Making 12 Volt System out of 6 Volt Batteries

Discussion in 'General Electronics Chat' started by Faffy, Mar 22, 2008.

  1. Faffy

    Thread Starter New Member

    Mar 22, 2008
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    I was wondering if anyone could help me!

    I have (16) 6 Volt batteries that I want to make into a 12 Volt Battery. What I think I am going to do is have (2) Banks of Batteries. (8) Batteries in one bank and (8) in the other.

    In both banks I will series all the batteries together and then to connect the two banks together I will go from a positive on the one bank and go to a negative on the other bank to connect the two banks and essentially make (1) big 12 Volt battery.

    I am curious if this makes sense to anyone or does anyone have a better idea to achieve this. I need to make a 12 Volt Battery because I am running a 12 Volt system.

    Thanks for the help!
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Read the material here in AAC's ebook to learn a bit about connecting batteries up in series and parallel.

    hgmjr
     
  3. scubasteve_911

    Senior Member

    Dec 27, 2007
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    I think it would be better to make 8 sets of 2 in series, so that you will have 12V sets in parallel with other 12V batteries. I think this would help out with wiring them all together, instead of having to use a really thick cable between two banks of 6V cells. I might be wrong, but it kind of makes sense.

    Steve
     
  4. recca02

    Senior Member

    Apr 2, 2007
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    If I understand your problem, there might be two ways to achieve this(see attachment).

    The lower one might be what you are planning..
    I can see one advantage in this, that a failure of one battery won't affect as much as a failure of a battery in the other combination.Then again you might not want to work with an unbalanced combination.

    Hopefully other members here can shed a light on some other advantages/disadvantages.

    Here is another thread that might help you.

    edit: http://forum.allaboutcircuits.com/showthread.php?t=10154
     
  5. hgmjr

    Moderator

    Jan 28, 2005
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    Here is another article on connecting batteries in parallel and series.

    The addition of a schottky-diode in line with each of the batteries in a parallel bank has some appeal to me. The disadvantage is that the diode will need to be sized to handle the anticipated current. The advantage is that it will prevent any one battery from seeing any of the other batteries in the parallel bank as loads.

    hgmjr
     
  6. John Luciani

    Active Member

    Apr 3, 2007
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    The 8 banks of two batteries would work (with or'ing diodes).

    Two banks of 8 eight batteries each driving a 48V to 12V DC-DC converter
    would work. Use or'ing diodes on the outputs of the DC-DC converters.
    If you use VIcor DC-DC converters you could parallel the converter
    and power booster without or'ing diodes.

    One bank of 16 batteries driving a 96V to 12V DC-DC converter would also
    work.

    An advantage of DC-DC converters is you would have very good line and
    load regulation. The disadvantage is cost.

    (* jcl *)
     
  7. Faffy

    Thread Starter New Member

    Mar 22, 2008
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    Thanks for the help. I have one more question. If I were to wire it with Two Banks of 8 Batteries how should I wire it?
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    A few of questions for you:

    1) What will be your average and peak loads, in Watts or Amperes?

    2) What is the amp-hour rating of your batteries? If you don't know, then what is the make and model of your batteries?

    If your batteries have different amp-hour ratings, you'll need to be able to switch them in and out. You'll need to connect the like-rated batteries in series, or in pairs.

    3) What is the battery technology? Sealed lead-acid? Deep-cycle marine-type? NiMH? Ni-CD? (automotive batteries would not last very long in a deep-cycle application)
     
  9. Faffy

    Thread Starter New Member

    Mar 22, 2008
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    1. We will be pulling around 10-15 Amps when in operation.
    2. I believe it is around 120 but they are Deka 6 Volt Batteries and they are all the same battery.
    3. Deep Cycle Lead Acid not sealed

    Thanks for the help
     
  10. hgmjr

    Moderator

    Jan 28, 2005
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    Yikes:eek:!
    At those current levels you will need some heatsinks for the schottky diodes to keep them from getting too hot.

    hgmjr
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Ok, another couple of questions:

    1) How sensitive will your load be as far as power fluctuations are concerned? IE: is your load banks of LED's, incandescent lamps, motors, something else?

    2) How do you plan on recharging the cells, or is that still up in the air?

    I certainly don't mean to sound like I'm badgering you.

