3 stage battery charger

System
System Posts: 2,511 admin
in Solar Beginners Corner #1
I have a battery bank with 880 ah at 12v total. I would like to use a 3 stage charger on my off days to charge my bank up. Can someone tell me how many amp charger I need and some good brand names as well. Thanks and sorry if I have not given enough info...Brian
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: 3 stage battery charger

    Welcome to the forum.

    For 880 Amp hours @ 12 Volts you would need at the very minimum a 45 Amp charger like this: http://www.solar-electric.com/dls-45.html
    At the other end of the spectrum is this 90 Amp unit: http://www.solar-electric.com/ioen12vo90am.html

    Now it will make a difference what type of battery they are: AGM's or FLA's. Also, if they're "tall case" batteries like L16's they'll want the higher charge current. Manufacturer & model could be helpful.

    Someone will inevitably ask "what's the application?" because we have a sort of holistic approach to everything around here. :p
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: 3 stage battery charger

    Now it will make a difference what type of battery they are: AGM's or FLA's. Also, if they're "tall case" batteries like L16's they'll want the higher charge current. Manufacturer & model could be helpful.

    I am using golf cart batteries. 8 - 6v energizer 220 ah. the reason I went with the m is I am just starting out and its only for a off the grid get away cabin. I want to learn all the ins and outs before I spend any great deal of money. I will take any advise I can get... thanks so much for your time. If I could I would like to get a charger that could bennefit me now and In the future if I expand to maybe 2000 ah battery bank or am I not looking at it right???
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: 3 stage battery charger

    Golf cart batteries are a good choice for starting with.
    However, four strings in parallel can be problematic in keeping all balanced. Generally if you need that amount of capacity you should increase the system Voltage. A 2000 Amp hour 12 Volt bank is completely out of the question; far too unmanageable.

    The way to design a system is to start by determining the loads. Then see how much you can reduce them. When you come up with a figure for how much you need in Watt hours you can see what sort of system Voltage you need. In fact just today I was explaining this to two other people; about the threshold for switching up to the next higher Voltage level. The 12 to 24 Volt number seems to be either 2000 Watts in peak power or 2600 Watt hours daily. Your 880 Amp hours will give you up to about 5.2 kW hours daily. That is a huge amount. It would be better to supply that as a 48 Volt system, or at least a 24. Here's the current breakdown:

    880 Amp hours @ 12 Volts wants 88 Amps of charge current @ 14.8 Volts. This is difficult to manage, as it is over the maximum of the largest charge controller available.
    440 Amp hours @ 24 Volts wants 44 Amps of charge current @ 29.6 Volts. Easily handled by a 60 Amp charge controller or even the MS 45.

    In terms of loads it's the same thing: equal amounts of power in Watts only the current is halved as the Voltage is doubled. Handling more than 200 Amps of DC is difficult at best.

    Might be rambling a bit here. Sorry.
    Do you have a load figure?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,654 admin
    #5
    Re: 3 stage battery charger

    It is difficult to "up size" an off-grid power system without spending lots of money and placing lots of the older equipment on EBay/Craig's List to get some of your money back.

    Roughly, if you try for more than 2x increase in system capacity/size (loads, battery bank size, etc.)--Enough will change that you will probably need new battery charger, new inverter, and some extensive rewiring.

    More or less--design the system for your expected loads and see what you get. You should always leave some margin for growth/miscalculations in usage.

    As you pick your components--you can now decide if you want the larger MPPT Charge Controller (and more expensive), an inverter with Generator Controller/Integrated Battery charger, etc...

    But without a starting point (requirements, loads), this does get rather confusing and an lead to circular discussions.

    We can start with your existing battery bank (assuming it meets your needs and they are still good)--and design the system around that--But it would be nice to double check your loads too.

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