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Thread: Connecting multiple batteries in series

  1. #41
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    Default

    Hi guys! I promised the test results for the 6-pack... however, I'm sorry to say I can't give it now. Will have to try again another day. Why? Because when I wanted to use the battery pack, it felt damn hot! I realised it was a short-circuit but couldn't find out where. Anyways, the first thing I did was to remove 1 batt to open the circuit... so that day couldn't really use it...

  2. #42
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    Nov 2004
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    Default Screw type

    Huggable has visited the shop earlier. The screw size for the tripod is 1/4 inch, not M6. For the screw/bolt, the shop has 2 types, ie the hexagonal, and round head cross types only. The shortest is 1 inch, ie 2.5cm. For the nuts, the shop has both the hexagonal and square nuts. The square type might be more useful if you need to secure it and prevent it from rotating in your custom project.

    Don: They don't have the countersunk screw. But you can visit any DIY shop to look for 1/4 inch countersunk screws, at the length you desire.

    Apparently this size is the same as those used to construct racks using 'L' brackets. Used to have quite a lot of them when I dismantled the workshop rack in my office!

    The shop is Lian Hup Hareware & Enginerring, at Blk 125, Bukit Merah Lane 1, #01-172.

    Hope this helps.

    Quote Originally Posted by donchua
    I will still need the info if your side is the 'Countersunk Philip head screw' type
    or without countersunk and not bolt type as shown above thread.

  3. #43
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    I have batterypack made of 24 X AA NiMH cells to power my DIYed headphone amplifier.
    here I some points to look out for when constructing a battery pack with large number of AA NiMH cells in series:

    1. Sanyo 2300 is 2300mAH typical and only 2100mAH minimun. normally the higher the mAH specification, the difference between the typical and minimun rating will increase unproportionally. In a battery pack with all cells in series, the total capacity is limited by the single cell with the lowest mAH capacity (the weakest link). Since you can't expect all your X cells' capacities to achive the typically rating, you should stick with the minimum rating for calculation of the capacity of the battery pack.

    2. Since all cells have different capacity, the cells with bigger capacity will still be giving out voltages when the cells with lesser capacity is already flat. This will cause over discharging of the latter cells, which will further decrease their capacity and in turn worsen the problem. This problem is worsen as the number of cells in a battery pack increase (since with more cells the difference between the largest cell and the smallest cells increase). To avoid the problem factory made battery pack will have cells with matching capacity. And because of this problem you should not use NiMH cells with high capacity rating since the variation of capacities for such cells are larger (the larger diffence between the min and typical rating). I could say that anything above 1800mAH is bad, unless you can buy a huge number of they, test the capacity of them individually and use only X number of cells with matching capactiy, which is impractical.

    3. Your smart HiMH charger is not that reliable or precise. it will charge some cells more while undercharge some cells by a little bit. This is okay if you run 2 or 4 cells in series, but problematic when running a large number of cells in series (I've experienced it myself). For battery pack with a large number of cells in series, it is a must to charge them together in a series too, instead of charging each one individually (or pairs of 2 in series) as most AA NiMH charger do. the point is that cells in series get equal amount of discharge when in use, so charge them in series will ensure that each cell get equal amount of recharging, instead of slightly (in you are lucky) different amount of recharging. Since such charger is not easily available, you will either have to look hard or do some DIY.

    4. commercial battery pack have all cells connected head to tail (industrial NiMH AA cells don't have a tip on the + side) by metal stipes using instantanious large current. the resistance of such connections between two cells are extremly low. while for consumer cells, the resistance of a tip to bottom connection is about 0.1ohm, while the internal resistance of a typical NiMH AA cell is only 0.025ohm. when you have X number of cells in series, thus X tip to bottom connections, the total resistance will also mutiply by X. It will be worse if your battery pack use those battery holders with springs connected to the -ve ternimal of each cells (i.e. the normal type of battery holder you get in SLS or SLT) . Such spring are made of steel, with resistance of up to 0.5ohm each, which will cause a series problem as the total resistance in the battery pack is increased to multiple ohm as a result of multiple such springs.

    So I will say watch out of all these problem (which are real serious problem for may 24 cells pack, maybe better for your 8 cell pack), and good luck!
    Last edited by zhoufang; 14th July 2005 at 03:11 PM.

  4. #44

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    wow then ur battery pack must be huge??? how many volts did u connect them to be? does it ever cross your mind to use SLA which may be better and more cost-effective?

