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Thread: On board DCDC charging

  1. #1

    On board DCDC charging

    OK - work with me here.

    My current battery set up is

    Start - Lithium
    House - Lithium
    These run through a simple switch - Off / batt 1 / Batt 2 / Batt 1&2

    Minn Kota 2 x 125amp Lithium each having their own Victron charger (connected with a breaker)

    Question

    Is it possible to run & DCDC charger to the front hatch & use it as a charging point ? I totally want to bypass the starting & house batteries.

    I want to use this charging station to charge camping batteries in lieu of taking a generator.

    Secondly - Could it be used to charge the leccy batteries individually ? ...... Scenario End of the day of spotlocking & have a 1hr run home - connect up one battery & charge it on the way home - topping up the battery with 40amps
    Next day - swap over & charge the other battery on the 1hr run to the fishing location ........ both batteries have had a 40amp top up.

    I can see this being an effective way of charging batteries when off grid - particularly NQ island camping trips when you may do hours of cruising every day ....... Any ideas , thoughts ?

    Chris
    Give a man a fish & he will eat for a day !
    Teach him how to fish
    & he will sit in a boat - & drink beer all day!
    TEAM MOJIKO

  2. #2
    Ausfish Platinum Member
    Join Date
    Mar 2015
    Location
    Kalbarri, WA

    Re: On board DCDC charging

    It would be possible, and I see what you are getting at. The problem, as I see it, will be with wanting to totally bypass both your House and Start batteries for that approx 1 hour run time. Both those batteries will be required to power systems during that time, power which is not being replenished. For your Start battery you have the load of providing both the power for ignition as well as the power ( assuming you have a late model fuel injected motor) for your fuel pump/s. And anything like power trim if adjusted during that time. If you have trim tabs, they are likely, but not necessarily, powered from House battery, which is also powering whatever electronics and accessories you are running during that time. If your batteries are enough to run this gear for this period of time AND get you started reliably next morning , you should be OK. Those with actual numbers on the kind of power draw a modern motor has while running should contribute here. But you want to not have them being charged on the way out either, putting all your charge in to the DC DC again. So those requirements will be for 2 hours.

    But the hardest part, as I see it, would be isolating your charging circuit ( alternator) from your Start supply to the motor. These are all wired up so it really is just plug and play, ie, hook up your battery leads to the motor and you have both starting and charging/running taken care of. You would have to rely on having wiring/switching arrangements that keep power supplied to the motor for running from the battery, but separating the charging circuit and the motor power requirements, so the charging circuit is feeding directly into the DC DC charger feed. If you are running a motor which is still under warranty, you could probably kiss that goodbye.

    You stated there is a lot of cruising going on, meaning your Start/House batteries will likely be pretty well charged at most times.. Which means that not a lot of your alternator charge will be going into House/Start batteries on that run home. So the actual reduction of power available to the DCDC in that time might not be that great anyway. if you have a 40 amp alternator, you might be putting 35 a/hr back in, instead of 40? Maybe a little less on the way out, as you have had a cold start on the motor, etc. Just remember that in series, amp/hour capacity is not cumulative. You are running 2 x 12v batteries in series, IIRC--put 40 amp hours into one, and 40 amp/hours into the other, and you have still only replaced a total of 40 amp/hours of capacity. Series means add voltage together/keep a/h the same, and parallel means keep voltage the same, add a/h together.

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