12V and 24 V Charging

System
System Posts: 2,511 admin
in General Solar Power Topics #1
I'm kind of new to solar systems and recently built a system of three 15 watt panels into a MorningStar 10 A charge controller into a 105 AH deep cycle battery. I use the system mostly for landscape lighting and to power an XM radio boombox.
I recently got a free APC 700VA UPS. The batteries were shot but I also got 40 6V 10ah batteries from a large computer UPS system. I wired two sets of 4 batteries for the APC because the UPS uses 24VDC. With the 8 6V batteries I can run my large laptop computer for a little over 2 hours. Also, if I plug the UPS into 120 VAC it charges the battery pack in a matter of hours. But I want to charge the batteries by solar. I want to keep this setup because it has a nice true sine wave inverter.

How can I do this with one set of panels (I am willing to buy 1 to 3 more panels)? Or do I have to have one set for 12V and another set for 24V charging? Can I also charge the batteries while also having the system plugged into 120 V AC?

tia,
tsp
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: 12V and 24 V Charging
    tsperez wrote: »
    6V 10ah
    With the 8 6V batteries I can run my large laptop computer for a little over 2 hours.


    Large laptops are about 90Watts, at 24V, that gives a 3.75 amp load. To run the batteries down to 50%, would take 2.6 hours, and I suspect you likely run them deeper than that. So the batteries are likely a little tired, but to recharge, you should have a separate 24V system.
    It would also be good to try to "match" batteries with a reliable digital meter, to put batteries of equal voltages in each string. ( Charge the batteries up fully, disconnect them all, and wait 3 hours, and measure the voltages )

    edit:
    1) Are you SURE the UPS has a pure sine inverter ? It'd be the first I've seen


    2) Are you using the laptop off 24VDC, or are you letting UPS convert it to 120v (-20% loss) and then the laptop's power supply re-convert that to 20V ?(another 10% loss)
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: 12V and 24 V Charging

    if you wish to use that ups you need to figure out what your loads are in watts and how many hours those watts are used for to gain wathours. this is minimumly figured on a daily basis as the pvs would also be figured in that manor. you can't use more than you can have generated and with losses figured into that too makes you generating source 25-50% larger in capacity.(varies) this does mean you have to be able to store twice what you figured you will need to draw in a day to keep from going too low in battery depth of discharge. don't forget that the ups itself with no load will still draw power too and over 24hrs it adds up. this adds to the requirements of the pvs and batteries too. i suspect it will be far more in pvs and batteries than you originally thought.
    in the meantime keep your other system that you already have until you have figured out just what it is you will need to make it all work from your backups. i would suggest you read over the forum to get better ideas on just how it is you will accomplish your goals and with what. the inverter is only one part of a system and many can devise systems on dc alone, but most of us use the 120vac system too that an ups inverter can provide.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: 12V and 24 V Charging

    i hope you get what i'm driving at in that post and that i am sorry for its bad wording. i tried to touch it up with an edit, but bbs failed to allow that.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #5
    Re: 12V and 24 V Charging
    niel wrote: »
    . i tried to touch it up with an edit, but bbs failed to allow that.

    I've found I have to use ADVANCED to edit. Still some quirks to get worked out of the new s/w
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • System2
    System2 Posts: 6,290 admin
    #6
    Re: 12V and 24 V Charging

    Let me try to answer a few questions:
    1 - Is it a true sine wave? <<It's an APC Smart-UPS 700 (model SU700NET) - specs say it has a true sine wave output.>>
    2 - Converted voltage many times? <<Yes! The UPS went from 120 VAC to 24 DC for the battery pack. The pack went from 24 to 120 VAC to the laptop power brick that changes 120 VAC to whatever the laptop uses. I do have a 12 V DC charger for the computer but I can't find it. :)
    I was just testing the UPS function of the APC with my homemade battery pack.

    I got the UPS to use the inverter function of the unit but when I took it apart I noticed that it was a 24V unit. I might just stick to my 12V system and use this setup simply as a UPS only with a much better battery pack (20ah vs. 7 ah). I'll post another question about 12 vs. 24 vs. 48 V systems.

    Thanks to all that replied!
    tsp
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  • System2
    System2 Posts: 6,290 admin
    #7
    Re: 12V and 24 V Charging

    The unit is called a 700 - it's rated at 700va but I think it is rated at 400 watts. It was purchased in 1999 I think. What's the current cost of a true sine wave 400 watt inverter?

    TIA,
    tsp
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  • System2
    System2 Posts: 6,290 admin
    #8
    Re: 12V and 24 V Charging

    Hey, I am no expert, and I don't claim to know much about this, but I would bet that if you crack open your APC or most other UPS and Powerstrips for that matter all your going to find is a Metal-Oxide Varistor ( http://www.radioshack.com/product/index.jsp?productId=2062574&cp=2032058.2032230.2032269&parentPage=family ).

    If your looking for a clean sine wave you may want to look for any isolation transformer ( http://en.wikipedia.org/wiki/Isolation_transformer ). They are commonly used for high end equipment and phone system. I have seen a lot of good products over the years from an American Company called ONEAC. ( http://www.oneac.com/home.asp )..
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #9
    Re: 12V and 24 V Charging
    Jhirley wrote: »
    Hey, I am no expert, and I don't claim to know much about this, but I would bet that if you crack open your APC or most other UPS and Powerstrips for that matter all your going to find is a Metal-Oxide Varistor ( http://www.radioshack.com/product/index.jsp?productId=2062574&cp=2032058.2032230.2032269&parentPage=family ).

    If your looking for a clean sine wave you may want to look for any isolation transformer ( http://en.wikipedia.org/wiki/Isolation_transformer ). They are commonly used for high end equipment and phone system. I have seen a lot of good products over the years from an American Company called ONEAC. ( http://www.oneac.com/home.asp )..


    ok, so what's wrong with the mov? this helps with eliminatining high voltage transients that could come from lightning or a big goof from the utility company. i use them on my utility power.
    as to an isolation transformer, well that does not make it a sinewave inverter. it may help in filtering out some of higher frequency aspects of the squarewave. here's what they said from their manual:
    "On-battery output voltage: Pseudo sine wave"
    that does not mean it is a sinewave and it may as well have said a psychotic squarewave.
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