    Quote Originally Posted by zhoufang
    I have batterypack made of 24 X AA NiMH cells to power my DIYed headphone amplifier.
    here I some points to look out for when constructing a battery pack with large number of AA NiMH cells in series:

    1. Sanyo 2300 is 2300mAH typical and only 2100mAH minimun. normally the higher the mAH specification, the difference between the typical and minimun rating will increase unproportionally. In a battery pack with all cells in series, the total capacity is limited by the single cell with the lowest mAH capacity (the weakest link). Since you can't expect all your X cells' capacities to achive the typically rating, you should stick with the minimum rating for calculation of the capacity of the battery pack.

    2. Since all cells have different capacity, the cells with bigger capacity will still be giving out voltages when the cells with lesser capacity is already flat. This will cause over discharging of the latter cells, which will further decrease their capacity and in turn worsen the problem. This problem is worsen as the number of cells in a battery pack increase (since with more cells the difference between the largest cell and the smallest cells increase). To avoid the problem factory made battery pack will have cells with matching capacity. And because of this problem you should not use NiMH cells with high capacity rating since the variation of capacities for such cells are larger (the larger diffence between the min and typical rating). I could say that anything above 1800mAH is bad, unless you can buy a huge number of they, test the capacity of them individually and use only X number of cells with matching capactiy, which is impractical.

    3. Your smart HiMH charger is not that reliable or precise. it will charge some cells more while undercharge some cells by a little bit. This is okay if you run 2 or 4 cells in series, but problematic when running a large number of cells in series (I've experienced it myself). For battery pack with a large number of cells in series, it is a must to charge them together in a series too, instead of charging each one individually (or pairs of 2 in series) as most AA NiMH charger do. the point is that cells in series get equal amount of discharge when in use, so charge them in series will ensure that each cell get equal amount of recharging, instead of slightly (in you are lucky) different amount of recharging. Since such charger is not easily available, you will either have to look hard or do some DIY.

    4. commercial battery pack have all cells connected head to tail (industrial NiMH AA cells don't have a tip on the + side) by metal stipes using instantanious large current. the resistance of such connections between two cells are extremly low. while for consumer cells, the resistance of a tip to bottom connection is about 0.1ohm, while the internal resistance of a typical NiMH AA cell is only 0.025ohm. when you have X number of cells in series, thus X tip to bottom connections, the total resistance will also mutiply by X. It will be worse if your battery pack use those battery holders with springs connected to the -ve ternimal of each cells (i.e. the normal type of battery holder you get in SLS or SLT) . Such spring are made of steel, with resistance of up to 0.5ohm each, which will cause a series problem as the total resistance in the battery pack is increased to multiple ohm as a result of multiple such springs.

    So I will say watch out of all these problem (which are real serious problem for may 24 cells pack, maybe better for your 8 cell pack), and good luck!

  5. #45
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    Quote Originally Posted by user12343
    wow then ur battery pack must be huge??? how many volts did u connect them to be? does it ever cross your mind to use SLA which may be better and more cost-effective?
    in audiophile world such a battery pack is really not considered huge.

    SLA is not really cheaper than NiMH on a per volt basis, at least that is the case for the price of SLA in SLT.
    The main reason of using AA NiMH over SLA is that it can fit inside my DIY amp, which only have 16mm in height left for battery pack.
    And NiMH have lesser internal resistance which is good for the powering of an amp, which I lost most of it due to the high resistance of the connections between cells.
    another reason of NiMH over SLA is for the environment. NiMH is either polluting nor poisonious. Where as I won't know how to dispose a SLA in singapore so that the lead won't end up in the air (incineration) or land (land refill). So when the greener way does't cost me more, I have no reason not to choose it.

  6. #46
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    side track abit... does anyone know where to get D-sized NiMH batteries? not those 2500mah D-sized ones...

    2500mah D batts kinda defeats the purpose doesnt it? big yet it has the same capacity as AAs...

    thx alot.

    ---
    SLA is a bad idea... even resistance increases when it is being used.

  7. #47

    Default

    SLAs can be disposed safely at automotive workshops. I used them to power up my car audio power amps at home.....


    Quote Originally Posted by zhoufang
    in audiophile world such a battery pack is really not considered huge.

    SLA is not really cheaper than NiMH on a per volt basis, at least that is the case for the price of SLA in SLT.
    The main reason of using AA NiMH over SLA is that it can fit inside my DIY amp, which only have 16mm in height left for battery pack.
    And NiMH have lesser internal resistance which is good for the powering of an amp, which I lost most of it due to the high resistance of the connections between cells.
    another reason of NiMH over SLA is for the environment. NiMH is either polluting nor poisonious. Where as I won't know how to dispose a SLA in singapore so that the lead won't end up in the air (incineration) or land (land refill). So when the greener way does't cost me more, I have no reason not to choose it.
    Last edited by user12343; 14th July 2005 at 08:24 PM.

