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  1. #1
    mtbr member
    Reputation: Gawain Tomlinson's Avatar
    Join Date
    Dec 2013

    Bike Trailer 12V LiPO Battery System

    Bike Trailer 12V LiPO Battery System-20180818_152302.jpg

    Bike Trailer 12V LiPO Battery System-20180810_005310.jpg


    This LiPO battery system was designed as a replacement for a Sealed Lead Acid (SLA) battery system. The SLA batteries were two salvaged batteries taken from a dead UPS system. That system was easy to maintain since it could be charged with a small automotive trickle charger. On the down side it was heavy, and not ideal in San Diego, CA, where there are a lot of hills.

    The LiPO system weighs about half of the SLA system, and has better power density on the batteries. However, LiPO batteries have to be carefully managed to prevent over voltage and over current during charging. LiPOs also must be disconnected at the end of the charging cycle to minimize the risk of fire.

    The system uses two off the shelf 2S3P battery modules that have a built in Battery Management System (BMS). Each battery module contains six 18650 LiPO cells, which can be easily changed by removing the top of the module. The charging power supplies are current and voltage limited preventing over charging or overheating during charging. The charge cycle is complete when the charging power supply’s indicator LEDs switch from red to green.

    The AC power should be switched off when charging is complete, and the system should be switched to OFF mode, which disconnects the battery modules from all external devices. When switched to OFF mode the batteries should hold their nearly full charge level for several months.

    When in RUN mode the battery modules are switched to a 4S3P configuration, producing an output voltage between 16.8V and 10V. The battery output feeds a 12V 6A voltage stabilizer which provides a constant 12V output.

    A test run of the system operated all of the trailer lights at max load, (headlights, tail lights, and warning whip) for 8 hours before the BMS disconnected the batteries.

    The system has reserved space for two more battery modules, doubling the capacity of the system.

    I have a PDF document with technical details. If you want a copy, please email me a request at .

  2. #2
    Reputation: Gritter's Avatar
    Join Date
    Dec 2010
    That's great, but you didn't tell us why you're carrying 12V around with you. Is it to power a car-radio for a beach-party? Is it merely for powering your trailer's lights?

    And you charge all of this by plugging it into AC power at home? No solar panels happening anywhere?

    Is there a motor being driven anywhere in all of this? What's going on here?
    Soma, Surly, Salsa, Schwalbe, SRAM, Sun-Ringlé

  3. #3
    mtbr member
    Join Date
    Jul 2014
    I have 12v outputs on my 48v e-bike. One is connected to the lighting circuit and switches on with the lights (12v rear, 48v front, both activated by a thumb switch). The other is a hard-wired 12v out that powers my USB plug (phone charger) and a car horn.

    They're not capable of putting out much ampage though, I couldn't run much of a sound system with them - that thing looks like it's built for an altogether more lively purpose!

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