24 volt panel charging 12 volt and 48 volt battery banks

System
System Posts: 2,511 admin
in General Solar Power Topics #1
Hi, I am a sailor in Mexico. My boat has a 48 volt motor in lieu of a diesel motor. I have six 90 amp glass matt batteries in two banks - two in a 12 volt "house" bank and four in a 48 volt bank to power the motor. I want to recharge all the batteries with a 24 volt 50watt solar panel. (I know it sounds small but it is sufficient for my needs because I use very little juice for the boat and the motor is only used for maneuvering into and out of an anchorage or marina). How do I configure this system - in terms of controllers etc.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: 24 volt panel charging 12 volt and 48 volt battery banks

    even if you were to only do the 2 batteries in the house bank with that pv you would lack sufficient power to properly charge them. this would also need downconverted for the house bank meaning it would be of an mppt type controller. the other battery bank would need an upconversion and i'm not aware of any controllers suitable for it being marketed at present. i believe when the classic comes out that it will be able to function in this capacity, but it won't do both at the same time that i'd be aware of. you need seperate charging systems designed to deliver at least a 5% charge rate and more pvs to deliver that rate. you may get away with as low as a 3% rate under some circumstances, but your 50w pv isn't even in the ball park for all of these batteries.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: 24 volt panel charging 12 volt and 48 volt battery banks

    lefty,
    i don't think 1 at a time will work out very well in a boat. for one the time needed for each battery at its 50% dod point would be 12.6hrs of full sun assuming a lossless mppt downconverting controller and no other losses like voltage drops. most get about 5hrs of full sun in the summer and maybe even 6hrs in some places so even thinking at 6 this is better than 2 days for each battery.
    2ndly if he needs to do the batteries in the electric motor it will be an unequal bank until fully charged. i assume the motor to be backup to the normal engine? if so it won't do well in an emergency to wait until the batteries can be charged.

    note that this was a responce to lefty wrights suiggestion of charging the batteries individually to achieve a better charge % that lefty deleted.
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  • Lefty Wright
    Lefty Wright Solar Expert Posts: 111 ✭✭
    #4
    Re: 24 volt panel charging 12 volt and 48 volt battery banks

    Niel, I deleted the post because there wasn't enough info to really make a valid comment.

    What did he mean by a 24V panel? OCV?

    The idea of a 48V DC motor as a sail boat auxiliary is an interesting idea. Since most sail boats sit for several days between uses small panels can work. But it seems like you'd need 4 panels of whatever size to charge a 48v bank.

    It sounds like he only uses the motor for a few minutes going in and out of the harbor. So the batts may never be run down much.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
    Re: 24 volt panel charging 12 volt and 48 volt battery banks

    good questions also, but i think we've established he won't do it with that 1 pv. it is interesting he calls himself sailiraq. what does iraq have to do with anything let alone mexico?
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  • Lefty Wright
    Lefty Wright Solar Expert Posts: 111 ✭✭
    #6
    Re: 24 volt panel charging 12 volt and 48 volt battery banks

    Agreed, he needs more panels.

    But I'm kind of intrigued with the idea of an electric motor in a sailboat. My fishing buddy's 14' boat has an electric trolling motor and we have crept around for hours on his little group 24 battery and it's never gone flat.

    Your typical 30 to 34 foot sailboat gets by with a 20HP gas or diesel engine.

    I'm guessing that this would equal a 10KW, or smaller, electric motor.

    If only used for getting into and out of harbor it might be used only 1/4 hour each time the boat was used.

    With 4 100W panels the batts could be charged in 2 days.

    Does this sound right?

    Engine maintenance was such a problem on my boat that after the engine turned into a lump of rust I threw it away and used the space for a chain locker.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
    Re: 24 volt panel charging 12 volt and 48 volt battery banks

    2 days give or take sounds about right to me and i know little about boats, but i have to agree that i would feel better knowing i'd have something to back me up. even if the batteries run down some it won't take too long to get enough in them to go again. (thinking of more open large water areas like the ocean)
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