  8. #48
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    Quote Originally Posted by user12343
    SLAs can be disposed safely at automotive workshops. I used them to power up my car audio power amps at home.....
    Thanks for the info.
    I'm sure that the automotive workshop will turn the lead into good value.

  9. #49
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    Hey Guys,

    Small tips from constructing my own battery back a few months ago.

    1. I bought Sanyo 1.2V 3600mAh C size battery (Those RC quick charge battery). 5 of them connecting in series to make up a pack. Cost $10 per battery.

    2. I bought "Voltage Regulators", so to make the out put fixed at 6V 2Amps where I can safely pump up to 14V of in-put voltage into the regulator. Cost $30, depends on model.

    3. I bought "Voltage Watch", Led display for battery capacity. Cost $30, depends on model.

    4. I use RC charger to quickly charge the cell up to 9amp. I could get it charge within 1hr or less per pack. Already have so not cost involved. If you need to buy, cost about $20~30 for a normal quick charger.

    5. also simple cables, connectors, Strink-tube. Cost about $15.

    The total set with 2 battery packs cost me about $175.

    Item 2 & 3 are permantely connected together. Item 1 I get 2 packs, where I can swap it any time. For this set up these are the benefits:

    A) For 1 pack alone, gives me more then 300 full power on my Minolta 5400HS flash. Enough for 1 day shooting.

    B) Because of the Regulator installed, I can safely pump all sorts of input voltage up to 14VDCs. Pretty safe for all flash & cameras usage.

    C) Charging time is less then 1hr per pack. In fact I plug into car battery to charge on the go before shooting. Absolutely no worry for power issue.

    Negative points:

    E) because of the regulators, only 2Amp of current is available. Reflash re-cycle time is Average for bigger flash. Smaller flash power it's absolutely FAST!

    F) when Flash pulling a lot of power thru the regulator, it warms up a bit. Not much of problem, but I should point out.

    Currently how I use them:

    I dis-connected the "Voltage Regulator". I plug it directly 5 cell to Minolta 5400HS & Sonly FX32 flash. They works! Also re-cycle time it FAST. I make connectors for this battery to power my Portable HDD to back up CF.

    Hope what I have done already helps in you battery pack building.

  10. #50
    vince123123
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    Default Re: Connecting multiple batteries in series

    Hey surfer18,
    Thanks for sharing.

    I'm trying to build a battery pack too. Would it be too much to ask you to help take some photos of your packs/parts so that we can see how your superpack works?

    Thanks!

    Quote Originally Posted by surfer18
    Hey Guys,

    Small tips from constructing my own battery back a few months ago.

    1. I bought Sanyo 1.2V 3600mAh C size battery (Those RC quick charge battery). 5 of them connecting in series to make up a pack. Cost $10 per battery.

    2. I bought "Voltage Regulators", so to make the out put fixed at 6V 2Amps where I can safely pump up to 14V of in-put voltage into the regulator. Cost $30, depends on model.

    3. I bought "Voltage Watch", Led display for battery capacity. Cost $30, depends on model.

    4. I use RC charger to quickly charge the cell up to 9amp. I could get it charge within 1hr or less per pack. Already have so not cost involved. If you need to buy, cost about $20~30 for a normal quick charger.

    5. also simple cables, connectors, Strink-tube. Cost about $15.

    The total set with 2 battery packs cost me about $175.

    Item 2 & 3 are permantely connected together. Item 1 I get 2 packs, where I can swap it any time. For this set up these are the benefits:

    A) For 1 pack alone, gives me more then 300 full power on my Minolta 5400HS flash. Enough for 1 day shooting.

    B) Because of the Regulator installed, I can safely pump all sorts of input voltage up to 14VDCs. Pretty safe for all flash & cameras usage.

    C) Charging time is less then 1hr per pack. In fact I plug into car battery to charge on the go before shooting. Absolutely no worry for power issue.

    Negative points:

    E) because of the regulators, only 2Amp of current is available. Reflash re-cycle time is Average for bigger flash. Smaller flash power it's absolutely FAST!

    F) when Flash pulling a lot of power thru the regulator, it warms up a bit. Not much of problem, but I should point out.

    Currently how I use them:

    I dis-connected the "Voltage Regulator". I plug it directly 5 cell to Minolta 5400HS & Sonly FX32 flash. They works! Also re-cycle time it FAST. I make connectors for this battery to power my Portable HDD to back up CF.

    Hope what I have done already helps in you battery pack building.

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