    This kind of information is very necessary to have in order to attempt the best solution for your application, and it is a normal part of what is called "systems analysis" - a gathering of facts about "what is". Insufficient information on the "front end" will very likely lead to a failed system on the "back end".
     
  12. Spoggles

    Well-Known Member

    Dec 2, 2005
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    Hello:

    Just a comment about amp hour ratings of SLA (sealed lead acid) Batteries. The AH of a SLA battery is based upon a 20 hour discharge period.

    A 12 v, 20AH battery maintain a 1 amp load for 20 hours.

    At the end of this period it would be a very good idea to disconnect and or recharge it as to discharge it further affects capacity and reduces the number of times that it can be recharged

    There is no way you supply 20 Amps (1C) for 1 hour from 20AH battery.


    Spoggles
     
  13. Faffy

    Thread Starter New Member

    Mar 22, 2008
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    1. Will be running LED Lighting as well as some low electronic devices.
    2. Will be recharging through solar and/or 110 45Amp Charger

    No problem Sgt Wookie I appreciate the help!
     
  14. anne

    Active Member

    Apr 20, 2008
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    I needed to replace a number of battery packs on my cordless tools last year. The prices were sufficiently knee weakening to induce me to get inside and see what was so special. I discovered that Dewalt, Milwaukee, Makita, et al.. don't actually use a single cell to power their 9.6v, 12v, 14.4v, and 18v, tools. The decimals should have been a giveaway to me.

    They do essentially what you are attempting to do. Except that they begin with 1.2v cells and series them until reaching the desired voltage. Once I got the hang of what was going on, I went looking for 1.2v single cell replacements on the web and got a bit of education on it. Initially I discovered that I wasn't saving enough on cost to make my labor at all worth while , which usually doesn't matter because I like a challenge. But just stringing batteries in series is like ditch digging. I was about to go ahead and get the tool pack replacements off the shelf when I discovered nicadlady.

    Great prices and the tech assistant guy kept me on the phone for half an hour making sure I completely understood what was up. Good company.
    http://www.nicdladyonline.com/specials.html
    They still list the special on the panasonic 1.2v NiMH 3000 mAh sub-C tabbed (having welded tabs so it's easier to gang them together) cells that I used. Panasonic is about as good as it gets namewise in these cells. They must have waylaid a containerload on the docks one foggy night. (if you don't have welded tabs, heavy copper de-soldering braid is excellent for joining cells together since it's heavy enough to carry current while it wicks solder extremely quickly - lessening the chance of damaging the cell with heat). ('sub-C' means that they are dimensionally just a bit smaller than standard 'C' cells. anyone foolish enough to try would not be able to replace these with standard 'C' cells - they would not physically fit in the space. perhaps thats the point) I've been pretty hard on these packs for over a year now and can confidently say that they are an improvement over the stock packs.

    Are you quite sure that you'll be pulling that many amps? Sounds high for LEDs and light load devices.

    If you've already got the 6v batteries that you intend to use, one little tip you might borrow from the tool packs is an inclusion of the little strip thermistor that comes tucked away between any two of the cells in the pack. The charger detects resistance at cell temp that tells it the batteries are ready (kind of like an automatic bread toaster) and stops charging. It may be that you will simply use one of these tool brand chargers and then you can just rob a thermistor out of an old battery pack of the same make as the charger and it (may!) give you the same protection against overcharge. Better experts here may have something to say about this.

    In any case, like i said about the tech help at nicadlady... they were really indulgent toward my very basic questions. You might give'em a call. Another good source for questions is the front desk of any BatteriesPlus storefront if one is nearby you. They rebuild packs right in the back so the person with the answers is usually someone on hand to talk to (rare these days).

    And with this is a thread hijack and a commercial endorsement. What is your forum coming to?
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Anne,
    Interesting info - however, he's talking about lead-acid/SLA batteries. Your 3000mAh translates to 3 AH.

    The big giveaway that he was talking about lead-acid batteries was the voltage. Deryk didn't actually mean 2v, 6v or 12v - he meant 2.116v, 6.35v and 12.7v - the typical output of a lead-acid or SLA battery.
     
  16. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    I suggest you to buy a 12 V lead acid battery to make your life easier. Its not very expensive.
     
  17. anne

    Active Member

    Apr 20, 2008
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