobile Radio.

Discussion in 'Homebrew and Kit Projects' started by EA7KCX, Mar 26, 2019.

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  1. EA7KCX

    EA7KCX Ham Member QRZ Page

    Hi everybody,
    My name is Pedro, EA7KCX.

    Since i bought my radio (yaesu FT897D) i have been wondered about operate it with batteries making some portable expeditions so i bought some lead acid Batteries. (Original Yaesu FNB-78-h battery are too expensive)

    It's important comment that, i haven't placement to make radio, so, i go up to the roof to make some contacts (see my profile) with a handmade endfed antenna.

    So, a month ago i started to learn about different batteries technologies and some mods with yaesu FT897,
    finally i choose lifepo4 batteries, why?
    1.- Battery Cell Voltage: A 2.8v to 3.65v per cell makes a nice 14.4 volts for a 4S pack of them
    (FT897D's manual marks a working voltages from 11.73v to 15.87v)
    2.- Other most poppular options like LiPo doesn't have the same propieties.
    3.- Safety (must be the first) Lifepo4 batteries are not so explosives like LiPo are.
    they only explodes while charging (worst case) but i'll show you how prevent it.

    What we need (the tutorial is almost beginning):
    1.- Batteries
    2.- BMS (Battery Managing System)
    3.- Cable and some connectors.
    4.- Soldering Skills

    1.- Batteries:
    As i've said, the working voltage of the yaesu ft897D is from 11.73v to 15.87v,
    so if i use 4 of them, voltages will be from 11.2v to 14.4v.

    These Voltages are completly safe for the Radio, because, at 14.4 the top max voltage is far away and at 11.73v the radio will be turned off and our batteries will be proctected for under voltage.

    OK, we have the batteries, next step.

    2.- BMS,
    Why we need it?
    When you are working with a delicated system as is a battery system, all cells must be balanced as well (same voltage per cell) so a BMS will help us.

    This model will provide us for a common port for charging and discharging:
    BSM will proctect our batteries for undervoltage and overcharging.

    Important information:
    When a Radio is transmitting a bunch of current will be drained form batteries, so, is a important feature to
    In this case, batteries are a 3C discharge (30A peak) and 10.000mAh and BMS could handle 35A without problem.

    Best option is look for features 15% upper than your application maximum usage

    Following the schematic provides by BMS manufacturer i proceed to solder them:
    Instalation at radio:

    Now, i solder de BMS cables to each cell for balance charging.

    A rear view of the radio.
    I've used a 4pin connector that handle 10A per pin, i'll use 2 pins for red and 2 for black.
    Finnaly assembly:

    It works great! I've to upload some vids making QSOs with 100W SSB, but i can guarantee to you that it works!

    Buy some connectors to charge the batteries throught the same connector.

    If you have any cuestion, ask me!


    Attached Files:

    US7IGN, KL4KF, VK4HAT and 1 other person like this.

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