Solar Panel Trickle Charger - Can I Reuse my existing 21W panel w/ USB output?

chrisisinclair Registered Users Posts: 1
Im looking to add a solar trickle charger for my subaru for when I go on extended trips. I already own a pretty decent portable panel (Anker 21W with 2 USB outputs). I use this camping and it works fairly well even without full sun. The car is a 2017 Subaru Outback with an Interstate size 24 battery with 130min reserver / 700CCA. Forget the exact capacity but I upgraded it from the tiny stock SLA.

Can I use a stepup converter to go from the 5V USB output up to 12V and then run that into a charge controller hooked to the battery?

Id like to make  this as clean and modular as possible - basically Id love to be able to easily disconnect the panel and continue to use it port ably as needed. If I do need to purchase another panel that is a possibility as well.

Is the best way to wire this direct to the battery or can I jump through the OBDII port or maybe even wire it somewhere in the fusebox? I would prefer to avoid using up the cigarette lighter.


  • BB.
    BB. Super Moderators, Administrators Posts: 33,501 admin
    The general method is to get a ~5-10+ Watt solar panel that has a OBDII port on the end of its cable:

    ~5 Watt is the "standard" for many cars that are shipped from overseas and sit in a lot before selling in the US.

    If you want a bit more power, then a 10 Watt would be pretty nice for a larger battery and/or if you have other loads (like a Lojack or similar).

    If you go with a >10 Watt panel, you probably should get a true 12 volt panel (Vmp~18 volts) and use a PWM solar charge controller... Or, you run the risk of "boiling your battery dry" from extended over charging (charge controller will stop charging when the battery is "full").

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset